Session Ch - Convection & Buoyancy.
ORAL session, Sunday, November 23
308, Moscone Center
In rapidly rotating flows, vortices form Taylor columns aligned with the vertical rotation axis \hatz. When the flow is thermally stratified the Taylor-Proudman theorem is modified so that \partial \vecv/\partial z is no longer zero but proportional to the horizontal temperature gradient \nabla_H T. This is the Thermal Wind Equation (TWE). With a proper \nabla_H T, pancake-shaped rather than columnar vortices form. Planetary vortices are pancake-like. An isothermal pancake vortex will not satisfy the TWE and creates a secondary flow similar to Ekman pumping. This flow creates a \nabla_H T in accord with the TWE. However, the vortex decays slowly, and for small Prandtl number, with the thermal rather than viscous, timescale: thermal conductivity acts to destroy \nabla_H T, but it is maintained by the secondary flow (which is forced by the imbalance in the TWE if \nabla_H T decays). Thus the thermal timescale regulates the secondary flow. Kinetic energy flows from the primary vortex into the secondary flow which transforms it to potential energy (as it advects heat against the stable stratification). The potential energy (stored as cold above hot fluid) is then thermally dissipated.