Tropical cyclone convection and intensity analysis using differenced infrared and water vapor imagery

A technique to identify and quantify intense convection in tropical cyclones (TC) using bispectral, geostationary satellite imagery will be presented. This technique involves differencing the Water Vapor (WV) and Infrared Window (IRW) channel brightness temperature values, which are available on all current operational geostationary weather satellites. Both the derived IRW minus WV (IRWV) imagery and the raw data values can be used in a variety of methods to provide TC forecasters with important information about current and future intensity trends; a component within the operational TC forecasting arena which has shown little improvement during the past few decades.

Several possible uses for this bispectral technique, both qualitative and quantitative, are explored and outlined in this presentation. Qualitative monitoring of intense convection can be used as a proxy for passive microwave (MW) imager data obtained from polar orbiting satellite platforms when not available. In addition, the derived imagery may aid in the TC storm center identification process, both manually and objectively, especially in difficult situations where the IRW imagery alone cannot be used such as when the storm circulation center and/or eye feature are obscured by a cirrus canopy. Quantitative methods discussed involve the predictive quality of the IRWV data in terms of TC intensity changes, primarily during TC intensification. Strong correlations exist between storm intensity change and IRWV values at varying 6-hr forecast interval periods, peaking between the 12-hour and 24-hour time periods. Implications for the use of the IRWV data on such objective satellite intensity estimate algorithms as the UW-CIMSS Advanced Dvorak Technique (ADT) will also be discussed.