ENSO Variability of the Southern Hemisphere Subtropical Westerly Jet, Ozone Croissant, Ozone Hole, and Polar Stratospheric Clouds

An important teleconnection exists between tropical convective outflow in the UTLS and climatological structures in the austral winter and spring. Lagrangian trajectories and a detailed momentum budget show that the Australian subtropical westerly jet (ASWJ) is due to outflow from convection over SE Asia and Indonesia. The ASWJ lies immediately equatorward of the zonally asymmetric maximum in column ozone, which is known as the ozone croissant (OC). The OC extends from the Southern Indian Ocean past Australia into the Pacific and reaches maximum zonal asymmetry during October. The ozone hole is usually displaced off of the pole away from the OC toward the Atlantic sector. The interaction of monsoon anticyclones, synoptic Rossby waves, and extratropical travelling planetary waves in maintaining the OC is discussed. The structure of the OC is intimately linked to the structure of the ozone hole, polar vortex temperatures, and polar stratospheric clouds (PSCs). The OC is also an integration of hemispheric transport, which can reflect tropical influences, including that of the El Nino Southern Oscillation (ENSO). During La Nina the polar vortex is stronger and displaced farther off the pole, the OC is more zonally asymmetric, and there are more PSCs and colder temperatures in the polar vortex above 16 km. During El Nino the polar vortex is weaker, more centered on the pole, midlatitude ozone is arranged in an annulus, and there are fewer PSCs and warmer temperatures in the polar vortex above 16 km. A dynamical explanation is suggested for this interannual variability which contrasts the strong longitudinally-focussed outflow in the UTLS from Indonesia during La Nina with the more longitudinally-dispersed, milder outflow events during El Nino.