Contribution of Tropical Cyclones to the Global Precipitation from Eight Seasons of TRMM Data: Regional, Seasonal, and Interannual Variations

Based on the University of Utah Tropical Rainfall Measuring Mission (TRMM) precipitation feature (PF) database, tropical cyclone PFs (TCPFs) are identified for over 600 storms that reached tropical storm intensity level or above around the globe during eight TC seasons from the period of 1998-2006. Each TC season includes 6 months yr(-1). Six basins are considered: Atlantic (ATL), east-central Pacific (EPA), northwest Pacific (NWP), north Indian Ocean (NIO), south Indian Ocean (SIO), and South Pacific (SPA). TRMM 2A25-(precipitation radar) and 3B42-(multisatellite) derived rainfall amounts are used to assess the impact of tropical cyclone (TC) rainfall in altering the regional, seasonal, and interannual distribution of the global total rainfall during the TC seasons in the six basins. The global, seasonal, and interannual variations of the monthly rainfall inside TCPFs are presented. The fractional rainfall contributions by TCPFs are compared in different basins. The TRMM 2A25 and 3B42 retrievals are compared in terms of the rainfall contribution by TCs. After constraining TC rainfall for being within 500 km from the TC center, 2A25 and 3B42 show similar results: 1) TCs contribute, respectively, 8%-9%, 7%, 11%, 5%, 7%-8%, and 3%-4% of the seasonal rainfall to the entire domain of the ATL, EPA, NWP, NIO, SIO, and SPA basins; 2) both algorithms show that, regionally, the maximum percentage of TC rainfall contribution is located in EPA basin near the Mexico Baja California coast (about 55%), SIO close to the Australia coast (about 55%), and NWP near Taiwan (about 35%-40%); 3) the maximum monthly percentage of TC rainfall contribution is in September for the ATL basin, August and September for EPA, August for NWP, May for NIO, March for SIO, and January and February for SPA; 4) the percentage of rainfall contributed by TCs is higher during El Nino years than La Nina years for EPA and NWP basins. The trend is the reverse for ATL and NIO, and nearly neutral for SIO and SPA. However, this study does not include enough years of data to expect the findings to be representative of long-term statistics of the interannual variations.