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  1. CASES99-Results L. Mahrt CASES99 Workshop Oct 2005

  2. Summary 1. radiative flux divergence important mainly for initial formation of the surface inversion. 2. boundary-layer structure assumes a variety of forms including dominance by elevated shear generation (upside-down structure). 3. When definable, surface based boundary layers are typically ONLY about 20 m deep, sometimes thinner. 4. Models of the “boundary-layer” must allow for z-less and upside-down conditions.

  3. Summary cont. 5. turbulence is often characterized by poorly defined intermittency 6.patches of turbulence often occur on scales smaller than 100 m with short lifetimes 7. temperature advection is generally important and can strongly influence the vertical structure; for example heat flux convergence roughly balanced by cold air advection. for weak turbulence with strongly stratified conditions, variable averaging width is required to define the meaningful perturbations, or else suffer enormous random sampling errors.

  4. Motion characteristics change from the small-scale side to the large-scale side ot the gap (SMALL-SCALE) MESOSCALE MOTIONS ARE: 1) much more horizontal 2) correlations between vertical velocity fluctuations and other quantities are weaker 3) correlations between vertical velocity fluctuations and other quantities vary dramatically between records and become small with sufficient averaging. 4) fluxes are not systematically related to the local gradient or bulk gradient in the boundary layer.

  5. Future • 1. Get rid of the “band-aids” and tuning and start all over with new model (huge job). An improved parameterization which compares better with data may worsen the performance of the tuned model. • 2 Analyze data from several sites with the same analysis strategy.Each site is unique in terms of drainage flows, low level jets, ambient conditions, surface roughness. For example advection at the FLOSS site vs low-level jet for CASES99.

  6. Working on now • Probability distribution of extremely weak turbulence for very stable conditions • The nature of the mesoscale motion (meandering) on scales just larger than turbulence • Improvement of bulk formulations with pdf of surface fluxes