The Cyclostrophic Adjustment of Vortices with Application to Tropical Cyclone Modification

Abstract

The cyclostrophic and hydrostatic adjustment of simple one-layer and multilayer vortex flows to the local removal and/or redistribution of mass and angular momentum are studied, and a detailed physical interpretation of the dynamics of adjustment is given for the one-layer model. The calculations provide insight into possible responses of tropical cyclones to modification by cloud seeding and facilitate an appraisal of the Simpson-Malkus modification hypothesis. Calculations for two- and three-layer models show that the maximum tangential velocity is increased whether or not mass transfer takes place predominantly inside or outside the radius at which the maximum occurs, and the central surface pressure decreases due to subsidence at one or both interface levels. However, the magnitude of these effects are comparatively small in relation to the strengths of the induced meridional circulation and corresponding changes in tangential wind speed outside the core, at, or beyond, the radii at which mass transfer occurs. Moreover, the estimated maximum change in tangential wind speed that might be produced in a tropical cyclone by following the seeding procedure suggested by Simpson and Malkus is small compared with observed natural variations.