Spatial Distribution of Rainfall Anomaly over the Pacific Basin

The CPC Merged Analysis of Precipitation (CMAP) is used to analyze the spatial distribution of rainfall anomaly over the Pacific Basin for four regular seasons for each year from 1979 to current. The CMAP data is global monthly precipitation on a 2.5 latitude-longitude grid (Xie and Arkin 1997). The 3-month total precipitation data were assembled from 1-month data. The four regular seasons (Jan-Feb-Mar, Apr-May-Jun, Jul-Aug-Sep and Oct-Nov-Dec) are showed here to give the more details of the interannual variability associated with the ENSO phenomena. The seasons are chosen as such because of the lag of the sea-surface temperature (SST) relative to the solar seasonal cycle. In the northern Tropics, for example, a maximum in SST (and in the associated warm, moist island climate) tends to occur during Jul-Aug-Sep rather than in Jun-Jul-Aug which is more traditionally regarded as summer in continental climates. The anomaly is defined as the difference between seasonal total and long term mean from 1979 to 2007. For the ENSO rainfall composite, the notation for relative year identity (0 and +1) in is as defined in Ropelewski and Halpert (1987).