The influence of convective outflow on water vapor mixing ratios in the tropical upper troposphere An analysis based on UARS MLS measurements

The source of increased water vapor mixing raregions of convective outflow. These studies dealt with varitios over the central and eastern tropical Pacific region during ations in relative humidity over a broad region of the tropthe 1992 E1 Nifio event is examined using measurements of ical upper troposphere (i.e., 200-500 hPa). Presently, it is upper tropospheric water vapor provided by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite. Horizontal winds on isentropic surfaces are combined with ISCCP cloud information to provide backtrajectory calculations free of high clouds. These calculations show that the water vapor mixing ratio of an air parcel in the cloud-free regions of the eastern Pacific decreases to approximately one-half of its original value within the first 30 hours after encountering deep convection. This analysis also finds a larger number of air parcels encountering deep convection within 30 hours of observation, and therefore having higher mixing ratios, in March-April 1992 compared to March-April 1994. Hence, increased deep convection over the equatorial central and eastern Pacific in 1992 contributed to the moistening of the downstream tropical upper troposphere.