Statistical Analysis of Low Layer Atmospheric Stability Distribution Characteristics in Urumqi
According to daily observation of four 100 m meteorological towers in Urumqi from June 2013 to April 2014 by 10 min meteorological data, this paper analyzes the A-F atmospheric stability applicability of the temperature difference method, temperature differencewind speed method, wind ratio method, Richard method, and Overall Richardson number method. It is found that the temperature differencewind speed method is more suitable for the classification of Urumqi City atmospheric stability. Using this method, we calculate the A-F stability and, further, conduct statistical analysis of the frequency distribution characteristics of Urumqi City and suburban stability. The results show that the frequency of stable condition is higher in suburbs than in urban area and the frequency of neutral condition is higher in urban than in suburb, and the frequency of unstable conditions is higher in southern suburbs and urban than in northern suburbs. The frequency of neutral condition is the highest in winter but the lowest in spring and autumn. The frequency of unstable condition is the highest in June but lowest in September and January. The frequency of stable condition is the highest in October and January but lowest in June and July. The proportion of the unstable is the maximum (88.3%-96.3% of all day) during daytime in summer, but minimum (51.3%-60%) in winter. The daily variation of unstable condition is in inverse of neutral and stable conditions. The frequency of stable condition is the highest at sunrise moment in suburb and 2 hours after sunrise in urban. The neutral condition at sunrise and 1-3 hours after sunset respectively reach their two peaks. The frequency of stable condition is higher in cold weather than in hot weather, and it is higher in calm weather than in windy weather in suburb, and the frequency of unstable condition is higher in rain weather than in heavy snow weather. The frequency of neutral and stable conditions are the highest before blowing sand but the unstable condition is the highest during and after sand blowing. The high frequency of atmospheric stability is in B, C and F category in spring and summer; the frequency of C and F category in summer in south suburbs and north suburbs is about 45%. The high frequency of atmospheric stability is B and E category in autumn (about 40%-50%). The high frequency of atmospheric stability is D category in urban, while is F category in south suburbs, north suburbs and north rural.