Mesoscale Variations of Water Vapor Inferred from the Millimeter-Wave Imaging Radiometer during TOGA COARE

Abstract

Autocorrelation analysis was applied to data acquired by NASA?s Millimeter-wave Imaging Radiometer during the 1992?93 Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment to quantify the spatial variability of tropical mid- and upper-tropospheric water vapor. Scenes including thin cirrus (as confirmed by lidar measurements) are associated with greater spatial variability of relative humidity (RH) than clear-sky scenes. Typical clear-sky RH spatial variabilities range between 2% and 3%, whereas values for some cirrus scenes are well above 5%. For both cirrus and clear-sky scenes, most of the RH spatial variability is on spatial scales of less than 10 km. Both the amplitude and spatial scale of observed brightness temperature variabilities are in fair quantitative agreement with a model based on the effects of adiabatic vertical displacements generated by boundary layer?forced gravity waves.