基于BJ-RUCv2.0预报系统对大雾形成和发展关键条件的数值分析

为了弄清北京地区持续性雾-霾天气过程的演变规律、揭示大雾形成和发展的关键条件，利用常规气象观测资料、高速路自动气象站观测资料和大气成分观测资料分析了2013年1月26~31日雾-霾天气过程的演变特征和有利于大雾形成和发展的天气形势。在此基础上，采用先进的北京快速循环同化中尺度数值预报系统（BJ-RUC v2.0）开展数值模拟，分析大雾形成的水汽、动力和热力条件，得出:模式对1月30日夜间至31日前半夜的雾区模拟较好，但对28日夜间至29日白天（大雾天气伴严重大气污染）雾区的模拟偏差较大。发现近地层的持续性东南风使950 hPa以下湿度增大是大雾形成的关键条件。上层（975~800 hPa）的明显暖平流导致逆温层的加强和维持，使大气层结稳定度增强，是大雾天气发展和维持的重要条件。另外，近地层950 hPa以下为风场辐合、其上层为风场辐散的结构有利于雾的进一步发展。

Numerical Analysis of Crucial Conditions for the Formation and Development of Heavy Fogs Based on BJ-RUCv2.0 Forecast System

In order to find out the evolution characteristics of successive heavy fog and haze processes and reveal crucial conditions for the formation and development of fogs in Beijing, this paper analyzes the weather evolution characteristics corresponding to the heavy fog and haze case occurred from 26 Jan to 31 Jan 2013. Conventional meteorological data, automatic weather station data, and atmospheric composition observation data are used in this study. The weather conditions that are favorable for the formation and development of fogs are also analyzed. Based on the above analysis, the complicated BJ-RUC v2.0 (Beijing Rapid Updated Cycle forecast system version 2.0) is used to simulate water vapor, momentum, and thermal conditions for fogs. The results indicate that BJ-RUCv2.0 can well simulate the area of advection fog that occurred from the night of 30 Jan to the early night of 31 Jan. However, large errors occurred in the simulation for the fog event accompanied with severe air pollution from the nighttime of 28 Jan to the daytime of 29 Jan. The crucial condition for the formation of the heavy fog is the increase in the atmospheric humidity below 950 hPa, which is attributed to successive southeasterly winds in the near surface layer. The atmospheric stratification stability and the inversion layer are strengthened by the obviously warm advection from 975 hPa to 800 hPa, which is an important factor for the development and maintenance of the heavy fog. In addition, the wind convergence near surface (below 950 hPa) and the wind divergence on the upper layer are favorable for the fog development.