The Use of Digital Warping of Microwave Integrated Water Vapor Imagery to Improve Forecasts of Marine Extratropical Cyclones

Abstract

A technique is described in which forecasts of the locations of features associated with marine cyclones may be improved through the use of microwave integrated water vapor (IWV) imagery and image warping of forecast mesoscale model fields. Here, image warping is used to optimally match mesoscale model output to observations of IWV measured by microwave sensors. In the mesoscale model simulations presented here (one of the March 1993 ?superstorm,? one of a rapidly deepening cyclone observed in the North Atlantic in February 1992, and one of the ERICA IOP 4 cyclone), the Pennsylvania State University?National Center for Atmospheric Research MM5 model is initialized from the standard National Meteorological Center (recently renamed the National Centers for Environmental Prediction) operational analysis. The simulations are then run until a time at which a Special Sensor Microwave/Imager (SSM/I) overpass occurs. For each simulation, the forecast pattern of IWV is then compared to the field shown in the SSM/I image. In all three cases, the MM5 moves the cyclones too slowly, and therefore places distinguishing features in the forecast IWV fields significantly upstream of their locations as revealed in the microwave imagery. To rectify these errors, the grid on which the source image (forecast field) is defined is then warped to match the target image (remotely observed IWV field) by choosing pairs of tie points corresponding to similar features in the two images. The values of all model moisture variables at all vertical levels are then carried to the new warped grid points and interpolated back to the original model grid. Model integration then proceeds with the new model fields. The model results at a subsequent time after the warping is applied are then compared with simultaneous model results in simulations in which no warping was applied as well as with model simulations in which a standard nudging technique is applied. Warping results in improved forecasts of cyclone minimum sea level pressure, tracks, and IWV fields over both the control simulations and the nudged simulations.