摘要:在气候变暖背景下，中国南方夏季降水存在明显的年代际变化特征。本文利用1920~2014年的逐月降水，以分析南方夏季降水年代际变率主模态为切入点，以研究南方夏季降水年代际变率空间分布型的年代际变化特征为重点，进一步研究了印度洋、北太平洋及北大西洋海温的年代际变率对南方夏季降水主模态年代际变率的可能影响机制。得到的主要结论包括：（1）指出中国南方夏季降水年代际变率的两个主模态为全区一致型和东西反相型降水模态。两个主导模态在1971/1972年发生了显著的年代际转变，在1925~1971年的第一主模态为东西反相型降水；在1972~2009年的第一主模态为一致型降水。不同主模态对应的海温异常关键区也在1971/1972年发生了相应的年代际变化。（2）揭示了全区一致型和东西反相型降水模态对应的环流场异常特征。一致多（少）型降水对应着中国南海及西北太平洋低空的反气旋（气旋）性异常，有（不）利于水汽自南海向南方地区输送。而贝加尔湖东侧低空的反气旋（气旋）性异常，有（不）利于冷空气向南方输送，并与来自南海地区的水汽在南方地区辐合，有利于南方地区降水一致偏多（少）。东多西少（西多东少）型降水对应着中国东南地区高空的正（负）异常中心，有利于高空辐散（辐合）及异常的上升（下沉）运动，其与南方地区东部低空的气旋（反气旋）性异常共同作用，有利于东部降水偏多（偏少）。与此同时，低空中南半岛反气旋（气旋）性异常及菲律宾地区反气旋（气旋）性异常，不（有）利于水汽自孟加拉湾及南海地区输送向南方地区西部，有利于形成东多西少（西多东少）的降水型。（3）揭示了印度洋海温、北太平洋海温和北大西洋海温协同影响南方地区东西反相型降水和一致型降水的机制。
关键词:中国南方夏季降水/
海温/
年代际变率/
主模态/
影响机制
Abstract:In the background of global warming, rainfall in southern China during boreal summer (June to August) shows distinct interdecadal variability. Using monthly rainfall data for the period of 1920-2014, the leading modes of the interdecadal variability of Southern China Summer Rainfall (SCSR) are revealed. Meanwhile, the interdecadal changes of spatial pattern of SCSR are uncovered. Finally, the underlying possible mechanisms connecting the sea surface temperature in the Indian Ocean, the North Pacific Ocean and the North Atlantic Ocean and the leading modes of SCSR on interdecadal timescale are analyzed. The main results are as follows. (1) The first two leading modes of the interdecadal variability of SCSR, i.e., the monopole pattern and the zonal dipole pattern, are uncovered. The dominance of these two modes experienced an obvious decadal change around 1971/1972. During 1925-1971, the dominant pattern of the interdecadal variability of SCSR is the zonal dipole pattern, while the monopole pattern prevailed during 1972-2009. The key regions of sea surface temperature associated with the first two leading modes also changed around 1971/1972. (2) The atmospheric circulation anomalies associated with the monopole pattern and the zonal dipole pattern of SCSR are uncovered. Corresponding to the positive (negative) phase of the monopole pattern, an anticyclonic (cyclonic) anomaly is located over the South China Sea and northwestern Pacific, which is (not) in favor of moisture transport from the South China Sea to southern China. The lower-level anticyclonic (cyclonic) anomaly over Lake Baikal may lead to more southward transport of cold air, which can converge with the moisture transported from the South China Sea and is favorable for the formation of positive (negative) phase of the monopole pattern. Corresponding to the positive (negative) phase of the zonal dipole pattern, a positive (negative) center is located over the eastern part of southern China, which is favorable for upper-level divergence (convergence) and anomalous ascending (descending) motion. When combined with the lower-level cyclonic (anticyclonic) anomaly, it may result in increased (decreased) rainfall in eastern part of southern China. Meanwhile, the anticyclonic (cyclonic) anomaly over Indo-china peninsula and the Philippines is favorable (unfavorable) for moisture transport from the Bay of Bengal to western part of southern China, which is in favor of generating the positive (negative) phase of the zonal dipole pattern. (3) The combined impacts of sea surface temperature in the Indian Ocean, the North Pacific Ocean and the North Atlantic Ocean on the monopole pattern and the zonal dipole pattern of SCSR are revealed.
Key words:Southern China summer rainfall/
Sea surface temperature/
Interdecadal variability/
Leading mode/
Impact mechanism
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