6A.19
Comparison of marine boundary layer turbulence structure in high wind conditions in different regions of maritime storms
Bernard A. Walter, Northwest Research Associates, Bellevue, WA; and P. O. G. Persson
The California Land-falling Jets Experiment (CALJET) was carried out along the California coast, and up to 1000 km offshore, during the winter of 1998 to 1) study the underlying physical processes that cause flooding rains and high winds in the orographically complex coastal zone, 2) explore the impact of potential future observing systems on short-term (<24 h) quantitative precipitation and wind forecasts, and 3) investigate the possible impact of El Nino-enhanced surface fluxes on storm development. Turbulence measurements were made by the gust probe system on the NOAA P-3 aircraft in different parts of maritime storms during CALJET. Multilevel crosswind flux stack patterns were flown in the low-level jet (LLJ) regions of (1) and (2) (below) and in a four stack north-south oriented pattern in (3). We will discuss data collected for the following cases:
(1) Feb. 2: in the prefrontal LLJ region wind speeds were 25-30 m/s and PBL conditions were statically slightly stable, but potentially unstable with evidence of mechanical mixing. Latent heat flux measurements show moderately large upward values in the jet region but 2-3 times larger values in the area just to the west of the jet region.
(2) Feb. 3: in the LLJ region of a secondary front wind speeds were 15-20 m/s and the PBL was again statically slightly stable but potentially unstable. In general latent heat fluxes were larger than the sensible heat fluxes by a factor of two but substantially smaller than the latent heat fluxes on the previous day. The latent heat flux was upward everywhere while a layer of downward sensible heat fluxes occurs at about 400-600 m at the upper level of the warm sector BL and at the warm frontal surface.
(3) Feb. 6: in the ridge between two storm systems turbulent fluxes were measured to study the impact of surface fluxes on subsequent storm development. Here the latent heat fluxes dominated the sensible heat fluxes. The flux stacks were flown in an area where there were large open mesoscale convective cells as seen in satellite imagery, and air-sea temperature differences were small (1 deg C). Wind speeds were 15-18 m/s. Over the region of the four stack patterns the latent heat fluxes decreased from south to north.
We will compare the vertical and horizontal variations of the fluxes (momentum, heat and moisture) and TKE and compare the dominant scales of flux transport in the three cases. This comparison may provide numerical modelers insights into the ability of existing turbulence parameterization schemes to properly characterize the turbulence in these disparate regions of maritime storm systems. For example, the presence of horizontal roll vortices may limit the ability of models to handle flux predictions because rolls are not properly treated in the models
Session 6A, Marine and Oceanic Bls
Friday, 11 August 2000, 10:15 AM-4:45 PM
Previous paper