THE STRATOSPHERIC POLAR VORTEX AND SUB-VORTEX - FLUID-DYNAMICS AND MIDLATITUDE OZONE LOSS

It has both suggested on the basis of certain chemical observations th at the wintertime Stratospheric polar vortex might act as a chemical p rocessor, or flow reactor, through, which large amounts of air - of th e order of one vortex mass per month or three vortex masses per winter - flow downwards and then outwards to middle latitudes: in the lower stratosphere. If such a flow were to exist, then most of the air invol ved would become chemically 'activated', or primed for ozone destructi on, while passing through the low temperatures of the vortex where fas t heterogeneous reactions can take place on polar-stratospheric-cloud particles. There could be serious implications for our understanding o f ozone-hole chemistry and for midlatitude ozone loss, both in the Nor thern and in the Southern Hemisphere. This paper will briefly assess c urrent fluid-dynamical thinking about flow through the vortex. It is c oncluded that the vortex typically cannot sustain an average throughpu t much greater than about a sixth of a vortex mass per month, or half a vortex mass per winter, unless a large and hitherto unknown mean cir cumferential force acts persistently on the vortex in an eastward or ' spin-up' sense, prograde with the Earth's rotation. By contrast the 's ub-vortex' below pressure-altitudes of about 70 hPa (more precisely, o n isentropic surfaces below potential temperatures of about 400 K) is capable of relatively large mass throughput depending, however, on tro pospheric weather beneath, concerning which observational data are spa rse.