PROVISIONAL ONLY ....Summary of Microscale Modelling Workshop held on 16^th December 2003, 9:00 - 16:00, at the University of Leeds .

Presentations

1. Introduction: Stephen Mobbs. (link to presentation). A review of the background, timetable and comments on the 1st workshop was presented. Questions particularly relating to particularly, grid structure and adaptation need to be addressed, in addition to those in the list provided in the presentation. A brief discussion of the results of the UWERN management committee 27/10/03 discussed the need to provide interim modifications to the BLASIUS code.

2. Brief Review: Alan Gadian. (link to presentation). A brief review of progress made was presented. An inter-comparison between CLARK, Smolarkiewicz, BLASIUS and the UM demonstrated many similarities. Future progress with microphysics in BLASIUS, and pressure solver issues were discussed. There were detailed comments relating to use of pressure solvers, whether the modification of the BLASIUS code was a distraction, and the merits, or otherwise of the use of different types of grids.

3. Building / Urban / Surface Scale modelling initiative: Ian Castro. (link to presentation). Developments in the urban scale model proposal (UWERN management meeting) and discussions with cfd vendors were described. There was much discussion as whether a Microscale model could ever be applied on the urban scale, with buildings. It was agreed that, as in workshop1, current Microscale models were not compatible, but if there were developments with unstructured grids and or terrain interstecing grids there might be some applicability. The developments and collaborations with cfd vendors were seen as positive and parallel developments to the Microscale model.

4. UWERN meso-scale model developments : Bob Plant (link to presentation). Progress in the area of meso-scale science areas were presented. The importance of being able to model slant-wise convection was emphasised. A workshop on 13th February was going aimed at bringing the community together to discuss these issues. There was seen to be overlap between Microscale and meso scale activities in UWERN and these should be pursued.

5. Issues for fine scale algorithms equations: Mike Cullen (link to presentation). A discussion of the important elements relating to a Microscale model were presented. The advantages of a unstructured approach, for steep terrain flow were discussed. Mesh structures, semi Lagrangian and use of the GCR + pre conditioner all have advantages. The suitability of using the UM, and the advantages of the equation structure and grids was illuminated, suggesting this is a viable platform for a Microscale model.

6. Different vertical grids and choices of Thermodynamic Variable : John Thuburn (link to presentation) and (link to figures). A presentation of the optimal choice of grid structure showed that the C grid structure / Charney Phillips approach had advantages for representation of normal modes, although C grids may have better conservation properties. The recommendation, from a purely dynamical viewpoint, is that a derivation of the C / Charney Phillips grid is optimum.

7. Efficient semi-implicit discretizations on terrain intersecting grids for high resolution atmospheric models : Luca Bonaventura (link to presentation) This talk presented the use of terrain intersecting grid structures for a atmospheric Microscale model. Advantages of the C grid, semi Lagrangian, approach were demonstrated with model results with rapid convergence to a solution. Development of the surface "skin" layer lower boundary conditions are improving the near surface solution. The approach of using a terrain intersecting Cartesian grid was demonstrated to be efficient and effective. This method is likely to be used as an alternative dynamical core in the LOCALE / DWD model, and was demonstrated as a dynamical structure for a Microscale model.

8. Results from a terrain interesting local area model: David Woodhead (link to presentation). This presentation showed some initial 2-d and 3-d results from work completed as a research student. Terrain intersecting, variable grids were displayed, first in two dimensions, and then in 3 dimensions. The equation set used was the "RAMS" formulation, with a split time scale technique for sound waves. Potential temperature is currently being included as a variable, and other issues include the lower boundary condition representation with a law of the wall formulation.

9. Development of a finite element ocean model at IC with adaptive meshing: David Marshall (link to presentation). This talk presented the progress made with an ocean model, using a variable mesh domain. The need to deal with steep topography and geometrically difficult boundary conditions largely influences the unstructured approach required. Good computationally efficient results were obtained and different Reynolds number solutions were produced. The application of this unstructured Finite Element Approach is well suited for this ocean modelling.

10. Issues about a fine scale model Simon Vosper (given by Alan Gadian): (link to presentation). Results from the MO, anelastic, Boundary Layer, dry BLASIUS code were presented.The use of this code with Gal-Chen co-ordinates was shown to give good results, but with slope limitations of ~ 45^o. A staggered C grid formulation proved advantageous, but the pressure solver required between ~ 40 and 68% of the total CPU, and was seen as another limitation as a Microscale model. CFL constraints present an issue as it uses explicit time integration. The stretched grid system has not been widely used.


Discussion

Questions were raised during each talk, and for a prolonged session at the end of the afternoon. Topics raised at the end of Workshop1 were also discussed, but not described below, where duplication occurs. Principally, "Equations Sets"; "What is the model for"; "Use of the UM as a Microscale model" were major repeated discussion items. It was questioned whether allocating effort into the BLASIUS code for pressure solver and microphysics improvements was worthwhile. I was noted, however, that these modules would be required in a Microscale code.

Specific discussion areas in the workshop

Equation set

At workshop 1, an equation set consistent with the incompressible equation set was defined as being most suitable, as well as being consistent with the UM equation set. There was further discussion, but although comments were expressed that at this scale, other sets could equally be used, there were no other comments. It was questioned whether allocating effort into the BLASIUS code for pressure solver and microphysics improvements were worthwhile. I was

Building Scale developments.
These developments (talk 3) were well received. Although they were seen as parallel and complementary programmes, it was also felt that the Microscale model could apply on the building scale, if a suitable grid system (non-terrain following) were implemented. It was hoped that the Microscale and the building scale developments could supplement each other.

Meso-scale developments.
After the talk on meso-scale developments, with a core interest in slant-wise convection, it was again felt that links could be maintained, but there was some discussion as to whether the scales were larger than the original scope for the Microscale framework.

UM development and use for a Microscale model.
This was discussed at some length, particularly at the end of fifth and sixth talks. Concerns were expressed about turbulence closure issues, whether the UM would continue in its present form, and how well the Gal Chen system can really cope with steep terrain, and how well it it could be used for steep slopes. Comments from two MO persons who couldn't be present, argued that it might be useful to try and alternative (e.g. terrain intersecting) grid structures as a useful experiment.
However, the alternative view was also strongly argued that the UM was now a viable option, new micro physics was being inserted, the model was well supported and there were changes being made, including the inclusion of variable horizontal grids in addition to the NWP plans described in the June 2003 letter from NWP at the MO. The inclusion of turbulence closure was being discussed and implemented, and this would be a possibility in future years.
Specific areas for enhancement include
1. Option to remove implicit gravity wave treatment, and explore improved implementation of semi-Lagrangian approach that then becomes possible.
2. More accurate coordinate transformation (but clearly still limited to 45 degree slopes).
3. Better (3d) turbulence model.
4. More complete microphysics.
There was no conclusion drawn from these discussions.

Grid systems.
Limitations were again seen in current grid systems. This topic was very much tied in with the questions raised above. A strong case was put forwards to implement a C / Charney Phillips type grid, from the dynamical viewpoint. However, there were no comments on this type of grid structure for use with radiation and microphysics codes, where other grids may be more suitable.
There were many comments in support of development of unstructured and adaptive grids. The application to ocean models was very clear and advantageous. However, many commented that this would present a significant effort It was felt that this would require more man resources than were available, and therefore unless more resource was apparent, it would be difficult to achieve these ends.
There was also much discussion about the implementation of a terrain intersecting grid approach. The advantages for steep terrains implementation, for simplicity of solution of the pressure equation, and the advantages of a Cartesian grid were stressed. A further opportunity to work with European colleagues in this area, would also assist with limited resources available.
There were no conclusions drawn in this discussion, and further discussions would occur.

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Actions following the workshop
An interim report has already been discussed at the UWERN management group, for short term developments required for UWERN. In the short term, modules for microphysics and modification of the pressure solver for BLASIUS, will be required for the middle of the year. A end of year report will be produced proposing a way forward, where all the above discussions will be included and action proposed. It is planned to implement these activities after the BLASIUS modifications have been completed

Attendees:

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