EVIDENCE OF MERIDIONAL MOTION IN THE SUMMER LOWER STRATOSPHERE ADJACENT TO MONSOON REGIONS

Twenty-one years of rawinsonde data were used together with 8 years of uninitialized European Centre for Medium-Range Weather Forecasts (ECM WF) analyses to describe the climatological structure of large-scale c irculations adjacent to monsoon regions in northern and southern hemis phere summers. In the upper troposphere and lower stratosphere, equato rward and poleward motions occur on the eastern and western sides of m onsoon regions, respectively. It is shown that significant meridional velocities (> 1 ms(-1)) penetrate the lower stratosphere up to a maxim um height of 50-30 mbar. Largest meridional velocities are observed in connection with the Asian monsoon in northern summer. Although evanes cent in height, these motions are relatively important for horizontal transport of constituents in the summer lower stratosphere, when plane tary waves are otherwise small. Asian and Mexican monsoons in this sea son are displaced sufficiently far from the equator, in close proximit y to the tropopause break, to have a significant role in stratosphere- troposphere (S/T) exchange. The companion paper by Chen (1995) provide s evidence of irreversible S/T exchange in the ''upper middle world'' during northern summer.