中国夏季气温对东亚土壤湿度异常响应的统计评估

基于欧亚夏季土壤湿度变化特征及其与中国夏季气温的相关分析,选取东亚地区作为土壤湿度异常影响中国夏季气温的陆面关键区,采用广义平衡反馈分析方法(GEFA)探讨了我国夏季气温对东亚地区土壤湿度异常的可能响应,并初步讨论了相关的物理过程。结果表明:中国夏季气温与东亚地区初夏和同期的土壤湿度异常具有密切的联系;进一步分析表明,夏季气温距平场对土壤湿度第一模态的响应最显著:当东亚中纬度及我国东部地区土壤湿度异常偏干时,夏季气温表现为一致增暖;而土壤湿度第二模态对长江流域至我国西部地区的气温有较弱的强迫作用;气温对第三模态的响应主要表现为华南地区的显著降温。并以对气温影响最为显著的土壤湿度异常第一模态为例,初步探讨了气温对土壤湿度异常响应的可能物理过程。当贝加尔湖以南以及我国东部的土壤偏干时,地表异常加热容易引起我国北方高层大气出现明显正异常和低层的反气旋性异常环流,上述环流异常容易导致温度偏高,同时不利于该区域降水的发生,进而导致土壤湿度偏低,上述正反馈机制可能是该区域土壤湿度与大气之间联系的一种可能途径。

Response of summer air temperature in China to soil moisture anomalies in East Asia and its statistical assessment

Based on the characteristics of summer soil moisture anomaly in Eurasia and its correlation analysis with summer temperatures in China, the East Asia was selected as the land-forcing key area and the possible responses of summer temperature in China to soil moisture anomaly in East Asia were discussed by using the Generalized Equilibrium Feedback Assessment (GEFA), and then the relevant physical processes were also preliminarily analyzed. Results show that the connections of summer temperature in China and soil moisture anomaly in East Asia are quite close in both early summer and summer. Further analysis shows that the response of summer temperature in China to the first EOF mode of soil moisture anomaly is the most significant: when soil moisture in mid-latitude of East Asia and eastern China is abnormally dry, the summer temperature in China is consistently warming. The second EOF mode of soil moisture has a weak forcing to temperature from Yangtze river basin to western China. The forcing of the third mode lower the temperature in South China apparently. Taking the first EOF mode of soil moisture, the most significant impact on temperature, for example, the possible process is simply discussed as follows. When the soil is dry to the south of Baikal lake and eastern China, the abnormal heating on land surface is likely to cause significant positive anomaly in upper atmosphere and anti-cyclonic circulation anomaly in low atmosphere in northern China, which may lead to a higher temperature and may inhibit the occurrence of precipitation in this area, thus decreasing the soil moisture. The positive feedback mechanism mentioned above may be a possible way linking soil moisture and the atmosphere in this region.