辐射雾雾滴谱拓宽的微物理过程和宏观条件

为研究南京雾的物理化学过程,2006～2007年冬季,在南京信息工程大学(原南京气象学院)院内进行了雾的外场综合观测实验,共获得27次雾过程资料,其中有22次过程进行了全过程不间断的雾滴谱和湍流观测.根据雾滴谱分布特征可以将辐射雾分为宽谱辐射雾(都为强浓雾,最大直径大于40μm)和窄谱辐射雾(多为浓雾,最大直径小于22...

The Microphysical Processes and Macroscopic Conditions of the Radiation Fog Droplet Spectrum Broadening

In order to study the physical-chemical processes of fog in Nanjing, field observations were conducted in Nanjing University of Information Science & Technology during the winters of 2006 and 2007, when 27 fog cases were acquired, including 22 cases of contiguous fog droplet spectrum data. According to the droplet spectrum distribution the radiation fog could be divided into wide-spectrum one, which is all extremely dense fog with the maximum diameter more than 40 μm , and narrow-spectrum one, most of which is dense fog with the maximum diameter less than 22 μm. During developing from dense fog to extremely dense fog, the radiation fog is characterized by the explosive deepening, whose nature is the fog droplet spectrum burst broadening, and the increase of number concentration and LWC. The macroscopic condition and microphysical process of the fog droplet spectrum burst broadening were detailedly analyzed in this paper, and the result shows that: the fog droplet spectrum burst broadening occurred during the period of temperature rapid decline (Super-saturation increase). The weak cold advection or the water evaporation from the wet surface after sunrise during the dense fog episode is apt to cause the burst broadening of the fog droplet spectrum. Early fog droplet spectrum broadening was mainly based on nucleation and condensation, but coalescence and condensation during the late period. The droplet spectrum “widening” has the characteristic of a ladder-type, but when the cooling rate and the degree of supersaturation are very large, the number of fog drops in all bins could increase, and the maximum diameter could enlarge continuously. The turbulence not only plays an important role in the vertical transmission of momentum, heat, and water vapor, but also is the important condition for fog droplet collision broadening.