Comparison of southward shift mechanisms of equatorial westerly anomalies between EP and CP El Niño
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Comparison of southward shift mechanisms of equatorial westerly anomalies between EP and CP El Niño

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  • Journal Title:
    Climate Dynamics
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    A composite analysis of observational data reveals that maximum westerly anomalies associated with both the EP and CP El Niños shift southward to 5° S during their mature phase (boreal winter), with different zonal locations. A zonal momentum budget analysis indicates that leading factors to cause the southward shift of the zonal wind anomaly for both EP and CP El Niño composites are anomalous pressure gradient force and anomalous meridional advection, while anomalous Coriolis force has an opposite effect. The difference in the longitudinal locations arises from the zonal shift of maximum SST anomaly centers between EP and CP El Niño. Prior to northern winter, the westerly anomaly for both types of El Niño is approximately symmetric about the equator. The advection by the climatological mean cross-equatorial wind leads to initial southward shift of the maximum westerly and subsequent development of an antisymmetric mode through a moisture-convection-circulation feedback and a wind-evaporation-SST feedback. An EOF analysis of the tropical Pacific surface wind field indicates that both the first and second leading modes are important in contributing to the southward shift of the maximum westerly anomaly with distinctive longitudinal locations for CP and EP El Niño.
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    Climate Dynamics, 60(3-4), 785-796
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    CC0 Public Domain
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