Determination of seasonal to interannual moisture transport variability using geostationary satellite data.

摘要

A detailed analysis of satellite-derived upper-tropospheric moisture and its transport is presented over a nineteen-month period of significant seasonal and interannual climate variability. An image feature tracking algorithm for deriving wind vectors was used in conjunction with a satellite brightness temperature to humidity conversion technique for obtaining upper level moisture transport.; Results indicate a dominant winter hemisphere Hadley cell (i.e., transport in the upper branch towards the winter hemisphere). Several contrasts between the El-Nino of 1987 and La-Nino of 1988 were realized. These included a stronger Hadley circulation during La-Nina (May November 1988) despite stronger convection and a more moist upper troposphere during 1987. Eastward moisture transport in the Northern Hemisphere was observed to extend further south during the Boreal summer and fall months during the El-Nino event of 1987. A water vapor transport index (WVTI) showed stronger transport for the subtropics during El-Nino with enhanced tropical transport during La-Nina The meridional moisture flux ( qv) indicated variations on the regional scale and its application for detecting known hydrologic anomalies.; Satellite pressure velocities were derived by applying the adiabatic method to satellite winds and the pressure level of the winds. Pressure velocity estimates were able to show seasonal mean subsidence and rising motion patterns in the deep tropics. The technique compares favorably (in sign) to model reanalysis estimates in the deep tropics over the ITCZ and the South Pacific subsidence zone. Satellite estimates, however, are about an order of magnitude less than the model reanalysis pressure velocity fields. Spurious results are obtained where the adiabatic assumption is less valid at high latitudes (i.e., where transient disturbances propagate eastward in the subtropics). A recommendation for further development is discussed.; The geographic distribution of maximum and minimum WVTI and qv centers compared quite well against model reanalysis-derived estimates despite stronger gradients in the model fields. Significant differences, however, between the model and satellite fields of qv were most apparent in the Eastern Tropical and Southeastern Pacific. Zonally averaged fields of qv confirmed these observations. The model transport fields consistently show weaker southward transport (or in some cases northward transport) in the Southern Hemisphere when compared against satellite estimates.