江苏不同强度降雨对能见度影响分析

利用江苏70个基本站多年逐时雨量、相对湿度、风向、风速以及同时段内最低能见度等观测资料,分析不同强度降雨对能见度的影响,并对比分析两种不同强度降雨造成的低能见度事件统计特征。结果表明:降雨是除雾以外,江苏低能见度的主要影响天气(14. 7%),其中稳定性弱降雨和短时强降雨影响最大。与低能见度雾事件不同,降雨造成的低能见度事件全天各时段均可能出现,发生时可伴随较强的风速(2 m/s),短强低能见度多见风速4 m/s(26. 6%)。江苏冬春两季为雨雾高发季,主要受降雨持续时间影响,对应的低能见度区间为500~1 000 m,有明显日变化。短强低能见度主要受雨强影响,多发生于6—9月,对应的低能见度区间为小于200 m,无明显日变化。两种降雨产生的低能见度事件有明显的空间分布差异,且雨雾低能见度发生时偏北风占主导,短强低能见度发生时则偏东风占主导。

Analysis of the influence of rainfall intensity on visibility in Jiangsu

Using the hourly observation data of rain, relative humidity, wind direction, wind speed, and minimum visibility in the same period from 70 national weather stations in Jiangsu Province, the impacts of different rainfall intensities on visibility was analyzed, and the statistical characteristics of two types of rainfalls with different intensities, which caused low-visibility weather, were compared and analyzed. The results showed that rainfall was the major reason for low-visibility weather in Jiangsu(14.5%) besides fog. Stable weak rainfall and short-time heavy rainfall showed the most obvious impacts. Unlike the low-visibility weather events caused by fogs, those caused by rainfalls may occur at any time throughout the day usually with high wind speeds(>2 m/s). In 26.6% of these events, wind speed would be>4 m/s. Winter and spring were seasons with most frequent rain fog weather in Jiangsu, which was mainly affected by the duration of rainfalls. The corresponding low visibility range was 500-1 000 m with obvious diurnal variations. Short-time heavy rainfall fog weather was mainly affected by the intensity of rainfalls, which mostly occurred during June and September, and the corresponding low-visibility range was less than 200 m without obvious diurnal variations. There was obvious spatial distribution difference between the low visibility weather events caused by the two types of rainfalls. When the rain fog weather occurred, the northerly wind dominated;when the short-time heavy rainfall fog weather occurred, the easterly wind dominated.