the southern region where the SSEC passes through. This provides the possibility for the appearance of a positive anomaly from the north and a negative anomaly from the south. shows that, in the far east near Niño-B and Niña-B regions, the temperature difference between the north and the south is usually maintained at about $4^{\circ}$C. A strong southward flow from the high-temperature area off Central America may result in a significant anomaly in the cold-tongue region. So, the EP El Niño events were always very strong. In addition, no matter how the Peru current varies, its temperature is always lower than that on the equator, with a difference bigger than $1.5^{\circ}$C. This indicates that the Peru current is not a unique water-supply source to the NSEC, but instead, there should also be a meridional transport of warm water from the north, as reflected by Niño-B index.

It follows from and (or from and ) that, before the occurrence of La Niña, the SSEC has already strengthened (the leading time is 5–7 months). Notice that the southeast sea area was very cold (see ), and a large part of the streamlines thrust at the central equatorial Pacific (see ), it was 