关键词: 边界层高度, 风沙强度, 地面要素, 河西走廊

Abstract: Taking the Hexi Corridor in the much wind-sand area of China as the research object, using the smoothing potential temperature method and T-LnP method, the variation characteristics of boundary layer height (BLH), its influencing factors, relationships between BLH and wind-sand intensities were analyzed, based on daily encrypt upper data every 50 m at 19:00, specified layer and characteristic layer upper data at 07:00 of Dunhuang, Jiuquan, Zhangye and Minqin stations over Hexi Corridor from 2006 to 2017. It was concluded that BLH was directly proportional to the dust intensity. Further the main causes of frequent and strong wind-sand weather in spring afternoon were obtained from the diurnal variation of surface wind speed, relative humidity and temperature difference of ground atmosphere. The characteristics of BLH in different circulation situations of sandstorm were obtained, and the relationship between the minimum height of wind speed ≥ 15 m·s^-1 and the different wind-sand intensities. The results show that the average annual BLH was 1 700-2 200 m, average monthly BLH was over 3 000 m from April to June, and that of Dunhuang was more than 3 500 m in April-May. The BLH is closely related to the maximum temperature, the lowest temperature and the maximum 0c m ground temperature, and directly proportional to the maximum temperature and the maximum wind speed. The BLH increased with the increase of dust intensity, and both that of strong sandstorm and strong wind in April were more than 3 100 m. The wind speed increased with the increase of dust intensity in spring. The maximum wind velocity time was 12:00-18:00. The maximum wind speed, the smallest relative humidity and the biggest difference of the ground temperature and air temperature in the daily variation of spring all occurred at 13:00-14:00, which was the period when the wind-sand weather appeared the most and the intensity was the strongest. The shorter the duration of sandstorm was, the higher the boundary layer height was, whose maximum were 2 800-3 100 m in the afternoon of April to June. The BLH of westerly trough in different sandstorm circulations was lower as a whole, that of horizontal westerly circulation was above 3 100 m in April, June and August, and which was higher than 3 580 m in August, while the northwest airflow circulation was higher than that of westerly trough circulation, and which was higher than 3 200 m in May and June. The lowest height of upper air velocity ≥ 15 m·s^-1 was lower in winter and spring than in summer and autumn, and the height of floating dust was highest which was up to 4884 m, that of strong wind with sand-dust was the lowest that was 2 471 m, and the height of strong wind and sandstorm at 07:00 was about 600 m higher than at 19:00. The BLH was obviously 1 000-2 000 m lower than height of upper air velocity ≥ 15 m·s^-1.

Key words: boundary layer height, wind-sand intensity, surface element, Hexi Corridor