近50年中国东部夏季降水与贝加尔湖地表气温年代际变化的关系

The interdecadal linkage of the summer precipitation in eastern China with the surface air temperature over Lake Baikal in the past 50 years

最近50年全球变暖,陆地增温幅度大于海洋,主要的增温中心位于亚洲北部、欧洲和北美等地区。因此,全球变暖有可能通过改变大尺度季风环流而影响中国气候变化。利用美国国家航空航天局空间研究中心(GISS)的逐月地表气温资料、NCEP/NCAR再分析资料及中国604个站逐月气温和降水观测资料,重点讨论了1951—2007年中国东部夏季降水与同期的北半球大陆地表气温年代际尺度变化关系。结果表明,近50年中国东部夏季降水异常主要表现为"南旱北涝"与"南涝北旱"两者年代际异常之间的转换,但在1996年之后,伴随北方干旱区向南发展,呈现出华北和长江中下游地区降水同时减少的特征。研究发现中国华北地区夏季降水与同期的环贝加尔湖地表气温在年代际尺度上存在显著的负相关关系;贝加尔湖地区地表气温增暖可能导致蒙古高原对流层出现异常的暖性反气旋,使得位于蒙古高原的气旋频数减少和强度减弱。由于华北降水与蒙古气旋的活动直接相关,从而导致华北地区夏季降水的持续性减少。自1996年开始贝加尔湖地区的地表气温进一步升高,导致中国北方干旱化加剧。由于环贝加尔湖地区是过去50年全球变暖的最显著地区之一,因此,全球变暖可能是通过关键区域的温度变化对中国的气候变化产生影响。

The recent change of global surface air temperature indicates that the land regions have warmed at a faster rate than the oceans, and the warming rate is bigger in higher latitudes than the lower latitudes. The warming centers are mainly located in North Asia, Europe, and North America regions over the past 50 years. Thus, the warming in higher latitudes over land possibly affects China climate by modulating the East Asian monsoon circulations. Many studies have explored the long-term trend of the summer precipitation in China, but they mainly focused on the decadal variations of East Asian Summer Monsoon （EASM）, the surface thermal anomalies over the Tibetan Plateau （TP）, Arctic Oscillation （AO） and the ENSO, but less attention has been paid to the possible impact of land surface air temperature （SAT）. In present study, on the basis of the monthly land surface air temperature of Goddard Institute for Space Studies （GISS）, the NCEP/NCAR monthly mean reanalysis data, as well as the 604 station-observed monthly mean temperature and precipitation datasets in China, we discussed the decadal linkage of summer precipitation anomalies in eastern China with the land surface air temperature changes in the Northern Hemisphere during 1951-2007. The results suggest that the summer precipitation appears a meridional seesaw spatial pattern in eastern China before 1996, and it has shifted from the ＂flooding in north and drought in south＂ pattern to the ＂flooding in south and drought in north＂ mode since the late 1970s. However, our evidences show that the summer precipitation anomalies both in northern China and in the lower-middle reaches of the Yangtze River have jointly appeared a decreasing trend after 1996, and the recent global warming has destroyed the previous summer precipitation anomalous pattern. It is found that the precipitation in north China bears a significantly negative correlation with the SAT near Lake Baikal on the decadal time scale, where the persistent warming over the past decades can generate an anomalous warmer anticyclone over Mongolian area and weaken the activities of Mongolian cyclone in the troposphere, and then reduce the summer precipitation in north China. Our analysis suggests that the SAT near Lake Baikal has again enhanced after 1996, and it results in a further decrease of the precipitation in north China. Past studies have suggested that Lake Baikal is one of the most obvious regions in the contex of global warming, implying that the global warming may affect the regional climate in China via the SAT changes in North Asia. However, the 10-year running correlation coefficients show that the close relationship between the SAT around Lake Baikal and the summer precipitation in China is mostly significant after 1990s, suggesting that the possible mechanism, such as the warming sea surface temperature （SST） in tropical Indian ocean and the cooling trend in the northwestern Pacific ocean, may be also one of the important factors to affect the long-term trend of the summer precipitation in China as proposed by the previous studies.