Science Issues from September 2002 VTMX Workshop

1. The performance of mesoscale numerical models in describing the wind, temperature, and turbulent structure of the valley atmosphere was mixed.
   • Basic flow patterns and temperature fields are captured, but …
   • The timing of important events (e.g., flow reversals) was often off by one or more hours
   • Details of the flows over certain segments of the valley were in error (e.g., jet structure, flow strength,…)
   • The vertical temperature structure showed persistent biases which are not yet understood
   • The agreement between modeled and observed turbulent heat fluxes and TKE was unsatisfactory.

2. Aspects of radiational heating and cooling in valleys do not seem to be adequately accounted for in numerical models.
   • Extreme cooling is observed in sinkholes
   • Can this behavior be explained and modeled?
   • How relevant is this phenomenon to larger-scale valleys and basins?

3. Wave-like features and ascending or descending layers of air were common along the sidewalls and may be common elsewhere but their significance for vertical transport and mixing is unclear.
   • What is actually happening during these events?
   • What causes them?
   • Is there any hope they can be modeled or predicted?
   • Does it matter?

4. LES and DNS look promising but can they deliver useful improvements in parameterizations for mesoscale models?
   • How can we generalize from highly idealized modeling conditions to the real world?
   • What insights into the basic physics of stable atmospheres can be gained?
   • How important are these insights for VTMX processes?
   • How can they be represented in more common models?

5. How important are breaking waves, which may occur hundreds of meters above the surface, to mixing processes in general and near the surface in particular?
   • Are these waves predictable?
   • What effects do they have on VTMX processes?
   • If effects are important, how can they be represented in models?

6. Commonly used closure assumptions relating eddy diffusivities to the gradient Richardson number are not accurate for slope flows in very stable conditions.
   • How badly does this affect the predictions of models?
   • What can be done to improve parameterizations in these circumstances?

7. How should intermittent turbulence be handled?

8. We had varying degrees of success with a variety of instrument platforms and measurement techniques.
   • Where do we go from here?
   • How can we improve out ability to measure and characterize mean and turbulent wind and temperature fields, particularly at elevations more than a few 10s of meters above the surface?
   • Can we get better performance out of existing instruments? How?
   • What new instruments might we deploy in a future campaign?
   • At what other locations should we deploy instruments? Why?

9. Surface energy balance data are needed …
   • What kind of energy balance measurements should we take?
   • Where?
   • Is the terrain so inhomogeneous that it's basically hopeless to get a representative reading?

10. What are the spatial and temporal scales of importance for VTMX processes (e.g., vertical fluxes of mass and heat, divergence, vorticity) in the Salt Lake Valley as a whole? How can they be deduced from analyses of model results? How can they be verified through observations?

11. How important are small scale terrain features to the structure of the atmosphere in the Salt Lake area? To what extent are observed VTMX phenomena peculiar to the Salt Lake area? What results from the Salt Lake studies can be transferred to other areas?

12. It is apparent that the flows in the Salt Lake Valley are influenced by a variety of external forcing mechanisms.
    • Was our study domain appropriate? Should it be changed? How?

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