一次黄海海雾的数据同化试验与形成机制研究

选取2012年4月14日的一次存在东西2片雾区的黄海春季海雾为研究对象，借助WRF（Weather Research and Forecasting）模式，采用循环3DVAR（3-Dimensional Variational）数据同化方案，考虑了湿度控制变量的背景误差协方差CV6，进行了AIRS（Atmospheric Infrared Sounder）卫星温度与湿度廓线数据的同化试验，并基于同化试验结果探讨了此次海雾的形成机制。同化试验结果表明：同化 AIRS 卫星温度与湿度廓线数据后，模式能成功再现海雾的形成过程，特别是东西2片雾区之间的晴空区的存在，这归功于AIRS数据的同化能够显著改善海上大气边界层的温湿结构、影响海雾的低层高压的范围与强度；机制分析揭示：东西2片雾均为典型的平流冷却雾，但二者厚薄和气团来源不同；海上高压控制黄海西岸陆地的暖空气入海，受低海温的冷却作用降温先形成逆温层，然后逆温层底部生成了较薄的西侧雾区；来自黄海中部的空气向东北移动至朝鲜半岛西部海域，高压下沉增温形成一个顶部较高的稳定层，从而生成较厚的东侧雾区；高压中心下沉区内，近海面风速小使得机械湍流弱，空气增温与海温暖舌共同作用下使得近海面气海温差小，海雾无法生成导致了晴空区的存在。

Data assimilation experiments and formation mechanism study of a Yellow Sea fog event

The spring Yellow Sea fog event with 2 large patches on 14 April 2012 is chosen for study. Using the WRF (Weather Research and Forecasting) model and cycling-3DVAR (3-Dimensional Variational) data assimilation (DA) scheme, combining with the background error covariance CV6 of the humidity control variable, DA experiments of AIRS (Atmospheric Infrared Sounder) air temperature and humidity profile data are carried out. The formation mechanism of the sea fog is investigated based on the results of the DA experiments. The DA experiments indicate that the DA of AIRS data can successfully reproduce the sea fog event, especially the clear sky region between the eastern and western fog areas. This result is contributed by the improvements of the structures of temperature and humidity in the marine atmospheric boundary layer, as well as the range and intensity of the low-level high-pressure system. The mechanism analysis reveals that both the eastern and western fog patches belong to typical advection cooling fogs while their thickness and air mass original breeding sources are different. The warm air over the land to the west coast of the Yellow Sea is moved over the sea surface by the high-pressure system, and an inversion layer is formed by the cooling effect of colder sea surface temperature (SST), then at its bottom the thin western fog patch occurs. The air from the central Yellow Sea moves northeastward over the sea region west to the Korean peninsula, then high-pressure subsidence results in a deep stable layer and the thick eastern fog patch occurs. Within the high-pressure region, near the sea surface weak winds make weak mechanical turbulence, air-sea temperature is small due to the joint action by warmer air by subsidence and SST warm tongue. Thus sea fog forming is suppressed and a clear sky region appears over the central Yellow Sea.