Water Vapor and Ice Clouds in the UT/LS: New Observations From Aura MLS

The Microwave Limb Sounder (MLS) on board the NASA Aura satellite, launched in July 2004, provides simultaneous global measurements of water vapor and cloud ice water content profiles in the upper troposphere/lower stratosphere (UT/LS). These new observations have revealed many features about the hydrological processes in the UT/LS that were not known before. Highlights of key discoveries using the MLS water vapor and cloud ice data will be presented, including the interaction of water vapor with clouds in the UT, dehydration near tropopause and stratosphere-troposphere exchange. The MLS water vapor measurement is also compared with the analyses from the Global Modeling and Assimilation Office (GMAO, GEOS-4). From 316 hPa to 147 hPa, the agreement between MLS and GEOS-4 is quite good, especially over the tropics. At 100 hPa, the GEOS-4 analyses are considerably lower than the MLS data, and the spatial correlation between tropical water vapor and cloud ice is negative for MLS but positive for GEOS-4. Efforts have been undertaken to correct the problems in the GEOS-4 water vapor data at 100 hPa. It is hoped that the new observations from Aura MLS will help improve climate model simulations and data assimilation products in the UT/LS.