气溶胶对我国中东部地区秋季降水的影响

EFFECTS OF AEROSOLS ON AUTUMN PRECIPITATION OVER MID-EASTERN CHINA

通过分析近50年来中国中东部地区降水资料发现,秋季降水与其他季节相比有明显减少趋势(每10年下降约54.3 mm),尤其自1980年代以来呈直线下降趋势(每10年降水减少5.6%)。从降水形成三个基本条件(水汽输送条件、稳定度条件、云微物理条件)出发,探究秋季降水减小的原因。结果表明,大气稳定度(对流抑制能(convective inhibition,CIN)以28.67(J/kg)/(10年)的速率增加,对流有效位能(convective available potential energy,CAPE)以12.81(J/kg)/(10年)的速率减小以及云微物理性质的变化(云滴有效粒子尺度减小)是导致秋季降水减少的直接原因,而这两个因素的变化与近20多年来气溶胶的大量增多有着非常密切的关系。因此,由空气污染造成的气溶胶浓度的增加可以作为导致中国中东部地区秋季降水减少的其中一个重要原因。由于秋季天气系统较稳定,主要受到大尺度系统影响,动力作用影响大于热力作用,所以减少了复杂中小天气系统和热力作用对降水的影响,故而更加突显出气溶胶对秋季降水的影响。

Observational data analysis indicates that precipitation decreases by 54.3 mm per decade in mid-eastern China in autumn for 1959--2008 and the decrease rate is 5.6% per decade from the 1980s to the present. This decreasing trend of precipitation is different from that in other seasons. We examine three mechanisms associated with the changes in water vapor transport, atmospheric stability and cloud microphysical properties, which may be responsible for the reduction of the autumn rainfall. The reduction of autumn rainfall are directly caused by the increase of the atmospheric stability, as indicated by the increased convective inhibition （CIN） whose increasing rate is 28.67 J/kg per decade, the decreased convective available potential energy （CAPE） whose decreasing rate is 12.81 J/kg per decade, and the change of cloud microphysical properties, such as the decreased cloud droplet effective radius. Furthermore, the changes of atmospheric stability and cloud microphysical properties may be closely related to the change of atmospheric aerosols, based on satellite observations over the entire mid-eastern China during autumn for 1980--2008. It is suggested that significantly increased aerosol concentrations produced by air pollution （with corrected visibility decreased by -2.7% per decade） are at least partly responsible for the decreased precipitation events, especially light rain events, in mid-eastern China over the past 20 years. The aerosols effect on precipitation is more obvious in autumn since the weather systems in autumn are more stable （when the dynamic effects are greater than the thermal actions） and the precipitation is influenced more by large-scale systems.