Joint EUROCS-GCSS Workshop

Lisbon, Gulbenkian Foundation

28 - 31 May 2001


The workshop was hosted by Pr. P. Miranda and funded by the Gulbenkian Foundation, the WCRP and  EUROCS (funded by EU Community).


Local organizer:  Pedro Miranda (Centro de Geofisica da Univ. Lisboa)


Scientific organizers:

Jean-Luc Redelsperger  (CNRM/GAME) , Chairman of EUROCS

Peter Duynkerke (IMAU), Chairman of WG1/GCSS

Wojciech W. Grabowski (NCAR), Chairman of WG4/GCSS




Diurnal Cycle of Deep Convection

Idealized Humidity






All results of the stratocumulus intercomparison of EUROCS/WG1 have been put on the web: Please have a look and give your comments.

Shallow Cumulus

Diurnal cycle of shallow cumulus convection.

1. Introduction

The  diurnal cycle of shallow Cumulus clouds has been studied using 3 Large Eddy Simulation (LES) models and 7 Single Column Models (SCM's). The case has been set up by Andy Brown (UK Met. Office), and is a idealization of observations made at the Southern Great Plains ARM site on June 21 1997. For a complete case description with results from both LES models and SCM's we refer to


2. Large Eddy Simulation studies.

Within the EUROCS framework three groups (MPI, UKMO and KNMI) have submitted LES results. The most notable conclusions from these simulations are:


i) LES models are well capable of reproducing realistically the diurnal cycle of the shallow cumulus topped boundary layer. The cloud cover amounts 20-30 % with a maximum around noon. Cloud base is around 1000 m, the highest cloud tops are at 2500 m. These results are in agreement with cloud observations during that day.


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


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



3. Single Column Model studies.

Single column model simulation were done by 6 groups:





(HIRLAM and MESO-INM model *1)


(RACMO model)






(CT01 *2).



The most notable results from the SCM's are:


i) Most models produce too high values for both cloud liquid water (2 to 5 times larger than LES and observation) and cloud cover (50-70 %).


ii) Most models have difficulties representing the diurnal cycle. Two models already have clouds very early in the simulation. Five models have difficulties with dissolving the clouds after sunset.


iii) Most models under predict the height of the cloud top, some of them even with 1000 m.


iv)  The two models with K diffusion performing mixing in the cloud layer give reasonable profiles of temperature and humidity. On the downside, both are rather noisy in the cloud layer.


v)   Two of the models with a mass flux scheme give a too strong drying at cloud base and a too strong moistening at the inversion. The other mass flux schemes give reasonable to rather good profiles and temperature and humidity.


vi)  There is a surprisingly large difference in the wind speed between the different models.


The overall conclusion is that most state-of-the-art climate and weather prediction models fail in reproducing realistically a simple diurnal cycle of a convective day in the presence of fair weather cumuli.



*1 = MESO-NH model with modifications made by INM

*2 = research model of S. Cheinet and J. Teixera


Diurnal Cycle of Deep Convection

1. An introduction by F.  Guichard was given which provided an overview of the problems of modelling the diurnal cycle of convection in large-scale models. Results provided by J. Slingo and G.-Y. Yang [University of Reading], C. Jacob [ECMWF] and J.-F. Royer et al. [Météo-France/CNRM] showed that the diurnal cycle of convection in the Tropics was significantly out of phase in the Met Office, ECMWF and Météo-France global models respectively. Output from the LMD climate model, provided by A. Lahellec and R. Tailleux, also point to the same default in the LMD climate model over Northern America. In contrast, results from C. Jones [Swedish Meteorological and Hydrological Institute] showed that a mesoscale limited area model (RCA05) was able to reproduce several aspects of the observed diurnal cycle of convection over Northern America, but the runs were performed at higher resolution than typical in a GCM.

The introduction also described the basic case being used in this study. The case is a 4-day convective period over the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in the central U.S for which a large amount of observations is available. This case is also being used by the ARM Single Column Modelling (SCM) working group and GCSS WG 4. The discussion focused on the first 24-hour period of the case because much of the later periods were dominated by large-scale forcing terms not related to the diurnal cycle. This issue had been raised at the previous EUROCS meeting (January, ECMWF) where suggestions had been made that the experiments would need refining for an in-depth investigation of the diurnal cycle of convection over land.

J. Petch and F. Guichard both presented results showing tests using more idealized forcing which could form the basis for a more focused inter-comparison case. Results from the Met Office SCM and CRM showed that using the surface forcing alone from the ARM SGP case with interactive radiation produced a  diurnal cycle of precipitating convection. Results from the CNRM CRM showed that a composite of the first days forcing, run for 4 days, also produced a diurnal cycle of convective rainfall. It also showed that  the effect of the large-scale forcing was to delay the initiation of convection on each of the 4 days. Sensitivity to the start time of the simulation was shown, with the main influence on the first 2 days. 

2. CRMs which have contributed to the inter-comparison include one from the Met Office and two from CNRM. Comparisons of these were shown and the main point stressed was the problems in predicting the onset of precipitation during the first day. These problems were the focus of more detailed talks. J. Petch showed that an increase in horizontal and vertical resolution could improve the timing of the first precipitation event. Transport terms from the model showed that a horizontal grid length of around 250 m was required to resolve the major eddies involved in transporting water vapour into the free troposphere, this also resulted in a much improved prediction of the timing of the first precipitation event. F. Guichard presented work of M. Tomasini which showed that timing could also be improved through improvement of the sub-grid turbulence scheme and the introduction of a sub grid condensation scheme.

3. SCMs which have contributed to the inter-comparison include models from LMD, Met Office, CNRM and ECMWF. All models where showed to precipitate too early when compared to observations of the first days rain event. This is an encouraging result because it suggests that SCM simulations of the first day of ARM provide a relevant case study for investigating the problems seen in the full 3-D versions of the large-scale models. In addition, R. Tailleux presented sensitivity test to the triggering function and P. Bechtold showed some results documenting the SCM methodology. 

4. Following discussions, it was decided to form a new inter-comparison case which will be more focused on the diurnal cycle. The simulation would begin close to sunrise and be a 4 day composite of the first day of the ARM case including the large-scale forcing. To avoid resolution problems discussed, the CRMs should  use a horizontal grid length of 250 m and no larger than 250 m anywhere in the vertical. The domain size would be halved to 250 km and the CRMs would include their own interactive radiation. Several diagnostics will be added to better describe transport terms and radiation fields. It is also planned to use the first part of this run with a smaller domain and higher resolution for an in-depth investigation of CRM performances regarding the representation of the earlier stage of convection. This work involves interactions with the group working on the diurnal cycle of cumulus. 

Finally, C. Jakob, W.-K. Tao and J.-P. Lafore presented interesting cases from LBA, TRMM (Southern America) and HAPEX (Western Africa) which could be exploited in the longer term. 

Idealized Humidity Convection 

The idealized humidity convection case is designed to show up the impacts of

mid-tropospheric humidity on convection. These impacts are thought to play a role in important climate mechanisms such as the Madden-Julian Oscillation,  in the differences between maritime and continental convection, and possibly in the diurnal cycle of convection. Moreover they provide an important conceptual test of the mixing-assumptions in convection scheme. The case-setup for the process-model comparison (CRM/SCMs) is designed to maximize the relevance of those comparisons to GCM applications.


J.L.Redelsperger first presented some high resolution CRM results from a TOGA-COARE study (Redelsperger, Parsons, Guichard 2001) in which the moisture deficit at heights around 2-4km was found to be a key predictor of convective activity.


S.Derbyshire described the EUROCS inter-comparison case. The case set-up was  based on strong nudging of mean profiles, appropriate to a situation where the large scales exert a control on the profiles of the column in question. The target profiles are specified with a potential temperature difference of 1K across the boundary layer and potential temperature increasing at 3K/km above the boundary layer. Relative

humidity is specified at 80% in the layer 1-2km and at a value RHt above 2km. (The boundary layer, below 1km, is not normally forced in these runs.)


The Met Office CRM was run for a pilot run A and the main intercomparison run B. Run A has instantaneous nudging of the mean profiles and only warm cloud physics. In run A, changes in RHt were able to switch convection between a non-precipitating shallow convection and vigorous deep convection. Run B used a nudging timescale of 1 hour and "full" 3-phase cloud physics.   In run B, changes in RHt were again able to switch the convection between almost non-precipitating shallow convection and vigorous convection, even though the 1hr timescale allows convection to stabilize the mean profiles significantly. 


J.Y.Grandpeix (LMD) described how he was using this case to review his  version of the Emanuel scheme. The scheme uses a pdf for mixing between cloudy and environmental air, and this pdf can be tuned towards the CRM results. The set-up of this case allows the CRM and SCMs to develop their own characteristic mass-flux profiles according to the environment, whereas in some other set-ups the mass-flux

profile and precipitation are controlled almost directly by the forcing.


S.Derbyshire presented a synthesis of the CRM and SCM results currently available, concentrating on the dependence of surface precipitation on RHt. The CRM gave surface precipitation increasing roughly linearly with RHt from 0.05 mm/hr at RHt=25% to 1.5 mm/hr at RHt=90%. The Met Office SCM was able to capture the trend with RHt but precipitated too strongly in the drier cases. The LMD SCM

(original formulation)  had only a weak trend with RHt, but this trend could be increased by changes to the mixing-formulation.


In addition to the originally funded participants, a number of others expressed interest in running the idealized humidity case, including J.M.Piriou (Meteo France), P.Bechtold (OMP), C.Jakob (ECMWF) and P.Soares (University of Lisbon) with SCMs. J.L.Redelsperger (CNRM) hopes to run the case with his CRM. Furthermore W.Grabowski (NCAR) is interested in running different cases with a similar methodology, and is considering proposing their adoption under GCSS-WG4.


The immediate priority is to synthesize machinable results from the various models. SCM modellers are asked to send in results in GCSS format by the end of July. S.Derbyshire hopes to go to Boulder in October and present a synthesis. The focus will then move onto consideration of sensitivity tests within GCMs.



The 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 definitely continue in future.

People working on diurnal cycle of deep convective clouds identified 2 tracks. The fast track is to continue to work on the idealized ARM case. For this case study, GCSS and EUROCS time frameworks are in phase. The slow track is to develop a new case study from LBA experiments. As the EUROCS funding ends in February 2003, the LBA case will be not be included in the EUROCS plans. Of course, EUROCS people are encouraged to participate in this case study.

Finally, it has been decided that in early 2002 there is to be a second joint EUROCS-GCSS workshop in Utretcht (hosted by KNMI). The precise date and format will need to be discussed in the coming months. A GCSS/WG4 workshop will also occur on 22-24 October 2001 in Boulder, Colorado. The two case studies for deep convective clouds will be discussed and some EUROCS participants plan to attend.

Two other workshops were announced by W.K. Tao. The second TRMM Latent Heating Algorithm Workshop, organized by M. Moncrieff, A. Hou and W.-K. Tao, is to take place on October 10-12 2001 at NCAR. A Cumulus Parameterization Mini-Workshop, organized by W.-K. Tao, D. Starr and Y. Sud, will take place on Nov 13-15 2001 at NASA/GSFC. For more details on these two latter workshops contact W.K. Tao directly -





e-mail address


Jean-Luc Redelsperger

Francoise Guichard

Herve Grenier                       

J. Philippe LaFore                 

Jean-Marcel Piriou                

Sara Chavarria  



Christian Jakob                      

Martin Koehler



Steve Derbyshire                   

Jon Petch                               

Adrian Lock                          

Alan Grant

Olaf Stiller                            

Alison Sterling                      

Pat Coggins



Peter Duynkerke

Stephan de Roode



Enrique Sanchez

Dolores Olmeda



Jean-Yves Granpeix

Sylvain Cheinet                     

Remi Tailleux                        

Alain Lahellec                                   

Herve Le Treut



Andreas Chlond                     

Frank Muller                         

Erich Roeckner



Pier Siebesma                       

Geert Lenderink

Roel Neggers

Aad van Ulden



Pedro Miranda           

Pedro Soares



Colin Jones



Joao Tiexiera



David Randall

Cara-Lyn Lappe



Wotjek Grabowski


Dept. of Geophysics - Univ. of Oslo

Jorn Kristensen



Stephen Lang



Wei-Kuo Tao



Rafael Terra



Peter Becktold   









Issues and current developments in PBL and deep convection schemes; Problems in coupling boundary layer and deep convection parameterisations (Chairman: W. Grabowski)


Issues and developments in PBL and deep convection parameterizations  (D. Randall CSU)


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


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


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


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


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


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


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


The CLIWA-NET project and the BBC-campaign

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


Final Day: Discussions on future plans

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





Stratocumulus (Chairman: P. Duynkerke)


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)


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. Koelmher, ECMWF)


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)




Diurnal cyle of deep convection (Chairman W. Grabowski)


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)



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


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


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)



Cumulus (Chairman P. Siebesma)

Synthesis of CRM results (P. Siebesma or A. Brown)


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)



Idealized humidity case (Chairman S. Derbyshire)


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


Some new CRM and SCM results  (S. Derbyshire)


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