Taking the largest precipitation anomalies within the Maritime Continent and Pacific Boxes in Figure 1 , indices of the strength of the Walker Circulation are computed (Curtis and Adler 2000). A detailed summary of the methodology can be found here. A table of the these values can be found here The time series of ENSO in terms of gradient of precipitation anomalies is shown in Figure 2.
Recently precipitation anomalies in the eastern Indian Ocean have been linked to MJO propagation and the initiation of El Ninos. An empirical scheme has been developed to determine when precipitation anomalies in the eastern Indian Ocean may be important for the development of El Nino. Detailed information about this technique is in press at Geophysical Research Letters (Curtis et al. 2001).
From this work a prediction index was developed and is shown with ESPI (Figure 3). Note that for the five strongest El Ninos the index is high about 12-16 months before the middle of the events. The index has recently shot up leading to a forecast of El Nino conditions.
Precipitation anomalies over the globe are quantified during El Nino and La Nina events. Figure 4 gives the average El Nino minus La Nina conditions for the 31 year period from 1979 through 2010.
Figure 5 is a reproduction of
Plate 4 in Curtis et al. (2001) showing the rainfall anomalies for the 1997-98 El Nino in relation to the
canonical El Nino-related weather patterns from Ropelewski and Halpert (1987).
Combining our prediction and monitoring efforts we present
the global precipitation scenario for the 2002-03 El Nino.
represents the average response to El Nino in time and space.