Airborne chemistry and dynamics at the edge of the 1994 Antarctic vortex

Abstract

Measurements of H2O, NOy, CH4, N2O, O3, HCl and wind speeds taken from the ER2 high-altitude research aircraft are used to examine the chemistry and dynamics near the edge of the Antarctic vortex in the period from late May to late October 1994. It is shown that, as the vortex evolves over this period, the horizontal gradients of quasi-conserved quantities steepen as the polar-night jet stream strengthens. By October, there is a mixing zone, 10° of latitude wide, centred on the wind speed maximum, across which air depleted in water, NOy, HCl and ozone has a poleward gradient in a statistical mean sense. Conversely, the recovery time of HCl in outer vortex air after exposure to polar stratospheric clouds (PSC) occurs sufficiently fast in early August that mixing-in of relatively unprocessed air seems to be the most viable explanation. The observations also show the vertical redistribution of water and NOy(presumably as HNO3) as a result of sedimentation in large PSC particles. Ozone loss as high as 25% occurred in early August at the vortex edge in PSC-processed but undenitrified air. Vertical profiles in outer vortex air suggest freer transport of processed air to midlatitudes at potential temperatures below 400 K (about 100 hPa, 16 km).