SpatioTemporal Characteristics of Hail and Its Influence Factors in Qinghai Plateau During 1980-2018
By using the daily data from 50 stations and ERA-Interim reanalysis data in Qinghai Plateau during 1980-2018, and the methods of linear regression, Pearson correlation analysis and probability density distribution, this paper analyzed the spatio-temporal characteristics of hail frequency, hail diameter, hail duration, and the effects of elevations, special layer heights, and surface temperature on hail. The results demonstrate that the mean hail frequency in Qinghai Plateau has decreased significantly in the recent 39 years, especially since 2000. Hail events are most seen in June and July, with a fast decline rate in a year. The mean single time hail duration has decreased significantly, while the occurrence of large hail events has increased since the middle-late of 1990s. From the spatial distribution, the high value areas of hail frequency and duration are in the south part of Qinghai Plateau with high elevation, while the high value areas of mean hail diameter are in the eastern part of Qinghai Plateau with lower altitudes. The hail diameter in 3-5 mm〖JP〗 and duration 2-3 min of hail events have the highest frequeney. The lower 0℃ and -20℃ isotherm heights are favorable for hail formation and prolonging the hail duration. The higher 0℃ and -20℃ isotherm heights play an important role in supporting the collision and growth of hail in the air. The decreases of hail frequency and hail duration are related to the significant increase in mean surface air temperature and decrease in diurnal temperature range as well as the rising of 0℃ and -20℃ layer heights.