87th AMS Annual Meeting

Thursday, 18 January 2007: 2:15 PM
Trends in Tropical Rainfall Characteristics : Observations and Modeling
217C (Henry B. Gonzalez Convention Center)
William K. M. Lau, NASA/GSFC, Greenbelt, MD
We present results from observation and modeling studies of long-term trend in rainfall characteristics. From analyses of shift in the rainfall probability distribution function using long-term (24 years) of GPCP and CMAP rainfall data, as well as ground-based global rainfall data, we find trends in more frequent occurrence of extreme heavy and light rain events, coupled to a decreasing trend in moderate rain events over much of the tropics during 1979-2003. Using TRMM rainfall products to identify characteristic cloud and rain structure, we find that the trends are consistent with a shift in the large-scale circulation associated with a) a relatively uniform increase in warm rain over the tropical oceans, b) enhanced ice-phase rain over the near-equatorial oceans, and c) reduced mixed-phase rain over the tropical ocean and land regions. Analysis of IPCC, 20th Century coupled model simulations indicate that overall the models simulated reasonably well the shift in the rainfall PDF qualitatively, but differ greatly in the regional geographic details of the rainfall patterns. The model results suggest that the changes in PDF are to a first order associated with an overall enhancement of the atmospheric water cycle in the tropics as a result of global warming.

Supplementary URL: