中亚干旱区降水准两年周期振荡及突变特征

Tropospheric Biennial Oscillations and Abrupt Changes of Precipitation in the Arid Central Asia

依据东英吉利大学气候研究中心(CRU)1930—2009年0.5°×0.5°分辨率的月降水量及NCEP/NCAR 1948—2009年2.5°×2.5°分辨率再分析逐月位势高度资料,分析了中亚干旱区年降水和季节降水的准两年周期振荡(TBO)特征和突变的时空变化及其可能影响机制。结果发现,中亚干旱区降水具有显著的TBO特征,其I区(哈萨克斯坦西区)、II区(哈萨克斯坦东区)、IV区(吉尔吉斯斯坦区)的年降水TBO相对具有连续性,而III区(中亚平原区)和V区(伊朗高原区)大致以20世纪60—70年代为分界点,存在相反变化。对季节降水而言,除II区年降水的TBO信号主要由夏季的变化决定,其他分区年降水TBO主要由冬季决定。降水突变分析发现,中亚干旱区降水的突变与TBO信号变化有很好的一致性,突变点上降水周期都有向TBO的跃变。另外,对整个亚洲中部干旱区而言,中亚干旱区西部降水突变发生在20世纪50年代初,东部于60年代末发生突变,新疆自80年代末出现气候转型,时间间隔为20年左右。季风区和受西风环流控制的亚洲内陆干旱区降水尽管都表现出TBO基本特征,但其控制因子可能有很大差异,对流层中上层的西风强度TBO可能是导致亚洲中部干旱区降水TBO的重要因子。

This study analyzed tropospheric biennial oscillations（TBO） and abrupt changes of precipitation in the arid Central Asia（ACA） and their regional differences during 1930-2009 using the monthly 0.5°× 0.5°gridded precipitation data from Climatic Research Unit（CRU） and the NCEP/NCAR monthly 2.5°×2.5°gridded geopotential height reanalysis data in 1948-2009.The results show that precipitation in ACA has significant TBO.The TBO of annual precipitation continued during 1930-2009 in subregions I（West Kazakhstan region）,II（East Kazakhstan region） and IV（Kyrgyzstan region）.However,there was an opposite trend in the intensity changes of TBO between sub-regions III（Central Asia Plains region） and V（Iran Plateau region） before and after the 1960s-1970s.The TBO of annual precipitation mainly resulted from winter precipitation in most of the sub-regions,except sub-region II where it mainly resulted from summer precipitation.Additionally,the temporally abrupt changes of precipitation were in good agreement with TBO signal changes in ACA,the periodicity of precipitation at abrupt change points all turned into TBO.From the perspective of the whole ACA region,abrupt change of precipitation occurred in western ACA in early 1950s,in eastern ACA in late 1960s and in Xinjiang in late 1980s,respectively.Although the precipitation＇s TBO was observed in both the monsoon regions of East Asia and the arid Asian inland region where the westerlies dominated,the forcing factors might differ from each other.The quasi-biennial oscillation（QBO） of westerly wind circulation in the middle-upper troposphere might be one of the major factors that influence the TBO of precipitation in ACA.