CASES 99 - A comprehensive investigation of the stable nocturnal boundary layer

Underlying this effort is the fundamental motivation to eliminate deficiencies in surface layer and turbulent diffusion parameterizations in atmospheric models, particularly where the Richardson number exceeds 0.25. This extensive nocturnal boundary layer (NBL) dataset is available to the scientific community at large, and the CASES-99 participants encourage all interested parties to utilize it. These preliminary analyses show that during nights where weak (< 2 m s-1) surface winds and strong static stability near the surface (exceeding 150 C km-1 to 20 m AGL) might otherwise indicate essentially nonturbulent conditions, that various, sometimes undefined, atmospheric phenomena can generate significant turbulent mixing, and therefore significant turbulent fluxes.

In many cases, a jet structure will form in the NBL between 50 and 200 m AGL, resulting in strong shear between the surface and jet maximum. Consequently, though surface winds are weak, turbulence can be a significant feature in the stable NBL. Further, contrary to some previous work studying nocturnal jets over the Great Plains, the wind direction in the jet is often influenced by an inertial oscillation and seldom confined to the southerly quadrant (e.g., the Great Plains low-level jet).