NUMERICAL STUDIES OF EFFECTS OF SURFACE FRICTION ON LARGE-SCALE ATMOSPHERIC MOTIONS¹

Abstract

A simple relationship is obtained between pressure changes associated with friction and the geostrophic drag coefficient. From this, the imbalance between frictionally induced mass inflow and outflow is shown to be one or two orders of magnitude smaller than either the inflow or outflow.Numerical integrations using the primitive equations are performed for an axially symmetric autobarotropic low-pressure system. The velocity components and pressure tendencies are found to depend critically on the drag coefficient.Two actual synoptic cases are studied using a quasi-geostrophic numerical model incorporating-release of latent heat. Computations are performed with and without surface friction. When friction is excluded, the 1000-mb Highs and Lows are more intense.Ttvo methods of computing the surface stress are compared. One is based on variations in terrain height and the other on the nature of the vegetation. Differences are large, especially over the western part of North America. A2

A modified sigma equations' approach to the numerical modeling of Great Lakes hydrodynamics

“…To simplify the numerical scheme, the boundary computations for rt (equations 16 and 17) are replaced by the linear extrapolations (equations A8 and A12) of immediately interior values, as is done. by Danard [1969]. At the free surface (, = 0), the horizontal stress components are replaced by the atmospheric wind stress.…”