Abstract:

Based on the observational atmospheric turbulent data obtained from 255-m tower in Tianjin, the characteristics of different atmospheric variables and turbulent transfer during the fog periods were studied. The results show that before the fog, there exists high humidity, and the height of inversion reaches to 100 m. The inversion of radiation fog is stronger than that of the advection fog. During the fog, the inversion continues strengthening. With the lifting of inversion, the neutral and unstable stratification occurres which means the dissipation of fogs. Meanwhile, the development of inversion in the radiation fog is more obvious than that in advection fogs, the height of radiation fogs is lower than that of advection fogs, and the main reasons for the dissipation of radiation and advection fogs are temperature and wind speed, respectively. The stratification is changed by the fog period, resulting in an unstable nocturnal atmosphere. The vertical transfer is weak and the horizontal transfer strengthened in the later stage. The increasing in the ratio of mean kinetic energy to turbulent kinetic energy before the fog can be treated as the signal of the occurrence of fog and the decreasing marks the dissipation of fog.

Key words: atmospheric boundary layer, fog, turbulent kinetic energy, Tianjin

摘要：

利用天津 255 米气象塔层大气边界层观测资料, 分析雾日各气象要素的特征, 研究湍流输送规律。结果表明: 雾前, 大气湿度较大, 逆温层高度约为 100 m, 辐射雾发生前的逆温强于平流雾; 雾中, 逆温层持续变强、增厚; 雾后, 逆温层出现抬升, 大气呈近中性偏不稳定的层结特征。辐射雾过程的逆温现象比平流雾明显; 辐射雾雾顶较低, 平流雾较高; 辐射雾的消散主要受温度影响, 平流雾主要受风速影响。雾天气过程改变了大气层结结构, 夜间可能呈现不稳定层结状态; 雾前和雾中不同高度的湍流垂直输送微弱, 雾过程后期的水平输送突然增强。辐射雾雾前不同高度的平均动能数值较小, 雾中呈增大趋势, 雾消散阶段逐渐增大, 湍流动能的增大是影响辐射雾消散的重要因素。雾前不同高度平均动能与湍流动能比值的突然增大可能是雾发生的湍流信号之一, 比值剧增之后降至雾前水平则为雾消散的信号。

关键词: 大气边界层, 雾天气, 湍流动能, 天津