一次入海温带气旋背景下的海雾观测分析和数值模拟

Observation and Numerical Simulation on a Sea Fog Event during an Extratropical Cyclone Entering the Sea

利用0.25°×0.25°逐小时ERA5再分析数据、中国气象局地面观测资料、卫星遥感监测资料以及WRF模式对2021年3月27~28日移入黄海的温带气旋引发大范围的海雾过程进行了观测分析和数值模拟,结果表明:(1)本次海雾发生时气海温差介于0.5℃~2℃,海雾成熟阶段出现了气温低于海温的现象。(2)入海气旋形成的湿空气辐合为海雾的发生和维持提供了水汽条件,低空急流带来的西南暖湿气流促进了逆温层的建立并输送水汽。(3)气旋入海以后,黄海海域出现了“双逆温”的现象,低层的逆温来自于低空急流的暖平流输送,高层的逆温是由气旋后部的干冷空气下沉增温造成。(4)在气旋和低空急流的共同作用下,近海面边界层大气湍流动能增加,这也促进了海雾在垂直方向发展。(5)湍流动能收支的诊断结果显示,切变项在海雾的发生和发展过程占据主导作用,当海雾在垂直方向发展时,湍流动能垂直输送项会明显增大。

An extratropical cyclone across the Yellow Sea caused a large-scale sea fog event from March 27 to 28,2021.To investigate this event,we used a comprehensive set of tools,including ERA5 reanalysis data with a spatial resolution of 0.25°×0.25°,ground observation data from the China Meteorological Administration,satellite retrieval data,and the WRF model.Our results were as follows.(1)In the initial stage of this sea fog event,the difference between air and sea temperatures ranged between 0.5℃ and 2℃.However,during its mature stage,this difference turned negative.(2)The moist air convergence driven by the extratropical cyclone served as the primary source of water vapor,which was essential for the formation and maintenance of the sea fog.Furthermore,the southwest warm and moist air flow,transported by the low-level jet,facilitated the formation of the inversion layer.(3)During this event,an interesting phenomenon was the appearance of a“double inversion”in the Yellow Sea.The inversion layer in the low level was caused by the warm advection of the low-level jet,while the higher-level inversion resulted from the sinking and warming of the dry and cold air behind the extratropical cyclone.(4)The combination of the extratropical cyclone and the low-level jet led to an increase in atmospheric turbulent kinetic energy within the near-sea surface boundary layer.This synergistic effect further promoted the vertical development of the sea fog.(5)The diagnostic results of turbulent kinetic energy budget showed that shear production played a dominant role in the occurrence and development of sea fog.When sea fog developed in the vertical direction,the vertical transport of turbulent kinetic energy increased significantly.