摘要:利用美国国家环境预测中心与国家大气研究中心（NCEP/NCAR）逐日再分析资料，针对北大西洋多年代际振荡（AMO）两个不同位相，对逐候200 hPa经向风异常进行EOF分析，发现在AMO正、负位相期间，欧亚副热带波列的季节内活动存在明显差异。利用超前—滞后回归，对比了不同AMO位相下副热带波列及其相联系的印度夏季降水的季节内活动演变特征，分析有关的大气环流，探究波列影响降水的机制。结果表明：在AMO负位相期间，由格陵兰岛以南北大西洋经大不列颠岛、地中海、黑海—里海向南亚北部传播的副热带波列的季节内演变，在印度中部引起下沉，导致中部及西北部季节内降水减少，波列负位相相反；在AMO正位相期间，副热带波列西起冰岛以南北大西洋经丹麦南部、俄罗斯西部、中亚向南亚东北部传播，对应该波列的季节内演变，辐合上升区在印度中部和东西两侧，使得该区域季节内降水增加，波列负位相相反。于是，AMO通过调制夏季欧亚副热带波列的季节内活动，可以对印度夏季降水的季节内变化空间型及演变发挥显著影响。
关键词:北大西洋多年代际振荡/
波列/
季节内变化/
印度夏季降水
Abstract:By using daily variables extracted from the NCEP/NCAR reanalysis, this study compares the intraseasonal activities of the Eurasian summer subtropical wave train during the two opposite phases of the Atlantic Multidecadal Oscillation (AMO). Significant difference is found based on pentadic mean 200-hPa meridional wind component. The associated intraseasonal variability of Indian summer precipitation is also different during the two AMO phases. Lead-lag regressions of 500-hPa wind field and vertical motion are then conducted to illustrate the AMO's modulation on the subtropical wave train and the Indian summer rainfall. The results suggest that during the AMO negative phase, the intraseasonal evolution of the positive-phase subtropical wave train has positive centers over the Great Britain and the Black-Caspian Sea but negative centers over the North Atlantic south of Greenland, the Mediterranean and north of South Asia in 200-hPa height. This pattern of wave train induces anomalous subsidence and reduced rainfall in central and northwestern India. It is opposite for the negative-phase subtropical wave train. In contrast, during the positive AMO phase, positive-phase subtropical wave train originates from the North Atlantic south of Iceland and propagates toward northeastern South Asia via southern Denmark, western Russia and central Asia. The intraseasonal evolution of this wave train leads to anomalous convergence and increased rainfall in most areas of India. It is opposite for the negative-phase subtropical wave train. This study highlights the AMO's modulation on intraseasonal variability of Indian summer rainfall through influencing the Eurasian summer subtropical wave train.
Key words:Atlantic Multidecadal Oscillation/
Eurasian subtropical wave train/
Intraseasonal variability/
Indian summer rainfall
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