Vertical Motion and Precipitation Computations

Abstract

Large-scale vertical motions are computed using a multi-level numerical model which employs the quasi-geostrophic filter and obtains vertical motions at four pressure levels. The vertical motion and precipitation computations are varied, using four different grid sizes, variable horizontal boundary conditions and subjective and objective analyses. Two storms of contrasting nature are studied. The geographic patterns of computed vertical motion and precipitation are maintained when the grid interval is reduced, but more detailed patterns appear. Agreement of cloud and precipitation patterns with areas of computed vertical motions is affected by the average upper wind flow. Variable horizontal boundary conditions had little effect on the vertical motions associated with the storm in the center of the grid in both cases. Vertical motion and precipitation computations using objective analyses lead to inconsistencies throughout the area of computation.