Impacts of Two Types of El Ni~no on Atmospheric Circulation in the Southern Hemisphere

Authors：

SUN Dan1;2 (孙 丹), XUE Feng¤1 (薛 峰), and ZHOU Tianjun1 (周天军)
¹State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
²Beijing Meteorological Bureau, Beijing 100089
Abstract：

Based on NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmo-spheric Research) reanalysis data from 1979 to 2010, the impacts of two types of El Ni~no on atmospheric circulation in the Southern Hemisphere (SH) are analyzed. It is shown that, when a warming event occurs in the equatorial eastern Paci¯c (EP El Ni~no), there is a negative sea level pressure (SLP) anomaly in the east-ern Paci¯c and a positive one in the western Paci¯c. Besides, there exists a negative anomaly between 40±S and 60±S and a positive anomaly to the south of 60±S. When a warming event in the central Paci¯c (CP El Ni~no) occurs, there appears a negative SLP anomaly in the central Paci¯c and a positive SLP anomaly in the eastern and western Paci¯c, but the SLP anomalies are not so evident in the SH extratropics. In particular,the Paci¯c{South America (PSA) pattern induced by the CP El Ni~no is located more northwestward, with a weaker anomaly compared with the EP El Ni~no. This di®erence is directly related with the di®erent position of heating centers associated with the two types of El Ni~no events. Because the SST anomaly associated with CP El Ni~no is located more westward than that associated with EP El Ni~no, the related heating center tends to move westward and the response of SH atmospheric circulation to the tropical heating changes accordingly, thus exciting a di®erent position of the PSA pattern. It is also noted that the local meridional cell plays a role in the SH high latitudes during EP El Ni~no. The anomalous ascending motion due to the enhancement of convection over the eastern Paci¯c leads to an enhancement of the local Hadley cell and the meridional cell in the middle and high latitudes, which in turn induces an anomalous descending motion and the related positive anomaly of geopotential height over the Amundsen-Bellingshausen Sea.

Keywords:

eastern Paci¯c El Ni~no, central Paci¯c El Ni~no, atmospheric circulation, Southern Hemisphere,Paci¯c{South America pattern

Citation:

Sun, D., F. Xue, and T. J. Zhou, 2013: Impacts of two types of El Ni~no on atmospheric circulation in the Southern Hemisphere. Adv. Atmos. Sci., 30(6), 1732{1742, doi: 10.1007/s00376-013-2287-9.

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