| The Temporal and spatial variation traits of the sandstorm during the past 50a are studied. It presented the types of the main influencing systems for the sandstorms in both northern and southern Xinjiang, analyzed its synoptic dynamic causes through choosing typical weather process in typical regions, revealed the new truth regarding the changing traits of Visibility, sediment flux, grain size parameters during the sandstorms, tested the simulating effect of the selected sandstorm models in Xinjiang. The following conclusions are thus drew:1,The sandstorms occurred in Xinjiang presents such a distributing features that more in the southern parts while less in the northern, more in the western while less in the western, more in the mountains areas while less in the basins, the high value region mainly locates in the southern edge of the Taklimakan Desert. Regarding the Taklimakan Desert as the central points, the sandstorms'active period in the southern regions is earlier than that in the southern, and eastern earlier than western, while more frequent in the southern than in the northern, western than eastern.2,The frequency of sandstorms in the gale zones in Xinjiang basically presented a descending tendency, which differed from the universal law we all know concerning sandstorms, the systematic sandstorms is comparably more while the local ones is quite little.3,Considered the different synoptic situations and dominant systems, the influencing systems for sandstorms in the southern Xinjiang can be categorized into the tramp-over-hill type, the Parity Superposed type and the front heat low developing type; while that in the northern Xinjiang can be divided into the Aral Sea ridge type, the Xinjiang high ridge type, the Siberia vortex type and the Ural ridge-type.4,The distribution style that a pair of horizontal positive and negative vorticity center exists with a positive vorticity and upward airflow in the lower level is quite advantageous for the development of sandstorms.5,The value of horizontal visibility by FD12 is double of eyes and with probability excursion bias for sandstorms with different grades. With subsiding of the sandstorm grade, there is a reduction in the value of average error between FD12 and eyes and the value of average absolute and average square error is 235.7m, while the RMES is 338.3m, which is big enough to change the grade of sandstorms.6,The sand flux consists well with the observed 2m wind speed. With the same wind speed conditions, the increasing range of sand flux in Ruoqiang is largest, followed with that in Cele, Tazhong is the third biggest one, while Xiaotang is the least. 7,The filtering function of wind power could cause different distribution situations of sand dust with different size in an identical desert region. In the source area of the Prevailing wind direction; the sand with big grain is more. In sandstorm weather processes, the sand source of Xiaotang Tansition zone is rich with both localized and importing sand sources, while the latter one is quite rare in tazhong. The mean grain size is minimum in Xiaotang, followed with Tazhong, and the rest ones are Kumtag Desert, Kubuqi Desert, Tengger Desert, Maowusu Sandland and Badain Jaran Desert in sequence.8,The selected numerical model for sandstorm simulation performed well in simulating the wind field in heavy sandstorms, which is better in the northern and eastern Xinjiang than that in the Southern Xinjiang. The time point for wind direction transition can be precisely simulated. A big error existed between the simulated results and the truth, and the area with missing prediction in the entire Xinjiang is large, especially in the northern and eastern Xinjiang. |
PDF Full Text Request