Problems Existed in Duststorm Intensity Division when Divided by Daily Timed Observed Visibility
用日定时观测能见度划分沙尘暴强度存在的问题

The duststorm observational data and the timed observational visibility data in the same day of Ningxia 24 stations from 1955 to 2003 were selected to analyze the problems existed in intensity division of duststorms in single station.The result shows that to divide the intensity of duststorm by the minimum timed observational visibility data in the same day has big unilateralism,the intensity of 53% duststorms can't be divided and,69% duststorms happened in unobserved time.Based on typical cases,the problems of applying daily minimum visibility in intensity division of duststorms and its deviation were analyzed,which has provided reference for the intensity division of historical duststorms.