A SATELLITE OBSERVATIONAL AND NUMERICAL STUDY OF PRECIPITATION CHARACTERISTICS IN WESTERN NORTH-ATLANTIC TROPICAL CYCLONES

Special Sensor Microwave/Imager (SSM/I) observations were used to exam ine the spatial and temporal changes of the precipitation characterist ics of tropical cyclones. SSM/I observations were also combined with t he results of a tropical cyclone numerical model to examine the role o f inner-core diabatic heating in subsequent intensity changes of tropi cal cyclones. Included in the SSM/I observations were rainfall charact eristics of 18 named western North Atlantic tropical cyclones between 1987 and 1989. The SSM/I rain-rate algorithm that employed the 85-GHz channel provided an analysis of the rain-rate distribution in greater detail. However, the SSM/1 algorithm underestimated the rain rates whe n compared to in situ techniques but appeared to be comparable to the rain rates obtained from other satellite-borne passive microwave radio meters. The analysis of SSM/I observations found that more intense sys tems had higher rain rates, more latent heat release, and a greater co ntribution from heavier rain to the total tropical cyclone rainfall. I n addition, regions with the heaviest rain rates were found near the c enter of the most intense tropical cyclones. Observational analysis fr om SSM/I also revealed that the greatest rain rates in the inner-core regions were found in the right half of fast-moving tropical cyclones, while the heaviest rain rates in slow-moving tropical cyclones were f ound in the forward half. The combination of SSM/I observations and an interpretation of numerical model simulations revealed that the corre lation between changes in the inner core diabatic heating and the subs equent intensity became greater as the tropical cyclones became more i ntense.