地球系统模式CESM模拟的ENSO变率与中国东部降水格局

根据地球系统模式（CESM）的千年控制模拟试验结果,以Niño3.4区的逐月海表温度变化为指标,辨识了212次El Niño事件、226次La Niña事件;分析了El Niño和La Niña事件发生当年及次年中国东部5-9月降水异常的空间格局;探讨了ENSO与华北、江淮、江南和华南4个区域旱涝的关系。结果表明：El Niño事件发生的当年5-9月,华北和华南地区降水减少2%~10%,长江中下游地区降水略有增加（0~2%）;次年,江南地区转为降水增加（2%~10%）,华北北部降水继续减少。在La Niña事件发生的当年,华北地区降水偏多（增加2%~10%）;次年,江淮地区降水显著减少（2%~5%）。ENSO增强会导致降水变幅加大。在El Niño衰减并向La Niña快速发展的年份,江南地区出现洪涝灾害的概率较其他年份高1倍以上。这些认识为深入揭示气候系统内部年际变率对中国东部降水格局变化与区域旱涝的影响作用、理解2016年长江中下游发生重大洪涝灾害提供了异常天气气候背景依据。

Relationship between ENSO Episode and the Spatial Pattern of Precipitation in Eastern China as Simulated inCESM Control Experiment

Based on the simulation of 1 000-year control experiment by the Community Earth System Model (CESM) with constant pre-industrial external forcing, 212 El Niño events and 226 La Niña events were identified according to the monthly SST (Sea Surface Temperature) of Nino3.4 region. Furthermore, the spatial pattern of May to September precipitation in eastern China in the El Niño (La Niña) episodes and their following years were illustrated. The relationship between the ENSO episodes and the floods/droughts of four regions including North China, Jianghuai, Jiangnan and South China in eastern China were analyzed. The results show that during the El Niño episodes, precipitation decreases by 2%-10% (with respect to the mean value of the whole 1 000 years) in North China and South China from May to September, and precipitation slightly increases by 0-2% in the Yangtze River Basin. In the following year of El Niño, precipitation in Jiangnan region turns to increase by 2%-10%, but precipitation in North China is still in decreasing conditions. During the La Niña episodes, precipitation in North China increases by 2%-10%. In the following year of La Niña, precipitation in Jianghuai decreases obviously by 2%-5%. The stronger El Niño (La Niña) events lead to more intense precipitation changing, and the percentages of precipitation anomalies increase. In the year when El Niño hasn’t vanished and La Niña starts to develop, the probability of flooding in the Jiangnan region might be more than twice as that in normal years. This finding provides background of abnormal climate for understanding the 2016 extreme flood in Yangtze River, and thoroughly reveals the influence of inter-annual internal variability in climate system on the changes of precipitation’s spatial patterns and regional flood/drought.