Analysis of Southern Hemisphere precipitation: climatology and ENSO-related variations

A new 20-year, monthly, globally complete precipitation analysis has been completed as part of the World Climate Research Program’s (WCRP/GEWEX) Global Precipitation Climatology Project (GPCP). This Version 2 of the community generated data set is a result of combining the procedures and data sets as described by Huffman et al (1997) and Xie and Arkin (1997). The global, monthly, 2.5*x 2.5* latitude-longitude product utilizes precipitation estimates from low-orbit microwave sensors (SSM/I) and geosynchronous IR sensors and raingauge information over land. The low-orbit microwave estimates are used to adjust or correct the geosynchronous IR estimates, thereby maximizing the utility of the more physically-based microwave estimates and the finer time sampling of the geosynchronous observations. Information from raingauges is blended into the analyses over land. In the 1986-present period TOVS-based precipitation estimates (Susskind) are adjusted to GPCP fields and used in polar regions to produce globally-complete results. The extension back to 1979 utilizes the procedures of Xie and Arkin (1997) and their OLR Precipitation Index (OPI).

The 20-year climatology of the Version 2 GPCP analysis indicates the expected features of a very stong Pacific Ocean ITCZ (N.H.) and SPCZ (S.H.) with maximum 20-year means approaching 10 mm/day. A similar strength maximum over land is evident over Borneo. Weaker maxima in the tropics occur in the Atlantic ITCZ and over South America and Africa. In the Southern Hemisphere the mid-latitude maxima are located southeast of Africa, in mid-Pacific as an extension of the SPCZ and southeast of South America.

Zonal averages over ocean peak at 8 mm/day at 7*N, with a secondary peak in the S.H. of 4 mm/day at 8*S with a broad mid-latitude maximum from 40-60 *S of about 3 mm/day. Poleward of 45* the GPCP analysis shows larger zonally-averaged values than most previous satellite-based estimates, although the values are similar to the Jaeger climatology.

Interannual variations of the global fields will be shown focusing on the recent ENSO events of the last 20 years, including teleconnections at mid and high latitudes. Results display the well-known precipitation anomalies of the Pacific Ocean and the land areas of South America, Australia and Africa. In addition, interesting anomalies over the southern oceans, especially between 40-60 *S between the longitudes of Africa and New Zealand are evident.