Unraveling the Stable Boundary Layer Puzzle Using Doppler Lidar and Other Data from CASES-99

Robert M. Banta

NOAA / Environmental Technology Laboratory
Boulder, Colorado

Concurrent measurements of the nocturnal low-level jet (LLJ) using high-resolution Doppler lidar and of near-surface fluxes using multi-level data on an instrumented tower have demonstrated the role of the LLJ in controlling near-surface fluxes under stable conditions at night. These measurements were obtained during the CASES-99 field project in southeastern Kansas during October 1999. Interaction with the Earth’s surface is an important aspect of numerical weather prediction (NWP) models. Nighttime, when the atmospheric boundary layer is stable, occupies a significant fraction of the diurnal cycle, but representation of sub-resolution vertical transport processes is crude. The reason is that this is a very difficult problem. Two field programs, CASES-99 and more recently Lamar 2003, were organized to better understand these processes. Analysis of CASES-99 data to date has shown why these processes are so hard to parameterize, and the roles of the nocturnal LLJ in controlling shear and mixing near the surface. This talk will address the difficulties of parameterization and will use analysis of data from ETL's high-resolution Doppler lidar to illustrate the role of the LLJ in SBL processes. This will lead to recommendations on how to extend these findings to attack the SBL parameterization problem.