2010年春季北京地区强沙尘暴过程的微气象学特征

Micrometeorological Characteristics during Severe Dust Storms in Spring of the Beijing Area in 2010

利用北京大学校园地区PM10质量浓度观测资料、中国科学院大气物理研究所325m气象塔气象要素梯度和湍流观测资料,分析了北京地区2010年3月20～22日两次强沙尘暴过程微气象学要素和沙尘参量的时空演变以及湍流输送特征,为理解北京地区强沙尘暴天气沙尘输送规律和微气象学特征提供参考。结果表明:3月20～22日强沙尘暴过程前后不同高度温度先升后降,气压和相对湿度则相反。强沙尘暴来临时,高层风速先迅速增大,低层风速增加略有滞后,风切变明显加强,PM10浓度最大值和风速极大值出现时间较吻合。强沙尘暴过境时,不同高度向下的湍流动量输送、向上的湍流热量输送和湍流动能明显加强。与3月21日非沙尘暴日相比,强沙尘暴过程湍流动量通量增加,有利于沙尘粒子的水平和垂直输送过程;由于冷锋过境,水平热通量增大;垂直热通量因白天温度垂直梯度减小而减小,夜间因逆温层被破坏而增加;水平湍流动能对湍流动能占主要贡献,垂直湍流动能仅占水平湍流动能的10%～25%。

Based on the PM10 concentration observations from Peking University and the profiles of meteorological parameters and turbulence measurements from the 325-m meteorological tower operated by the Institute of Atmospheric Physics, Chinese Academy of Sciences, the variations in micrometeorological and dust parameters and the characteristics of turbulent transfer were analyzed during two severe dust storms occurring during 20-22 March 2010, which can provide references to studies of dust transport discipline and micrometeorological characteristics during severe dust storms in the Beijing area. The results indicated that temperature at different levels increased at first and then decreased during the severe dust storms, however, air pressure and relative humidity oppositely evolved. As the severe dust storms broke out, wind speed at higher levels increased earlier than that at lower levels, and wind shear became intense. The maximumvalues of PMIO concentration almost coincided with those of wind speed. Considerable increases were shown in downward turbulent momentum fluxes, upward turbulent sensible heat fluxes, and turbulent kinetic energy at different levels. Comparing with the clear day on 21 March, turbulent momentum fluxes enhanced and helped with dust transport. Because of the cold front system accompanying with dust storms, horizontal sensible heat fluxes apparently became larger, and vertical sensible heat fluxes increased at night due to the breakdown of inversion layer, but dropped at daytime owing to the minished temperature vertical gradient. Horizontal turbulent kinetic energy accounted for the largest proportion of turbulent kinetic energy, and vertical turbulent kinetic energy took up only 10%-25% of horizontal turbulent kinetic enerRy