POLAR VORTEX CONDITIONS DURING THE 1995-96 ARCTIC WINTER - METEOROLOGY AND MLS OZONE

The 1995-96 northern hemisphere (NH) winter stratosphere was colder th an in any of the previous 17 winters, with lower stratospheric tempera tures continuously below the type 1 (primarily HNO3) polar stratospher ic cloud (PSC) threshold for over 2 1/2 months. Upper tropospheric rid ges in late Feb and early Mar 1996 led to the lowest observed NH lower stratospheric temperatures, and the latest observed NH temperatures b elow the type 2 (water ice) PSC threshold. Consistent with the unusual cold and chemical processing on PSCs, UARS MLS observed a greater dec rease in lower stratospheric ozone (O-3) in 1995-96 than in any of the previous 4 NH winters. O-3 decreased throughout the vortex over an al titude range nearly as large as that typical of the southern hemispher e (SH). The decrease between late Dec 1995 and early Mar 1996 was simi lar to 2/3 of that over the equivalent SH period. As in other NH winte rs, temperatures in 1996 rose above the PSC threshold before the sprin g equinox, ending chemical processing in the NH vortex much earlier th an is usual in the SH. A downward trend in column O-3 above 100 hPa du ring Jan and Feb 1996 appears to be related to the lower stratospheric O-3 depletion.