2002 Annual

Tuesday, 15 January 2002
Assigning water vapor wind heights by weighting functions
William H. Raymond, CIMSS/Univ. of Wisconsin, Madison, WI; and G. S. Wade
A major unsolved problem with water vapor wind data estimates from the upper-troposphere 6.7-micrometer water vapor band on the Geostationary Operational Environmental Satellite (GOES) Imager (channel 3) is its exact placement in the vertical column. Satellite water vapor channel observations are known to be depth-averaged assessments of the relative humidity. Details about the averaging of the upper-tropospheric observations, valid for GOES or those of other satellite platforms, are not retrieved as part of the observation. But details about the vertical placement can be accurately estimated from forward radiative models that mimic the instrument spectral characteristics. A new technique has been developed to assimilate satellite radiances or brightness temperatures directly into a numerical forecast model. This new procedure captures some of the best features from both profile retrieval as well as direct radiance assimilation. The advantage of the new scheme is that an adjoint is not required, no linearization is needed, and the procedure is under the control of the modeler, provided satellite observations are available. A by-product of the new scheme is the knowledge of the weighting functions that describe the assignment value given to each vertical layer. Consequently, given water-vapor wind data, these weighting functions allow the guess wind field to be intelligently modified. Details and examples will be presented.

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