乌鲁木齐机场持续浓雾的爆发性特征及成因分析

Analysis on the Explosive Characteristics and Trigger Conditions of Persistent Heavy Fog at Urumqi Airport

摘要: 利用常规气象资料，乌鲁木齐国际机场跑道自动气象观测系统(AWOS)、边界层风廓线雷达、微波辐射计等实时监测资料以及逐时新疆区域自动气象站资料，对乌鲁木齐机场2014年11月~2017年3月出现的47次持续浓雾天气的爆发性特征进行分析，主要结论如下：1) 乌鲁木齐机场持续浓雾天气中，爆发性发展个例占总数的34%，其中突变为强浓雾的又占爆发性发展个例的62.5%。2) 浓雾爆发性发展前后，地面相对湿度基本上处于并维持 ≥ 85%，风向维持或转变为北–东北和西–西北风，风速0~2 m/s。浓雾出现前5~15 min内的3.5℃•h⁻¹~12℃•h⁻¹、30 min内3.5℃•h⁻¹~12℃•h⁻¹的气温突降，或1~3 h内的1.5℃•h⁻¹~3℃•h⁻¹的持续降温，分别对应着能见度不同程度的迅速降低。边界层500 m以下以偏北和偏西风为主，近地层气温降低，相对湿度迅速增大到85%甚至95%左右，贴地逆温得以建立或加强。3) 浓雾爆发性发展前后，绝对湿度条件较稳定，近地层和地面的降温冷却作用，使得对相对湿度在短时间内达到高湿成雾条件，贴地逆温得以建立或加强，从水汽和层结两个方面都对浓雾爆发性发展有着触发作用。4) 辐射降温和局地偏北风平流降温是地面和近地层降温的主要原因。在有利的天气形势下，机场爆发性浓雾发生的预报关键点在于对地面和近地层降温时段和强度的预报，局地风场变化是温度预报的重要关联变量。

Abstract: Utilizing conventional meteorological data, real-time data from the automatic weather observation system (AWOS), boundary layer wind profiler radar, and microwave radiometer at Urumqi Interna-tional Airport, as well as hourly data from regional automatic weather stations across Xinjiang, this paper analyzes the explosive characteristics of 47 persistent heavy fog events occurring at Urumqi Airport from November 2014 to March 2017. The main conclusions are as follows: 1) Among the persistent heavy fog events, 34% showed explosive development, of which 62.5% abruptly intensi-fied into heavy fog. 2) While the explosive development of heavy fog was occurring, surface relative humidity persisted at or above 85%, with wind direction maintaining or shifting to norther-ly-northeasterly and westerly-northwesterly winds at 0~2 m/s. The temperature decreases of 3.5˚C•h⁻¹~12˚C•h⁻¹ within 5~15 minutes prior to fog onset, the temperature of 3.5˚C•h⁻¹~12˚C•h⁻¹ drops abruptly within 30 minutes, or sustained decreases of 1.5˚C•h⁻¹~3˚C•h⁻¹ in the preceding 1~3 hours, correspond to rapid visibility reduction to varying extents. In the boundary layer below 500 m, northerly and westerly winds prevail, along with decreasing ground layer temperature and rapidly rising relative humidity to around 85% or even 95%, during which ground temperature inversion is formed or intensified. 3) Before and after the explosive development of heavy fog, absolute humidity conditions remained relatively stable. The ground layer cooling strengthened relative humidity, rapidly attaining fog-forming threshold, during which ground temperature inversion was formed or intensified. Both the cooling and inversion played triggering roles in water vapor and stratification to the explosive development of the heavy fog. 4) Radiative cooling and advection cooling are the main reasons for surface and ground layer cooling. Under advantageous weather conditions, the key to forecasting the airport’s explosive fog lies in predicting the timing and inten-sity of surface and ground layer cooling, of which the local wind field is an important correlated var-iable.