The scenario described in Fig. 8 is common for major
El Nin˜o episodes. Figure 9 shows the evolution of sea
level pressure anomalies over the Philippine Sea for
each major warm and cold episode in comparison with
the Nin˜o-3.4 SST anomalies. One of the conspicuous
features is that the rapid rise (drop) of pressure over
the Philippine Sea often occurs in late fall and early
winter. In most episodes, the establishment of the Philippine
Sea anomalies leads the warm (cold) peak by 1–3
months. This important feature can also be seen from
the composite evolution depicted in Fig. 10. Another
noticeable feature is that the pressure anomalies normally
persist for one to two seasons after their establishment.
The peak pressure anomalies tend to lag corresponding
SST anomalies. This feature agrees with the
finding of Wang (1995b) that the sea level pressure
(SLP) anomalies in the western North Pacific have a
maximum positive correlation with the central Pacific
warming at a lag of 3 months. The persistence is obvious
for both the composite and individual episodes (Figs. 9
and 10).
The correlation coefficients between the precipitation indices in the Andeas and the SST anomaly indices for El Niño region 3.4 are weakly positive in the northern subregion, neutral in the central subregion and moderately negative in the southern subregion, particularly in February. The correlation coefficients between the precipitation indices and the SST anomaly indices for El Niño 4 region are very small in the north and moderately negative in the central and south subregions, particularly in February.
The correlation analysis indicates that precipitation in the northern coast is strongly related to the SST anomaly indices for El Niño region 1+2, mainly in the period January-March. During El Niño events, as defined by SCOR, the relationship intensifies, confirming the results of previous studies (Woodman, 1999, [and numerous others]). The correlation coefficients between the precipitation indices in the Peruvian Amazon region and the SST anomaly indices for the four El Niño regions are small in magnitude.
Figure 3 depicts the correlation between the precipitation indices and SST anomales for the El Niño 1+2 region for the calendar months October to March. Figures 4 and 5 show the results of the correlation between precipitation indices and SST anomaly indices for El Niño 3.4 and El Niño 4 regions, respectively. In these figures the magnitudes of the correlation coefficients are indicated by the size of the open and shaded circles. Stronger positive correlations, represented as large shaded circles, are shown in Figure 3 for the northern coast from November to March. Similarly, in Figure 4 moderate positive correlations are observed in the northern coast from November to March, and in Figure 5 moderate positive correlations are observed along the Andean region in November. Moderate negative correlations with both El Niño 3.4 and El Niño 4 are observed along the Andean region in January, February and March (Figures 4 and 5).
[November is characterized by positive correlations with respect to all SST indices at all latitudes of the Andeas. It’s there for one month and then goes away. What is so special about November? Is this just due to one ENSO?]
[Do you have the possibility of using other colors in Figures 3-5? The tendency for precipitation has become to use green for wet (positive correlations) and brown for dry (negative correlations).
Table 3 shows the lagged correlation coefficients between SST anomaly indices in El Niño 3.4 and El Niño 1+2 regions for six calendar months for the years 1950-2006. Each row is the correlation between Nino 3.4 in a specific calendar month and Nino 1+2 for months preceding, simultaneous to, or following that month. The month of largest correlation magnitude in each row is shaded. Positive lags are months where Nino 1+2 follows Nino 3.4. The results indicate that SST anomalies in the El Niño 3.4 region in October and November could be used to predict December SST anomalies in the El Niño 1+2 region. [Why not try a table organization where the ordinate is the Nino 3.4 month and the abscissa is the Nino 1+2 month? That would make it much