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ENSO对中国冬半年降水影响的不对称性及机制分析

ISSN号：1004-4965
期刊名称：《热带气象学报》
时间：0
分类：P461.2[天文地球—大气科学及气象学]
作者机构：[1]中国气象科学研究院,北京100081, [2]中国科学院大学,北京100049, [3]广东省气象台,广东广州510640
相关基金：国家自然科学基金项目（41221064）;公益性行业（气象）科研专项经费项目（GYHY201306004）共同资助.

关键词：气候学, 中国降水特征, ENSO, 季节内振荡, 冬半年, climate, characteristics of precipitation over China, ENSO, intraseasonal oscillation, winter halfyear

中文摘要：

利用1979—2010年观测和再分析资料，诊断分析ENSO对中国华南冬半年降水的影响及其机制。结果表明，在ElNina冬半年期间，东亚沿岸上空对流层低层南风的增强导致了水汽输送明显偏多，水汽在华南辐合，使得大气可降水量和比湿增加，降水显著偏多。而在LaNina冬半年期间，这些大气要素并没有呈现显著的相反变化，负异常的量值很弱并在统计上不显著。通过进一步分析ElNina和LaNina冬半年期间季节内振荡的特点，给出一种华南冬半年降水对ENSO信号不对称响应的物理解释。ElNina期间，热带西太平洋到南海地区的季节内振荡不活跃，与ElNina相联系的西北太平洋反气旋性环流异常造成的水汽输送以及水汽辐合在华南能够稳定维持，致使华南降水明显偏多。但在LaNina冬半年期间，季节内振荡很活跃，与LaNina相联系的西北太平洋气旋性环流异常受到季节内时间尺度的扰动影响，ENSO的年际变化信号被季节内振荡破坏，使得西北太平洋和华南的年际异常信号不能得到稳定维持，导致与ENSO信号相联系的年际变化在统计上不显著。因此，热带西太平洋到南海地区的季节内振荡强度在ElNina和LaNina冬半年期间的差异，是华南冬半年降水对ENSO信号不对称响应的一个主要原因。

英文摘要：

The impact of ENSO on the precipitation over China in winter half year is investigated by using observed and reanalysis datasets in 1979-2010. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nina episodes, which are caused by the enhanced warm and humid southwesterliesalong the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China,and the convergence of water vapor over southern China increases the precipitable water and specific humidity in the atmosphere. In La Nina episodes, no reverse precipitation anomalies with statistical significance appear over southern China. Although atmospheric elements are changed reversely, they are not statistically significant as those in El Ni no periods. The possible physical mechanism of the asymmetric impact of ENSO cycles on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations （ISOs） in El Nino and La Ni na, respectively, in winter half year. By comparing the characteristics of ISOs in El Nina and La Nina, a physical mechanism is proposed to explain the asymmetric responses of the precipitation over China toENSOin winter half year. In El Nina episodes, over western North Pacific （WNP） and South China Sea （SCS）the ISOs are inactive and exert little effect on the water vapor transport and convergence, inducing the positive precipitation anomalies with statistical significance over southern China in El Nino episodes. In La Nina episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the asymmetric responses of precipitation over China to ENSO in winter half yearare possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nina and La Nina.