Formation of the Anomalous Summer Precipitation in East China in 2010 and 1998: A Comparison of the Impacts of Two Kinds of El Ni~no |
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Institution: | Chengdu University of Information Technology, College of Atmospheric Science, Chengdu 610225
Nansen-Zhu International Research Centre, Institute of Atmospheric Physics,Chinese Academy of Sciences, Beijing 100029
Civil Aviation Flight University of China, Guanghan 618307;Nansen-Zhu International Research Centre, Institute of Atmospheric Physics,Chinese Academy of Sciences, Beijing 100029;Nansen-Zhu International Research Centre, Institute of Atmospheric Physics,Chinese Academy of Sciences, Beijing 100029;Chengdu University of Information Technology, College of Atmospheric Science, Chengdu 610225 |
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Abstract: | In the summers of 1998 and 2010, severe floods occurred in the middle and lower reaches of the Yangtze
River. Although an El Ni~no event took place preceding each of the summer floods, significant differences
between the two summer floods and the two El Ni~no events were identified. The 1997/98 El Ni~no is a
conventional one with strongest warming in the central-eastern Pacific, whereas the 2009/10 event is an El
Ni~no Modoki with strongest warming in the central Pacific. In this study, summer rainfall anomalies (SRA)
in the two years were first compared based on the rainfall data at 160 stations in mainland China, and a
significant difference in SRA was found. To understand the underlying mechanism for the difference, the
atmospheric circulation systems, particularly the western North Pacific anticyclone (WNPAC), the western
Pacific subtropical high (WPSH), and the low-level air flows, were compared in the two years by using the
NCEP/NCAR reanalysis data. The results display that the WNPAC was stronger in 2010 than in 1998, along
with a northwestward shift, causing weakened southwesterly from the Bay of Bengal to the South China Sea
but intensified southerly in eastern China. This resulted in less water vapor transport from the tropical Indian
Ocean and the South China Sea but more from the subtropical western Pacific to East Asia. Subsequently,
the rainband in 2010 shifted northward. The difference in the WNPAC was caused by the anomalous
ascending motion associated with the warming location in the two El Ni~no events. Furthermore, the role
of tropical sea surface temperature (SST) in modulating these differences was investigated by conducting
sensitivity experiments using GFDL AM2.1 (Geophysical Fluid Dynamics Laboratory Atmospheric Model).
Two experiments were performed, one with the observed monthly SST and the other with June SST persisting
through the whole summer. The results suggest that the model well reproduced the primary differences in
the atmospheric circulation systems in the two years. It is found that the difference in El Ni~no events has
shaped the rainfall patterns in the two years of 1998 and 2010. At last, the case of 2010 was compared
with the composite of historical El Ni~no Modoki events, and the results indicate that the impact of El Ni~no
Modoki varies from case to case and is more complicated than previously revealed. |
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Keywords: | El Ni~no and El Ni~no Modoki summer rainfall in the middle and lower reaches of the Yangtze
River western North Pacific anticyclone AGCM sensitivity experiments |
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