湛江吴川机场一次大雾天气过程诊断分析

Diagnosis and Analysis of a Heavy Fog Weather Process at Zhanjiang Wuchuan Airport

摘要: 本文使用湛江吴川机场自动气象观测系统(AWOS)数据、ERA5再分析资料(水平分辨率为0.25˚ × 0.25˚) 对2023年1月13日湛江吴川机场一次大雾天气过程进行诊断分析，结果表明：大雾前期连续性小雨轻雾天气使近地面层水汽充沛，地面湿度基本达到饱和状态。大雾前后较弱的风速条件与低云的覆盖，使近地面层水汽得以聚集。大雾发生前低层的水汽辐合区与弱上升运动促进了湿层厚度的增加。起雾阶段冷平流的侵入使近地面层水汽凝结达到饱和，低层偏南风到西南风风向的转变与风速的增大也有利于北部湾的水汽输送至机场上空。大雾期间的下沉运动抑制了低层水汽向上扩散，大雾中期低层水汽辐合区的出现促进大雾的发展与维持。在层结结构上，大雾发生前近地面层存在浅薄的弱逆温层，大雾发生时转为等温层结构，相比于逆温层较不利于大雾的长时间维持。此次大雾的消散主要是由于日出之后地面温度的升高使近地面层的垂直温度梯度增大，中低层的水汽逐渐向上扩散，地面相对湿度降低导致。

Abstract: This article uses data from the Zhanjiang Wuchuan Airport Automatic Meteorological Observation System (AWOS) and ERA5 reanalysis data (horizontal resolution of 0.25˚ × 0.25˚) to diagnose and analyze a heavy fog weather process at Zhanjiang Wuchuan Airport on January 13, 2023. The results show that the continuous light rain and fog weather in the early stage of the heavy fog caused abundant water vapor in the near surface layer, and the ground humidity basically reached saturation. The weak wind speed conditions and low cloud coverage before and after heavy fog allow water vapor to accumulate in the near surface layer. The low-level water vapor convergence zone and weak upward motion before the occurrence of heavy fog promote the increase of wet layer thickness. The intrusion of cold advection during the fogging stage causes the condensation of water vapor in the near surface layer to reach saturation. The change in wind direction from southerly to southwesterly in the lower layer and the increase in wind speed are also conducive to the transport of water vapor from the Beibu Gulf to the airspace above Zhanjiang Airport. The sinking motion during heavy fog suppresses the upward diffusion of low-level water vapor, and the emergence of low-level water vapor convergence zones in the middle of heavy fog promotes the development and maintenance of heavy fog. In terms of layered structure, there is a shallow weak inversion layer near the ground before the occurrence of heavy fog. When heavy fog occurs, it transforms into an isothermal layer structure, which is less conducive to the long-term maintenance of heavy fog compared to the inversion layer. The dissipation of this heavy fog is mainly due to the increase in ground temperature after sunrise, which leads to an increase in the vertical temperature gradient near the ground layer, and the gradual upward diffusion of water vapor in the middle and lower layers, resulting in a decrease in relative humidity on the ground.