中国大陆东部相对湿度变化与海陆热力差异的关联性初探

The Variation of Relative Humidity in the East of Chinese Mainland and Its Association with Sea-Land Thermal Contrast

相对湿度是制约雾与霾形成和转换以及影响能见度的最关键环境气象参数。而海陆热力差异是影响我国东部及沿海雾霾天气的重要气候背景。立足于中国大陆东部和沿海地区所处的地理环境,综合海陆热力差异这一要素,从低层大气环流变化及水汽输送等角度,对相对湿度多时空尺度的变化及其热动力成因和机制进行了尝试性分析。结果表明,50多年来,中国东部冬季海陆热力差异主要形成于我国长江以南地区和黑潮(包括源区黑潮和东海黑潮)以东海域。由此构建的海陆温差指标显示,该纬向海陆热力差异存在显著的准7年和准4年的年际变化以及准17年的年代际变化,同时还有明显的长期增强趋势,其主要与我国长江中游地区-黄淮流域-华北地区及以东沿海一线(负相关区)和华南地区(正相关区)的相对湿度变化密切关联。其中,冬季纬向海陆热力差异的减弱(增强),主要造成低空季风环流的西南风(东北风)异常,进而调控源自孟加拉湾东部和我国南海海域(东中国海及以东海域)的水汽向我国大陆东部的输送,并可通过制约水汽输送和降水等形式影响以上地区相对湿度的变化。纬向海陆热力差异的增强很可能引起华北等地区相对湿度的减小,而导致华南地区相对湿度的显著增加,反之亦然。此成果可为明确重点区域相对湿度变化与雾霾发生发展的关系和未来演变等研究工作的深入开展,以及为有关雾霾天气的预测预警报服务提供必要的科学依据和保障。

Relative humidity is one of the most key environmental meteorological parameters for the formation and transformation of the fog and haze,and it can impact the atmosphere visibility. Sea-land thermal contrast is the important climatic background for the fog and haze weather in the eastern and coastal China. Considering the geographical environment and the sea-land temperature difference in the east of Chinese mainland,the multi-scale spatio-temporal variations of the relative humidity（ RH） and the associated thermodynamic causes and mechanisms were tentatively analyzed from the perspective of changes in atmospheric circulation,water vapor transport and the precipitation. The results showthat the sea-land thermal contrast mainly formed in the south area of Yangtze river and the east sea area of Kuroshio（ mainly include the Kuroshio at source area and in East China Sea）in recent 50 years. Thus the sea-land temperature deference（ SLTD） indicator was built by the subtraction of averaged temperature between the two areas. And this zonal sea-land thermal contrast was subject to an obvious long-term increasing trend superposed by distinct interannual（ quasi-4 a and quasi-7 a） and interdecadal（ about17 a） changes. The correlation analysis indicated that the SLTD had a close relationship with the RH anomalies in the band areas that including the middle reaches of Yangtze river,the Huanghuai area,the North China and the coastal zones east of it（ negative correlation area） and the South China（ positive correlation area）. Regression analysis found that the weakened（ enhancement） of the zonal sea-land thermal contrast in winter mainly results in the southwest（ northeast） anomalies of the monsoon circulation,which tends to regulate the water vapor transport from the eastern bay of Bengal and the South China Sea（ the east China seas） to the east of Chinese mainland,and then it can impact the changes of RH at above areas through the restricttion in the form of water vapor transportation and precipitation. In addition,the strengthening of the SLTD was likely to cause the RH decrease in the North China,while significantly increase in the South China,and vice versa. The analysis above is attempted to provide an important scientific basis for figuring out the RH variation and its relationship with the occurrence of the fog and haze in the hotspot areas as well as the evolution in the future,which is very significant to the scientific adaptation to the climate and environment changes in development areas in the eastern China.