STRATOSPHERE-TROPOSPHERE OZONE EXCHANGE OBSERVED WITH THE INDIAN MST RADAR AND A SIMULTANEOUS BALLOON-BORNE OZONESONDE

The stratosphere-troposphere (ST) mode operation of the Indian mesosph erestratosphere-troposphere (MST) radar provided evidence of multiple stable layer structures near the tropopause and also of its ''weakenin g'' during late night hours on several occasions. Mass exchange can ta ke place between the troposphere and the stratosphere during periods o f such weakening. To examine whether there is any transport of ozone f rom the stratosphere to the troposphere at the time of tropopause weak ening at tropical latitudes, simultaneous observations were carried ou t using the Indian MST radar located at Gadanki (13.5 degrees N, 79.2 degrees E), now fully operational in MST mode, and ozonesonde flights from Trivandrum (8.9 degrees N, 76.6 degrees E). Four campaigns of sim ultaneous observations were conducted during January 3-8, November 9-1 6, and December 5-10, 1994, and June 7-24, 1995. The results show occu rrence of the tropopause weakening several times during January 3-8, N ovember 9-16, and December 5-10, 1994. Simultaneous observations of oz one profiles, particularly on January 7-8, November 10 and 16, and Dec ember 7-8, 1994, the days of tropopause weakening, show evidence of a decrease in stratospheric ozone and a corresponding increase in tropos pheric ozone after this event, the total ozone remaining essentially c onstant on these days with respect to other days. Tropopause weakening on January 4-5, 1994, however, does not show any considerable change in the ozone profiles. The results are presented here relating the deg ree of tropopause weakening to the extent of vertical mass exchange be tween the troposphere and the stratosphere. An effort has been made to examine the role of horizontal advection of ozone in increasing tropo spheric ozone at the region of interest; the geographical distribution of tropospheric ozone residual (TOR) has been analyzed by the two dat a sets obtained independently from Meteor 3 total ozone mapping spectr ometers (Meteor 3 TOMS) and the Upper Air Research Satellite (UARS). S imultaneously, the possibility of horizontal transport of ozone from t he areas surrounding Tirupati and Trivandrum in increasing tropospheri c ozone due to synoptic scale circulation has also been verified by cl ose inspection of synoptic weather charts at 1000, 700, 500, and 300 h Pa obtained from the National Center for Medium-Range Weather Forecast ing general circulation model at 0000 and 1200 UTC on January 7 and 00 00 and 1200 UTC on January 8, 1994.