possible for the SSEC to transfer cold water to the later. In addition, due to the impact of the SECC, the temperature in the central Pacific between $4^{\circ}$S–$8^{\circ}$S is higher than that on the equator. So not all inclined streams of the SSEC contribute to the cooling of the central equatorial Pacific. The water temperature of the ones to the south of Niña-A region could be tremendously raised on their ways. It is why this detecting region was carefully selected. verifies that the SST on Niña-A region is always lower than that in the central equatorial Pacific bounded by $4^{\circ}$S–$4^{\circ}$N from $170^{\circ}$E to $140^{\circ}$W. We note that the choice of this detecting region for CP type variation is based on the actual scope of SST anomalies, and on the sensitive passages of ocean currents. In this regard, the conventional Niño-4 region (bounded by $5^{\circ}$S–$5^{\circ}$N and $160^{\circ}$E–$150^{\circ}$W) is abandoned in our study.

On the Occurrence of El Niño
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From the previous section we see that not only the CECC, but also the two Niño indices, contribute to the occurrence of El Niño. Their impacting scopes need to be clarified. The historical El Niño events also need to be re-understood from 