Computation of the Large Scale Vertical Velocity

Abstract

Vertical velocities are computed at four levels over a Northern Hemisphere grid in addition to a lower boundary value which is applied at terrain pressure and includes effects of frictionally- and terrain-induced vertical velocities. The latter, as computed here, have somewhat smaller maximum magnitudes and less irregularity than the frictionally-induced vertical velocity. The calculations show that the terrain and friction effects markedly influence the ?-fields in the lower troposphere but largely disappear by 500 mb for the rather heavily smoothed mountains used in these experiments. Computations with several static stability parameters, namely a constant value, a value varying with pressure only, and a point-variable value, exhibit the greatest differences in the maximum vertical velocities, as much as 50 per cent, at 300 mb. At lower altitudes the differences are only about 10 per cent. Similarly when computations were made utilizing the term f? versus fM2 in the coefficient of ?2?/?p2 in the ?-equation, differences in ? up to 50 per cent occurred, but mostly the differences were only 10 to 25 per cent. The computed vertical velocities during a severe west coast storm appear to show good correlation with the weather.