SYNOPTIC ANALYSES OF TWO STRONG SANDSTORMS IN THE HINTERLAND OF TAKLIMAKAN DESERT

Two strong sandstorms occurred in the Taklimakan desert on the July 11￣13, 1996.On 11 at 15:40 to 17:50, there appeared the first sandstorm in Xiao Tang, maximum wind velocity was 15 0 m/s, wind direction was NNW, and minimum visibility was less than 50 m. On 12 at 19:50 to 20:30, there appeared another sandstorm in Xiao Tang, maximum wind velocity was 9 3 m/s, wind direction was WNW. Applying synoptic meteorology method, this paper obtained conclusion as follows: (1) Controlled by subtropical high pressure, air temperature rose, atmospheric pressure reduced, humidity dropped obviously day by day on July 6 to 10 in the Tarim basin. It resulted in concentration of local unstable energy. (2) At afternoon on 11, an obvious short wave splinted from the front part of upper level low vortex moved eastward, which formed obvious air pressure difference of north south, and part of cold air turned over Tianshan mountain and came into the Tarim basin. Plenty of potential energy turned into kinetic energy, which resulted in leaning north gale of lasting long time. At the same time, there was a north south belt of convergence in lower air formed in east west wind. These two factors acted together and led to very strong sandstorm. (3) At evening on 12, routine surface observation station around Tarim basin couldn't observe the existing stronger sandstorm in the hinterland of desert. By analyzing upper level and surface weather chart, and satellite cloud picture, we discovered that south upper cirrus entered the basin and combined with the colder cumulus mass left in the center of basin. There formed small low, therefore caused limited range but longer time sandstorm weather in the hinterland of the desert. (4) When sandstorm occurred in the hinterland of Taklimakan desert, ground weather factor varied evidently. Wind velocity suddenly increased; Visibility rapidly decreased, the minimum visibility was only 2 m; Evaporation is violent; Relative humidity and air temperature dropped strongly. (5) When center and edge of the desert appeared sandstorm, wind condition was different evidently. Wind velocity variation in the center was large, that of the edge was less. Wind force strengthened from afternoon to evening. (6) Satellite cloud picture proved that the strong sandstorm at afternoon on 11 belonged to system weather, and the strong sandstorm at evening on 12 belonged to local weather.