南京冬季辐射雾雾水沉降特征研究

The Deposition Characterisitics of Radiation Fog Water in Winter of Nanjing

利用2007年11月15日至12月29日在南京市郊开展的雾外场观测试验所获取的雾滴谱、三维风资料,利用涡度协方差法,主要分析了南京冬季辐射雾雾过程中的雾水沉降特征,并探讨了一次辐射雾与辐射—平流雾雾水沉降特征的差异。结果表明:辐射雾成熟阶段的雾水沉降量占总沉降量的90%以上;发现20μm以上的大雾滴对沉降起主要贡献,而大雾滴主要受重力沉降机制影响,重力沉降量约占总沉降量的82%,而雾水的湍流沉降量相对较小;直径7μm以下与40μm以上的雾滴对总沉降量几乎无贡献;雾的液态水含量与雾水沉降量之间线性相关,说明雾液态水含量对雾水沉降量有直接的影响,雾水沉降集中在能见度50 m以下的强浓雾阶段;辐射雾发展阶段近地面小雾滴在湍流扩散作用下以一定的周期向雾层上方输送,使得雾水通量谱具有明显的振荡特征,而辐射—平流雾的雾水通量谱不具有振荡特征。

The intensive field observation experiments were conducted in the northern suburb of Nanjing from November 15 to December 29 in 2007.We used an ultrasonic anemometer-thermometer in combination with a size-resolving cloud droplet spectrometer capable of providing number counts in 20 droplet size classes.Our study focuses on the physical characteristics of fog and quantifying the fog deposition flux by using direct eddy covariance flux measurements,as well as the fog water deposition differences between radiation and advection fog.The resullts are as follows：The fog water deposition flux during the mature stage of radiation fog could be 90%of the to-tal deposition flux.Droplet sizes above 20 μm contributed mostly to the fog deposition,which was mainly gravity settling and it was 82% of the total deposition flux,while the turbulent deposition was relatively small.Droplet sizes below 7 μm and above 40 μm con-tributed little to the overall deposition flux.The fog water deposition flux depended linearly on liquid water content of the fog,which in-dicated that the liquid water content of the fog influenced directly on the deposition flux.In the development stage of radiation fog, there was obvious fluctuation of fog water flux due to intensive turbulence,while for advection fog there wasn’t this phenomenon.