A Numerical Study of the Influence of Advective Accelerations in an Idealized, Low-Latitude, Planetary Boundary Layer

Abstract

Steady, longitudinally invariant, barotropic, boundary layer flow is numerically studied at low latitudes where advective accelerations may he large and the Coriolis parameter is small. Flow is generated by specifying the pressure gradient field independent of the flow. It is found that as the flow approaches the equator, advective terms associated with the large latitudinal variation of the Coriolis parameter become important. As the flow crosses the equator, adjective accelerations may become important to the extent that the boundary layer downstream from the equator is radically different from the Ekman boundary layer. Compared to Ekman flow, the wind vector may rotate with height in the opposite direction, and the boundary layer depth may be considerably thinner and less dependent on latitude. The cross-isobar flow of this advective boundary layer is deeper and may be stronger, so that spatial transitions between this boundary layer and a quasi-Ekman boundary layer can produce significant vertical motion.