华南黑碳气溶胶浓度与南海夏季风关系的年代际突变

Interdecadal change in the relationship between black carbon aerosol over southern China and South China Sea summer monsoon

利用重建的华南区域黑碳气溶胶(Black Carbon,BC)浓度资料,分析其与南海夏季风在年际尺度上的关系。结果表明,华南区域BC浓度与南海夏季风的关系在2000年前后有明显的突变,由显著负相关变为显著正相关,即由高BC浓度弱季风变为高BC浓度强季风。通过合成对比分析,发现1988—1999年(第一时间段)的华南BC主要气候效应是间接辐射强迫作用:华南BC使云粒子半径减小,抑制华南区域春季降水,增加了云的生命期,从而使到达地面的短波辐射减少,表面和低层大气降温。负温度异常激发了异常反气旋,在南海区域即有东风异常。到夏季,东风异常减弱了季风强度,同时抑制了南海地区的降水。2000—2010年(第二时间段)的华南BC主要气候效应是直接辐射强迫作用:春季高BC浓度通过直接气候效应,增暖大气,加强降水,但是雨日减少,从而使到达地面的短波辐射增多,表面和低层大气增温。正温度异常激发了异常气旋,在南海区域即有西风异常一直维持到夏季,增大了季风强度,同时增强了南海地区的降水。

In this study,a set of reconstructed black carbon(BC)data is used to analyze the relationship between BC over southern China(SC)and the South China Sea(SCS)summer monsoon(SCSSM)on the interannual time scale.An abrupt change of the relationship appears at around 2000.Before 2000,there is a negative correlation between them,namely larger BC concentration corresponding to weaker SCSSM,while positive correlation begins in 2000.By means of composite and contrast analyses,it is found that a major climate effect of BC over SC is attributed to the indirect radiative forcing during the first period(1988—1999):Namely,the reduced cloud particle radiuses related to BC over SC suppress the spring precipitation,yet increase the cloud lifetime,which decreases the amount of solar radiation,thus leading to a cooling at the surface and in the lower atmosphere.The negative air temperature anomalies excite an anomalous anticyclone with easterly anomalies over the SCS.In summer,the anomalous easterlies weaken the SCSSM and decrease the precipitation over the SCS.During the second period(2000—2010),the main BC climate effect is direct radiative forcing:The warmer atmosphere associated with the larger BC concentration enhances the spring precipitation,while decreasing the number of rain days,which in turn increases the amount of solar radiation,thus leading to a greater warming at the surface and in the lower atmosphere.The positive air temperature anomalies excite an anomalous cyclone with westerly anomalies over the SCS.In summer,the anomalous westerlies enhance the SCSSM and the precipitation over the SCS.