18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Tuesday, 31 July 2001: 8:15 AM
Validation of boundary-layer parameterizations in a maritime storm using aircraft data
P. Ola G. Persson, CIRES and NOAA/ETL, Boulder, CO; and B. Walter, J. W. Bao, and S. A. Michelson
Poster PDF (1.4 MB)
During the California Landfalling Jets Experiment (CALJET), the NOAA P-3 aircraft was used to obtain numerous measurements of fluxes of surface momentum, sensible heat, and latent heat, and to document the boundary layer structure associated with maritime cyclones. On February 6-7, 1998, the aircraft obtained a north-south cross-section of the atmospheric structure and surface fluxes in the cold-air region between two large maritime cyclones off the coast of California. The fluxes were obtained in 4 flux stacks connected by slow ascent/descents and dropsonde data to give a uniquely complete structure of the lower troposphere. The extensive CALJET observational coastal network documented the structure of these storms as they made landfall.

These observations are used to validate several planetary boundary layer (PBL) parameterization schemes using both "off-line" methods and 3-D modeling. The off-line method uses the observed mean flow and thermal characteristics, while the latter relies on the model atmosphere and surface characteristics. The 3-D numerical experimentation is done with the Penn State/NCAR Mesoscale Model (MM5) using the Burk-Thompson, high-resolution (Blackadar), and MRF PBL schemes. The results show significant differences in the offshore PBL depth and surface heat fluxes between the schemes. The coastal precipitation can vary by as much as 50% from one scheme to another in some locations. The results from the 3-D model testing method are sensitive to the SST fields used and the model initial conditions. For instance, AVHRR SST analyses, verified with P-3 AXBT observations, were prefered since the ECMWF SST analyses in this region of the Pacific Ocean were as much as 1.5C too warm during this anomalous SST year. Observed and parameterized/modeled fluxes in other CALJET cases will also be presented to provide more generality.

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