ENVIRONMENTAL INFLUENCE ON TYPHOON-BOBBIE PRECIPITATION DISTRIBUTION

The distribution and intensity of tropical cyclone precipitation has b een known to have a large influence on the intensification and mainten ance of the system. Therefore, monitoring the tropical cyclone convect ive rainband cycle and the large-scale environmental forcing mechanism s that initiate and maintain the tropical cyclone convective rainbands may aid in better understanding and predicting tropical cyclone inten sification. To demonstrate how the evolution of the tropical cyclone p recipitation can be monitored, the frequent Special Sensor Microwave/I mager (SSM/I) observations of precipitation from Typhoon Bobbie (June 1992) were used to help better delineate Bobbie's convective rainband cycle. Bobbie's SSM/I-observed convective rainband cycle was then rela ted to the tropical cyclone's intensity change. To obtain a better und erstanding of how Bobbie's convective rainbands were initiated and mai ntained, total precipitable water (TPW) over the ocean regions, mean m onthly sea surface temperatures (SSTs), and analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) model were examined . The SSM/I TPW helped to substantiate the ECMWF-analyzed regions of d ry and moist air that were interacting with the system's circulation, while the mean monthly SSTs were used to determine whether the western North Pacific, where Bobbie traversed, was warm enough to allow for s ufficient energy flux to support convection. The ECMWF model was emplo yed to examine the environmental forcing mechanisms that may have init iated and maintained Bobbie's convective rainbands, such as mean verti cal wind shear, environmental tropospheric water vapor nux and diverge nce, and upper-tropospheric eddy relative angular momentum flux conver gence. Results from the analyses of Typhoon Bobbie suggested the follo wing: 1) The SSM/I observations bf Bobbie's precipitation were able to detect and monitor convective rainband cycles that were similar to th ose observed with land-based and aircraft radar, in situ measurements, and SSM/I observations of western North Atlantic tropical cyclones. 2 ) The evolution of Bobbie's intensity coincided with the SSM/I-observe d convective rainband cycles. 3) The SSM/I observations of the TPW ove r nonraining ocean regions were able to substantiate the ECMWF-analyze d moist and dry regions that were interacting with Bobbie's circulatio n. 4) In regions of warm SSTs and weak vertical wind shear, the enhanc ement of the precipitation in Bobbie's inner-core convective rainbands coincided with the inward convergence of upper-tropospheric eddy rela tive angular momentum, while the initialization of Bobbie's outer-core convective rainbands appeared to coincide with the large horizontal c onvergence of moisture, 5) The dissipation of rain in the inner-core c onvective rainbands appeared to be associated with inward propagation of newly formed outer convective rainbands, strong vertical wind shear (above 10 m s(-1)), and cool SSTs (below 26 degrees C).