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

Jinshuang Zhu,Ruiqing Xie,Yudi Liu,Haijie Chang

doi:10.3390/atmos9070266

Jinshuang Zhu, Ruiqing Xie + Show 2 more

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https://doi.org/10.3390/atmos9070266

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Abstract

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 Niño years. Two models of the heat source distribution during two types of El Niño events were constructed, and the causes of different CEP-ITCZ anomalies for two types of El Niño events were analyzed through the Gill model. The results show that the CEP-ITCZ precipitation is approximately 4.0° southward, and the intensity is enhanced by 3.6 mm/day during the mature period of Eastern Pacific El Niño (EP-El Niño), while during the mature period of Central Pacific El Niño (CP-El Niño), it is only 0.8° 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 Niño 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 Niño 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.

Highlights

Intertropical Convergence Zone (ITCZ), as one of the important systems of the tropical atmosphere, has important impacts on global atmospheric circulation
In EP-El Niño 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
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

Summary

Introduction

Intertropical Convergence Zone (ITCZ), as one of the important systems of the tropical atmosphere, has important impacts on global atmospheric circulation. The Central and Eastern Pacific ITCZ (CEP-ITCZ) is located to the north of the equator most of the time and shows high particularity relative to other regions. Xie et al [1,2], Philander et al [3], and Chang et al [4] proposed positive feedback mechanisms for “wind-evaporating-SST”, “cloud-SST” and “the cross equatorial wind-upwelling current”, respectively, and explained the reasons for the CEP-ITCZ continuously occurring to the north of the equator. Marshall et al [5] and Frierson et al [6] found that the mean position of the ITCZ north of the equator is a consequence of northwards heat transport across the equator by ocean circulation. Compared to the ITCZ in other regions, the season and interannual variation of CEP-ITCZ are small and are generally

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