A Theory for Isallobaric Air Flow in the Planetary Boundary Layer

Abstract

The concept of the isallobaric wind is extended to include frictional boundary layer effects by use of a simple quasi-balanced analysis which filters out inertia-diffusion oscillations. It is found that transient modifications to Ekman-like flow also possess a spiral hodograph structure. In contrast to Ekman-like flows, the divergence of the isallobaric flow component increases to the top of the boundary layer while the vorticity reaches a maximum within the boundary layer; both quantities are proportional to the Laplacian of local rate of pressure change rather than the Laplacian of pressure. Applications to idealized intensifying and moving systems are given. It is found that the isallobaric correction provides enhanced low-level upward motion in advance of a moving low pressure center and subsidence to its rear.