Spatial and temporal distribution of visibility and its causes in the Bohai Rim regio

• 1、College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000

Abstract：By using daily surface observation data from meteorological observation in Bohai Rim region(35-42.5 N、116-123.5 E）from 2002 to 2017, this paper analysis of low visibility weather with a visibility of less than 10 km and its causes. The results show that the annual spatial distribution of days of low visibility in the Bohai Rim region is uneven. Which shows the characteristics that it often occurs in coastal areas and seldom in inland. It often occurs in plains, and seldom in mountainous areas, and it often occurs in urban areas, seldom in villages. The low-visibility days for 0-10 km feature is characterized by a double peak, with more in summer or winter and less in spring or autumn. During the day, low visibility is most likely to occur at 08:00, and followed by 20:00. And its least is 02:00. Low visibility weather is mainly caused by weather phenomena such as fog, haze and precipitation. More than 60% of low visibility weather occur when the surface relative humidity is greater than 80%. The average wind speed at the time of low visibility was small and the average wind direction was southeast. Low visibility weather is more likely to occur in cloudy or on overcast day.

Keywords： low visibility spatiotemporal analysis the Bohai Rim region