Accession Number : ADA319136

Title :   Utah Local Area Model Sensitivity to Boundary Conditions for Summer Rain Simulations.

Descriptive Note : Master's thesis,

Corporate Author : UTAH UNIV SALT LAKE CITY DEPT OF METEOROLOGY

Personal Author(s) : DeSordi, Steven P.

PDF Url : ADA319136

Report Date : AUG 1996

Pagination or Media Count : 122

Abstract : The Utah Limited Area Model is integrated over a period of approximately 2 weeks during the summer floods that occurred in 1993 over the Upper Mississippi River Basin. The central goal is to determine the sensitivity of the simulated precipitation pattern to the method of specifying the upper and lateral boundary conditions. Three different upper boundary conditions are tested. The first does not allow feedback from the local model upon the pressure field at the model top. The second includes a modification of this field suggested by Klemp and Durran (1983) to allow vertical propagation of gravity waves through the model top. The third tested upper boundary condition specifies a pressure modification designed to eliminate w at the model top, as proposed by Innocentini et al. (1993). Model forecasts using the first two boundary conditions overpredict rainfall over Iowa, whereas the third simulation underpredicts the rainfall here and in most other regions. All simulations are poor with regard to heavy rain that was underpredicted southwest of Iowa where the NCEP reanalysis rainfall is relatively superior. Some of the limited area simulations are relatively better in the southeast portion of the country, where they provide more realistic rainfall structure than does the NCEP reanalysis. The limited area model predictions are also rather sensitive to the model used for boundary conditions. Boundary conditions interpolated from NGM model analyses and 6-h forecasts produce significantly more realistic regional Utah Limited Area Model simulations than boundary conditions interpolated from the NCEP reanalysis. There is relatively less sensitivity to the spectral relaxation of limited area forecasts to outer model results, although this did generate rainfall in some regions that were excessively dry.

Descriptors :   *WEATHER FORECASTING, *RAINFALL INTENSITY, *ATMOSPHERE MODELS, THESES, VERTICAL ORIENTATION, PATTERNS, FLOODS, MISSISSIPPI RIVER, BASINS(GEOGRAPHIC), SUMMER, GRAVITY WAVES.

Subject Categories : Meteorology

Distribution Statement : APPROVED FOR PUBLIC RELEASE