【摘要】 夏季南亚高压（SAH）中心呈青藏高原和伊朗高原双模态分布，表现为东—西振荡的形式。同时，SAH的东缘还存在规律性的向东亚地区东伸或西退至青藏高原，表现为另一种形式的东西振荡。本文利用NCEP1逐日再分析资料、APHRODITE逐日降水数据以及印度地区逐日降水数据，研究了SAH这两类东—西振荡的联系以及它们对亚洲地区环流和天气影响的差异。结果表明，SAH中心的双模态东—西振荡位相可显著影响其东缘东伸/西退的发生及其幅度。尽管在SAH中心呈青藏高原和伊朗高原模态时，均可以出现SAH东缘的向东亚东伸，但青藏高原模态下发生东伸的频率明显高于伊朗高原模态；在伊朗高原模态时则更容易出现SAH东缘的西退。而且，在青藏高原模态下发生的SAH东缘东伸的幅度也比伊朗高原模态时更大。进一步研究发现，SAH中心的双模态东—西振荡主要与印度北部及整个青藏高原地区的降水异常型密切联系，并与异常降水有关的热力和动力作用变化相耦合。而SAH东缘的东伸/西退则通过引起西太副高的西进/东退，与东亚地区偶极子型的降水异常（青藏高原中东部、长江与黄河之间的中下游地区的降水异常与长江以南地区的相反）相联系。此外，SAH中心为青藏高原模态且东缘发生东伸时，与SAH中心为伊朗高原模态且东缘发生西退时，青藏高原西部与中东部的降水异常总是呈显著反位相变化。更多还原

【Abstract】 The South Asia high(SAH) center is characterized by bimodal distribution [i.e., the Tibetan Plateau(TP)mode and Iranian Plateau(IP) mode], showing an east–west oscillation pattern. In addition, the eastern edge of the SAH also regularly extends eastward to East Asia or retreats westward to the TP, manifesting another type of east–west oscillation. Using NCEP1 daily reanalysis data, APHRODITE daily precipitation data, and daily India precipitation data,this paper investigates the relationship between the two types of east–west oscillations of the SAH and the differences in their impacts on the circulation and weather in Asia. The results show that bimodal east–west oscillation of the SAH center can significantly affect the occurrence and amplitude of the eastward extension/westward retreat of the eastern edge of the SAH. Although the eastern edge of the SAH can extend eastward when the SAH center is in the TP or IP mode, the frequency of the eastward extension of the eastern edge of the SAH in the TP mode is significantly higher than that in the IP mode. In the IP mode, the eastern edge of the SAH is more inclined to retreat westward, and the magnitude of the eastward extension of the eastern edge of the SAH in the TP mode is larger than that in the IP mode. Further analysis reveals that the bimodal east–west oscillation of the SAH center is closely related to the rainfall anomaly pattern in North India and the TP region and is coupled with the variation of thermodynamic effect related to rainfall anomaly. The eastward extension/westward retreat of the eastern edge of the SAH is related to the dipole rainfall anomaly pattern in East Asia(i.e., rainfall anomalies in the central and eastern TP and the middle and lower reaches of the Yangtze Riverand Yellow River are opposite to those in the southern region of the Yangtze River), resulting in the westward extension/eastward retreat of the western Pacific subtropical high. Furthermore, when the SAH is in the TP mode and its eastern edge extends eastward and when the SAH is in the IP mode and its eastern edge retreats westward, rainfall anomaly in the western TP is always opposite to that in the central and eastern TP.更多还原