A Comparative Analysis of the Impacts of Two Types of El Nino on the Central and Eastern Pacific ITCZ

The precipitation data from the Global Precipitation Climatology Project (GPCP) and CPC Merged Analysis of Precipitation (CMAP) were used to investigate the discrepancy of Centre and Eastern Pacific ITCZ (CEP-ITCZ) during two types of El Nino years. Two models of the heat source distribution during two types of El Nino events were constructed, and the causes of different CEP-ITCZ anomalies for two types of El Nino events were analyzed through the Gill model. The results show that the CEP-ITCZ precipitation is approximately 4.0 degrees southward, and the intensity is enhanced by 3.6 mm/day during the mature period of Eastern Pacific El Nino (EP-El Nino), while during the mature period of Central Pacific El Nino (CP-El Nino), it is only 0.8 degrees southward, and the intensity is enhanced by 3.2 mm/day. The meridional mode of the SST anomaly by means of EOF (Empirical Orthogonal Function) can indirectly affect the CEP-ITCZ by influencing the atmospheric Rossby wave response. In CP-El Nino years, the meridional mode of the SST anomaly is weak, and the atmospheric Rossby wave response enhances the northern and southern trade-wind zones at the same time. The anomaly of cross-equatorial flow is weak and the CEP-ITCZ moves southward a little. At the same time, the wind convergence zone is enhanced, and it is more conducive to the vertical transport of water vapor. In EP-El Nino years, the meridional mode of the SST anomaly is strong, and the atmospheric Rossby wave response strengthens the meridional wind on the northern side of the equator, leading to the southward shift of the CEP-ITCZ. At the same time, the wind convergence zone is weakened and widened, and to a certain extent, it suppresses the vertical transport increase of water vapor caused by the sea surface evaporation.