Breaking planetary waves in the stratosphere

Abstract

Satellite-borne IR radiometers are turning the Earth's stratosphere into one of the best available outdoor laboratories for observing the large-scale dynamics of a rotating, heterogeneous fluid under gravity. New insight is being gained not only into stratospheric dynamics as such, with its implications for pollutant behaviour and the ozone layer, but also indirectly into the dynamics of the troposphere, with its implications for weather forecasting. Similar dynamical regimes occur in the oceans and in stellar interiors. A key development has been the construction of coarse-grain maps of the large-scale distribution of potential vorticity in the middle stratosphere. Potential vorticity is a conservable quantity which has a central role in the dynamical theory, but is difficult to calculate accurately from observational data. We present the first mid-stratospheric potential vorticity maps which appear good enough to make visible the ‘breaking’ of planetary or Rossby waves, a phenomenon ubiquitous in nature and arguably one of the most important dynamical processes affecting the stratosphere as a whole.