一次海雾过程大气波导形成机理的数值研究

Numerical Modeling Study on the Formation Mechanism of an Atmospheric Duct During a Sea Fog Event

依据船舶导航雷达与沿岸气象探空观测数据得知,2005年6月1～3日黄海海域发生了1次大范围波导现象;进一步结合卫星云图与沿岸测站水平能见度观测,发现此次波导伴随1次明显的平流海雾过程。利用WRF模式对此次海雾与波导过程进行了数值模拟,发现:(1)海雾始于黄海中部,绝大部分海雾的雾顶由于弱逆温、湿度梯度较小而不存在波导;(2)雾区随其北部低压的逐渐东移而向东扩展,呈现西部薄、东部厚的结构,雾体顶部由于存在逆温与湿度锐减而形成了波导,混合均匀的雾体则成为波导基础层,薄雾顶部为非贴海表面波导,而厚雾顶部则为悬空波导;(3)雾区受低压西部冷空气的影响向南消退,波导基础层逐渐变薄乃至消失,雾体之上的逆温与湿度锐减层随之下降,非贴海表面波导被强度较弱的贴海波导所替代。分析结果表明:黄海平流海雾与波导有密切的联系,海雾形成及其发展改变了海洋大气边界层的温度与湿度垂直结构,从而导致了波导的发生与演变,大气波导可认为是海雾的"副产品"。

Judged from marine navigational radar and sounding observations, an atmospheric duct process occurred over the Yellow Sea from 1-3 Jun 2005. Further combining with satellite imagery and horizontal visibility, we find that this duct process is associated with an advection sea fog event. The WRF model was employed to reproduce this duct, and results are as follows： 1） the sea fog originated in the middle part of the Yellow Sea, due to weak inversion and the minor temperature gradient, duct did not happen on most of the fog top~ 2） following with northern low pressure moving easterly, the fog area expanded east forward with a structure of thin in west while thick in east. Because of the inversion and intense humidity gradient, duct happened on most of the fog top with a well mixed sea fog as base layer. Over thin and thick sea fog, non-touching-sea-level surface duct and elevated duct exist respectively; 3） influenced by the cold air in the western low pressure, sea fog gradually dissipated towards south with the base layer getting thinner even vanished, that resulted in the inversion and intense humidity gradient declining. Thus the non-touching-sea-level surface duct is replaced by the weak touching-sea-level surface duct. The principal findings of this study are that advection sea fog over the Yellow Sea has a close relationship with the duct, the evolution of the sea fog changed the vertical structure of temperature and humidity in marine atmospheric boundary layer, that directly lead to the duct＇s occurrence and development, i.e. this duct can be considered as a by-product of the sea fog.