Executive Summary

• To revise the CFRP methodology paper based on the comments from the referees following the submission of the paper to Monthly Weather Review, and to complete a draft synthesis paper using the CFRP, CASP II and BASE cases.
  Outcome: Revised draft of the CRFP paper to be completed by September 21 and resubmitted to Monthly Weather Review. Outline of a second synthesis paper completed; this draft to be finished by December with submission by March 2000.

• To complete a study of the north-east and north-west Atlantic Basins aimed at documenting the cloud property variations in a frontal regime as the first step in developing a methodology to generalize the outcomes from the CRM studies of specific field experiments.
  Outcome: The workshop established the effectiveness of the large-scale survey technique in identifying model problems in generating mid-level cloud and in providing the setting for the FASTEX case studies. The final step in the process of undertaking a survey/modelling study over the FASTEX period has yet to be completed and is a goal for a workshop in 2000.

• To design a GCSS study based on FASTEX IOP 16.
  Outcome: The initial simulations for FASTEX study were presented. The design of revised simulations was completed and October was set as the date for the new simulations to be sent to the UKMO. Preliminary report on the intercomparison is to be presented to the Science Panel Meeting in December.

• To re-examine the problem of the representation of clouds in a GCM forced by sub-grid scale orography.
  Outcome: The focus of Working Group 3 should be on upslope clouds and stably stratified gravity wave generated clouds. An important problem identified was to test if the concepts used in gravity wave drag schemes were valid for parameterising the generation of sub-grid scale orographic clouds in GCMs.

The workshop showed that the working group had learnt from the previous CFRP, CASP II and BASE studies and this experience was applied to the new FASTEX case. The working group recognised FASTEX is a unique data set that gives the rare opportunity to validate the LAM and CRM FASTEX case studies against an ISCPP/GCM ensemble study. The workshop developed a proposal to use the complete set of FASTEX cases to achieve this objective.

1. Introduction

• To revise the CFRP methodology paper based on the comment from the referees following submission to Monthly Weather Review and to complete a draft synthesis paper using the CFRP, CASP II and BASE cases.
• To complete a study of the north-east and north-west Atlantic Basins to document the cloud property variations in a frontal regime as the first step in developing a methodology to generalize the outcomes from the CRM studies of specific field experiments.
• To design a GCSS study based on FASTEX IOP 16.
• To re-examine the problem of the representation of clouds in a GCM forced by sub-grid scale orography.

Nineteen scientists attended the meeting, with expertise in GCMs (Climate and Forecast Centres), LAMs and CRMs as well as those with field observing experience. Most attended all sessions of the workshop. The program for the meeting is attached as an appendix.

The workshop showed that the working group had learnt from the previous case studies (CFRP, CASP II and BASE) by applying the experience to the design of the new FASTEX case. The working group recognised FASTEX is a unique data set that gives the rare opportunity to validate the LAM and CRM FASTEX case studies against an ISCPP/GCM ensemble study. The workshop developed a proposal to use the complete set of FASTEX cases to achieve this objective.

2. Outcomes from the synthesis of the CFRP, CASP II and BASE Case Studies

Peter Yau reported on behalf of Kit Szeto on the progress towards writing a synthesis paper based on the CFRP, CASP II and BASE cases. All the LAM and CRM simulations for the three cases have been completed. Coarse grid and SCM simulations have been completed for all but the BASE case and these will be done by September. A draft paper should be completed by December this year, with submission expected by March 2000.

Significant conclusions based on all three cases include:

• CRMs are able to reproduce both the frontal cloud fields as well as the embedded mesoscale and cloud-scale features of three synoptic systems occurring in three vastly different environments.

• The CRM domain needs to be large enough to encompass the whole storm environment and resolutions need to be fine enough to resolve the cloud scale features. The quality of the LAM simulations supplying the boundary conditions to the CRM can have a big impact on the results.

• The capacity of the CRMs to simulate the observed multiple layering in clouds has not been assessed in these case studies but it was agreed that the CRM's resolution in the vertical was too coarse to generate a realistic multi-layered structure in these simulations.

• SCMs are able to simulate the large-scale frontal thermal environment and the associated cloud fields when there is great attention to ensure that the SCMs are forced correctly. The SCM simulations were very sensitive to the parameterization of sub-grid-scale cloudiness and microphysics. Problems in handling sub-grid baroclinic forcing of cloudiness were revealed in the SCM simulations. The CFRP, CASP and BASE cases have not conclusively shown that SCMs are a suitable tool to test cloud parameterizations associated with frontal layer cloud systems.

• The GCM simulation run in forecast mode is complimentary and avoids some of the problems associated with the SCMs.

• Spurious circulations induced by the inappropriate representation of different components of a cloud system should be more of a problem in the LAMs because cloud motions on the relevant scales are more explicitly resolved by the CRM. However it is not clear what effects these spurious circulations in the LAM may have on the CRM nested within it. Furthermore it is also not clear that CRMs can be run with out a convective parameterization at resolutions of greater than 1km.

• The CFRP, CASP II and BASE simulations have pointed to the need to parameterize the sub-grid-scale vertical motion associated with the cross-frontal circulation. Part of the challenge is how to couple the sub-grid-scale vertical motion to the microphysics.

• So far the Working Group 3 strategy has been successful in the sense that problems in the hierarchy of model simulations have been identified when applying the methodology to the three cases. Several data sets from high resolution model simulations (CFRP, CASP II and BASE systems) have been archived. However, these data sets have yet to be applied to the development of new cloud parameterizations for use in climate models.

3. Outcomes from the large-scale observations to resolve cloud property variations

The next stage in this investigation is to determine whether these model errors are also evident in a survey undertaken over a limited period such as the FASTEX experiment. Individual cases within the FASTEX IOPs can then, in principle, be modelled at high resolution by the LAMs and CRMs to establish the physical basis for the errors and to provide the basis for parameterizations to overcome the global model defects.

Mark Webb presented a complimentary study that showed comparisons of the midlatitude simulations of models from the UKMO, ECMWF and the Laboratoire de Meteorologie Dynamique (LMD) with ISCCP, ERBE and ECMWF re-analysis data, using a range of compositing techniques. It was found that clouds with mid-level tops account for about 30% of the cloud radiative forcing in mid-latitudes, and that the models represent these poorly. It will be necessary to identify which types of mid-level cloud (ie. convective or frontal) contribute most to the total cloud radiative forcing in these areas if the relevant model parameterizations are to be improved.

This workshop established the effectiveness of the large-scale survey technique in identifying model problems and in providing the setting for the FASTEX case studies. The final step in the process of undertaking a survey/modelling study over the FASTEX period has yet to be completed and is a goal for a workshop in 2000.

4. FASTEX IOP 16 Intercomparison: Preliminary Assessment

The table of the current status of intercomparison model runs for GCSS shows that most of the participants had completed either the 24 km or 12 km runs but none had yet attempted the 4 km simulations.

Current Status of Intercomparison Model Runs

Key: Y = Yes, ie run already carried out.
N = No, ie run will not/cannot be carried out
I = Intended, ie will be carried out when possible
? = May be carried out but not definite yet.
+ (in model column) = Run from ARPEGE starting data rather than UKMO

Each group made a presentation on the status of their simulations and their commitment to the intercomparison. Following discussions based on the provisional presentations, it was agreed that the analysis would focus on a region 9.0 (latitude) by 15.3 (longitude) subdivided into nine boxes each 300 km by 300 km. The workshop agreed upon the format of runs to be sent to the UKMO and the following data to be included:

• Cloud top temperature and optical thickness at 0900 and 1200 GMT
• Hourly single level data:
  Rain, PMSL, Fluxes, Integrated water and water vapour paths, and cloud cover
• Hourly model level variables:
  Primary model variables, microphysical prognostic variables
• Diagnostic variables:
  Q1, Q2 Short and long wave radiative fluxes, flux divergence, cloud fraction and microphysical conversion terms
• Algorithms for ice fall speed and particle size.

The UKMO will undertake the following data processing with a preliminary report on the data to be available to the GCSS Science Panel Meeting in December. The analysis will include:

• Cross-sections along the diagonal of Box 5 for comparison with the dropsonde and radar observations
• Box means and variances
• Covariances of omega, u, v and other primary variables
• Comparison of model cloud cover, optical thickness with available radar and/or ISCCP data

Action Items agreed upon were:

• Modellers to be supplied with the algorithm to derive ISCCP parameters from the models
• ISCCP data to be provide for the nine boxes
• Ice and cloud cover distributions averaged over the nine boxes from the aircraft radar reflectivity measurements
• Omega distributions are to be calculated for the Doppler radar
• The possibility of using SMI data in the analysis is to be investigated.

The provisional comparison of the system with the simulations showed that:

• The system had two distinct fronts that were visible on radar and these features were generally captured by the models
• There were model differences in the speed of the system and in the optical thicknesses generated by different models
• When sublimation cooling was switched off the UKMO model showed only one cloud head
• There was very little difference between the 12 and 24 km resolution simulations performed by the UKMO, but vertical resolution was important. As a result all revised runs are to be made with 45 vertical levels as opposed to the 38 levels used in the UKMO operational model.
• It should be noted that there are two sets of analyses being used to initialise simulations. The WG3 intercomparison is using a UKMO analysis. The FASTEX-CSS project is using an ARPEGE analysis

5. The impact of sub grid scale dynamics and orography on the representation of clouds in GCMs

Some interest was expressed in the sub-grid-scale orographic parameterization developed by Leung and Ghan. This parameterization includes the sub-grid-scale effect of orography on the generation of clouds and precipitation and shows marked improvement in the local hydrology of the area.

The questions asked were:

• Where should the working group focus?

The consensus was that is should be on the upstream effect of orography on the cloud and on stably stratified gravity wave generated clouds

• How do we get a better representation of the orography from the perspective of the clouds?

CRM experiments need to be designed that relate the cloud formation to the wind stress generated by the mountains.

• What types of clouds can be captured?

Cloud resolving models need to be designed to determine the distribution and types of clouds and compared with in situ and satellite observations. At present there is insufficient data to test the parameterisation of these effects in models. For example is it valid to use the same concepts used in gravity wave schemes to generate clouds?

The UKMO has a team involved in the MAP program, mainly interested in dry problems and are also initiating new work on sub-grid orogaphic cloud processes. Approaches are to be made to see if the Working Group 3 questions can be entrained into the ongoing work at the UKMO.

6. Action Items

• Report on the Workshop to the GCSS Science Panel in December 1999
• Revision of CFRP paper in the light of MWR reviewers comment by end of September 1999
• Draft of CFRP, CASP II BASE paper by March 2000
• Workshop coupled to a WG2 workshop in Reading 2000 to
  • Finalise the FASTEX case
  • Report on the GCM-FASTEX climatology studies
  • To link the Case studies to the Climatological studies using the suit of FASTEX cases.

7. Workshop Participants

Peter Clark
JCMM, UKMO
paclark@meto.gov.uk

Sid Clough
UKMO
saclough@meto.gov.uk

Klara Finkele
Irish Met. Service, Dublin
klara.finkele@met.ie

Richard Forbes
JCMM, UKMO
rmforbes@meto.gov.uk

David Gregory
ECMWF, Shinfield Park, UK
dgregory@ecmwf.int

Christian Jakob
ECMWF, Shinfield Park, UK
paj@ecmwf.int

Peter Jonas
UMIST, Manchester, UK
peter.jonas@umist.ac.uk

Jack Katzfey
CSIRO Atmospheric Research, Australia
jack.katzfey@dar.csiro.au

Claire Kennedy
UMIST, Manchester, UK
claire@dopey.phy.umist.ac.uk

Humphrey Lean
JCMM, UKMO
hwlean@meto.gov.uk

Phillipe Lopez
Meteo-France
lopez@cnrm.meteo.fr

Burkhardt Rockel
GKSS, Germany
Burkhardt.Rockel@gkss.de

Brian Ryan
CSIRO Atmospheric Research Australia
brian.ryan@dar.csiro.au

Cath Senior
Hadley Centre, UKMO
casenior@meto.gov.uk

George Tselioudis
GISS, Colombia University, New York, USA
gtselioudis@giss.nasa.gov

Mark Webb
Hadley Centre, UKMO
mjwebb@meto.gov.uk

Damian Wilson
Hadley Centre, UKMO
drwilson@meto.gov.uk

Peter Yau
McGill University, Canada
yau@rainband.meteo.mcgill.ca

13 Acronyms

Appendix: Workshop Program

Review of Working Group objectives for the workshop (Brian Ryan - 30 min)

• What are the GCSS objectives?
• Why are we here?
• What do we want to accomplish?
• What did we learn from FRED?
• Reviewers' comments from FRED

Review of CASPII and BASE intercomparison (Peter Yau - 30 min)

• The CASP II case observations
• Review of CASP simulations by using fine-grid, coarse-grid and SC models
• Update on new model results from RAMS, ECMWF and GESIMA?
• Scientific results and conclusions from the model results

Coffee

Review of CASP and BASE intercomparison (Peter Yau - 45 min)

• The BASE case observations
• Simulations by using fine-grid, coarse-grid and SC models including updated results.
• Scientific results and conclusions from the model results.

Discussion for outline of paper bring together conclusions from CFRP, BASE and CASPII

• What can we say about CRMs?
• What can we say about single column models?
• What can we say about coarse-grid models /GCMs?
• What can we say about spurious circulations generated by the models?
• What implications for the future improvements of CRM cloud schemes
• What have we learned from the exercises?
• What implications for the future improvements of GCM cloud schemes?
• What can we say about the general methodology/strategy?

Lunch
Large-scale observations to resolve cloud property variations

Use of large-scale observations to resolve cloud property variations

with dynamic regime: A test case of the north-east and north-west Atlantic basins (George Tselioudis).

Model simulations of the north-east and north-west Atlantic cloud type variations with

dynamic regime: Role of resolution, running mode (weather vs climate) and

cloud parameterization. (Chris Jakob).

A study of mid-latitude weather systems in the UKMO Climate Model. (Mark Webb).

Discussion on the connection between field experiments and large-scale

observations and their role in climate model evaluation.

Thursday: 15 July

The FASTEX IOP 16 intercomparison

Overview of case (what happened, observations available etc), UKMO Modelling results highlighting interesting science so far. (Humphrey Lean 45 mins)

Intercomparison project - what we are trying to do plus relationship with FASTEX-CSS (Peter Clark - 15 mins)

Coffee

Summaries of progress and future plans in intercomparison for each model (1hr 45 min).

Each one to include:

• Model overview + any recent improvements esp microphysics
• Any progress so far with runs
• Plans for production of results
• Comments on intercomparison

(a) DARLAM Jack Katzfey
(b) RAMS Jack Katzfey
(c) MC2 Peter Yau
(d) GKSS Burkhart Rockell
(e) MesoNH Phillipe Lopez
(f) HIRLAM Klara Finkle
(g) UM box data Humphrey Lean/Peter Clark

• Evaluation of cloud-system lifetime during FASTEX (Jean-Pierre Chaboureau)

• ISCCP observations of the FASTEX cases: large-scale picture and comparisons with model simulations (George Tselioudis).

Lunch

Overview of Progress so far - any synthesis data (Peter Clark)

Discussion of Future work led by Brian Ryan

• Overall aims

Coffee

• Microphysics, what sensitivity tests it would be sensible to do given what we know about what is in each model.
• Agree plans for synthesis

Friday 16 July

Sub-grid-scale of clouds and orography in representation in GCMs

The problem of sub-grid-scale representation of clouds and orography

• Example case study (Jack Katzfey)

Discussion of parameterising subgrid scale effects due to orography (Jack Katzfey)

Coffee
Workshop summary and report to GCSS

Lunch
Depart from workshop