Abstract:
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.