Estimating Lower Tropospheric Vertical Motion from Surface Pressure and Pressure Tendency Data Alone

Abstract

Existing methods for calculating synoptic and meso-alpha scale vertical motion rely on upper air sounding data which confines the calculations to restricted regions of the earth's surface and to sounding times. In this paper a method is proposed which estimates vertical motion up to about 600 mb using only sea level pressure and pressure tendency data. The general approach is to integrate the continuity equation upward from the top of the planetary boundary layer where the vertical motion can, in theory, be estimated from surface data using simple Ekman theory. The free atmosphere divergence is then estimated by interpolating linearly from its surface quasi-geostrophic value, calculated through the quasi-geostrophic vorticity equation evaluated using surface pressure and pressure tendency data, and a zero value at the assumed level of nondivergence taken to be in the middle of the troposphere. As an example, the method was applied and partially tested in an atmosphere simulated by a primitive equations forecast model. The results suggest that if the vertical motion at the top of the boundary layer can be reliably specified, the method should be able to provide quantitative information on the vertical motion up to 700 mb with qualitative information available at least up to 500 mb. Since the results in a model atmosphere cannot be considered conclusive, a test with real data is indicated in which care should be taken to assure that non-quasi-geostrophic effects are removed from the pressure and pressure tendency data.