WG3 ANNUAL REPORT FOR 1995

This report was presented at the 4th GCSS annual meeting on December 14, 1995 in Washington, D.C.

1. ONGOING ACTIVITIES

a. Main Scientific Issues

Layer cloud systems are a major component of the extra-tropical region and they consequently play a critical role on the water and energy cycles of the region. This working group is setting out to be sure that the critical aspects of these systems are suitably represented within climate models. Some specific concerns and challenges are:

• It may be that if GCM models maintain their 200-300 km grid resolution, we will have to focus on some frontal-parameterization in much the same way as done for convection in order to account for all the interacting processes.
• The structure of layering within and around these systems is still poorly observed and probably poorly handled.
• There is a real concern that the water budgets of the component system are not well handled by climate models.
• The issue of orographic effects on the systems has barely been touched. With a number of relevant cases now under examination within the group or about to be, we are in an excellent position to address these issues.

b. Summary and recommendations from workshop

A very successful workshop was held at NASA Goddard Institute for Space Studies on November 1-3, 1995. There were 24 presentations made during the workshop. These were organized into those concerned with observations (mainly layering), cloud system modeling and the use of satellite information, column models, and global climate models. A draft report on this workshop is shown in Attachment 1 and it is also available on the home page. It is expected that this report will be completed in January, 1996. A number of specific actions arising from the workshop are shown in Section 4 of this report.

This workshop marks an important step in the evolution of the working group. Collective results were shown, coordinated activities were planned, and we received strong encouragement from the GCM community that our efforts are being appreciated.

A brief summary of some of these aspects follows. The specific presentations and discussions in regards to layering were very impressive. Having the involvement of the cloud profiling radar community and the in-situ observational community is a big boost to our efforts. This will maintain a strong observational component.

Several cloud system simulation studies were shown (Table 1) and these are characteristic of a number of typical situations found in different regions of the world (Table 2). Several of these carried out initial tests of large scale computations and there was a good discussion as to how to proceed with these calculations in the future.

A wide variety of extra-tropical layering cases have been chosen for study. The cases were from southern Australia, New Zealand, the US Rockies, the east coast of Canada, the Arctic Ocean, the eastern Atlantic, northern Germany, and the North Sea. The focus in most of the cases was on extra-tropical frontal systems, although the two US Rockies cases (Colorado upslope case and the precipitation over the Rockies) were largely generated by anticyclonic systems in interaction with topography. The cases varied in their evolution. Rapid evolution occurred in the Canadian East Coast case in particular, whereas the northern Canadian case was probably the most steady state. None of these was atypical of the region and so they form a very good basis for studies aimed at assessing their representation within climate models.

From a collective point of view, the situations also reflect a number of different situations such as: flat surface (over ocean, sea ice and land), orography (Rockies, Southern Alps, Baltic Region), frontal forcing (varying from very weak to very strong), and varying sub-cloud conditions (from very dry to very moist).

A number of state-of-the-art simulations of extra-tropical layer clouds have been performed. Several models were used in these calculations. These were: DARLAM (Australia), MM5 (US), RAMS (US and NZ), MC2 (Canada), Szeto-Cho (Canada), Unified (UK), REMO (Germany), and GESIMA (North Sea).

The cases are also unique in the sense that some of them represent excellent testbeds for the examination of particular processes. This includes different phases of particles (Canadian East Coast, US upslope, Scotland multi-layer), the role of sublimation or evaporation (Arctic, Australia and eastern Atlantic cases), as well as ice nucleation and timing (US upslope case). From an examination of the cases collectively, it is expected that we will eventually make substantial progress on the scaling of frontal circulations and on the efficiency of precipitation production.

Several of the cases (both US cases, Germany case, New Zealand case) will also allow us to gain a better appreciation of the role of topography on these systems and as testbeds for dealing with sub-grid orography within climate models.

Some initial attempts (by the upslope Rockies, the eastern Atlantic, the Australian, and the northern Canadian cases) have been made to estimate the larger scale parameters from these high resolution simulations. There was no consensus on the overall implications of these results, other that in all cases there was a major impact on the large scales. There was some concern that the large scale effects will be quite depend upon the location within the storm in which the calculations were made.

The use of the ISCCP information within the effort was certainly well-received. None of the cloud system modelling efforts have used this information before and it will be an important addition to the ongoing studies.

Preliminary tests with a column model were well-received. It was felt this technique had promise as a critical bridge towards developing acceptable parameterizations. There was a lively discussion as to how to properly force such a model and there was general consensus on the requirements and on the need for the group to collectively work on this issue.

The GCM community pointed out that their simulations have difficulties in the mid-latitudes. They don't for example feel that they are properly simulating the cloud fields associated with extra-tropical systems. They wonder if, at the scale of 200-300 km now typically used, they won't need some form of frontal adjustment, in the manner now done for convection.

Upcoming observational efforts include SALPEX over New Zealand and FASTEX over the north Atlantic. A major issue for SALPEX is orographic alteration of cloud fields and suggestions by the group for minor alterations to the plans were discussed. For FASTEX, there was acknowledgment that this large effort should provide excellent information for the working group. The possibility of stationing a cloud profiling radar at Shannon was mentioned as a possible enhancement.

Given the circumstances of several of the participants, it was also suggested that some simple recommendations be made to allow for enhanced involvement. These recommendations are:

• Climate modelling centres should view this GCSS initiative as a positive contribution to their mandate and should allow some of their scientists to participate in our activities.
• An effort be maintained to fully appreciate the large scale impacts of mountain upslope conditions since these situations also provide some of the best information of slantwise ascent and ice nucleation.
• Global climate modelling centres are encouraged to pay more attention to the analysis of the time evolution of individual cloud systems.

Extensive use is being made on the working group's home page (http:/www.msc.ec.gc.ca/GEWEX/GCSS/GCSS_wg3.html). This draft annual report is for example on our home page. Because of the difficulty of some European scientists to access this during normal hours, some consideration is being made to developing a mirror system in Europe.

After the first workshop at ECMWF, considerable attention was paid towards establishing an acceptable list of parameters for large scale calculations from cloud system model results. The latest version of this document is attached (Attachment 1) and it is also available on our home page.

A small review of the use of column models for climate studies has been carried out. Most of the previous experience with these models has been to drive them with large scale GCM output and to use them for diagnostic studies. Having high resolution cloud system output to compare against is a nice addition to the use of these column models. Much of the information is available on our home page and this will be updated as progress is made.

The list of researchers participating in the activities of the working group continues to grow (see Attachment 2). It is hoped that more Asian interactions will be developed to allow for a more complete global initiative.

d. Related publications

The review article on extra-tropical layer clouds systems, by Brian Ryan, will be published in the Bulletin of the American Meteorological Society in January, 1996.

The review article on critical processes within extra-tropical layer cloud systems should be completed by about March, 1996. It has been held up due to problems in acquiring information on the GCM grid-scale depiction of these features. These elements are critical to providing the necessary focus for the article.

Several other journal articles are in preparation. These consider the nature and large scale impacts of systems over Australia and northern Canada. A total of three journal articles should be completed by spring, 1996.

The importance of the working group is being felt within the regional water and energy cycle experiments of GEWEX. BALTEX, GCIP and MAGS scientists are all actively involved in the working group and it is hoped that GAME scientists will become so as well. Planning documents for MAGS and hopefully GCIP discuss GCSS efforts in particular. It is expected that the BALTEX program will begin to have a strong GCSS component as well. Some initial communications in regards to WG3 involvement within GAME have been made, several WG3 members are from Japan, and there is interest in China as well.

2. NEW RESULTS

a. Modelling

A number of modelling studies already do or expect to serve as excellent means of addressing a number of issues that may have important climate impacts. Briefly, some of the issues addressable within specific cases are shown in Tables 1 and 2.

Some preliminary studies have examined the issue of the scales at which GCMs must be run in order to simulate critical features. As expected, the structures of the produced systems depend on scale with sub-structures being increasingly unresolved with increasing grid-length. A more systematic study of this issue is needed of course.

There were concerns about the accuracy of layer cloud fields predicted by the GCM simulations. In contrast, many of the CRM simulations yielded cloud fields which compared favourably with satellite measurements. Future intercomparison efforts should be very useful for clarifying these issues.

The important issue of precipitation efficiency was addressed in a couple of studies. It can be zero in many Australian situations and it was suggested that there is a bifurcation of precipitation efficiency occurring at high latitudes, at least over the Arctic. If near-surface moisture levels are high, there will be a high efficiency; if values are below say 80%, then it is impossible for any precipitation to be produced. All the vapour goes into cloud. This may have an important feedback for the Arctic climate. If moist conditions re present, near-surface saturation is produced through the sublimation of the resulting precipitation,; if dry conditions prevail, then there is no process to lead to saturation within the cloud and dry conditions are maintained.

b. Observations

There are now several cloud profiling radars in use around the world. The data from these is beginning to be used for deducing a better climatology of cloud layering and for deducing the structure of layering in relation to specific organized cloud systems. The combination of specific observations from such facilities in combination with an analysis of sounding information is quite promising.

The importance of sub-cloud dry conditions is being better appreciated. This can either be under dry, warm instances such as over Australia or dry, cold conditions often found over parts of the Arctic for example.

3. OBSERVATIONAL REQUIREMENTS

A draft of this document was produced in 1994. No changes were made to it over the last year. The document is available through our home page.

4. PLANS

It is clear that several different types of extra-tropical layer cloud systems occur and the focus of the group will begin to shift to more fully recognizing this. Focal points will be on three major areas: oceanic, coastal and continental systems. Orographic effects will of course need to be considered within the continental and possibly the coastal situations.

a. Actions arising from workshop #2

The workshop identified a number of specific actions that need to be addressed. For simplicity, these are loosely divided into fast track items that use existing models or data to begin to make impacts on GCM parameterizations, and research track items that are leading to better understanduing and improvements in the models. These are summarized here.

fast track:

• An initial model intercomparison study with one of the selected cases will be carried out at the 1996 workshop. The Australian case, being well documented and over fairly flat terrain, will be the initial case. Brian Ryan will prepare the dataset for this study for distribution.
• The use of column models to bridge the gap between cloud system models and global climate models will be pursued. This critical step is a major part of our GCSS strategy and so we need to be starting the process now of gaining experience in this effort. Simple calculations will first be done largely using the 2d results from the Beaufort Sea and Australian cases. All progress will be reported to the group as a whole through updates on the home page. A progress report will be made at the 1996 workshop. This effort will be led by Kit Szeto and Lubomir Levkov.
• The large scale requirements from cloud system models will be amended in light of suggestions made at the workshop. This will involve more information on the water cycling by the systems, and the need for more surface information. The information will be added to the WG3 home page. It is expected that the validation of the large scale effects will include radiative properties, budgets and precipitation efficiencies. This is to be accomplished by Kit Szeto and is expected to be completed by January, 1996.
• To allow for open exchange of relevant information, a procedure for doing this will need to be established. To begin with, a procedure for interacting with ISCCP will be needed. This may also include a request that potential vorticity be one of the variables made available for each of the efforts. Standardization of the data archive formats for cloud system models is also urgently needed. Draft ideas will be posted on our home page by January, 1996. This will be led by Ron Stewart and George Tselioudis.
• A discussion of the unique aspects of all the chosen cases will be made available to all participants. A global map showing the locations of these systems will be produced as part of this initiative. It is expected that this documentation will be completed by January, 1996 and will be led by Ron Stewart.
• The cloud system calculations for several cases will continue. As these simulations are completed, the attention will shift towards the large scale calculations. At the next workshop, the full large scale effects of all the simulated cases should be presented.

• An overview of the microphysical-dynamical parameterizations required by the different model types will be established and an action plan for assessing appropriate observations for developing these will be established. This work will be completed by autumn, 1996 and will be led by Doug Johnson.
• The occurrence, nature and impacts of layering will be better defined using the cloud sensing radar now (or soon to be)available. As appropriate, this information will start to be analyzed from global and system relative frames of reference. Ongoing progress is to be made available to the group through appropriate correspondence including our home page and major progress is expected by autumn, 1996 and will be led by Taniel Uttal and Gerald Mace.
• A consistent definition of precipitation efficiency will be developed. This is one measure of the requirements from climate models to simulate the critical features of the systems. This effort will draw upon past efforts in regards to this parameter and investigations of systems in different regions will be asked to determine this parameter. The dialogue on this issue, as well as the final definition, will be handled in large part through our home page. It is expected that this effort will be completed by August, 1996. The effort will be led by Brian Ryan.
• A survey of the occurrence of liquid layers on top of deeper clouds will be undertaken. Although this situation certainly occurs, it is not yet clear whether this is common enough to be important globally. This background study will be led by Brian Ryan.
• A strategy for making meaningful calculations of orographically affected systems needs to be established. A first action in this regard is that Brian Gaudet will ask David Randall to summarize the means that this situation is currently handled within global climate models. This summary should be completed by January, 1996 and will be posted on our home page to solicit suggestions for further actions in light of our need to account for these systems.

It is expected that there will be some modest suggestions for enhancements of the SALPEX initiative over New Zealand. An attempt to have a cloud profiling radar to FASTEX will be made as well. It may be that in each experiment, specific coordinated measurements could be conducted with the purpose being to produce validation datasets for the GCM column model studies.

A special effort will be made to develop a strong working group participation within GCIP.

The continued use of cloud profiling radar information is strongly encouraged as well as one of the most important sources of information on cloud layering.

c. Production of Datasets

It is expected that the datasets for the special case studies will be continually improved over the year with the Australian one being prepared for special consideration at the 1996 workshop. It is likely that most of the special cases identified at the GISS workshop will be handled in this manner. The cases are summarized in Table 1 and a comprehensive list of required data will be established, including data formats.

5. 1996 WORKSHOP

The objectives of this workshop will build on our ongoing efforts. Particular focus will be paid to:

fast track:

• first model intercomparisons
• large scale impacts from different regions
• column model progress
• ISCCP intercomparisons

• layering and microphysical parameterizations
• precipitation efficiency
• occurrence of liquid layers
• strategy for orographic systems

Consideration is also being given to having a statement on the representation of extra-tropical layer clouds within climate models. If such a statement were updated every year, it would serve as a basis for assessing our progress.

It is expected that in 1997 the working group will be ready for other model intercomparison studies. Cases required for such a study will be identified at the 1996 workshop as appropriate.

6. TIMELINE

A brief timing of actions is shown below:

1995
Nov 10 Draft WG3 report on home page
Dec 15 Summary of workshop presented at GCSS meeting

1996
Jan Draft of data exchange procedures on home page
Jan Completion of workshop report
Mar Review article on climate impact issues completed
Oct/Nov Workshop #3: first intercomparisons
Nov Articles started on large scale results
Nov SALPEX experiment over New Zealand

1997
Jan FASTEX over eastern Atlantic Ocean
Oct/Nov Model intercomparison of selected case(s)

• ADDITIONAL ITEMS:
  TABLE 1: Extra-tropical layer cloud simulations from Workshop #2 report on the home page.
  TABLE 2: Fundamental processes in different regions from the Workhop #2 on the home.
  FIGURE 1: Map of WG3 activities from the home page.
  ATTACHMENT 1: Large Scale Computations from the home page.
  ATTACHMENT 2: Participants from the home page

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