NORTHERN-HEMISPHERE MID-STRATOSPHERE VORTEX PROCESSES DIAGNOSED FROM H2O, N2O AND POTENTIAL VORTICITY

MLS H2O, CLAES N2O and potential vorticity calculated from UK Meteorol ogical Office data are used to study mid-stratospheric vortex processe s in the northern hemisphere winter of 1991-92. Areas of moist air (at approximately 20 hPa) and N2O-poor air (at approximately 10 hPa) are well-correlated with high values of potential vorticity and there is l ittle or no large scale mixing across the vortex edge. We find evidenc e for the descent of relatively dry mesospheric air to the 840 K (appr oximately 10 hPa) level, as well as descent of moist air from the uppe r stratosphere to the 655 K (approximately 20 hPa) level. A reduction in the areas of the vortex and both the moist and N2O-poor regions is observed and there is evidence of moist and N2O-poor air parcels being extruded from the vortex.