Structural Changes and Convective Processes in Tropical Cyclones as Seen in Infrared and Water Vapor Satellite Data

Abstract

Abstract : In the western North Pacific Ocean, tropical cyclone (TC) hazards, including strong winds, storm surge, high waves, and heavy rainfall, threaten archipelagos, densely crowded coastlines, and naval forces ashore and afloat. To accurately forecast TC track and intensity, meteorologists at the Joint Typhoon Warning Center (JTWC) must start from a thorough understanding of the TC's current structure. To accomplish this mission, they rely heavily upon satellite observations, particularly measurements in the water vapor (WV) and infrared (IR) channels on geostationary satellites. Therefore, it is critical to develop products that identify key TC structures in geostationary satellite data and track them over time, as these data are often the only real-time information available to the forecasters. This project examined satellite brightness temperatures in the WV and IR channels in 5 typhoon-strength TCs during the 2012 season to first identify the eye, eyewall, and regions of deep convection, and then to investigate the evolution of those features over time. The eye was defined in this study from the storm center out to the location of the minimum second derivative of IR brightness temperatures. The eyewall, which contains the strongest winds and deepest convective clouds, was divided into lower, middle, and upper sections using IR and WV brightness temperatures. The IR brightness temperatures in the upper eyewall and the eyewall slope, particularly in the region of the steep IR Tb gradient that included the lower eyewall, were found to be moderately negatively correlated to TC intensity.