低云在不同季节对东海黑潮海洋锋响应的个例研究

Case Study of Low-Cloud Response to the East China Sea Kuroshio Fronts in Different Seasons

本文采用高分辨率的CALIPSO（Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations）卫星资料,结合欧洲中心的再分析资料,在东海黑潮区域分别选取冬、春、夏季的典型个例,对比分析层积云、层云、海雾3种边界层云。分析结果显示,层积云发生在高空槽后,云顶1.2~2.5km,云底0.7~2km,云顶平滑度差,海气界面不稳定,地表偏北风,边界层不稳定,底层混合均匀,云层上方有逆温层存在;层云发生在高空槽前,伴有强烈冷平流,位于地面低压前部,云顶高度300~700m,较平滑,云底不接地,海气界面稳定,地表南风,边界层稳定,有不接地逆温,云区无下沉运动;海雾发生在高空槽后,低层有暖平流,地面位于高压中心,雾顶小于700m,底部接地,雾顶最为平滑,海气界面稳定,地表南风,风速很小,边界层稳定,逆温层很低,并伴有强烈下沉运动,地表相对湿度大于90%。黑潮锋通过影响海气边界层,进而影响低云的高度、形态等特性,三种低云高度自南向北均逐渐下降,在SST大梯度区有突变,海雾与低云性质相似,在一定条件下可以相互转化。

Three typical cases representing different seasons were selected to study the differences of stratocumulus,stratus and sea fog over the East China Sea Kuroshio,using the CALIPSO satellite data and reanalysis data provided by the European Center for Medium-Range Weather Forecast（ECMWF）.The results show that stratocumulus,whose cloud top with poor smoothness is about 1.2~2.5km above the sea level and the cloud base height is about 0.7~2km,occurs after the upper trough.The characteristics include unstable air-sea interface and marine atmospheric boundary layer（MABL）,prevailing northerly winds and an inversion above the stratocumulus.Meanwhile,stratus,whose cloud top height is about 300~700m,takes place before the upper trough accompanied by intense cold advection.The characteristics contain stable air-sea interface and MABL,prevailing southerly winds and no subsidence in the cloud area.Sea fog occurs after the upper trough along with low level warm advection.It＇s above the centre of high pressure.The top of the fog is less than 700 m,and is the smoothest.Its bottom is grounded.The air-sea interface and MABL are also stable but with strong subsidence.The sea surface prevails southerly wind and the relative humidity is above 90%.The East China Sea Kuroshio Fronts influence the height and the morphological of low cloud by effecting MABL.The height of three types of low cloud are all decreasing from south to north,and have a sharp transition across the SST gradient zone.Sea fog and stratus are similar,and under certain conditions can be mutual conversion.