(Hosted by IMAU University of Utrecht and KNMI De Bilt)

8-10 April 2002


General conclusion


Diurnal cycle of shallow cumulus

Diurnal cycle of continental deep convection

Idealized humidity case

PACIFIC Intercomparison Case for 3d GCM's


The workshop was hosted by the KNMI and IMAU.

Scientific organizers: J-L Redelsperger (CNRM/GAME), P. Siebesma (KNMI), S. de Roode (IMAU)


Monday 8 April (KNMI, De Bilt)


Opening & Practical issues (P. Siebesma & JL Redelsperger)

Status for each case: SCM/RCM/GCM evaluation, and improvement.

      Diurnal cycle of Stratocumulus (S. De Roode, IMAU)

      Diurnal cycle of Cumulus (G. Lenderink, KNMI )

      Diurnal cycle of Deep convection (F. Guichard, CNRM/GAME)

      Idealized case on humidity sensitivity (S. Derbyshire, UKMO)


Tuesday 8 April: (University of Utrecht, IMAU)

PARALLEL SESSIONS S1 & S2: Individual Presentations of the participating institutes with a focus on the evaluation and improvements of physical parameterisations in the SCM/RCM/GCM, plans for the coming year and assessments on participation with upcoming 3d-GCM cases, Publications.


S1: 9:00-13:00 Stratocumulus

      LES and SCM Simulations of FIRE stratocumulus case: A sensitivity study

(A. Chlond and F. Mueller, MPI Hamburg)

      HIRLAM-SCM results (J. Calvo & D. Olmeda, INM)

      The impact of changing the large-scale horizontal advection in LES and SCM

(P. Goggins UKMO)

      Impacts of variability in subsidence on stratocumulus (M. Khler ECMWF)

      Stratocumulus convection in the Arpege Climate model: 1D and 3D evaluation of 2 PBL models (H. Grenier, CNRM/GAME).

      LES of CBL and stratocumulus on a large domain (S. de Roode IMAU)

      Discussion, Action items, Future plans

S2: 9:00-13:00 Humidity Sensitivity Case

      Overview of results (S. Derbyshire, UKMO)

      Results from CRM (JL Redelsperger, CNRM/GAME)

      Results from SCM & GCM at LMD & issues on parametrization (JY Grandpeix LMD)

      ARPEGE SCM and GCM results and Improvements (JM Piriou CNRM/GAME)

      Discussion, Action items, Next steps, Future plans for SCM and GCM, Publications

S1: 14:00-19:00 Shallow Cumulus

      SCM Simulations with ECHAM of the ARM diurnal cycle (A. Chlond & F. Mueller, MPI )

      SCM simulations with the 1D-HIRLAM model (D. Olmeda & J. Calvo, INM)

      Statistical Cloud scheme in 1D-RACMO (G. Lenderink KNMI)

      Evaluation of Mass flux closures in 1D-RACMO (R. Neggers KNMI)

      The French Climat/Arpege SCM: The work done on conserved variables. (P. Marquet CNRM/GAME, presented by H. Grenier CNRM/GAME)

      A multiple mass-flux scheme for dry and moist convection: tests on BOMEX and ARM. (S. Cheinet LMD)

      Trigger function in the ECMWF-model. (A.P. Siebesma & C. Jakob KNMI, BMRC, ECMWF)

      Open Discussion, Action items, Future plans, Publications

S2 14:00-19:00 Diurnal Cycle Deep Convection

      Status of the case and results from 5 different standard RCM/GCM (F. Guichard CNRM/GAME)

      The predictability of the development of deep convection: Some very preliminary results. (J. Petch UK Met. Office) (Presented by S. Derbyshire)

      Diagnostic analysis of the cases (F.Guichard CNRM/GAME)

      1D simulations of the diurnal cycle of land based deep convection with the Kain-Fritsch scheme in the HIRLAM 1D model (C. Jones SMHI)

      Boundary layer/Deep convection coupling: impact on the phase and intensity

of the diurnal cycle of deep convection, New concepts. (R. Tailleux LMD)

      Analysis of thermodynamical (in)stability of CRM simulations (JP Chaboureau CNRM/GAME)

      Results from ECMWF 1D model (JP Chaboureau & M. Koelher CNRM/GAME, ECMWF)

      Open Discussion, Action items, Future plans, Publications , Shallow-Deep cloud bridge


Wednesday 10 April (University of Utrecht, IMAU)



Conclusions, issues and plans from parallel sessions

      Idealized case on humidity sensitivity : S. Derbyshire

      Diurnal Cycle of deep convection. F. Guichard

      Diurnal Cycle of stratocumulus. S. De Roode

      Diurnal cycle of shallow cumulus: G.Lenderink


Reports from the GCM PACIFIC case.

      Overview of the Pacific-Case and Compilation of the Results from 8 RCM/GCM groups

(A.P. Siebesma & G. Lenderink KNMI)

      3d-GCM results with the ARPEGE Model (H. Grenier CNRM/GAME)

      3d-GCM results with the Met.Office Model (A. Lock, S. Debyshire UKMO)

      3d-LAM results with RACMO (G. Lenderink, KNMI):

      3d-GCM results with ECMWF Model (M. Kohler, ECMWF)

      3d-GCM results with the MPI Model: ensemble runs ( ???, MPI)

      Discussions on Future of the GCM Pacific Case


General discussion on future EUROCS plans, future workshop, cost statement, publications.

The After-EUROCS

      The CLIWA-NET EU project (E. Van Meeijard, KNMI)

      The CLOUDNET EU project (KNMI)

      The VI framework and the different possibilities (JL Redelsperger)



General conclusions

The general conclusion from the workshop was that beyond the 2nd Year report, a lot of promising works are going on. A general feeling was also that more and more theoretical and physical insights are brought in the evaluation and improvement of cloud schemes.

During the final discussion, we discussed about the next workshop, the publications and the after-EUROCS. It was decided:


(Lead by P. Duynkerke, S. De Roode, H. Grenier)



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. The turbulence structure of the boundary layer during nighttime and daytime agree rather well with the observations. However, small differences in the entrainment rates are the major cause of the differences in the simulated diurnal cycle of the liquid water path.

Current model results of a sensitivity test in which the mean subsidence rate has been changed will be analyzed in detail. A few new sensitivity tests will be performed. One includes the diurnal variation of the subsidence rate, which will be prescribed on the basis of ECMWF results recently analyzed by Martin Khler. It is aimed to run this simulation for 5-7 days.

The set-up of the stratocumulus case, the available observations and the LES results will be compiled by the IMAU (S. De Roode) and will be reported in a scientific paper (Duynkerke et al.).


SCM results

There is broad disagreement in the SCM results. Some models predict a cloud layer that gradually dissipates, whereas other models maintain a solid cloud layer. It is currently unclear how to explain these differences. The analysis of the model results is complicated by the different physical packages that have been used. It has been decided that the SCMs participating in the intercomparison for the FIRE 1 case would re-run the case and perform five sets of simulation according to the following procedure:


The model results must be submitted to the IMAU before 15 July 2002 ( Herve Grenier has offered to take the lead in the analysis of the SCM results. A modified data protocol for the SCM results at Any comments on this format are welcome.


The SCM participants should summarize the following issues (1 page) to send to Herve Grenier (



The stratocumulus working group will join the regional climate simulation experiment set-up by Christian Jakob and Pier Siebesma. This case includes both stratocumulus and cumulus, and their transition (see below Pacific intercomparison case).


Diurnal cycle of shallow cumulus

(Lead by Pier Siebesma and Geert Lenderink)

Following is a summary of the updates of the various participating models on the Single Column Model (SCM) studies such as presented at the workshop. The LES results have been yet published and the GCM/RCM part is mainly discussed below (Pacific intercomparison case).


ARPEGE-climate version

The turbulence scheme has been replaced by a new scheme based on prognostic turbulent kinetic energy. This has reduced the amount of noise significantly. In addition, the Kain-Fritsch (KF) convection scheme (similar to the one used in MESO-NH) has been introduced, and changes to the condensation/evaporation of cloud liquid water have been made. Together, these changes led to a significantly better simulation of the diurnal cycle of Cu.



A new statistical cloud scheme has been introduced. Also changes in the numerical time integration have been made, and changes in the mixing formulation of the massflux convection scheme have been attempted. However, so far this did not lead to a significant improvement of the simulation, possibly caused by the noisy behavior of the turbulence scheme.



The cloud condensation and convection scheme (STRACO) has been replaced by a new cloud condensation scheme (Rasch-Kristjansson) and the KF convection scheme (with adaptations made by Colin Jones from the Rossby Climate Center). This reduced the amount of clouds from fully cloud covered in the STRACO version to realistic values (close to 20 %) with the new schemes.



The formulation of the closure of the massflux scheme has been investigated. A closure based on the convective turbulent velocity scale of the subcloud layer combined with the cloud fraction seems to work very well, with a good timing of diurnal cycle of the clouds. A simple statistical cloud scheme in RACMO gives realistic values for the cloud cover.



The closure of the convection scheme has already shown to improve the simulation significantly. In addition, the triggering function for deep and shallow convection has been investigated and its positive impact in the full 3d_GCM has been demonstrated. Especially the cold temperature bias near the tropopause has been reduced substantially.



HIRLAM, ARPEGE, ECHAM and ECMWF will send in their latest SCM updates to Geert Lenderink before June 1st. After this date the results will be documented in an intercomparison paper.


Diurnal cycle of continental deep convection

(Lead by Francoise Guichard & Jon Petch)


An idealized case has been designed from the ARM observed dataset, in order to address the abilities of models to represent the diurnal cycle of deep convection over land. 5 SCMs and 3 SCMs have been working on this case study and results from most of them have already been provided. Some additional work is still needed for improving the case (in particular replacing the actual surface heat fluxes by more realistic ones which have been derived directly from observations) and checking the consistency of model results (initial conditions, forcing...).


However, the key point is that the analysis of both the GCSS and idealized cases show that better results and consistency are found among CRMs than SCMs. It also appears that deep convection occurs earlier in many SCMs than it does in CRMs. When data on each time step were available (instead of 3-h mean values), it was found that convection was "directly" considered as deep in SCM runs, without any transition regime involving shallow cumulus (in contrast with CRM realizations) and that several fields (e.g. rainfall, cloud water path, cloud cover...) were quite noisy because of a frequent on/off behavior of the parameterizations (a feature improved in the new SCM version of the UK Met Office compared to the previous one for this case).


We also began to investigate the ability of models to represent the diurnal cycle of atmospheric stability, closely linked to the surface and boundary layer time evolution (F. Guichard). It shows distinct behaviors of the models, in particular for the CIN weaker in SCMs than in CRMs. This suggests that the links between convection and these parameters are treated differently in these 2 types of model. In parallel, more sophisticated stability parameters such as GCAPE and GCIN have been developed and their analysis, in particular with respect to convective regimes, is currently under study at LMD (R. Tailleux).


The development of the boundary layer properties (e.g. BL height) was found closely linked to surface heat fluxes values, through their interactions with the boundary layer scheme in the ARPEGE climate SCM (H. Grenier). Complex sensitivities of deep convection sequences to the triggering criteria and to the downdraught effects were highlighted with the HIRLAM SCM (C. Jones). That shows the essential role of the triggering function and the strong impact of parameterized downdraughts, through large rain evaporation rates, which will be contrasted with CRM ones.


A sensitivity of 2D CRM runs (UK Met Office model, J. Petch presented by S. Derbyshire) to the initial conditions showed that the amount of rain could significantly vary from one run to the other, depending on the initial random noise. The timing of rain was a more robust feature (afternoon/evening). This sensitivity could be linked to the relatively small size of the domain coupled to the relatively weak forcing of the idealized case. When deep convection occurred in the form of 2 deep cells developing as far away as possible from each other, rainfall rates were high and the opposite for cells developing close to each other, suppressing each other. Indeed, the scatter between the runs substantially decreased with more realistic enhanced surface heat fluxes. The analysis also pointed to the impact of the convection sequence on one day on the one happening the following day within this idealized framework, a feature also shared with MesoNH CRM runs. Based on a sensitivity study to the horizontal resolution for the "shallow convection" case of EUROCS (thanks to A. Brown), some pilot high resolution 3D runs (100m & 250m) have been performed with the same model (Met Office CRM, J. Petch) for the idealized case. They document the initial dry and shallow convective phases prior to the onset of deep convection, and should be helpful for in-depth investigations of these transition phases.


MesoNH CRM runs (CNRM J.-P. Chaboureau) have been analyzed in terms of CAPE/CIN, theta_v and BL height time variations, showing that the model is able to reproduce a diurnal cycle of these parameters, as observed. A sensitivity study to the resolution in 2D did not show a systematic delay of rainfall with decreasing resolution (except at 4 km resolution). These distinct sensitivities to the resolution between the CNRM & Met Office CRMs are possibly linked to different treatments of subgrid scale microphysics & turbulence schemes. Preliminary low resolution 3D CRM runs were also presented by J. -P. Chaboureau. ECWMF SCM runs performed by JP Chaboureau and M. Koehler at the ECMWF show the same "too early timing of rainfall", as pointed out by C. Jakob during previous EUROCS workshops as a characteristic behavior of the ECMWF SCM.




During the course of the remaining 11 months, we plan to focus on:

(a)    transition regimes (e.g., transition from shallow to deep convection)

(b)   triggering aspects (links with CIN)

(c)    downdraughts (their importance and treatment)

(d)   other parameterization issues.



CRM results must be further analyzed, in order to describe/explain/understand the different convective phases, from (a) dry to (b) shallow and finally (c) deep convection. We wish to raise the following questions:

In parallel, we wish to extend the work of J. Petch on high resolution runs to larger domains. This will allow including also the deep convective phase in one single simulation. This work is closely linked to GCSS WG1-WG4 activities and questionings towards a common case study.


On the base of SCM results, we wish to address the following questions:



To address these questions, we need to complete and document model datasets (deadline June 1st) this includes the following:


Final runs will be performed with more realistic surface heat flux dataset and the stability study must be completed. It will also include an analysis of theta_v profiles and diurnal variations, BL height, condensation level and cloud parameters (diagnostics partly computed from the time-height series provided by the participants).

We are interested in the results from SCMs runs of the shallow cumulus case when deep convection is turned on. We wish to take advantage of the work already done by participants to the shallow cumulus case in order to contrast these 2 realizations (shallow cumulus case and idealized case). These two cases differ mostly by their initial conditions and possibly by large-scale advection of sensible heat and moisture. This analysis should be possible for at least 3 SCMs which have been run for both cases (ECMWF, SMHI and CNRM).


We propose to perform systematic sensitivity tests of SCM runs, documenting the role of downdraughts and trigger criteria, (turned on or off). A set of runs would be proposed.


Finally the impact of modifications/improvements of parameterizations in RCM/GCM runs should be address in terms of their impact on the representation of the diurnal cycle of deep convection.



Several people wished to write papers in connection with the work, which has been done or is currently in progress within EUROCS. This includes:



Idealized humidity case

(Lead by Steve Derbyshire)



During year 2, considerable progress has been made with the idealized humidity case. The case has been run with many more models (now 2 CRMs and 5 SCMs). This workshop was the first opportunity to discuss those new results properly, and to hear about first results with GCMs.




An outline for a paper based on this case was discussed and broadly accepted. We have a lot more detailed work to do on the CRM-SCM comparisons but the process of drafting a paper should help to drive us forward.


Summary of outcomes:



        SHD starts drafting paper on SCM/CRM work

        SHD looks at BL comparisons

        SHD contacts Julia Slingo re GCMs, climate and moisture sensitivity

        SHD to update web pages

        Optional additional case with intermediate 60% humidity

        GCM modellers evaluate GCM sensitivity of existing SCM modifications

        To produce diagnostics based on zonal qv and others (JMP and JYG please liaise and tell to SDB your thoughts)

        To aim for an interim report on GCM tests by July (as requested by JLR)



        Peter Bechtold has submitted further results which SBD have not yet had a chance to analyze. Although not a funded participant, he remains very interested in the case.

        SDB would like to include some SCM sensitivity tests in the paper, not just best results. This will help to show that the case can be used to develop the SCMs. So please dont write off your first versions completely!




PACIFIC Intercomparison Case for 3d GCM's

(Lead by Pier Siebesma and Geert Lenderink)

General conclusions

Five Models within the EUROCS framework (ARPEGE,ECMWF,RACMO,UKMO,ECHAM)and one external (Japanese Climate Model (JCM) have participated in an intercomparison study for GCM's over the Northern Pacific Ocean for July 1998. From this studies the following general conclusions can been drawn:

        All models strongly overestimate the liquid water path (LWP) and cloud cover (CC) in the trade wind regions.

        Most models strongly underestimate LWP and CC in the Stratocumulus regions.

        Strong differences in the subsidence rates are encountered.



More model specific conclusions:


ARPEGE-climate: Too deep PBL-height, too high integrated water vapour content (IWV).

ECHAM: Too high sea surface temperature (SST), too high IWV

RACMO, JCM: Overall too low cloud cover (CC) and too low LWP.

UKMO: Too high IWV and Outgoing Longwave Radiation (OLR) and too low LWP in the intertropical convergence zone (ITCZ).


General discussion

During the individual presentations a couple of drawbacks have been noticed:

        A monthly mean over only one strip does not have sufficient statistics. For instance, the difference between the monthly means over two neighboring strips within one model is of similar magnitude as the difference between the monthly means over the same strip for 2 different models (UKMO). Similarly the ECHAM model made several runs with initial conditions with different random perturbations also gave substantial differences between the ensemble members. These results suggest that longer averaging periods and/or areas should be used.

        Separate monthly means over nighttime and daytime give strong differences in cloud parameters such as cloud cover, liquid water path and ice path (RACMO). To address this more specifically, different monthly means over daytime and nighttime should be requested as output.

        The ITCZ is just at the edge of the required diagonal. Extension of the diagonal further to the south would allow a better analysis of the ITCZ.

        The prescribed diagonal strip crosses Hawaii. This was done deliberately since the presence of observational data here. Unfortunately this hinders the analysis since some models do resolve Hawaii while others do not. These differences show up in the subsidence fields and complicate the intercomparison between the models in the vicinity of Hawaii.


As a result of these drawbacks the following changes for the intercomparison are proposed:



All the participants will be contacted and asked if they are able to redo the Pacific simulations with the modifications such as sketched above. If a majority reacts positively, results should be resubmitted before Sept 15 so that the results can be presented during the Madrid workshop in mid-November.