EUROCS

EUROPEAN PROJECT On CLOUD SYSTEMS

In CLIMATE MODELS

 

Contract Number:

EVK2-CT-1999-00051

 

 

Second Year Project Report

March 2000 - February 2002

 

 

Co-ordinator

Jean-Luc Redelsperger

 

 

 

http://www.cnrm.meteo.fr/gcss/EUROCS/EUROCS.html

 

 

 

 

 

 

 

 

Section 1: SUMMARY

 

Section 2:EXECUTIVE PUBLISHABLE SUMMARY

 

Section 3:STRATOCUMULUS OVER THE OCEANS

 

Section 4:DIURNAL CYCLE OF SHALLOW CUMULUS OVER LAND

 

Section 5:DIURNAL CYCLE OF DEEP CONVECTION OVER LAND

 

Section 6:IDEALIZED HUMIDITY CASE

 

Section 7:NEW DEVELOPMENTS OF CLOUD PARAMETRIZATIONS

 


Participants information:

N

Institution/Organisation

Street name and number

Post Code

Town/City

Country Code

Title

Family Name

First Name

Telephone N

Fax N

E-Mail

1

Centre National de la Recherche Scientifique

42 Ave. Gustave Coriolis

31

Toulouse

France

Dr.

Redelsperger

Jean-Luc

33

561079475

33

561336078

Jean-luc.redelsperger

@meteo.fr

2

European Center for Medium-Range Forecasts

Shinfield Park

RG2

9AX

Reading

UK

Dr.

Beljaars

Anton

44

1189499035

44

1189869450

Paa@ecmwf.int

3

UK Meteorological Office

London Road

RG12

2SZ

Bracknell

UK

Dr.

Derbyshire

Steve

44

1344854551

44

1344854493

Shderbyshire

@meto.gov.uk

4

Institute for Marine and Atmosphere Research

Heidelberglaan 8 PO Box 80125

3584 CS

Utrecht

NL

Dr.

Van Dop

Hans

31

302533273

31

302543163

H.vanDop

@phys.uu.nl

5

Instituto Nacional de Meteorologia

Apartado 285, Paseo de Las Morenas S/N

E28071

Madrid

Spain

Dr.

Calvo

Javier

34

915819663

34

915319767

J.calvo@inm.es

6

Swedish Meteorological and Hydrological Institute

Folkborgsvagen 1

SE-601 76

Norrkoping

Sweden

Dr.

Jones

Colin

46

114958652

46

114958001

Colin.Jones@smhi.es

7

Laboratoire de Meteorologie Dynamique du CNRS

Universite P. Et M. Curie

4, Place Jussieu

75005

Paris Cedex

France

Dr.

Grandpeix

Jean-Yves

33

144277462

33

144276272

Jyg@blakey.lmd.

jussieu.fr

8

Max-Planck-Institut fuer Meteorologie

Bundesstrasse 55

20146

Hamburg

Germany

Dr.

Chlond

Andreas

49

4041173212

49

4041173350

Chlond@dkrz.de

9

Royal Netherlands Meterological Institute

Wilheminalaan 10

PO Box 201

3730

AE de BILT

NL

Dr.

Seibesma

Pier

31

302206760

31

302210407

Siebesma@knmi.nl

10

University of Lisbon

R. Escola Politecnica 58

1250

Lisbao

Portugal

Dr.

Miranda

Pedro

35

1217500885

35

113953327

Pmiranda@fc.ul.pt


Section 1

SUMMARY

March 2000 - 28 February 2002

 

Web Page: http://www.cnrm.meteo.fr/gcss/EUROCS/EUROCS.html

 

1.1 Objectives

The project mainly aims to improve the treatment of cloud systems in global and regional climate models, which directly relates to the RTD priority 2.1.3 "improved model treatment of physical processes (in particular clouds)." In addition, benefits will also be gained for hydrology and severe weather issues (RTD 1.5.2 "Improved flood and drought forecasting").

Clouds probably remain the largest source of uncertainty affecting evaluations of climate change in response to anthropogenic change. That explains for a large part why the range of simulated temperature changes in response to a CO2 doubling (1.5 to 4.5 C) is quite invariant for almost 20 years (e.g. Report of Intergovernmental Panel on Climate Change: Dickinson et al. 1996). The recent interest to develop capability to predict regional climate changes stress the importance to better represent clouds in models. For example, the prediction of distributions of mean and extreme precipitation is highly dependent on the cloud representation in models. The climate community must thus give more consideration to the problem of cloud representation in General Circulation Models (GCMs) and Limited Area Models (LAMs) which are applied to climate issues. As most of European models applied to climate issues are also used to produce short and medium range forecasts, prediction of severe weather systems will directly benefit from EUROCS.

 

EUROCS concentrates its efforts on 4 major and well identified deficiencies of climate models in representing clouds:

        stratocumulus over ocean

        diurnal cycle of cumulus

        diurnal cycle of precipitating deep convection over continents

        sensitivity of deep convection development on the moisture profile.

 

These issues (identifying our 4 case studies) are considered of great magnitude as they lead to major deficiencies in the predicted global and regional climates. Some of these issues have been addressed in the past, but others as of yet have not.

 

The specific aims of the project are:

        To produce comprehensive 4-D data sets using several and Large Eddy Simulations (LES) and Cloud Resolving Models (CRMs) on cases defined above which address critical problems associated with the prediction of cloud in regional and global climate and Numerical Weather Prediction (NWP) models.

        To use the LES/CRM data sets to investigate deficiencies in climate and NWP models using 9 different Single Column Models (SCMs) as a test bed. Specific issues to be addressed will be the general failure of climate regional and global models to predict stratocumulus amounts, the diurnal triggering of boundary layer convection and deep precipitating convection over land, and the lack of sensitivity of deep convection development on moisture profile in these models. Once the reasons of deficiency are identified, physically-grounded corrections will be brought in SCMs.

        To improve climate and NWP models ability to represent both the mean structure (horizontally and vertically) and time variability of cloud water and cover for the critical cases defined above. Six different European climate models will be used in EUROCS making it of large benefit to the whole community.

        To bring together a critical mass of the scientific community across Europe working in various areas of Cloud and Climate research, with the focused aim of improving cloud representations in climate and NWP models.

 

1.2 Participants and their modeling plans

The strategy used in EUROCS to address these issues is based on the use of a hierarchy of models and observations to integrate cloud studies across the full range of scales. Numerical models range from regional and general Climate Models (CMs) through Single Column models (SCMs) to Cloud Resolving Models (CRMs) and Large Eddy Simulations (LES). Observations collected will vary from global satellite measurements to local observations of individual clouds through lidar and millimetric radars. Table 1.1 illustrates how the ten participants are involved in various aspects of this research by listing the models they are using.

 

Table 1.1 Partners and model involvement.

Partners

CRM/LES

SCM

CM

CNRM-GAME

Yes

Yes

Yes

ECMWF

No

Yes

Yes

UKMO

Yes

Yes

Yes

IMAU

Yes

Yes

No

INM

Yes

Yes

No

SMHI

No

No

Yes

LMD

No

Yes

Yes

MPI

Yes

Yes

Yes

KNMI

Yes

Yes

No

UL

No

Yes

No

 

 

1.3 Milestones

To date, the project is on task and progressing as expected. Table 2 lists the deliverables as set up by the project. The expected date and whether that deadline was achieved is noted.

 

Table 1.2 Project deliverables and current status.

Target

Date

Deliverables

Status

 

April 2000

D1 - Choice and organization of observations of stratocumulus case to initialize and evaluate SCMs and LES

D2 - Choice and organization of observations of diurnal shallow convection case to initialize and evaluate SCMs and LES

D3 - Choice and organizations of observations of diurnal deep convection case to initialize and evaluate SCMs and CRMs

 

Done

 

Done

 

Done

 

June 2000

D4 - Coice of idealized deep convection case with different mid-tropospheric vapor profiles to initialize SCMs and CRMs

Done

 

February 2001

D5a - Reference simulation with LES of stratocumulus case and inter-comparison with observations

Done

 

 

August 2001

D5b - Ensemble simulations to study the sensitivity to initial conditions and forcings

Done

 

February 2001

D6a - Simulation with LES of diurnal Shallow convection case and inter-comparison with observations

Done

 

 

August 2001

D6b - Ensemble simulations to study the sensitivity to initial conditions and forcings

Done

 

February 2001

D7a - 2D simulation with CRMs of diurnal deep convection case and inter-comparison with observations

Done

 

 

June 2001

D7b - 3D simulation with CRMs of diurnal deep convection case and inter-comparison with observations

Done

 

February 2001

D8 - Simulations of idealized deep convection studying the sensitivity to mid-trospheric humidity

Done

 

 

February 2001

D9 - First drafts of articles on EUROCS activity on CRM

Done

 

May 2001

D10 - Dataset from LES runs for stratocumulus case to evaluate and to improve SCMs

D11 - Dataset from LES runs for diurnal shallow convection case to evaluate and to improve SCMs

Done

 

Done

 

May 2001

D12a - Dataset from 2D CRM runs for diurnal deep convection case to evaluate and to improve SCMs

Done

 

August 2001

D12b - Dataset from 3D CRM runs for diurnal deep convection case to evaluate and to improve SCMs

Done

 

May 2001

D13 - Dataset from CRM run for idealized deep convection case to evaluate and to improve SCMs

Done

 

February 2002

D14 - Improvement of cloud and boundary layer parameterizations with SCMs to represent stratocumulus

D15 - Improvement of cloud and boundary layer parameterizations with SCMs to represent diurnal shallow convection

D16 - Improvement of deep cloud parameterizations with SCMs to represent diurnal variations of deep convection

D17 - Improvement of deep cloud parameterizations with SCMs to represent effect of various mid-tropospheric humidity profiles

D18 - Comparison of characteristics of stratocumulus, diurnal cycle shallow and deep convection as simulated by current GCMs, LAM and available satellite observations

D19 - Drafts of articles on EUROCS activity on CRMs and SCMs

 

 

Done but need to be pursued

(See D22)

April 2002

D20 - Implementation of improved cloud schemes in GCMs

On task

 

August 2002

D21 - Climate runs with improved cloud schemes in GCMs

On task

 

October 2002

D22 - New SCM runs in using CRM datasets to fix new potential problems in climate runs with improved cloud schemes in GCMs

On task

 

Dec. 2002

D23 - New climate runs with last improvements in cloud representations

 

 

February 2003

D24 - Comparison of characteristics of stratocumulus, diurnal cycle shallow and deep convection as simulated by improved GCMs, LAM and available satellite observations

 

 

February 2003

Drafts of papers in referee journal describing EUROCS results

 

 

 

1.4 Deviations from Work Plan

At the end of first year, a minor delay was noticed due to an unexpected delay in hiring people in one group: results of one of LES models were not available. This last group successfully made up the time. At the end of the second year, there are no deviations from initial work plan. In regard to the strong interest of the community, more developed work than scheduled has been performed on diagnostics of current climate simulations (See section 4.5).

 

1.5 Meeting reports

The second EUROCS meeting was hosted by Pr. P. Miranda and funded by the Gulbenkian Foundation, the WCRP and EUROCS. The workshop was held in Lisbon, Portugal from May 28 through 31 2001. The workshop took place in conjunction with the GCSS-WG1 and WG4 workshop (International programme GEWEX Cloud System Studies). It means that EUROCS is now a project largely recognized by the international community and in particular the GEWEX programme of WCRP. In fact, it is fair to say that EUROCS serves as an example in USA in the sense that EUROCS was successful in bringing together a critical mass of the scientific community with the focused aim of improving cloud representations in numerical models (The 4rd objective of EUROCS).

 

This joint EUROCS-GCSS workshop was very successful and participants recommended that we pursue such joint workshops in the future. In particular, a joint workshop between PBL-clouds experts and deep convective clouds experts was appreciated and especially useful. GCSS/WG1 and EUROCS will participate on similar case studies of PBL clouds for the 2 coming years. Therefore, it was recommended that joint GCSS/WG1 and EUROCS workshops should continue in future when possible.

This workshop was clearly an important milestone for EUROCS with a lot of discussions and promising results. For each case study, clear conclusions were drawn from the chairmen.

 

All 10 participating institutions were attended by the Project primary investigator as well as by complementary staff. There were 43 attendees, 34 relevant to EUROCS project. Figure 1.1 outlines the meeting agenda and Fig 1.2 gives the list of participants.

 

A third workshop was scheduled at the end of January in Utrecht but was postponed due to the brutal decease of Peter Duynkerke, one of main EUROCS PI and workshop co-host. This workshop will be held from April 8 through April 10 2002 in Utrecht.


Figure 1.1 Agenda for the EUROCS-GCSS meeting held in Lisbon, Portugal (Host University of Lisbon).

 

Joint EUROCS - GCSS workshop

Lisbon

28-31 May 2001

 

Monday 28th May (Morning):

 

PLENARY SESSION: 9.00-12.45

 

9.00: Welcome

Opening by P.Duynkerke, W. Grabowski, JL Redelsperger

Practical issues (P. Miranda)

9.10-12.45 Issues and current developments in PBL and deep convection schemes; Problems in coupling boundary layer and deep convection parameterisations

9.10-9.30: Issues and developments in PBL and deep convection parameterizations (D. Randall CSU)

9.30-9.50 Ways to address the issue of compensating errors in physical parameterizations (JM Piriou CNRM)

9.50-10.10 A new parameterization of sub grid scale cloud variability for numerical models (E. Roeckner MPI)

10.10-10.30 Flux-gradient relationships in cumulus parametrizations (A. Grant UK Met)

 

11.00-11.30 The interface between PBL and deep convection seen from the convective side : a possible set of interface variables. (J.Y. Grandpeix LMD)

11.30-11.50 Turbulence and clouds in a global atmospheric model (J. Teixeira NRL, with S.Cheinet and P. Siebesma)

11.50-12.05 TKE analysis of deep convection (A. Stirling UK Met)

12.05-12.25 The diurnal cycle of convection over tropical South-America: Observations, GCMs and SCMs (C Jakob and A. K. Betts ECMWF)

12.25-12.45 The CLIWA-NET project and the BBC-campaign

(A. van Lammeren and A. van Ulden, KNMI)

 

Monday 28th May (Afternoon): PARALLEL SESSIONS S1 and S2

S1: 14.15-18.00: Stratocumulus (Chairman: P. Duynkerke)

Case presentation and CRM/SCM/GCM issues (P. Duynkerke, IMAU)

Individual talks on CRM (15-20 minutes by talk including discussions):

      Mesoscale fluctuations in the stratocumulus-topped boundary layer (S. de Roode, P. Duynkerke and H. Jonker IMAU)

      LES results with Meso-NH (E. Sanchez & J. Cuxart INM)

      Status report on CRM runs at MPI (A. Chlond and F. Mueller MPI)

      Sensitivities in the Met office LES to resolution and radiation scheme (P. Coggins UKMO)

Synthesis of CRM results (P. Duynkerke)

Individual talks on SCM and GCM:

      Representation of Sc in Arpege NWP version: FIRE case study and general behaviour in forecasts (JM Piriou, CNRM)

      Status report on SCM and GCM runs at MPI: Achievements and further plans (A. Chlond and F. Mueller MPI)

      SCM results with 1D Meso-NH (E. Sanchez & J. Cuxart INM)

      UK Met Office SCM and GCM results (A. Lock UKMO)

      Improved Sc diurnal cycle representation with a SCM (H. Grenier, CNRM)

      Turbulence and clouds in a global atmospheric model (J. Teixeira NRL)

      Results from SCM studies (S. Cheinet LMD)

      The role of large-scale vertical and horizontal advection in the FIRE I stratocumulus maintenance: the ECMWF GCM and SCM (M. Koelher, ECMWF)

 

 

Monday 28th May (Afternoon): PARALLEL SESSIONS S1 and S2

S2: 14.15-18.00: Diurnal cyle of deep convection (Chairman W. Grabowski)

ARM Case presentation and CRM/SCM/GCM issues (F. Guichard CNRM)

Individual talks on CRM:

      Sensitivity of CRM simulations to subgrid scale parameterizations" (M. Tomasini and F. Guichard CNRM)

      Semi-idealized CRM simulations with no large scale advection (J. Petch UKMO)

      An idealized diurnal case for the intercomparison (F. Guichard CNRM)

Synthesis of CRM results (J. Petch)

Individual talks on SCM/GCM:

      1D against 3D evaluation of convection parameterizations/models (P. Bechtold LA)

      Comparison between various triggering parametrisations within Emanuel and Tiedtke schemes (R. Tailleux LMD)

Synthesis of SCM results (F. Guichard)

Synthesis of GCM results (F. Guichard)

 

 

Tuesday 29th May: PARALLEL SESSIONS

S3: 9.00-10h30: Stratocumulus (Chairman P. Duynkerke)

Synthesis of SCM results (P. Duynkerke)

GCM experiments

      3D runs on Sc FIRE case with the regional model HIRLAM used in climate mode (C. Jones SMHI)

      3D runs on Sc FIRE case with the LMD GCM (A. Lahellec LMD)

Synthesis of GCM results (P. Duynkerke)

Discussion and future work

 

S4: 9.00-12h30: Diurnal cyle of deep convection (Chairman W. Grabowski)

Discussion and future work on ARM case (F. Guichard and J. Petch)

Future possible cases

      Impact of organized convective systems on the atmosphere as estimated from explicit simulations of convection and african easterly wave. (J.P. Lafore, etal. CNRM)

      LBA studies at ECMWF (C. Jakob ECMWF)

      Convective Systems Observed and Simulated during TRMM Field Campaigns (WK Tao NASA/GSFC)

Discussion on future cases and strategy (W. Grabowski NCAR)

 

S5: 11.00-12h30: Cumulus (Chairman P. Siebesma)

Case presentation and CRM/SCM/GCM issues (P. Siebesma)

Synthesis of CRM results (P. Siebesma)

 

S6: 14.00-18.00: Cumulus (Chairman P. Siebesma, KNMI)

Individual talks on SCM and GCM:

                  SCM studies at LMD (S. Cheinet LMD)

                  Status report of MPI: Achievements and further plans (A. Chlond and F. Mueller MPI)

                  Results and developments at NRL (J. Teixeira NRL)

                  Massflux budgets of shallow cumulus (S. de Roode and C. Bretherton IMAU & Un. Washington)

                  SCM results with 1D MesoNH model including new mixing lengths (E. Sanchez & J. Cuxart INM)

                  Status on development and tests with 1D HIRLAM (L. Olmeda & J. Cuxart INM)

                  Talk on works performed at KNMI, ECMWF & UL (P. Siebesma or colleague)

Synthesis of SCM results (G. Lenderink)

Synthesis of GCM results (P. Siebesma & C. Jakob)

Discussion and future work

 

 

 

 

Tuesday 29th May: PARALLEL SESSIONS

S7: 14.00-18.00: Idealized humidity case (Chairman S. Derbyshire UKMO)

Introduction: Role of dry air intrusions on cloud development as observed and simulated (JL Redelsperger, D Parsons and F. Guichard, CNRM & NCAR)

Case presentation and CRM/SCM/GCM issues (S. Derbyshire UKMO)

CRM and SCM results (S. Derbyshire)

Links between sensitivity to q profile and mixing fraction probability distribution at entrainment (J.Y. Grandpeix LMD)

Discussion and future work (S. Derbyshire)

 

 

Wednesday 30th May

PLENARY SESSION 9.00-18.00: (Chairman J.L Redelsperger)

9.00-10h30: Reports from PARALLEL SESSIONS Stratocumulus

11.00-12.30: Reports from PARALLEL SESSIONS Cumulus

 

14.00-15.30: Reports from PARALLEL SESSION Diurnal cycle of deep convection

15.30-16.30: Reports from PARALLEL SESSION Idealized humidity case

16.45-18.00: Discussions on future EUROCS & GCSS plans

C. Jakob : A proposal of common evaluation in GCM for three cloud types and transition (SCu, Cu and deep Cb)

Thursday 31th May

9.00-12h30: Discussion on EUROCS status after 15 months: lacks and next actions

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 1.2 List of participants to the EUROCS-GCSS meeting held in Lisbon, Portugal

CNRM : Jean-Luc Redelsperger, Francoise Guichard, Herve Grenier, J. Philippe Lafore, Jean-Marcel Piriou, Sara Chavarria

Colorado State Univ. : David Randall, Cara-Lyn Lappe

ECMWF : Christian Jakob, Martin Koehler

IMAU: Peter Duynkerke, Stephan de Roode

INM : Enrique Sanchez, Dolores Olmeda

KNMI: Pier Siebesma , Geert Lenderink, Roel Neggers, Aad van Ulden

LA : Peter Becktold

LMD : Jean-Yves Granpeix, Sylvain Cheinet, Remi Tailleux, Alain Lahellec, Herve Le Treut

MPI: Andreas Chlond, Frank Muller, Erich Roeckner

NASA/GSFC: Stephen Lang, Wei-Kuo Tao

NCAR/MMM : Wotjek Grabowski

NRL : Joao Tiexiera

SMHI : Colin Jones

UCLA : Rafael Terra

UKMO : Steve Derbyshire, Jon Petch, Adrian Lock , Alan Grant, Olaf Stiller, Alison Sterling, Pat Coggins

Univ. of Lisbon: Pedro Miranda , Pedro Soares

Univ. of Oslo: Jorn Kristensen

 

 

 

 

 


Section 2

EXECUTIVE PUBLISHABLE SUMMARY

 

 

Contract n

EVK2-CT-1999- 00051

Reporting period:

March 2000 February 2002

Title

EUROCS : EUROPEAN PROJECT on CLOUD SYSTEMS in CLIMATE MODELS

Objectives: EUROCS aims to improve the treatment of cloud systems in global and regional climate models. In addition, benefits will also be gained for hydrology and severe weather issues. Clouds probably remain the largest source of uncertainty affecting evaluations of climate change in response to anthropogenic change. The recent interest to develop capability to predict regional changes of climate, stresses the importance of better representing clouds in models. EUROCS concentrates its efforts on 4 major and well identified deficiencies of climate models: stratocumulus over ocean, diurnal cycle of cumulus, diurnal cycle of precipitating deep convection over continents, and sensitivity of deep convection development on the moisture profile. These issues are considered of great magnitude as they lead to major deficiencies in the predicted global and regional climates. The strategy used to address these issues is based on the use of a hierarchy of models and observations to integrate cloud studies across the full range of scales. Numerical models range from General Circulation Models (GCMs) through Single Column models (SCMs) to Cloud Resolving Models (CRMs) and Large Eddy Simulations (LES).

Scientific achievements
General achievements

-The choice and organization of observations to initialize and evaluate SCMs and LES have been achieved for: stratocumulus, diurnal shallow convection, diurnal deep convection, and idealized deep convection cases with different mid-tropospheric vapor profiles.

-Reference simulations with LES of stratocumulus and cumulus cases and inter-comparison with observations have been successfully performed.

-Comprehensive datasets quantitatively describing the diurnal cycle of boundary layers with stratocumulus and cumulus have been built and made available

-Reference simulations with CRMs of diurnal deep convection and inter-comparison with observations and simulations of idealized deep convection studying the sensitivity to mid-tropospheric humidity have been successfully performed

-Comprehensive datasets quantitatively describing the diurnal cycle of deep convection and the response of convective atmosphere to dry air layers have been built and made available

-Detailed analysis of simulations with SCMs and CRMs on each case study have allowed to identify general deficiencies in standard cloud schemes, demonstrating that the setup of cases is well suited to address the major issues identified by the EUROCS project.

-Improvements of existing cloud parameterisations and developments of new cloud schemes have been realized. Evaluation of these new schemes have been performed against the datasets built from detailed simulations.

-Comparisons of cloud characteristics as simulated by standard GCMs have been performed along different perspectives.

Detailed achievements

i) Stratocumulus case

The 6 LES models all capture the strong diurnal variation in liquid water path, the observed turbulence profiles and clearly show a decoupled boundary layer during daytime and a well-mixed and decoupled boundary layer during the night. The diurnal variation in boundary layer properties leads to a strong diurnal variation in the surface fluxes which has large implications for the surface energy balance and sea surface temperature in coupled ocean-atmosphere models.

Results from nine SCMs have been compared with the observations and LES results. Most of SCMs predict a much too low liquid water path and thus tend to dissipate the stratocumulus too quickly. This results in a much larger amount of downwelling shortwave radiation absorbed at the sea surface. In some SCMs the cloud layer becomes so thin that the cloud emissivity properties become affected leading to a significant decrease in the downwelling longwave radiation at sea surface. Improvements of current schemes are currently tested and new schemes developed in parallel

ii)Cumulus case


The LES models are capable of reproducing realistically the diurnal cycle in the presence of shallow cumulus clouds. LES models do behave similarly and give approximately the same timing as the observations for the onset and offset of the clouds. The cloud cover amount reaches about the same maximum value as observed. The diurnal variation of cloud base height is similar to observations. The sub-cloud layer structure seems hardly affected by the clouds on top, meaning that the issue of parameterization is less complicated .

SCMs generally produce too high values of cloud liquid water and cloud cover. In addition, they have difficulties to correctly reproduce the diurnal cycle, in particular with dissipating the clouds after sunset. Improved schemes are currently tested in SCMs. An evaluation of GCM results have been performed in parallel, in defining a case across the Pacific Ocean where all clouds studied in EUROCS are persistently present.

iii)Diurnal deep convection

A comprehensive survey of GCMs and RCM used in EUROCS have shown that deep convection frequently occurs too early in the daytime. NWP and climate models share the same default though the regional climate model leads to a better diurnal cycle than GCMs. In other hand, CRM simulations of an observed case show that CRMs compare reasonably well with observations, though a sensitivity to the resolution and to sub-grid scale parameterisations was found - two connected issues, stressing the importance of boundary layer circulations. A more appropriate idealized case for studying the diurnal cycle of deep convection over land has been designed from the real case. This case has been run by participants. Analysis of outputs show that the wrong diurnal phase of rainfall found in GCMs is reproduced in these idealised SCM runs. These results suggest that this GCM weakness can be properly analyzed within the joint CRM/SCM framework of EUROCS. The atmospheric stability has been found dissimilar in CRMs and SCMs, the CIN (Convective INhibition) in particular being much weaker in SCMs. From the obtained results, motivated changes in SCM and GCM parameterisations are being considered by modellers.

iv) Sensitivity to humidity profile

Two independent 3D CRMs have been run on the case (each with four different values of the environment relative humidity) and give very similar answers. Five SCMs have also been run on the same case, and give a considerably wider range of answers. In the CRM runs, clear impacts of mid-level humidity have been demonstrated and simulations converge rapidly to a quasi-steady convective ensemble. Significant variations are found in surface precipitation as a function of environment relative humidity, and between different SCM schemes and the CRMs. These differences require further analysis but show the potential of this approach to evaluate the SCM schemes. Scope for improving the schemes has been identified, including changes to the convective closure and to the mixing-PDFs. Results of this case are already starting to influence GCM parametrizations. Overall the level of agreement between the CRMs, and the magnitude of the sensitivities found, indicates that we can assess the performance of the SCMs and in turn make progress with GCM parametrizations.

Socio-economic relevance and policy implications

The economic and social impacts of this project will result in the expected improvements in cloud parameterizations. In improving cloud parameterizations, we would improve cloud and precipitation events of importance to human activities, such as agriculture, transport, some kinds of industry, as well as the atmospheric pollution forecast which depends on the ability to make precise weather forecasts. The study on the deep convection case should also contribute to improve the forecast of summer convective systems. Heavy precipitation and severe flood events associated with these systems are recognized as a threat to social and economic life in many regions of Europe.

 

Conclusion

At the end of the second year, the project stays on the right tracks and on time. The choice of case studies with the observations to initialize and evaluate all the hierarchy of models having been achieved, reference simulations with explicitly resolved cloud models have been successfully performed. Comprehensive datasets produced from these simulations have allowed to analysis in details the simulations performed with SCM. That has led to the identification of general deficiencies in standard cloud schemes used in climate models. This point demonstrates that the set-up of cases is well suited to address the major issues of climate models in representing clouds.

Improvements of current schemes have been made in using these datasets. New schemes have been also developed in parallel, more physically based and exploiting the detailed analysis of CRM and LES simulations. These improvements and developments firstly tested in SCMs, are currently integrated and tested in the full GCMs.

Because the EUROCS programme constitutes the largest European contribution to GEWEX Cloud System Studies (GCSS is a non-funded programme of WCRP), EUROCS has been active and influential in a co-ordinated manner within GCSS.

 

Keywords: CLOUDS, CLIMATE, PRECIPITATION, BOUNDARY LAYER


Section 3

STRATOCUMULUS OVER THE OCEANS

 

Gathered and Prepared by:

Peter G. Duynkerke and Stephan De Roode

 

Case Leader: IMAU

Participating Partners: CNRM-GAME, ECMWF, UKMO, INM, SMHI, LMD, MPI, KNMI, and UL

WEB Page: http://www.phys.uu.nl/~wwwimau/EUROCS/

 

 

3.1 Motivation

The primary objective of EUROCS is to improve the treatment of cloud systems in general circulation models (GCMs) and regional circulation models (RCMs). The present research focuses on the representation of stratocumulus over the ocean in these three-dimensional models. This report section addresses the full diurnal cycle of stratocumulus off the coast of California based on observations of the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE).

The extensive areas of sub-tropical marine stratocumulus clouds off the West coast of large continents lie beneath the descending branch of the Hadley circulation. The large static stability associated with the cold sea-surface temperatures (SSTs) and atmospheric subsidence results in extensive marine stratocumulus cloud decks with an areal coverage of about 40 - 90%. Due to their high albedo, these stratocumulus decks have a significant cooling effect on the underlying ocean. This cooling is only slightly offset by the downward infrared emission from the cloud.

In atmospheric GCMs, however, the amount of subtropical marine stratocumulus is usually under predicted, even when the observed SSTs are prescribed (Jakob, 1999). As a result, in such models the net surface heat flux into the ocean is overestimated in these regions. In a coupled atmosphere-ocean model this can lead to positive SST biases of about 5K. It is now well established that these model errors have a significant influence on the (sub) tropical circulations (Philander et al., 1996; Ma et al., 1996; Nigam, 1997). Furthermore, the stratocumulus cloud cover can act as feedback (or a thermostat) which reduces the intensity of tropical convection and damps the tropical circulation as a whole (Miller, 1997). Therefore, it is vitally important to consider the full life cycle of stratocumulus.

The goal of this study is to assess the quality of the representation of stratocumulus in the GCM (weather and climate) and RCM models. We will therefore perform an intercomparison between FIRE I observations and model results. The FIRE I experiment (Albrecht et al., 1988) provided a comprehensive observational set of data on marine stratocumulus on San Nicolas island (SNI) during July 1987. These observations will be used in LES and SCM simulations to study the diurnal variation of stratocumulus (section 3.3 and 3.4). Moreover, cloud parameters (Minnis et al., 1992; Rossow and Schiffer, 1999) derived from satellites are used to verify the representation of stratocumulus in GCMs and RCMs over a larger region (sections 3.5 and 4.5). We will focus on the monthly-mean diurnal variation and monthly mean values of cloud parameters and surface energy balance.

In Duynkerke and Teixeira (2001) the ECMWF Re-Analysis (ERA) results for July 1987 are compared with stratocumulus observations for the same period made during the FIRE I experiment. They concluded that the ERA cloud thickness is overestimated and cloud cover and liquid water path are strongly underestimated compared with the FIRE I observations. As a result the ERA downwelling shortwave radiation at the surface is much larger than observed. They argued that the large difference between the ERA downwelling shortwave radiation at the surface and that observed in FIRE I can lead to large biases in the sea-surface temperature in a coupled ocean-atmosphere model. Therefore, this study focuses on representation of the diurnal variation of cloud properties (boundary layer depth, liquid water path, optical depth, etc.), surface energy balance and implications for a coupled atmosphere-ocean model, turbulence dynamics (entrainment, decoupling, etc.) in the boundary layer, and shortwave optical properties of inhomogeneous 3-dimensional cloud fields.

 

3.2 Case Description

 

3.2.1 Surface based observations

The FIRE I experiment (Albrecht et al., 1988) provided a comprehensive observational set of data on marine stratocumulus during July 1987. From the observations the following parameters will be used: cloud cover, liquid water path, cloud-base and cloud-top height, and downwelling shortwave and longwave radiation at the surface (Duynkerke and Teixeira, 2001).

A description of the temporal evolution of the cloud conditions on San Nicolas Island during July 1987 can be found in Blaskovic et al. (1991), Betts (1990) and Albrecht et al. (1990). Hignett (1991) describes the detailed turbulence profiles throughout the boundary layer, taken on 14 and 15 July 1987. These turbulence data have been successfully modelled with a 1.5-order turbulence closure scheme (Duynkerke and Hignett, 1993). The overall picture is of a cloud layer that progressively thins during the late morning into the afternoon, both by raising cloud base and lowering the inversion, but that thickens again during the evening.

 

3.2.2 Satellite observations

Betts et al. (1992) and Minnis et al. (1992) have derived cloud parameters from the Geostationary Operational Environmental Satellite (GOES). Figure 3.1 shows the low-cloud faction derived from GOES data over the Extended Time Observations (ETO) area (Betts et al., 1992) for July 1987. The ETO data were analysed on a 2.5o latitude-longitude grid covering the area between 10o - 40o N and 110o - 145o W. Minnis et al. (1992) analysed the data on finer grids: a 1o and 0.33o latitude-longitude grid, respectively. They compared the satellite derived values, on the 0.33o latitude-longitude grid, with observations performed on San Nicolas Island. They concluded that the diurnal variation of satellite retrieved values of cloud amount, optical depth and cloud-top height shows very good agreement with the surface-based observations on San Nicolas island. The satellite data of Betts et al. (1992) and Minnis et al. (1992) were thus verified at SNI and this data will now be used over the ETO region to verify the GCM and RCM predictions (section 3.5).

 

3.2.3 Large Eddy Simulations and Single Column Model Simulations

The LES and SCM model simulations were started on 14 July 0800 UTC (= 00 LT) lasting at least 37 hours (37 LT). The initial and boundary conditions were based on the observations described in Blaskovics et al. (1991), Hignett (1991), Duynkerke and Teixeira (2001). Both LES and SCM use the same initial conditions and vertical resolution. From the measured potential temperature and specific humidity profiles the initial potential temperature and humidity profiles were determined. The goal is to simulate as closely as possible the typical monthly-mean diurnal variation. Therefore the initial conditions were not

 


 

 


Figure 3.1 Mean low-level cloud cover for July 1987 from GOES for the ETO region.

 

 

 

 

exactly tuned to the conditions on 14 July 1987 but were more representative of the monthly-mean conditions.

 

3.3 Large Eddy Simulation results

LES results have been now received from six different models. All models have simulated the case defined and have performed sensitivity simulations with respect to sea-surface temperature, inversion properties, long wave radiative heating at cloud base and grid resolution. In Figure 3.2 we have compared the liquid water path of all LES models with the observed values. The observed values are the hourly-mean values during 14 and 15 July 1987 (denoted as 0 to 48 hours) and the hourly monthly-mean diurnal variation. The LES models all capture the strong diurnal variation in LWP due to the forcing imposed by the shortwave heating of the cloud layer. Like the observations the maximum cloud thickness is found during the night, and the cloud deck gradually thins until noon. However, the thinning is not sufficient to break up the cloud; in all LES models the cloud cover remains equal to one. A good deal of the differences among the models in the simulated LWP can be attributed to variations in the entrainment rates. Models that have larger entrainment rates mix a larger amount of warm and dry air from above the inversion into the cloudy boundary layer, which supports a thinning of the cloud layer and a subsequent lower LWP. The importance of the entrainment rate on the cloud evolution is reflected in the performed sensitivity studies. They show that the LES results are most sensitive to changes in the inversion jumps. This can be understood by the fact that the entrainment rate strongly depends on the both total water content and temperature jumps across the inversion. Since a drier inversion supports more evaporation of cloud droplets this will not only tend to dry out the cloud, but it will also enhance the production of turbulence kinetic energy which, in turn, leads to a larger entrainment rate.

 

 

Figure 3.2 The observed and modelled liquid water path (LWP) from 6 different LES models as a function of time for 14 and 15 July 1987 (denoted from 0 to 48 hours). The open circles are the hourly mean observed values whereas the filled dots are the hourly monthly-mean values. The linestyles (LES results) are according to the legend.

 

The LES results are also compared with the turbulence profiles observed by Hignett (1991). During the night the boundary layer is vertically well-mixed. However, during daytime the negative buoyancy fluxes and minimum vertical velocity variance around cloud base indicate that the cloud layer is decoupled from the subcloud layer. In the presence of decoupling the entrained air at cloud top is only used to warm and dry the cloud layer. Instead, if the boundary layer is coupled and well-mixed, the entrainment acts both on cloud and the subcloud layers. Further, the cloud is cut off from the moisture input from the surface. Besides solar absorption in the cloud layer, decoupling is an important mechanism that leads to a thinning of the cloud layer and the observed diurnal cycle in the cloud thickness.

 

The diurnal variation in boundary layer properties leads to a strong diurnal variation in the surface fluxes, that can have large implications for the surface energy balance and sea-surface temperature in coupled atmosphere-ocean models. The mean-diurnal LES properties are summarized in Table 3.1. The downward component of the solar radiation is the major term to the surface energy balance. Because the transmission of shortwave radiation through the cloud is a function of the magnitude of the LWP, it can be concluded that LWP variation among the LES models leads to largest uncertainty in the surface energy balance. Due to the presence of the stratocumulus cloud layer, which is sufficiently optically thick for longwave radiation and emits radiation as a black body, the net longwave radiation at the surface is about zero.


 

Laboratories

H

[W m-2]

LE

[W m-2]

Fs(z=0)

[W m-2]

LWP

[g m-2]

IMAU

3.1

23.1

211

90

MPI

4.1

23.0

171

116

UKMO

7.4

20.3

134

166

INM

5.1

22.6

178

128

NCAR

13.9

24.3

201

109

WV

8.6

28.1

185

95

mean LES

7.0 3.9

23.6 2.6

180 27

117 28

Table 3.1. The mean-diurnal LES properties from 12 to 36 LT. H and L denote the surface sensible and latent heat fluxes, respectively, and Fs(z=0) represents the downward shortwave radiation at the sea surface. The mean values and the standard deviations are computed from the six LES results.

 

 

 

3.4 Single Column Model results

Nine SCMs have performed the standard case simulation and its results have been compared with the observations and LES results. In comparison to the LES results, there is more disagreement among the results from the SCMs. It is found that the different SCM results are most sensitive to the magnitude of the entrainment rate at the inversion. The difference in entrainment rate, due to different turbulence parameterisations, leads to large difference in the amount of heat and moisture entrained from above the inversion. About half of the single column models predict a much too low liquid water path and thus tend to dissipate the stratocumulus too quickly. This results in much lower modelled liquid water paths (see Figure 3.3), and subsequently a much larger amount of downwelling shortwave radiation absorbed at the sea surface (Table 3.2). It implies that if a horizontally extended stratocumulus cloud layer is not well represented in a coupled ocean-atmosphere model this may lead to an erroneous warming bias of the sea surface temperature. In some SCMs the cloud layer becomes so thin that the cloud emissivity properties become affected leading to a significant decrease in the downwelling longwave radiation at sea surface.

 

 

 

Figure 3.3. The observed and modelled liquid water paths from 9 different single column models as a function of time for 14 and 15 July 1987 (denoted from 0 to 48 hours). The open circles are the hourly mean observed values whereas the filled dots are the hourly monthly-mean values. The IMAU LES results are shown as reference. The linestyles are according to the legend.

 

Laboratories

H

[W m-2]

LE

[W m-2]

Fs(z=0)

[W m-2]

LWP

[g m-2]

KNMI

4.0

26.2

272

33

INM

6.1

21.0

140

157

CSU

14.6

24.5

250

160

LMD

0.2

15.9

237

41

MPI

29.6

5.5

119

156

CNRM

23.9

24.2

281

56

UKMO

10.2

26.0

173

75

CNRM 2

-

29.7

271

16

ECMWF

0.1

39.0

280

79

mean SCM

9.9 10.9

23.6 9.2

225 64

87 59

Table 3.2. The mean-diurnal SCM properties from 12 to 36 LT. H and L denote the surface sensible and latent heat fluxes, respectively, and Fs(z=0) represents the downward shortwave radiation at the sea surface. The mean values and the standard deviations are computed from the nine SCM results. CNRM and CNRM-2 stand for climate and NWP versions of ARPEGE model.

 

 

 

3.5 Climate Model simulations

In order to make an inventory of the quality of General Climate Models (GCMs) and Regional Climate Models (RCMs), data of present day models were scheduled to be collected and compared with the SNI and satellite data. The data from the ECMWF model have been analysed. Figure 3.4 shows the monthly mean low cloud cover from the ECMWF model. This can be compared with the observed cloud cover retrieved from a satellite as shown in Figure 3.1. From a comparison of Figures 3.1 and 3.4 it can be concluded that the ECMWF model is under predicting the cloud cover by about 20%. It was decided during the EUROCS workshop in Lisbon to systemize this sort of analysis. It was proposed to make comparisons through the Pacific ocean in sampling the different cloud regimes (Stratocumulus, Cumulus, Cumulus Congestus and Cumulonimbus) and their transitions. This part is reported in section 4.5.

 


 

 


Figure 3.4 Mean ECMWF low-level cloud cover for July 1987 for the ETO region.

 

 

 

 

3.6 Conclusions and future work

All LES results are now available and analysed. With the LES models, sensitivity simulations have been performed to the sea-surface temperature, inversion properties and grid resolution. New sensitivity simulations have been performed with respect to subsidence and wind shear at the inversion. Results of nine SCMs are available and analysed. They have been compared with the LES results and observations. About half of SCMs predict a much too low liquid water path and thus tend to dissipate the stratocumulus too quickly. This results in a much larger amount of downwelling shortwave radiation absorbed at the sea surface. This explains that in coupled ocean-atmosphere models erroneous warming biases of the sea surface temperature are observed. The SCMs are currently performing sensitivity analysis with respect to different boundary conditions, forcings and vertical resolutions. Modified physics used in SCM are also tested and new schemes developed in parallel, in using the comprehensive datasets issued from LES. These new or modified schemes are also currently integrated in GCMs.

 

 

 

Section 4

DIURNAL CYCLE OF SHALLOW CUMULUS OVER LAND

 

Gathered and Prepared by:

A. P. Siebesma and G. Lenderink

 

Case Leader: KNMI

Participating Partners: UL, CNRM-GAME, ECMWF, UKMO, INM, SMHI, LMD, and MPI

WEB Page: http://www.knmi.nl/samenw/eurocs/ARM/

 

4.1 Introduction and Motivation

Underestimation and an inadequate phase of the diurnal cycle for cloud cover over land are known to occur in climate and weather numerical models. This can have dramatic consequences on the behaviour of the boundary layer. During summer seasons, diurnally driven boundary layer clouds are commonly seen over continental regions and play a crucial role in determining the surface energy budget. On a given day failure to capture the variation of shallow cumulus clouds adequately, may lead to errors in predicted surface temperature and moisture and so contribute to failures of predicting the onset of more vigorous deep convection. On seasonal timescales, persistent biases in the surface radiation budget can lead to systematic errors in continental scale hydrological budgets which are important for predicting impact of seasonal and anthropogenic climate variability. Using the strategy of a hierarchy of models and observations such as pointed out in the EUROCS proposal we will present the intermediate results on the above raised issues.

 

4.2 Case description

The case was released on the internet http://www.knmi.nl/samenw/eurocs/ARM/ early September 2000. It is based on the one originally set up by Andy Brown (UK Met. Office) and is composed on observations made at the Southern Great Plains (SGP) ARM site on June 21 1997. On this day, cumulus clouds developed at the top of an initially clear convective boundary layer. The large scale forcing was weak compared to the surface forcing. Non-precipitating cumulus clouds started to form around 14:30 UTC (8.30 local) and disappeared at around 23.30UTC (17.30 local). A maximum cloud cover of around 30% was reached. Because this is the first inter-comparison study on the diurnal cycle of cumulus everything is kept as simple as possible but yet realistic. For this reason, surface fluxes, the tendencies due to radiation and large-scale advection, are prescribed all during the simulation. The required simulation starts at 11.30 UTC, just before sunrise with a stable dry boundary layer based on radiosonde observations. The simulation is required to run from 11.30 UTC June 21 throughout the whole day until 2.00 UTC June 22, well after sunset when all the clouds should have dissolved again. For a detailed case description plus the required output we refer to the web address mentioned above.

 

4.3 Large Eddy Simulation studies

Within the EUROCS framework three groups (MPI, UKMO and KNMI) have submitted LES results. Three important conclusions can be drawn from these results:

        LES models are well capable of reproducing realistically the diurnal cycle of the shallow cumulus topped boundary layer

        Results of previous steady state cases of cumulus over sea still apply to the present case where strong diurnal cycle is present

        The sub-cloud layer structure seems hardly affected by the clouds on top.

 


Concerning the first conclusion, all three models behaved very similar. They all transformed an initially stable boundary layer into a convective dry boundary layer without clouds, developed subsequently a conditionally unstable layer with clouds and finally, just after sunset slid back into a stable clear nocturnal boundary layer. Directly related is the correct timing of the appearance and disappearance of the cumulus clouds as well as the time evaluation of cloud cover, cloud base height, and cloud top height. In Figure 4.1 we show the time evaluation of the total cloud cover of the three LES models. Note that all three models do behave similarly and actually give approximately the same timing as the observations for the onset and offset of the clouds. Also the cloud cover amount reaches about the same maximum value as observed. Cloud base height (not shown here) is for all three models increasing from about 600m around the onset at 15.00 UTC to 1250m at 23.30 just before the clouds disappeared. Again these results compare quite well with observational ceilometer measurements at the central facility at the ARM site.

 


Figure 4.1. Total cloud cover as a function of time of the 3 LES models.

 

 

 

Concerning the second conclusion, previous inter-comparison studies based on BOMEX and ATEX show cloud cover and mass flux profiles that have a maximum value around cloud base and are then monotonically decreasing with height. Furthermore those studies show typical lateral fractional entrainment rates of 1~3 10-2 m-1 and slightly higher fractional detrainment rates. We repeated these calculations for the present case for each model result during each hour of the simulation and found similar results. Note that this is quite an interesting result, since throughout the simulation the mean vertical profiles do change substantially. So apparently these results are robust fingerprints of shallow cumulus that not only occur during controlled steady state conditions but also under fast varying conditions such as the present diurnal cycle.

Finally, concerning the last conclusion it turns out that the sub-cloud layer has quite the same characteristics as the dry convective boundary layer. For instance, the vertical velocity variances sw2 of the three models, when non-dimensionalised appropriate, do exhibit the same behaviour as in the dry convective boundary layer. Similarly the ratio of the minimum buoyancy flux and the surface buoyancy flux is almost all the time from sunset to sundown quite close to 0.2, the same value as found in typical dry convective boundary layers! This means that the top entrainment mechanism and hence the ventilation of moisture and heat into the free atmosphere is not strongly affected by the clouds. The only difference is that in the case of a dry convective boundary layer heat and moisture is deposited in a rather thin entrainment layer while in the case of a cumulus topped boundary layer it is redistributed in a much deeper cloud layer. This finding makes the issue of the parameterization of the cumulus-topped boundary layer much less complicated.

The overall conclusion is that the results of the LES models are such that they can serve as an excellent 4D-dataset that can be used as a test-bed for evaluation and improvement of the parameterizations of these processes in GCMs.

 

 

4.4 Single Column Model results

The final results of 1D version of 6 operational weather and climate models (ARPEGE, ECMWF, ECHAM4, HIRLAM, MESO-NH, and RACMO) have been obtained and processed. In addition, we obtained results of several research models [CT01, MULTI-MF (both Cheinet & Teixera) and MESO-INM (Cuxart & Sanchez)] and new/experimental releases of operational models (ARPEGE, ECMWF, ECHAM5). Most participants have run their model on different vertical resolutions and produced all output requested. The results are analyzed and reporting is in progress. The results of the SCMs confirm the results of previous inter-comparisons: most models produce too high values of cloud liquid water and cloud cover; see Fig. 4.1 showing the time evolution of cloud cover. In addition, most models have difficulties with the diurnal cycle, in particular with dissipating the cloud after sunset. Some models have a fairly good diurnal cycle, both in cloud liquid water as in cloud cover (e.g., RACMO, MESO-NH); other models are characterized by the complete absence of a diurnal cycle (ECHAM4, HIRLAM). The other models are in between these extremes; for example, MESO-INM has a rather good diurnal cycle in cloud liquid water but not in cloud cover, and in ECMWF the clouds appear at the right time, but after sunset thick clouds remain.

 

All operational models use a combination of a diffusion scheme for turbulent transport in the subcloud layer and partly in the cloud, and a mass flux scheme for turbulent transport in the cloud layer. A realistic balance between mass flux activity and turbulent diffusion activity is essential to be able to predict clouds realistically. Most models underestimate the mass flux activity and overestimate activity of the turbulent diffusion scheme. This generally leads to a too shallow boundary layer with too thick clouds and too much liquid water, with HIRLAM most outspoken in this respect (see Fig. 4.2 showing relative humidity profile at 15.30 LT). In ARPEGE, however, a very active turbulent diffusion scheme leads to a very deep layer well mixed layer. On the other extreme, ECMWF has too much mass flux activity. Because in the ECMWF model cloud cover and cloud liquid water is directly coupled to mass flux activity, this also leads to thick clouds. Two operational models (ARPEGE and ECHAM4) are hampered by noise generated by the turbulence scheme (see Fig. 4.2.).

 

Experimental versions of ECMWF and ARPEGE showed improvements compared to their operational versions. In ECMWF a different closure for the mass flux scheme leaded to much better results. In ARPEGE a different turbulence scheme leaded to a reduction of the noise. In contrast, a pre-release of ECHAM5 did not behave better than the operational ECHAM4. Two research models (MESO-INM, and CT01) attempted to do mixing by turbulent diffusion only. The results of these models are reasonable, though not better than the better operational models (MESO-NH and RACMO). On the downside the results are characterized by a large degree of noise. On the other extreme, MULT-MF uses a multiple mass flux approach with very promising results retaining very well the thermo-dynamical structure of the Cu clouds (though this physics package is not yet complete)

Figure 4.2 Total cloud cover as a function of time of the single column models (note that the time is local time). The LES results are also shown.

 

 

Figure 4.3 Vertical profile of relative humidity at 15.30 local time.

 

 

4.5 Climate Model Simulations

In the previous section we have summarized the findings of partners for their parameterization packages in a Single Column Model (SCM) environment. Although this method has obvious advantages, such as controlled external conditions, there are also serious drawbacks, the most important one being the lack of interaction with the large scale dynamics. Also it still remains uncertain whether the prescribed forcings in the SCMs are realistic enough.

Therefore a natural next step is to evaluate all the participating GCM models in a full 3d environment. This will be done for both the operational parameterization packages and for the improved packages based on the SCM studies. To this purpose the month July 1998 has been selected for an GCM intercomparison study over the Eastern Pacific ocean. All the participants have been asked to send in monthly mean profiles and near surface fields from grid points located at positions at or near the points as indicated in Fig.1. The main reason for this choice are

      All the cloud types studied within EUROCS (Scu, Shallow Cu and deep Cu) are persistently present in this area.

      The area has a well-defined large scale circulation. As a result monthly means deviate only marginally from climatology.

 

So far 5 groups from EUROCS have submitted preliminary results (Arpege, ECHAM, RACMO, UKMO and ECMWF). Also two external groups joined in this intercomparison with their model ( Japan Climate Model and NOGAPS, the operational model of the Naval Research Laboratory from the USA).

 

 

 

      The model outputs will be compared with observations with the emphasis on cloud related variables. These include: cloud cover, liquid water path (LWP), outgoing longwave radiation at the top of the atmosphere, precipation, etc.. For all these variables satellite data have been made available. Furthermore ECMWF analysis fields are also used as a comparison tool .

      As a preliminary example we show in Fig.2 the monthly mean LWP for all the models along the cross section of Fig. 1. This illustrates that most models underestimate LWP in the stratocumulus regions and strongly overestimate the LWP in the trade wind region. This has far reaching implications for the radiation budget near the ocean surface. In the upcoming period more runs will be done and they will be analysed in detail.

 

 

 

 

 

.

 

Fig. 4.4: Proposed cross section for GCMs, which includes: the persistent stratocumulus regions off the coast of California, the trade wind regions around Hawaii and the Intertropical convergence zone in Indonesia. All models provide data for the locations indicated in the figure.

 

 

 

 

 

 

Fig. 4.5: Liquid water path of the models along the proposed cross section (Fig.4.4) along with GPCP observations.

 

 

 

4.6 Conclusions and future work

The LES model results compared well enough with the observations in order to be used as 4D Data sets for evaluating parameterization issues. Many of the results found for steady state marine cumulus were reconfirmed by the present case. The results have been documented in a paper that has now been accepted for publication.

The Single Column Model runs have now been completed. All the participants have done the simulations, analysed them and made modifications where necessary. The results will be documented in an intercomparison paper. Also several papers will appear that will address the various modifications in the parameterization packages of the participating groups.

The next phase is to assess these findings in a 3d-GCM context. To this purpose we have defined a case for over the Pacific Ocean. Most participating groups have already submitted results for their operational parameterization packages. These results can serve as a baseline to judge the capability of present climate models to simulate the hydrological cycle in the Hadley Circulation. These results will be carefully analysed. A following step will be that all participants will rerun the same case with the modifications which were based on their SCM findings


Section 5

DIURNAL CYCLE OF DEEP CONVECTION OVER LAND

 

Gathered and Prepared by:

F. Guichard and J. Petch

 

Case Leaders: CNRM-GAME and UKMO

Participating Partners: ECMWF, INM, SMHI, and LMD

WEB Page: http://www.cnrm.meteo.fr/gcss/EUROCS/deepdiunland.html

 

 

5.1 Motivation

Results from many studies, including several analyses performed within EUROCS, show that the diurnal cycle of convection is significantly out of phase in global models (including both climate and NWP models). The deep convection usually occurs several hours earlier than observed in the models and often the amplitude of the cycle is too weak. This situation is particularly worrying because the energy and water budgets are strongly influenced by this diurnal cycle of deep convection, especially over land. From a broader perspective, the 1K warming which occurred during the last century also show a pronounced diurnal structure (IPCC, 2001), the night-time warming being much stronger (possibly because of higher cloud covers at night - e.g., Dai et al. 1999). Therefore, it is important to properly simulate the actual diurnal cycle of convection in order to be able to capture its possible fluctuations in the context of a climatic change.

 

5.2 Case description

 

The case study must allow us to investigate the simulation of the diurnal cycle of deep convection over land. However, we first needed to evaluate the ability of the models to reproduce deep convection over land. This led us to focus on a case of mid-latitude deep convection over the ARM (Atmospheric Radiation Measurement ) SGP (Southern Great Plains) site in Oklahoma. Relevant data were readily available there, both to set up and to validate the simulations, including surface data, large-scale advection of temperature and moisture and wind profiles - see Krueger et al. (1999) for details. Moreover, the ARM Single Column Modelling (SCM) working group and GCSS WG4 also study this case, which contributes to strengthen our links with these communities.

The diurnal cycle of deep convection over the SGP region can be particularly complex and not representative of many other regions as it can involve complex couplings with synoptic scale circulation and a nocturnal low-level jet. Thus, observations from this well instrumented area often include weather conditions, which are too complex for a basic study of the diurnal cycle of deep convection over land. For this reason, the case study has been organised into two sets of simulations, hereafter referred to as the real case and the idealised case.

A careful examination of the different IOPs led us to retain the 4-day period June 27-31 1997 for the real case simulations, the 27 June being also used as a starting point for the design of the idealised case. The design of this second case is similar in that time-varying surface forcing, large-scale advection and wind nudging are still applied to the models, but these quantities are now adapted (light filtering) from their values from one single day (27 June 1997) and are repeated at least twice (2-day runs). In addition, the simulation begins 12h later, in the early morning rather than in the late afternoon, which is more meaningful in regards to our goals and to the specific difficulties encountered in modelling of nocturnal boundary layers. Simulations are integrated for 2 days in order to evaluate the robustness of the diurnal features and the possible impact of an unphysical initialisation of the model. For example, the CRMs are initiated with horizontally homogeneous profiles of moisture and convection and this could have implications for the development of convection.

Designing the idealised case required extensive analysis and sensitivity studies (e.g. the start time and the large-scale forcing). A comparison of the ARM product for surface heat fluxes with direct point measurements has shown that the diurnal amplitude of this product is apparently significantly too low (sensitivity studies to the magnitude and formulation of surface heat fluxes are currently investigated).

In practice, EUROCS participants had to apply only minor changes to their numerical codes input data being provided in the same format for both cases. Information for simulating this case has been added to the EUROCS web page. Model results have also been made available on this web page in the form of sets of figures documenting each model run and how it compares with observations, including also some consistency checking (e.g., closure of the moisture budget). Finally, a list of additional diagnostics has been defined in order to further investigate vertical transport and boundary layer processes. Also, new quantities documenting the characteristics of simulated convection have been computed from model outputs, including CAPE (Convective Available Potential Energy) and CIN (Convective Inhibition) - measuring the atmospheric stability, condensation level etc... This will allow us to answer some basic and crucial questions among which the following: Are the models able to reproduce the observed diurnal cycle of atmospheric (in)stability? How are the differences related to boundary layer structures? What are the links between stability and convection in the models? How distinct are these links in CRM and SCM runs?

 

Figure 5.1: Real case (GCSS-ARM Case 3a), model moisture bias, root mean square error and correlation coefficient with observations (upper panel) and cloud mass flux, cloud fraction and cloud water (lower panel) - The pink and blue areas delineate for each vertical level the envelope of the 3 CRMs and 4 SCMs simulations respectively, 4-day mean profiles, domain averaged for CRMs.

 

5.3 Cloud-Resolving Models

 

Figure 5.2: Real case, time series of normalised rainfall (rainfall divided by 24-h mean rainfall) for the first rainy event.

 

The real case has been carried out by three CRMs, the UKLEM (UKMO), MesoNH and ComeNH (CNRM-GAME). A partial summary of their evaluation is given in Fig. 5.1 and 5.2, together with SCMs performances (detailed in next section). These results are consistent with Xu et al. (2002) and Xie et al. (2002) conclusions. There are still differences among CRMs. Some of them can be traced back to particular aspects of the models. For instance, the increase of the scatter between CRMs for cloud fraction and cloud cover above 600hPa is probably linked to distinct parameterisations of the microphysics (Fig. 5.1). However, the consistency between the CRMs is much better than among SCMs, as indicated by the width of the coloured envelopes in Fig. 5.1. A closer look at the first rainy event (Fig. 5.2) also show that it is difficult to reach a close agreement in terms of timing and duration of this event among CRMs. Additional sensitivity studies have shown that these features are particularly sensitive to the resolution (though this sensitivity appears to be model dependent) and to the treatment of sub-grid scale processes (turbulent scheme, sub-grid condensation). Both of these findings point to the conclusion that a proper representation of small-scale processes in the boundary layer is crucial and that further investigation in this area is needed. To address this issue, we focus on the early stage preceding moist convection with a smaller 3D domain and higher resolution for an in-depth investigation of CRM performances regarding the representation of this stage by relatively coarse CRM grids. This work involves interactions with the group working on the diurnal cycle of cumulus, which has the more expertise on this issue.

The idealised case has also been carried out by the three CRMs. This is illustrated in Fig. 5.3 with time series of various fields derived from a CRM run, showing a clear diurnal cycle of both convection and atmospheric stability, closely linked together in the simulation, the onset of convection occurring when CIN is minimum, CAPE and CIN respectively decreasing and increasing later during the convective events, as expected. Preliminary analysis indicates that the modification of the starting date (early morning for the idealised case) is beneficial to the simulated diurnal cycle of CAPE and CIN. Each day, rainfall maxima occur in the afternoon/evening. However, it takes place earlier during the two last days, possibly linked to the evolution of moisture profiles with time, as suggested by Petch et al. (2002). The minimum of CIN preceding rainfall occurrence is also much smaller the first day than later on, possibly linked to the horizontal variability being weaker on the first day (the model is initiated from horizontally homogeneous fields). The amplitude of the diurnal cycle of CAPE and CIN is also decreasing with time, which could be related to the too weak diurnal variation of the boundary layer previously found for the real case.

It is also noticeable that the magnitude of the 24-h mean rainfall rate can vary from day to day. Indeed, we found differences among a series of sensitivity studies to the horizontal resolution, which could not be simply explained in terms of variation of the resolution. This finding maybe connected to the sensitivity analysis performed by UKMO, who investigated the impact of different initialisation procedures (initial random noise) and found a variety of 24-h mean rain values as illustrated in Fig.5.4. Shallow cumulus is shown to develop at the same time in all of the ensembles (Fig. 5.4, left panel) but the runs differ significantly once the convection begins to deepen, leading to distinct rainfall rates (Fig.5.4, right panel). This weakness could also be to some extend be amplified by the 2D framework used for both of these sensitivity tests and the horizontally homogeneous initial profiles of temperature and moisture. This point clearly deserves further examination.

The timing of rainfall appears as a more robust feature, and we expect that the analysis currently underway will help to determine the parameters controlling this timing, from dry to moist and raining phases of convection, and to identify the mechanisms involved in CRMs runs.

 

Figure 5.3: Ideal case, CRM run, 4-day time-height series of (a) cloud condensate (10-5 g g-1 blue isoline) and equivalent potential temperature qe, (b) potential virtual temperature qv in the lower atmosphere (also shown are the boundary layer height (red curve) and cloud condensate 10-5 g g-1 blue isoline); 4-day time series of (c) CIN, CAPE and vertical kinetic energy (black, blue and red curves respectively), and (d) precipitation, latent and sensible heat fluxes (black, blue and red curves respectively) (CNRM-GAME).

 

 

 

Figure 5.4: Ideal case, time series of cloud top height (left panel) and rainfall (right panel) for the first day of CRM simulations with different initiation procedures, the shaded area delineates the standard deviation from the mean, the red curve corresponds to the UKMO SCM run .

 

Figure 5.5: Ideal case, time series of rainfall (upper panel) and CIN (lower panel).

 

 

5.4 Single Column Models

For the real case, results from four SCMs have been provided, by UKMO, ECMWF, LMD and CNRM. Results show that precipitation occurs too early in all the SCMs (Fig. 5.2), suggesting that this weakness, shared by many GCMs, can be properly analysed within this joint CRM/SCM framework. This also motivated the design of an idealised case. The performances of and consistency among these models are much weaker than among CRMs as previously noticed (Fig. 5.1). We also found large differences between CRMs and SCMs downward convective fluxes, usually very weak in SCMs runs, whereas their magnitude is comparable to the magnitude of upward cloud mass fluxes in CRMs, leading to the cloud mass flux being much larger in SCMs than CRMs (Fig. 5.1). Though this finding could be influenced by the choice of criteria necessary to diagnose this quantity in a CRM[1], it suggests that the formulation of downdrafts should be carefully examined in parameterisations with the help of dedicated CRM outputs. Also clear from SCM providing this information is the highly intermittent nature of convection in these models, in disagreement with CRM results.

For the idealised case, results show that deep convection usually occurs too early (Examples on Figs 5.4 and 5.5). In the UKMO SCM, early rainfall is due to fast deepening of convection rather than it going off too early in general. Convection instantly penetrates up to 8km and the shallow cumulus phase is missed (Fig 5.4, left panel, red curve). It also appears that correct values of CIN are difficult to reproduce in SCMs, in contrast with CRMs (Fig. 5.5, lower panel). Indeed in SCMs, CIN is frequently an order of magnitude weaker than observed (same problem as for the real case). The strong links between observed large-scale CIN values and deep convection shown in Xie et al. (2002) indicate that it is necessary to explain the source of these differences between CRMs and SCMs, and to investigate their consequences in terms of the mechanisms involved in the initiation/triggering of convection in both types of models. As designed by EUROCS, close collaboration between CRM and SCM groups will only allow to progress on these difficult issues. For example, close collaboration between the CNRM-GAME and the ECMWF began last December.

 

Observations

Regional model

 

local time (h)

 

Figure 6: Observed (left panel) and modelled (right panel) mean time of maximum precipitation for each of 51 days between June 10- July 31st 1993. A clear signal is that Max rainfall generally occurs early-late evening local time. This is captured by the regional model (SMHI). The primary error is in the SE USA, possibly because it is close to the model boundaries.

 

 

5.5 Climate & NWP Models

 

Diagnostics have been provided by large-scale and mesoscale modellers. Comparisons have been performed between results from GCMs (UKMO-Climate, ARPEGE-Climate , ARPEGE-NWP, ECMWF-NWP models) and the CLAUS observations (Yang and Slingo 2001). This work shows that the two NWP models are affected by a similar phase bias as Climate models. Output from the LMD climate model also pointed out the same default in the LMD model.

In contrast, results from SMHI showed that the mesoscale limited area climate model (RCA05) was able to reproduce several aspects of the observed diurnal cycle of convection over Northern America (Fig. 5.6), but the runs were performed at higher resolution than typical in a GCM. One can notice the specific diurnal cycle of convection over the SGP-ARM site previously stresses. A summary of SMHI results is available on the EUROCS web site.

 

5.6 Conclusions and future

 

This second EUROCS year has been mainly organized towards three activities. The analysis of the real case simulations with SCMs and CRMs have been completed, our results being consistent with Xu et al. (2002) and Xie et al. (2002) conclusions. They show a more consistent behaviour of CRMs compared to SCMs. However, they also indicate that, in terms of timing of convection, CRM simulations of convection over land are sensitive to the resolution (Petch et al., 2002) and to sub-grid scale parameterisations - two connected issues, stressing the importance of boundary layer circulations. These results are available on the EUROCS web site.

A more appropriate ideal case for studying the diurnal cycle of deep convection over land has been designed from the real case. It has been tested and made available to the participants. This case has already been run by participants. Analysis of outputs from this case show that the wrong diurnal phase of rainfall found in GCMs is reproduced in these idealised SCM runs, and precipitation occurs usually earlier in SCMs than in CRMs. The atmospheric stability is also dissimilar in these two types of model, the CIN in particular being much weaker in SCMs. Also, a sensitivity test to the initialisation procedure in UKMO CRMs show a significant impact of the initial noise, suggesting than ensemble of CRM runs might be helpful.

Diagnostics from GCMs and mesoscale climate models have also been done. Analyses of results are consistent with our current knowledge of this problem. NWP and climate models share the same default though the regional model leads to a better diurnal cycle than GCMs.

From the obtained results, motivated changes in convective parameterisations have been considered by modellers, and will be tested in SCMs and GCMs. At the same time, the CRM simulation of the early phase of diurnal cycle will continue to be deeply investigated as few is known. Finally, close collaborations between CRM and SCM groups have been built and will allow to improve the diurnal cycle of deep convection in SCMs and GCMs


Section 6

IDEALIZED HUMIDITY CASE

 

Gathered and Prepared by:

Steve Derbyshire

 

Case Leader: UK Met Office

Participating Partners: CNRM-GAME, ECMWF, INM, SMHI, Un of Lisbon and LMD

WEB Page: http://www.cnrm.meteo.fr/gcss/EUROCS/deephumidity.html

 

6.1 Motivation

The sensitivity of moist convection to mid-level humidity is an important issue in climate variability (e.g. Parsons et al 2000, Redelsperger et al. 2002), and provides an idealized test of convection representation in weather and climate models. Johnson (1997), reviewing tropical observations from the TOGA-COARE experiment, shows clear associations between observed convection strength and relative humidity profiles. The more strongly convecting cases tend to have significantly moister profiles in the mid-troposphere (whereas in the boundary layer the relative humidity varies little between strongly and weakly convecting cases).

Links between convection and humidity are thought to play a role in the Madden-Julian Oscillation (an important component of the climate system which is often not well modelled); in the differences between convection over oceans and over continents (including Europe); and in the differences between cyclonic and anticyclonic weather in mid-latitudes.

 

The sensitivity of convection to humidity is also relevant to certain technical model problems. In weather and climate models, numerical "gridpoint storms" can occur when resolved-scale saturation is approached in a convectively unstable column. Modellers usually try to prevent this undesirable phenomenon by tuning the rate of parametrized convection (e.g. Betts and Miller 1993), but the need for such tuning may partly reflect deficiencies in the response of current convection schemes to humidity.

 

Parametrization of convection requires not just observed associations but a clear and quantitative understanding of mechanisms. The tropical observations might be explained by various mechanisms:

(a) loss of buoyancy within clouds by entrainment of subsaturated environmental air

(b) radiative impacts on temperature

(c) convergence and moistening caused by convection

In this project therefore we seek to use idealized CRM-SCM comparisons to help separate and quantify the mechanisms, especially the entrainment mechanism (a). Most current convection schemes attempt to represent entrainment in some form. But the values used differ widely between schemes, and many schemes do not use a single entrainment profile but rather assume a range of mixing within the convective cloud-field. Such variation is represented in different ways following Arakawa-Schubert, Kain-Fritsch or Emanuel buoyancy-sorting concepts. Hence it may not be appropriate to test these schemes by evaluation of a "standard" entrainment-profile derived from CRMs. Instead here we seek to use the humidity-sensitivity as a benchmark for all the schemes, which is linked to entrainment but not tied to any specific formulation.

 

Here we examine the convective humidity-sensitivity in a quasi-steady scenario with profile nudging. The quasi-steady scenario avoids complications of time-development, which are studied in other components of EUROCS. Profile nudging effectively incorporates a simplified model of the dynamical feedback on the temperature profile when the convecting region is smaller than the characteristic dynamical response scale. In this scenario the dynamics act to balance much of the convective heating (Q1); see Sobel & Bretherton (2000) and Randall & Cripe (1999) for related discussion. Inclusion of such nudging is intended to show the humidity impact more clearly and make the CRM-SCM setup more relevant to the performance of convection schemes in GCMs.

 

6.2 Case description

Two cases have been run with the UKMO CRM, a pilot simulation (A) and the main intercomparison case (B). Each case involves a range of humidities.

 

6.2.1 Run A (pilot CRM run)

The CRM pilot run was based on simple warm-rain physics (Kessler), with rapid relaxation of potential temperature and specific humidity to target profiles (at heights above 1km). The target humidity profile was varied at heights above 2km. A sea-surface temperature was prescribed, with a potential- temperature difference of 1K across the boundary layer no wind-forcing. A sketch of the specification is shown in Fig. 6.1. The pilot run confirms that changes in the mid-tropospheric humidity can switch the convection regime between shallow non-precipitating convection and vigorous deep convection, with changes to the shape of the convection profiles as well as the magnitude and depth.

Figure 6.1 Sketch for prescribed target profiles of potential temperature and humidity. The target profile specification is the same in the intercomparison run B as in the pilot run A, except that the relative humidity is defined over water or ice according to temperature.

 

6.2.2 Run B (main intercomparison case)

 

For the formal intercomparison of different models it was decided to use 3-phase cloud physics in the CRM (since the SCMs are designed to allow for ice processes). The relaxation timescale was specified as 1 hour, which is longer than a typical timestep in the SCMs (e.g. 30 minutes in the Met Office SCM). A moderate mean wind profile was specified, to help promote surface evaporation even in the absence of convective gusts (these are represented in the surface scheme for some but not all models). Wind, temperature and humidity profiles are nudged towards target profiles using a relaxation time of 1 hour. However this relaxation is imposed only at heights above 1km. The target temperature profiles for nudging are defined through potential temperature (Fig. 6.1) A specific humidity profile is prescribed by combining a relative humidity target with the potential temperature target profile. The target relative humidity is specified as 80% for z between 1km and 2km. Above 2km, it is specified as (a) 25% (b) 50% (c) 70% (d) 90% (Fig. 6.1). The simulations are run for 12 hours to reach a statistically steady state.

 

6.3 Cloud Resolving Model results

In the first-year report we showed the strong dependence of convection strength and depth on humidity, as evaluated using the UK Met Office CRM, but were unable to say to what extent that dependence reflected features of that particular model. During the second year we have strengthened the CRM component of this project substantially, by the addition of a second CRM, run by J.L.Redelsperger at CNRM/GAME. This work was not scheduled in the working plan but judged as a necessary work.

 

Figs. 6.2 and 6.3 show the very encouraging level of agreement between the two CRMs. The qualitative agreement in the trend towards deeper and stronger convection in moister profiles is excellent, but the agreement is also remarkably quantitative in many respects. This agreement gives us confidence in the use of the CRMs to test the SCM performance.

 

 

 

Figure 6.2 Compilation of mass flux results from the UK Met Office CRM for the four different values of RHt. The stronger, deeper convection is with the moister profiles.

 

Figure 6.3. As Figure 2 but for the CNRM-GAME CRM. Note the generally good agreement with the previous results.

6.4 Single Column Model results

 

Some results from the UK Met Office and LMD SCMs were shown in the first-year report and are not reproduced here. Five single-column models have now been run with 4 values of the humidity parameter RHt: UK Met Office, LMD, Meso-NH and two versions of the ARPEGE model (climate and NWP versions).

 

As noted in the first-year report, the UK Met Office SCM captures the surface precipitation values reasonably well but not the shapes of the convection profiles. The LMD SCM has more realistic shapes but gave rather low values of precipitation and weak dependence on RHt. Some tuning of the mixing parameters in the LMD scheme was carried out in response to these results. Owing to the postponement of the January workshop, due to sad and exceptional circumstances, the SCM synthesis and comparisons have not yet been discussed as a group, and the following results and interpretations should therefore be regarded as provisional.

As with the CRMs, we shall focus here on the updraught mass fluxes, although other diagnostics will also be intercompared. We shall also concentrate on the new results from year 2 of the project.

 

Figure 6.4. Corresponding mass-flux results for the Meso-NH SCM using the Kain-Fritsch-Bechtold convection scheme (plume radius 500m), shown as solid lines. For comparison the results of the CNRM-GAME CRM are plotted as dashed.

 

Figure 6.5. As Fig 6.4, but for the ARPEGE SCM climate version, with 3 hour CAPE adjustment timescale (solid lines), and CNRM-GAME CRM dashed.

Figure 6.6. As Fig 6.4 but for the ARPEGE SCM NWP version (solid). Again the CNRM-GAME CRM is shown dashed.

 

 

 

Results from the Meso-NH SCM run with the Kain-Fritsch-Bechtold convection scheme in collaboration with the University of Lisbon are shown on Fig. 6.4. The scheme can approach the CRM results for intermediate RHt values, but seems to have a less strong dependence on RHt. Fig. 6.5 shows results from the CNRM ARPEGE SCM, climate version, using a 3 hour convective adjustment timescale. This timescale matched the CRM better than the alternative 1 hour timescale. Fig. 6.6 shows corresponding results from the NWP version of ARPEGE. Again the 3 hour adjustment timescale seems more or less optimal. This SCM is possibly the closest to matching the CRM behaviour in the humidity case.

 

6.5 Climate and NWP models

 

Work on implementation of the results from this case in global models is still at an early stage, because the SCM results require further discussion and assessment. However various modifications to the SCMs have been made and can now be tested in climate or NWP models. These modifications concern both

i) the "closure" which controls the overall rate of convection

ii)    the convective profile shapes, especially in relation to statistical assumptions about mixing.

 

At UKMO, a convective closure which is explicitly sensitive to column relative humidity has been developed and tested, motivated by the EUROCS results. This development has given sufficient benefit that it is likely to be used operationally from April 2002. At CNRM-GAME, modifications of existing schemes are currently tested.

 

6.6 Conclusions and further work

 

A great deal of progress has been made with the idealized humidity case during year 2 of EUROCS project. Two independent CRMs have now been run on the case (each with four different values of the relative humidity parameter RHt) and give very similar answers. Five SCMs have also been run on the same case, and give a considerably wider range of answers.

 

In the CRM runs clear impacts of mid-level humidity have been demonstrated both in the pilot run A and in the intercomparison run B with 1hr nudging time. Run B converges rapidly to a quasi-steady convective ensemble. Significant variations are found in surface precipitation as a function of humidity, and between different schemes and the CRM. These differences require further analysis but show the potential of this approach to test the schemes. Scope for improving the schemes has been identified, including changes to the convective closure and to the mixing-PDFs.

The synthesis of these results needs to be discussed in more detail, at the forthcoming Workshop (Scheduled in April 2002), to give a firm basis for conclusions about GCM work. However the results of this case are already starting to influence GCM parametrizations.

Overall the level of agreement between the CRMs, and the magnitude of the sensitivities found, indicates that we can assess the performance of the SCMs and in turn make progress with GCM parametrizations..


 

Section 7

NEW DEVELOPMENTS OF CLOUD PARAMETERIZATIONS

 

 

7.1            CNRM-GAME (gathered by JF Royer)

The current physical parameterization schemes used in both the operational and climate versions of the ARPEGE model are being evaluated on their capacity to simulate cloud cover and its diurnal cycle. These studies confirm that in both versions the diurnal cycle of convection over the continents is systematically shifted with convection occurring too early in the afternoon, instead of late in the evening as observed. This defect appears in most GCMs, and is a symptom of the excessively fast response of the planetary boundary layer (PBL) to the diurnal march of solar forcing, part of which could be due to the equilibrium hypothesis between production and dissipation of turbulence on which are usually based diagnostic boundary layer schemes. Therefore it appears necessary to improve the current parameterisations both by representing more accurately the mixing processes in the PBL, and by introducing prognostic variables, which in their evolution could introduce the inertia needed to delay the occurrence of convection. A good candidate for this is the Bougeault-Lacarrre turbulent kinetic energy (TKE) parameterization, which has been introduced in a test version of ARPEGE-Climat. However its performance is limited by inaccuracies in the treatment of liquid water by the large-scale equations. As a starting point, a prognostic treatment for liquid water (developed by P Lopez) has been implemented in ARPEGE-Climat and tested in monthly simulations. This prognostic treatment appears to have a promising potential, but for the time being its applicability for longer climate simulations has been limited by cases of numerical instability appearing recurrently at the beginning of summer. A new PBL scheme following the Grenier-Bretherton parameterization, formerly tested in 1-D cases, has been fully re-written and evaluated in global simulations. The new PBL model contains a new length scale, a new PBL height estimate, an estimate of TKE transport and explicitly deals with entrainment at the top of convective boundary layers. A parameterization of radiatively driven fog has also been introduced. This new PBL model impacts positively on ARPEGE-climat GCM, mostly in terms of PBL height and cloud cover in Stratocumulus regions. Nevertheless, lack of vertical resolution is thought to be responsible for unrealistic fog situations simulated near the eastern coastlines of sub-tropical oceans, and its potential improvements seem also limited by the lack of a liquid water transport in the large-scale model. The possibilities of improving the interactions between boundary layer and convection will also be investigated by modifications in the closure and triggering of the convection scheme, and the representation of shallow convection. Modifications have been introduced in the convection scheme in order to increase the importance of buoyancy in its design. A cloud vertical velocity equation with the buoyancy as the source term has been added; organised entrainment and detrainment are computed with the help of this equation. The triggering condition is based upon the sign of this computed cloud vertical velocity, and a CAPE (vertical integral of buoyancy) closure condition is considered instead of a moisture convergence condition. These modifications together with the inclusion of a convective precipitation scheme enable the representation of shallow convection using this improved convection scheme. The future work will incorporate all these developments in the library of the new version of ARPEGE-Climat so as to facilitate the tests and improvement of these different approaches, separately and in combinations.

 

 

 

7.2            ECMWF (gathered by A Beljaars)

Parametrization work at ECMWF has been coordinated with the EUROCS activities and benefited substantially from the EUROCS partnership. The activities related to the EUROCS project are the following:

 

i) Development of a mass flux term in addition to the boundary layer diffusion. This opens the way to a more unified approach to boundary layer diffusion and shallow convection. The scheme was developed in collaboration with KNMI and has resulted in code for the ECMWF model which is currently under test. It will be part of a package to be introduced in operations later this year.

 

ii) Development of a new cloud base/cloud top detection routine to support the ECMWF convection scheme (in collaboration with KNMI). The scheme has a substantial beneficial impact on systematic errors in the tropics and will be part of a package of model changes to be introduced in operations (Jakob and Siebesma, 2002).

 

iii) A study of the diurnal cycle of convection in the ECMWF model during the LBA experiment. The study was not conclusive, but clearly indicated the complexity of the physics of the diurnal cycle, and emphasized the importance of shallow convection and boundary layer coupling. It also demonstrated the potential of the single column modelling concept. Furthermore, LBA cases may be highly suitable for future study by CRM's. (Betts and Jakob, 2002)

 

iv) The single column version of the ECMWF model has been upgraded and made available to EUROCS's partners.

 

v) The EUROCS project has been provided with 3D model fields for inter comparison of the Pacific stratocumulus to cumulus transition. A month of short range forecasts and a month from a long integration has been produced for July 1987.

 

In the final year of the EUROCS project, the emphasis at ECMWF will be on the 3D testing and implementation of the model changes mentioned above. The planned collaboration with CNRM/GAME will be used to test the new cloud base/cloud top algorithm on the deep convection diurnal cycle case and to do additional diagnostics on the diurnal cycle in the 3D model environment.

 

 

7.3            LMD (gathered by JY Grandpeix)

Several modifications on physical parameterizations of boundary layer and deep convection have been realized during the second year of EUROCS and mostly tested in the SCM framework.

In the final year of EUROCS, the various improvements will be implemented in the 3D GCM. After tuning the model, we will study global statistics of the cloud diurnal cycle and of the seasonal cycle of cloud cover and precipitation. Then we would like to focus on three items~:

 

(i) Cloud cover and cloud radiative forcing~: the improvement of the simulation of deep convection related clouds over land is an important issue for the LMDZ GCM. The problem has been exemplified on the ARM case~; further improvements will be necessary.

 

(ii) Ocean/land precipitation difference at mid-latitudes~: the present LMDZ version yields an excess of precipitation over land relative to ocean. This problem is related both to the deep convection scheme closure and to its sensitivity to relative humidity profile. It should be greatly improved by changes made for the ARM case and for the idealized humidity case (see sections 5 & 6).

 

(iii) Walker circulation~: the ability of the GCM to represent correctly the Walker circulation depends strongly on the sensitivity of the deep convection scheme to SST. The work done on the scheme closure and triggering should allow a better representation of this circulation. Especially, it should enable a good simulation of the winter monsoon over the Indian Ocean.

 

 

 

7.4            Max-Planck-Institut fr Meteorologie (Gathered by A Chlond )

Participating colleagues: A. Chlond, F. Mller, I. Sednev, E. Roeckner

 

EUROCS aims to improve the treatment of cloud systems in global and regional climate models. The MPI-M concentrates its efforts on two major and well identified deficiencies of climate models: representation of subtropical marine stratocumulus, and of diurnal cycle of shallow cumulus over land. The strategy used to address these issues is based on the use of a hierarchy of models and observations to integrate cloud studies across the full range of scales. Numerical models range from a General Circulation Model (GCM ) through a Single Column model (SCM) to Large Eddy Simulations (LES).

 

The atmospheric general circulation model ECHAM (European Center Hamburg) used at the MPI-M is based on the weather forecast model of the European Centre for Medium Range Weather Forecasts (ECMWF). Numerous modifications have been applied to this model at the Max Planck Institute for Meteorology and the German Climate Computing Centre (DKRZ) to make it suitable for climate forecasts, and it is now a model of the fourth generation. A detailed description of the ECHAM4 model can be found in Roeckner et al. (1996). In the standard model version a 19-level hybrid sigma-pressure coordinate system is used. The vertical domain extends up to the pressure level of 10 hPa. Prognostic variables are vorticity, divergence, logarithm of surface pressure, temperature, specific humidity and mixing ratio of total cloud water. The physical parameterization package includes the following processes related to the representation of shallow cloud systems:

 

The turbulent surface fluxes are calculated from Monin-Obukhov similarity theory. Within and above the atmospheric boundary layer, a first order closure scheme is used to compute the turbulent transfer of momentum, heat, moisture, and cloud water. The eddy diffusion coefficients are calculated as functions of turbulent kinetic energy which is obtained from the respective rate equation. The parameterization of cumulus convection (shallow, mid-level, and deep), is based on the bulk mass flux concept of Tiedtke. However, organized entrainment is related to buoyancy instead of moisture convergence, organized detrainment is computed for a spectrum of clouds detraining at different heights, and an adjustment-type closure is used for deep cumulus convection instead of the moisture convergence closure applied in the Tiedtke scheme. Moreover, the water loading is considered in the buoyancy calculation, the cloud water detrained at the top of cumulus clouds is entering as a source term in the stratiform cloud water equation. The stratiform cloud water content is calculated from the respective budget equation including sources and sinks due to phase changes and precipitation formation by coalescence of cloud droplets and gravitational settling of ice crystals . The convective cloud water detrained at the top of cumulus clouds is used as a source term in the stratiform cloud water equation. Fractional cloud cover is parameterized in terms of relative humidity.

 

A first survey of the GCM ensemble run reveals that with respect to subtropical marine stratocumulus ECHAM produces a too shallow boundary layer and predicts a too low liquid water path but with a timing in phase compared with the observations. In addition, with respect to the representation of shallow cumulus convection ECHAM does not produce a realistic diurnal cycle.

 

Based on a detailed analysis of the SCM and GCM simulations deficiencies in the current paramterizations are identified and physically-grounded corrections will be brought into the parameterizations and implemented in the ECHAM-SCM/GCM and evaluated against the same case studies. In particular, the following steps are planned:

 

        modification of the numerical time-integration scheme to allow for the exact radiative-diffusive equilibrium balance

        use of the modified moist Bougeault-Lacarrre length scale formulation in the diffusion scheme

        use of the statistical cloud scheme instead of the relative humidity scheme

        modification of the entrainment and detrainment rates in the cumulus convection scheme to match those diagnosed from the LES simulations

 

 

 

 

7.5            SMHI (gathered by C Jones)

In the EUROCS project, SMHI contributes with the 3D Regional Climate Model (RCA) developed from the Numerical Weather Prediction (NWP) limited area model HIRLAM. Allied to this an identical single column version of RCA is also being extensively used. Parameterisation developments within EUROCS should, therefore, directly benefit both the regional climate modelling and weather prediction groups at SMHI.

Use of the single column model allows the development of parameterisation schemes in a well constrained setting and direct verification of physical parameterisations at the process level, versus observations and models that fully resolve the process being parameterised (eg LES). New parametric approaches developed in the single column framework can then be tested in the 3D setting of the RCA model.

 

The advantage of a regional model, over a fully global model, is that the regional model domain can be designed in such a manner that the phenomenon of interest can be isolated geographically, while the influence of the rest of the global atmosphere is defined by the model boundary conditions. Where the boundary conditions are defined by an analysed field (eg ECMWF analyses), this is generally a good representation of the truth. The result is one can study a particular feature in a well defined meteorological setting, with the large scale flow defined by the analysed boundary conditions, while still allowing some of the degree of freedom of the 3D system. The definition of the model domain can isolate a particular regional phenomena (eg the subtropical Stratocumulus deck), or encompass an entire planetary cicrculation (eg the Walker/Hadley Circulation and associated cloud fields). Regional Models can also be viewed as GCMs of the future as they are presently run at resolutions in the range 20-50km, a probable GCM resolution in 10 years time. Developments made in the EUROCS project, through the use of RCA, we hope will feed into future GCM developments as GCM resolutions increase.

 

The single column version of RCA has now been integrated for 3 of the EUROCS defined case studies, namely the FIRE Stratocumulus case, shallow cumulus case and the diurnal cycle of deep convection case. In all 3 cases improvements in model physical parameterisations have resulted, these will now be tested with the 3D system.

 

The Diurnal Cycle of Stratocumulus.

As an initial contribution, the 3D RCA model was integrated in climate mode for the month of July 1987 with observed Sea Surface Temperatures. The model was run at 0.4 resolution with 24 vertical levels. The mean diurnal cycle of various key stratocumulus parameters were compared to observations. The key results were as follows:

 

1.      A cloud scheme based on both Relative Humidity and (prognostic) cloud water (Xu & Randall 1996) performed better than one based on solely Relative Humidity (Slingo 1987). In particular both the predicted cloud fraction and cloud water amounts were more realistic with the former.

2.      The mean diurnal cycle was well simulated. The timing, within the diurnal cycle, of maxima and minima in cloud amounts and liquid water paths (LWP) were well represented when compared to observations.

3.      The amplitude of the diurnal cycle was underestimated. The daytime minimum in LWP was overpredicted and the nocturnal maxima underpredicted. As a result, in the monthly mean, clouds were too reflective to solar radiation with too low a simulated LWP field. This result comes from the underprediction of the diurnal cycle and results in too little solar radiation reaching the sea surface. This type of error, in a coupled ocean-atmosphere climate model, would cause a serious error in the SST field and indicates how diurnal cycle errors can lead to significant model errors due to the non-linear relationship between clouds and the diurnal cycle of solar radiation.

 

The daytime excess LWP appears linked to an underestimate of cloud absorption of solar radiation. Increasing the cloud absorption and overall model atmospheric absorption of solar radiation closer to observed values, led to a reduction of LWP in the daytime minimum period and an improvement in the model simulated surface radiation budget. Further work is ongoing with the single column model to assess the importance of solar absorption in the diurnal cycle of Stratocumulus clouds.

 

Use of the single column model for the FIRE Stratocumulus case assisted in determining the cause of the RCA overestimate of the nocturnal maximum of LWP. It also indicated the crucial importance cloud microphysics plays in setting the LWP of simulated Stratocumulus clouds. In a high resolution 40 level version of the single column RCA used for the FIRE case, the model LWP collapsed rapidly towards very low values. The cause of this was traced to precipitation removal. In fact to the initiation of the cloud water collection process by precipitating droplets. In this process precipitation droplets rapidly collect smaller cloud water droplets through which they are falling and deplete the cloud of cloud water, the water being lost as precipitation. The process became unrealistically large as the thickness of a vertical layer became small, in this case ~50m, resulting in a rapid depletion of the cloud water from within the cloud. (This process, too a lesser extent, is considered to be the likely cause of the overall underestimate of LWP in the 24L 3D model also). Correcting this led to the precipitation formation process being less sensitive to model vertical resolution and a more realistic cloud water evolution. This small modification to the precipitation production term increased the cloud water amounts in the single column model by ~100% and halved the amount of solar radiation reaching the surface. High vertical resolution is clearly a requirement for accurate representation of Stratocumulus clouds, here the single column model aided greatly in highlighting a key model sensitivity to vertical resolution. This improvement will now be tested in 3D on the July 1987 FIRE case, an improved overall simulation of the cloud and cloud-radiation interaction is expected.

 

The diurnal Cycle of Shallow Cumulus Clouds over Land.

Most parameterisations of shallow convection parameterise the thermodynamic effect of shallow convection, through the effect it has on the humidity and temperature fields. The cloud field associated with the shallow convective mixing is not generally parameterised and is often either not represented at all, or left to be simulated by the resolved large scale cloud scheme (The Kain Fritch convection scheme used in RCA (Kain & Fritch 1990) contains no formal parametrisation of shallow convective cloud fraction). In both cases the associated cloud errors are likely to be very large.

 

In the middle of a typical summer day, over continental Europe, cloud fractions associated directly with shallow convection can often occupy 20% or more of the sky. The fact that they occur during periods of maximum solar input (summer time, middle of the day) makes the solar radiative effect of these clouds important to parameterise. In EUROCS we have introduced a parameterisation of shallow convective cloud fraction due to Albrecht (1981) into the single column version of RCA. This has been tested and tuned using the EUROCS shallow cumulus case. The shallow cumulus cloud fraction is linked directly to the liquid water content of the shallow convective updrafts and the relative humidity of the environment into which these updrafts detrain. This means the shallow convective cloud fraction is linked directly to shallow convective activity and the convective sub-cloud layer. The shallow convective cloud water, generated by the convection scheme, is retained in these shallow convective clouds and evaporation/precipitation processes are allowed to occur as with large scale clouds. Most importantly the shallow convective clouds are then radiatively active. Compared to using the large scale cloud scheme to diagnose shallow convective cloud fractions, this approach proved far more successful in the single column tests.

 

These developments are now being brought into the 3D regional model and will be tested over continental Europe and USA and over the shallow convective regions of the Pacific. A systematic error in RCA (and in many other models) is an underprediction of summer clouds over continental regions. This leads to an associated overestimate of surface solar radiation and a near surface warm bias. It is hoped that these systematic errors will be improved by the inclusion of a radiatively active shallow cumulus cloud fraction as developed in the single column test case.

 

 

 

7.6            INM (gathered by J. Calvo)

Two different approaches are followed at INM. One using a SCM version of the research model Meso-NH and other using a SCM of the operational weather forecast model HIRLAM.

 

Meso-NH SCM

Results from the LES simulations have been used to improve the representation of boundary layer clouds using a pure turbulent scheme written with conserved variables. The scheme includes a statistical cloud condensation scheme allowing simulation of high cloud covers (gaussian distribution following Sommeria-Deardoff (1976) and low cloud cover clouds (skew asymmetrical function following Bougeault , 1982). It is not straight forward that such a scheme could represent correctly both types of clouds.

The turbulence scheme (Cuxart et al 2000) uses a diagnostic mixing length based on Bougeault-Lacarrere (1989). The mixing length has been generalized to include the effects of condensation and evaporation on virtual temperature. The new formulation gives good results for the case of diurnal cycle of stratocumulus but tend to produce too stratiform clouds for the shallow cumulus case. Further improvement can be achieved using the cloudiness to compute the effective buoyancy. Using this new approach the results are closer to LES results and compare better with shallow cumulus simulations using mass-flux approaches. The cloud cover is still to high but the SCM simulations with the new mixing length are able to maintain a conditionally unstable profile in the cloud.

 

HIRLAM SCM

Simulation of deep convection and boundary layer clouds have been performed in using vertical resolution used in the operational forecast model (40 levels in the whole atmosphere). Several developments have been carried out in collaboration with SMHI (see above). A new formulation based on Kain-Fritsch convection (1990) and Rasch-Kristjansson condensation is able to reproduce much better the diurnal cycle of deep convection compared to the standard modified Sundqvist scheme. The simulation of stratocumulus have been found very sensitive to the details of the microphysics formulation. In general stratocumulus clouds seems to give to high values of precipitation in HIRLAM simulations. A new formulation of the parameterization of precipitation depending on vertical model resolution improves significantly the evolution of liquid water path and therefore the radiative fluxes reaching the surface.

The improved schemes are now ready to be tested in 3D Limited Area Model HIRLAM simulations.

 

 

7.7            UKMO (gathered by S. Derbyshire)

Results from SCM and CRM studies under EUROCS, including the stratocumulus case, the diurnal cycle cases and the idealized humidity case, are being used in various ways to guide GCM parametrization development.

 

Some versions of the Met Office climate model have problems with marine stratocumulus. Analysis linked to the EUROCS stratocumulus case has helped trace the reasons for these problems. The existing boundary layer scheme seemed to give excessive buoyancy production at cloud base due to diffuse representation of the cloud-base in the SCM, and insufficient diurnal decoupling compared to LES and to observations.

 

The Met Office will shortly hold a Workshop on the diurnal cycle problem, to which the EUROCS results form an important input. The problem is viewed as important but difficult, and there is a debate about the extent to which a quasi-steady convection scheme can capture the diurnal cycle, and also about the role of model resolution. The EUROCS projects have provided a basis of documented evidence to underpin this debate.

 

The idealized humidity case shows that convection has a strong sensitivity to humidity as well as to the temperature profile, and that current parametrizations have deficiencies in capturing that response. Based on the EUROCS results a simple moisture-sensitive convective closure has been implemented, which gives improved results in handling localized disturbances in the tropics.


 

References Cited

 

Albrecht B.A. 1981 Parameterization of Trade Cumulus Amounts: Journal of Atmospheric Science. 38 No1. 97-105

Albrecht, B.A., D.A. Randall and S. Nicholls, 1988: Observations of marine stratocumulus clouds during FIRE. Bull. Amer. Meteor. Soc., 69, 618-626.

Albrecht, B.A., C.W. Fairall, D.W. Thomson, A.B. White, J.B. Snider and W.H. Schubert, 1990: Surface-based remote sensing of the observed and the adiabatic liquid water content of stratocumulus clouds. Geophysical Research Letters, 17, 89-92.

Betts, A. and C. Jakob, 2002: Evaluation of the diurnal cycle of precipitation, surface thermodynamics and surface fluxes in the ECMWF model using LBA data. Submitted to J. Geo. Research.

Betts, A.K., 1990: The diurnal variation of California coastal stratocumulus for two days of boundary layer soundings. Tellus, 42A, 302-304.

Betts, A.K., P. Minnis, W. Ridgway and D.F. Young, 1992: Integration of satellite and surface data using a radiative-convective ocean boundary-layer model. J. Appl. Meteor., 31, 340-350.

Betts, AK and Miller, MJ (1993): The Betts-Miller scheme (In: The Representation of Cumulus Convection in Numerical Models, AMS Monographs vol 24 no 46 ed.KA Emanuel and DJ Raymond )

Blaskovic, M., R. Davies and J.B. Snider, 1991: Diurnal variation of marine stratocumulus over San Nicolas Island during July 1987. Mon. Wea. Rev., 119, 1469-1478.

Bougeault, P. 1981:Modeling the trade-wind cumulus boundary layer. Part II: A high-order one-dimensional model", J. Atmos. Sci,38,2429-2439

Bougeault, P., 1982: Cloud-ensemble relations based on the gamma probability distribution for higher-order models of the planetary boundary layer, J. Atmos. Sci, 39, 2691-2700

Bougeault, P. and P. Lacarrere (1989): Parameterization of orography-induced in a mesobeta-scale model", Mon. Wea. Rev., 117,1872-1890

Cuxart, J., Bougeault, Ph. and Redelsperger, J.L., 2000: A multiscale turbulence scheme apt for LES and mesoscale modelling. Q. J. R. Meteorol. Soc., 126, .1-30

Dai, A., I. Fung, and A. D. Del Genio, 1997: Clouds, precipitation, and temperature range, Nature, 386, 665-666.

Dai, A., F. Giorgi, and K. E. Trenberth, 1999: Observed and model simulated precipitation diurnal cycle over the contiguous United States. J. Geophys. Res., 104, 6377-6402.

Duynkerke, P.G. and P. Hignett, 1993: Simulation of diurnal variation in a stratocumulus-capped marine boundary layer during FIRE. Mon. Wea. Rev., 121, 3291-3300.

Duynkerke, P.G and J. Teixeira, 2001: Comparison of the ECMWF Re-analysis with FIRE I observations: Diurnal variation of marine stratocumulus. (accepted in J. of Climate)

Gray, W. M. and R. W. Jacobson Jr., 1977: Diurnal variation of deep cumulus convection. Mon. Wea. Rev., 105, 1171-1188.

Hignett, P., 1991: Observations of the diurnal variation in a cloud-capped marine boundary layer. J. Atmos. Sci., 48, 1474-1482.

IPCC Third Assessment Report - Climate Change 2001: The Scientific Basis, Contribution of Working Group I, J. T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P. J. van der Linden and D. Xiaosu (Eds.) Cambridge University Press, UK. pp 944.

Jakob, C., 1999: Clouds in the ECMWF Re-Analysis. J. Climate, 12, 947-959.

Jakob C. and P. Siebesma, 2002: Decision making in a bulk mass-flux convection parametrization - Influence of triggering, updraught properties and model climate. Submitted to QJRMS

Johnson, RH (1997): Recent observations of deep convection: TOGA COARE. (In: Proceedings of 1996 ECMWF Workshop "New insights and approaches to convective parametrization..)

Kain J.S. and M.J.Fritsch 1990: A 1D entraining/detraining plume model and its application in convective parameterization: Journal of Atmos Sci 47 2784-2802

Krueger,S. K., R. T. Cederwall, S. C. Xie, and J. J. Yio, 1999: GCSS Working Group 4 Model Intercomparison Procedures for Case 3: Summer 1997 ARM SCM IOP. Technical note.

Ma, C.-C., C.R. Mechoso, A.W. Robertson and A. Arakawa, 1996: Peruvian stratus clouds and the tropical Pacific circulation: A coupled ocean-atmosphere GCM study. J. Climate, 9, 1635-1646.

Miller, R.L., 1997: Tropical thermostats and low cloud cover. J. Climate, 10, 409-440.

Minnis, P., P.W. Heck, D.F. Young, C.W. Fairall and J.B. Snider, 1992: Stratocumulus cloud properties derived from simultaneous satellite and island-based instrumentation during FIRE. J. Appl. Meteor., 31, 317-339.

Nigam, S., 1997: The annual warm to cold phase transition in the eastern equatorial Pacific: Diagnosis of the role of stratus cloud-top cooling. J. Climate, 10, 2447-2467.

Parsons, DB, Yoneyama, K and JL Redelsperger, 2000: The evolution of the tropical western Pacific atmosphere-ocean system following the arrival of a dry intrusion. QJRMS vol 126, 517-548.

Petch, J. C., A. R. Brown and M. E. B. Gray, 2002: The impact of horizontal resolution on convective development in simulations of the diurnal cycle over land, submitted to Quart. J. Roy. Meteor. Soc.

Philander, S.G.H., D. Gu, D. Halpern, G. Lambert, N.-C. Lau, T. Li and R.C. Pawcanowski, 1996: Why the ITCZ is mostly north of the equator. J. Climate, 9, 2958-2972.

Randall, D and Cripe, D (1999): Alternative methods for specification of observed forcing in single-column models and cloud system models. JGR vol 104 24527-24545.

Rasch, P. J. and J. E. Kristjansson (1997) :A comparison of the CCM3 model climate using diagnosed and predicted . J. Climate, 11, pp. 1587-1614

Redelsperger, J.L., D. Parsons and F. Guichard,.2002: Recovery processes and factors limiting cloud-top height following the arrival of a dry air intrusion observed during TOGA-COARE. J. Atmos. Sci, in press.

Roeckner, E., K. Arpe, L. Bengtsson, M. Christoph, M. Claussen, L. Duemenil, M. Esch, M. Giorgetta, U. Schlese, and U. Schulzweida, 1996: The atmosperic general circulation model ECHAM-4: Model description and simulation of present day climate. Report No. 218, Max-Planck-Institut fr Meteorologie, Hamburg, Germany, 90 pp.

Rossow W.B. and R.A. Schiffer, 1999: Advances in understanding clouds from ISCCP. Bull. Amer. Meteor. Soc., 80, 2261-2287.

Slingo J.M. 1987 The development and verification of a cloud prediction scheme for the ECMWF model: Q.J.R.Meteorol. Soc 113, 899-928

Sobel, AH and Bretherton, CS (2000): Modeling Tropical Precipitation in a Single Column. J.Climate vol. 13, 4378-4392.

G. Sommeria y J. W. Deardorff (1977): Subgrid-scale condensation in models of nonprecipitating clouds, J. Atmos. Sci, 34, 344-355

Xie S., Cederwall, R. T., Xu K.-M., Bechtold P., Cripe D. G., Del Genio A. D., Ghan S. J., Gregory D., Hack J. J., Iacobellis S. F., Klein S. A., Krueger S. K., Lohmann U., Petch J. C., Randall D. A., Rotstayn L. D., Somerville R. C. J., Sud Y. C., Von Salzen K. , Walker G. K., Wolf A., Yio J. J., Zhang G. and Zhang M., 2002: Intercomparison and evaluation of cumulus parameterizations under Summertime midlatitude Continental Conditions, 2001, submitted to Quart. J. Roy. Meteor. Soc.

Xu K & D.A.Randall 1996: A Semiempirical Cloudiness Parameterization for use in Climate Models: Journal of Atmos Sci. 53 No21 3084-3102

Xu, K.-M., Cederwall, R. T., Donner, L. J., Guichard, F., Grabowski, W. W., Johnson, D. E., Khairoutdinov, Krueger, S. K.,L., Petch, J., C., Randall, D. A., Seman, C. J., Tao, W.-K., 2002, To appear in Quart. J. Roy. Meteor. Soc.

Yang, GY. and JM Slingo, 2001: The diurnal cycle in the tropics. Mon. Wea. Rev., 129 ,784-801.


Annexe A

EUROCS Publications List

 

Peer Reviewed Articles :

Authors

Date

Title

Jounal

Reference

Duynkerke, P.G and J. Teixeira,

2001

Comparison of the ECMWF Re-analysis with FIRE I observations:Diurnal variation of marine stratocumulus

J. of Climate

Accepted

Xu, K.-M., Cederwall, R. T., Donner, L. J., Guichard, F., Grabowski, W. W., Johnson, D. E., Khairoutdinov, Krueger, S. K.,L., Petch, J., C., Randall, D. A., Seman, C. J., Tao, W.-K., Xie, S. C., Yio, J. J., et Zhang, M.-H.,

2001

An intercomparison of cloud-resolving models with the ARM summer 1997 IOP data.

Quart. J. Roy. Meteor. Soc.

Submitted

Betts, A.K. and C. Jakob

2002

Study of diurnal cycle of convective precipitation over Amazonia using a single column model

J. G

Submitted

Xie S., Cederwall, R. T., Xu K.-M., Bechtold P., Cripe D. G., Del Genio A. D., Ghan S.J., Gregory D., Hack J. J., Iacobellis S. F., Klein S. A., Krueger S. K., Lohmann U., Petch J. C., Randall D. A., Rotstayn L. D., Somerville R. C. J., Sud Y. C., Von Salzen K. , Walker G. K.,Wolf A., Yio J. J., Zhang G. and Zhang M.

2002

Intercomparison and evaluation of cumulus parameterizations under Summertime midlatitude Continental Conditions,

Quart. J. Roy. Meteor. Soc.

Submitted

Petch, J. C., A. R. Brown and M. E. B. Gray

2002

The impact of horizontal resolution on convective development in simulations of the diurnal cycle over land

Quart. J. Roy. Meteor. Soc.

Submitted

Xu, K.-M., Cederwall, R. T., Donner, L. J., Guichard, F., Grabowski, W., Johnson, D. E., Khairoutdinov, M. Krueger, S. K. , Petch, J., C., Randall, D. A., Seman, C. J., Tao,W.-K., Xie, S. C., Yio, J. J., and Zhang, M.-H

2002

An intercomparison of cloud-resolving models with the ARM summer 1997 IOP data,

Quart. J. Roy. Meteor. Soc.

In press

Jakob C. and P. Siebesma

2002

Decision making in a bulk mass-flux convection parametrization - Influence of triggering, updraught properties and model climate

Quart. J. Roy. Meteor. Soc.

Submitted

Redelsperger, J.L., D. Parsons and F. Guichard

2002

Recovery processes and factors limiting cloud-top height following the arrival of a dry air intrusion observed during TOGA-COARE.

J. Atmos. Sci

In press

Betts, A.K. and C. Jakob

 

2002

Evaluation of the diurnal cycle of precipitation, surface thermodynamics and surface fluxes in the ECMWF model

Journal of Geophysical Research

In press

 

 

Non-refereed Literature:

Authors

Date

Title

Event

Type

Derbyshire, S. H.

July 2000

Constrained quasi-equilibrium simulations of moist convection

Royal Meteorological Society Millennium Conference,

Cambridge, UK

Presentation

Derbyshire, S. H.

Nov. 2000

Constrained quasi-equilibrium simulations and the influence of ambient humidity
on deep convection.

ARM-GCSS Meeting, Silver

Spring, Maryland, USA

Presentation

Redelsperger, J.L. & e EUROCS colleagues

Dec 2000

The EUROCS programme,

 

GCSS (GEWEX

Cloud Systems Studies)

SSG Meeting, Tokyo, Japan.

Presentation

Redelsperger, J.L. & e EUROCS colleagues

Seot 2001

European project on Cloud Systems

in Climate Models

4th International Scientific Conference on the Global Energy & Water Cycle, Paris

Presentation

Beljaars A., Redelsperger J.L. &

EUROCS colleagues

 

Jan 2002

The EUROCS programme

GCSS (GEWEX

Cloud Systems Studies)

SSG Meeting,, Reading, UK

Presentation

F. Guichard, J. Petch, I. Beau, J.-P. Chaboureau, J.-Y. Grandpeix, H. Grenier, C. Jakob, C. Jones, J.-P. Lafore, J.-L. Redelsperger, J.-F. Royer, R. Tailleux

and M. Tomasini

April 2002

EUROCS activity toward the diurnal cycle of deep convection over land

EGS conference

Presentation

F. Guichard, J. Petch, I. Beau, J.-P. Chaboureau, J.-Y. Grandpeix, H. Grenier, C. Jakob, C. Jones, J.-P. Lafore, J.-L. Redelsperger, J.-F. Royer, R. Tailleux

and M. Tomasini

May 2002

The diurnal cycle of deep convection over land: contribution from EUROCS

GCSS Workshop on the Representation of Cloud Systems in

Large-Scale Models

Alberta, Canada

Presentation

Petch J. & F. Guichard

May 2002

Sensitivity of CRM simulations to the initiation procedure

 

 

GCSS Workshop on

the Representation of

Cloud Systems in

Large-Scale Models

Alberta, Canada

Presentation

 

 

Petch J. & F. Guichard

Sept 2001

The diurnal cycle of deep convection in a CRM: Results from EUROCS

Royal Meteorological Society, 2nd national conference

Manchester, UK

Presentation

 

 

R. Tailleux, JYs Grandpeix, A. Lahellec, F. Cheruy

Sept 2001

Role of convective inhibition in deep convection triggering: a GCM study

 

4th International Scientific Conference on the Global Energy & Water Cycle, Paris

Poster

 

 

Piriou JM

Jan 2002

Diurnal cycle of tropical deep convection: a diagnostic study in ARPEGE

WGNE

Report

 



[1] The situation would be the same if we were using observations instead of CRMs outputs, but this type of information is not available from observations.