夏季海洋性大陆区域OLR年际变动与中国长江中上游旱涝的关系

VARIATIONS OF OLR IN MARITIME CONTINENT REGIONS IN ASSOCIATION WITH DROUGHTS AND FLOODS IN THE UPPER AND MIDDLE REACHES OF YANGTZE RIVER OF CHINA IN BOREAL SUMMER

利用1979—2007年的NECP资料、GISST月平均资料和中国160个降水测站资料,用SVD方法分析了热带海洋性大陆区域OLR与夏季中国降水场的关系。结果表明:孟加拉湾、南海季风槽、南太平洋辐合带(SPCZ)、印尼群岛及其附近海域的对流活动与我国夏季长江中上游降水场存在密切联系。若孟加拉湾、南海季风槽、南太平洋辐合带区的OLR偏高(偏低),及东印度洋、印尼群岛附近的OLR偏低(偏高),则夏季长江中上游及以北地区的降水偏多(偏少)。定义了与长江中上游降水相关的海洋性大陆区域OLR指数IMCOLR,并由IMCOLR指数确定高低值年再进行合成分析,发现印尼群岛及其海域气柱内净的辐射和海表热通量的异常增加,有利于该地区对流活动增强和OLR负异常的产生和维持;而孟加拉湾、南海和热带西太平洋存在海表热通量的减弱和辐射冷却的加强,有利于对流活动减弱,导致潜热释放异常减少和维持OLR正异常。热带海洋性大陆区域对流活动IMCOLR与海表温度异常间的相关关系表明,热带海洋性大陆地区对流活动的年际变动可受到热带印度洋海温异常和太平洋区域"三级型"海温异常的共同影响。这些热力强迫异常可导致对流层低层大气异常响应,产生P-J类遥相关,影响中国长江流域中上游降水异常。

Using the monthly mean data fromNECP, GISST dateset, along with station rainfall data in China from 1979 to 2007, we have investigated the relationships between Outgoing Long-wave Radiation （OLR） and the summertime rainfall in China by performing the SVD analysis. Our results show that the convective activities around the Bay of Bengal, monsoon trough in South China Sea, the South Pacific convergence zone （SPCZ）, and the Indonesian Islands and as well as the surrounding waters are significantly correlated with the summer time rainfall in the upper middle reaches of Yangtze River. When the OLR is higher （lower） than normal over the Bay of Bengal, monsoon trough region, and the South Pacific convergence zone（SPCZ）, and lower（higher） than normal over the south Indian Ocean and around Indonesian Islands, the precipitation in the upper and middle reaches of Yangtze River will be significantly more （less） than normal. An index IMCOLR as derived from OLR is defined in Maritime Continent, which associates with rainfall in the upper and middle reaches of Yangtze River. Composite differences of several quantities between high index IMCOLR and low index years show that the anomalous increases in the net radiation of air column and the thermal fluxes at sea surface around Indonesian Islands facilitate stronger convections and henceforth less OLR there. This anomalous heating forces the atmosphere to respond to weaken the surface thermal fluxes in the Bay of Bengal, leading to weaker convections, and henceforth more OLR there. It is found that IMCOLR is well correlated with SSTA showing a triple like structure in tropical Indo-Pacific. These anomalous thermal forcings lead to anomalous response of atmosphere lower troposphere, resulting a P-J like pattern and henceforth affecting the anomalous precipitation in the upper and middle reaches of Yangtze River.