SPACE-TIME VARIATIONS IN WATER-VAPOR AS OBSERVED BY THE UARS MICROWAVE LIMB SOUNDER

Water vapor in the upper troposphere has a significant impact on the c limate system. Difficulties in making accurate global measurements hav e led to uncertainty in understanding water vapor's coupling to the hy drologic cycle in the lower troposphere and its role in radiative ener gy balance. The Microwave Limb Sounder (MLS) on the Upper Atmosphere R esearch Satellite is able to retrieve water vapor concentration in the upper troposphere with good sensitivity and nearly global coverage. A n analysis of these preliminary retrievals based on 3 years of observa tions shows the water vapor distribution to be similar to that measure d by other techniques and to model results. The primary MLS water vapo r measurements were made in the stratosphere, where this species acts as a conserved tracer under certain conditions. As is the case for the upper troposphere, most of the stratospheric discussion focuses on th e time evolution of the zonal mean and zonally varying water vapor. St ratospheric results span a 19-month period and tropospheric results a 36-month period, both beginning in October of 1991. Comparisons with s tratospheric model calculations show general agreement, with some diff erences in the amplitude and phase of long-term variations. At certain times and places, the evolution of water vapor distributions in the l ower stratosphere suggests the presence of meridional transport.