Wednesday, 17 January 2007
ENSO and Global Daily to 3-Hourly Precipitation Extremes
Exhibit Hall C (Henry B. Gonzalez Convention Center)
A statistical description of global precipitation at the daily and 3-hourly time scales from the Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis (TMPA) and the CPC Morphing Technique (CMORPH) is generated for recent seasons. Particular attention is paid to interannual variations of the “high” tail of the distributions to help answer the question: ‘Is the El Niño/Southern Oscillation (ENSO) related to a global increase in locally extreme rainfall?' Initially TMPA daily rainfall was analyzed and extreme rainfall frequency was defined as the number of days within a given season that exceeded the 98th percentile of rainfall for all seasons between 1998 and 2005. The correlation pattern between extreme daily precipitation frequency and Nino 3.4 in the tropics mimicked the correlation pattern between seasonal mean rainfall and Nino 3.4 during the 1998 to 2005 period. In fact, the correlations between extreme precipitation frequency and seasonal rainfall were strongly positive over most of the tropics, and very significantly positive for areas with climatological rain rates near 2 mm day-1 in January-February-March (JFM) and April-May-June (AMJ). These grid blocks tended to be on the periphery of the dominant rainfall features (e.g. the convection centers, Intertropical Convergence Zone, and monsoons), where transient weather systems are important, and several of these grid blocks were in regions with typically strong ENSO-precipitation linkages. Thus, certain areas are very likely to have a strong increase in the probability of extreme daily precipitation during a phase of ENSO, including Southeast Asia and central Philippines in JFM of La Niña, and central Pacific, south of the ITCZ, from October to March of El Niño. Three-hourly precipitation will likewise be examined. The results from TMPA will be compared to those from CMORPH (at a minimum) as part of the Pilot Evaluation of High Resolution Precipitation Products (PEHRPP).