The Role of ENSO in the South Asian Monsoon and Pre-Monsoon Signals Over the Tibetan Plateau
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概要
- 論文の詳細を見る
El Nino and the Southern Oscillation (ENSO), and the South Asian (SA) summer monsoon interact with each other. In a previous paper, the process from the SA-monsoon to ENSO was discussed. In this paper, the process from ENSO to the monsoon is described. As the consequence of ENSO events, a set of characteristic distributions of the temperature, wind and moisture is formed over the central and eastern Pacific Ocean. The anomalies of these fields are characterized by a "butterfly pattern" above the 500 hPa level, and a "horseshoe pattern" below 500 hPa. The patterns begin to appear in the winter, and influence the SA-monsoon in the following spring and summer. The distinct pattern of the butterfly shape may be explained by the extended Matsuno-Gill type dynamics, because the Pacific sector is dominated by the ENSO heating. On the other hand, the Indian sector is characterized by the land-sea monsoon circulation. It is important to note that the anomaly components of this local circulation are controlled largely by ENSO. The air temperature anomaly of the layer between 200 and 500 hPa moves westward in the latitude belt of 20°-35°N over the Asian sector, which is associated with the butterfly pattern in the Pacific sector. During this migration, the signal provides a precursory background over the Tibetan Plateau in April-May-June at its peak, setting the stage for the initiation of the SA-monsoon. Another signal emanates also from the tropical Pacific to the Indian sector, in May-June-July at its peak, in conjunction with the horseshoe pattern of the sea surface temperature in particular. These signals emanate from the eastern part of the ENSO region, contribute to the establishment of the thermal contrast anomalies between land and ocean, and the anomalous wind system over the Indian sector, including the upward motion over the Indian subcontinent. The EOF (empirical orthogonal function) analysis of the sea surface temperature in the broader NINO3 region (15°N-15°S, 150°W-90°W) indicates that the two leading modes well represent the fields of horizontal wind and temperature for the Pacific sector (the first mode) as well as the Indian sector (the second mode). Finally, the features associated with the 1976 climate shift are discussed. In the process from the SA-monsoon to ENSO, the mode of connection changed dramatically circa 1976; however, in the process from ENSO to the monsoon, the mode is almost the same before and after 1976. The reason for this asymmetry, in the change of the relationship, is discussed.
- 社団法人日本気象学会の論文
- 2003-10-27
著者
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Yang Song
Climate Prediction Center National Weather Service National Oceanic And Atmospheric Administration
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MIYAKODA Kikuro
Center for Ocean-Land-Atmosphere Studies
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KINTER III
Center for Ocean-Land-Atmosphere Studies
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Miyakoda K.
Center for Ocean-Land-Atmosphere Studies
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Kinter 3
Center for Ocean-Land-Atmosphere Studies