降水对雾中能见度参数化的影响

E ffect of Rainfall on Param eterization of Fog V isib ility

雾的能见度是雾滴数浓度和含水量的函数,可以利用雾滴数浓度和含水量进行参数化得到能见度拟合值。但是当雾中有降水存在时,降水会影响雾滴数浓度和含水量,进而影响能见度参数化。2009年1月19日至3月5日在湖北恩施雷达站进行了包括雾微物理特征、雨滴谱及雨滴末速度、能见度以及基本气象要素的观测。利用不同的能见度参数化公式得到能见度拟合值,并与实测值进行对比分析,考虑雾中降水影响时的能见度拟合值要比不考虑降水时的能见度偏差大,因此在有降水伴随雾产生时,降水的效应可忽略不计。同时,利用40%的雾滴谱观测数据建立了良好的模型用于拟合当地的能见度,并利用Gultepe公式得到相应的参数,对当地的能见度进行了计算和预报。

Fog visibility is a function of fog droplet number concentration and liquid water content, both of which can be used to parameterize the visibility. However, when fog and rain are coexisting,rainfall can affect the fog droplet concentration and liquid water content, in such as to affect the visibility parameterization. The fog microphysical characteristics, the raindrop spectrum, the velocity of raindrop, the visibility, and some basic meteorological elements were measured in Enshi, Hubei Province, China from 19 January to 5 March 2009. The different formulas were used to parameterize the visibility, which were compared with the observed ones. When the influence of raindrops was considered, the errors of the calculated visibility values with respect to the observed ones were much higher, in such a way that the impact of rainfall should be neglected. It is suggested that fog visibility can be parameterized only using fog spectrum, which can be obtained by the fog droplet spectrometer regardless of the presence of rainfall. 40% of the droplet spectra data have been employed to construct an adequate model to simulate the visibility. Furthermore, together with the parameters from Gultepe formula, the local visibility can be calculated and predicted.