海雾对沿海地区的影响程度初探——2008年春季两次黄海海雾过程分析

IMPACT OF SEA FOG ON COASTAL AREA:ANALYSIS OF TWO CASES OVER THE YELLOW SEA IN SPRING 2008

利用多种观测资料、再分析资料和WRF模式,对2008年4月29—30日和5月2—3日两次黄海春季海雾进行对比分析,研究黄海海雾影响沿海地区的因素。分析表明:(1)两次海雾过程均属于平流冷却雾过程。在低层水平方向上,合理的高、低压配置,使气流持续地从暖湿海面输送到冷海面上,有利于形成深厚的海雾,进而在海风的作用下影响沿海地区。在垂直方向上,边界层内上干下湿的结构有利于海雾的发展与维持。(2)边界层内稳定持续的逆温层结构,使水汽在逆温层内累积,有利于海雾的发展与维持。雾顶的长波辐射冷却作用以及雾层内适度的湍流有利于海雾的发展与维持;而低层风速增大会引起机械湍流的迅速增长,进而导致海雾消散。(3)海雾影响明显时,对应黄海海域上空的暖平流较强,水汽通量较大,暖湿平流来源于较暖的海面。反之,对应黄海海域上空的暖平流较弱,水汽通量较小,暖湿平流来源于较冷的海面。

To understand the impact of sea fog on coastal area, we analyzed two sea fog cases occurred in April 29—30 and May 2—3 over the Yellow Sea in 2008 using observation data, reanalysis data, and WRF（Weather Research and Forecasting, v3.8） simulation. The two events were of advection cooling type, and took place due to interaction of high and low pressures at a low level, from which warm-moist air was transported continuously from warm to cold sea surface. In vertical direction, a two-layered boundary structure（upper dry layer and lower moist layer） was conducive to the formation and development of sea fog. In addition, a stable and sustaining inversion layer existed in the boundary layer, which favored vapor accumulation in an inversion layer. Meanwhile, long-wave radiation cooling on fog top and moderate turbulent mixing inside the fog helped stay and development of sea fog, whereas high wind increased turbulence and dissipated the sea fog. Above the sea fog area, warm advection and vapor flux were strong, or if they were weak, warm moist from relatively cold sea surface would form no fogs.