基于多源数据的北疆一次持续性浓雾天气过程的演变特征

Evolutionary Characteristics of a Persistent Dense Fog Esipode in Northern Leeside of Tianshan Mountains based on Multi-source Data

利用常规高空地面、机场跑道自动观测系统(AWOS)、微波辐射计及FY-4A新一代静止气象卫星等资料对2019年12月9—13日发生于北疆沿天山一带的一次持续性浓雾天气进行观测特征及演变分析,结果表明:(1)浓雾天气过程发生在500 hPa高空脊区控制、低层不断有暖平流东伸、地面位于蒙古冷高压后部均压场的大尺度环流背景下;(2)浓雾发生前,地面明显升温有利于地表融雪、水汽蒸发,为浓雾的形成和维持提供有利的水汽条件;浓雾维持期间,地面维持1 m·s^(-1)左右的弱风场、温度露点差≤2℃、空气接近饱和、准噶尔盆地低洼地形均为浓雾维持提供有利环境条件。浓雾消散期间,风速增大,急剧降温,快速增湿,有利于雾滴凝结为米雪,使得浓雾消散;(3)Brunt-Vaisala(布伦特-维萨拉频率,N~2)指数能较好地反映浓雾期间边界层稳定度,并能提炼出相关稳定度阈值。浓雾期间相对湿度≥85%高度层主要集中在100 m以下的近地层,持续深厚的湿度层为浓雾形成和持续提供较好水汽条件,浓雾期间强逆温层顶主要维持在600 m高度,当逆温层顶高度抬升时,有利于雾滴及气溶胶粒子、水汽粒子向上扩散,能见度好转;(4)FY-4A卫星的多通道可见光及红外通道差图像能较好地监视白天及夜间浓雾的形成、维持及生消变化。

The persistent dense fog episode that occurred from December 9 to 13,2019 in the northern regions of Xinjiang along the Tianshan Mountains was analyzed based on routine meteorological data,automated weather observing system(AWOS)data,and microwave radiometer data.The results showed that:(1)The occurrence of the dense fog episode coincided with the dominance of an upper ridge system in the region,accompanied by a persistent eastward extension of warm advection at lower levels and uniform surface pressure behind the cold high-pressure system in Mongolia.(2)The melting snow,which was the result of surface temperature rising in the days before the dense fog episode,provided favorable conditions for the formation of dense fog.The combination of weak winds,abundant saturated moist air near the surface,the stable stratification,and the low-lying topography of the Junggar Basin made it difficult for dense fog to dissipate.(3)Near-surface radiation cooling was conducive to the maintenance and strengthening of the inversion layer beneficial to the dense fog.(4)The multi-channel visible and infrared channel difference images of the FY-4A satellite could monitor the formation,maintenance and dissipating of dense fog during the day and night.