| Taklimakan Desert,located in the Tarim Basin,is the second largest flow desert in the world with the specificity of the extreme drought climate,the large area of moving dunes and the complex types of dunes.The desert posing a serious threat to the agricultural and pastoral production and transportation with the southward flowing of it in the northern margin of Qinghai-Tibet plateau.Wind is the dynamic source for desert flows,preventing the source of power is essential to prevent the expansion of desert flows and the further development of desertification.Studying the wind dynamic characteristics of the desert and the expansion trend of the desert under the wind power environment are of great significance for the formulation of major strategic measures such as preventing desert flow and curbing desertification development.The rates of sand transport by wind plays the most important role in its aeolian surface processes.The “Fryberger Method” provides a useful and accessible way of evaluating the relative rates of sand transport(drift potential,DP)from measurements of wind data.With this method,a number of different estimations of DP about Taklimakan Desert had been proposed for the past decades.In this paper,we recalculated the DPs using the definition equation in which the arguments are the every measurements of wind velocity rather than the calculation model in which the arguments replaced by the midpoint of each velocity category,the aim was to clarify the cognition of the wind-energy environments in the sand sea.The calculations in the paper showed that the DP values of 22 meteorological stations ranged from 0.7VU to33.4 VU in 2007,thus the wind regimes should be classified into the Low-energy wind environments by using of the “Fryberger classification”.Based on the analysis ofresultant drift potential(RDP),involving the RDP similarity(Cluster Analysis of Inner Product Similarity)and the region adjacency of a RDP type,the RDPs had been classified into five types,those were(1)Korla type in eastern Taklimakan,the RDPs showing W-S directions(abbr.W-S type);(2)Xinhe type in the northern region,as S type;(3)Cele type in the western region,as E type;(4)Minfeng type in the southern region,as E-NE type,and(5)Special type,the RDPs at three stations were obviously different from their adjacent regions.The maximum average DP was caused by the NW wind regime,which happened in Cele type,and the lowest ratio of the directional variability of the winds(RDP/DP)was induced by the NE wind regime,which happened in Korla type.As a contrast,in the convergence zone between the NW and the NE wind regimes,the DPs was relative lower(Xinhe type with the minimum of DP),and the ratio of RDP/DP was higher(Minfeng type with the multi-direction effective winds)than the above two types.The cumulative DP from spring to summer in 2007 had reached to81.29%~98.79% of the annual DP,only in May being 22.7% to 56.8%;whereas in winter except February,almost no effective winds had occurred over Taklimakan.In the southern desert,the positions of the wind convergence zone under the strong wind weather shifted eastwards,compared with the normal weather condition(between of Yutian-Minfeng),of which,more movements eastwards in May(Qiemo-Ruoqiang)than that in February(Minfeng-Qiemo).During the period from 2005 to 2007,the inter-annual variation of RDP showed as ±33% in magnitude and ±9.6° in direction overall the desert;but some specific stations with larger variation of the RDPs,such as±80% in magnitude at Alar and ±24.4° in direction at Kuqa.Only the factor of wind considered,the circulation of DP along the simulated boundary in a specified direction,provides an accessible method of analysing the trend of expansion of the desert.Based on the theory of cubic Bezier curve,simulated the boundary curve of the desert,which a smooth closed curve passing through the meteorological stations around the desert.The direction that perpendicular to the boundary and point outside the desert was the specified direction.Calculated the integral of the component of the DP in this direction along the boundary curve.As a whole,there was a contraction trend based on the circulation in 2007,and average circulation was – 27 191 VU/km.The desert divided into two areas,the north and the south,by the line Kashi to Ruoqiang,there was a strong contraction trend in the whole north,average circulation is –51 565 VU/km,compared with the north,the south wasweak,only –584 VU/km,and showed a somewhat strong expension trend between Yutian and Hetian and the vicinity of Qiemo(about 4 832 VU/km).By all accounts,the desert showed a contraction trend,but expension southward,and mainly in the southwest and southeast of the desert.those were(1)Qiemo-Ruoqiang section is located in the southern of the Korle type;(2)Ruoqiang-Korle section is northern;(3)Korle-Aksu section is located in the southern of the desert,belong to Xinhe type;(4)Aksu-Kashi section is located in the northern of the Cele type;(5)Cele-Yutian section is sourthern;(6)Yutian-Qiemo section is located in the northern of the desert,belong to Minfeng type.Comparison between Korle type and Cele type,the sectional circulation of two sections in the northern are larger than two southern,because the angle between DP and northern section is bigger,and the DP is greater.Comparison between Korle-Aksu section and Yutian-Qiemo section,located in the intersection of winds between the north-east wind and the north-west wind,are two low-value areas of DP in the desert.But average circulation of Korle-Aksu section is much lager than Yutian-Qiemo section,due to DP almost vertical to the section in Korle-Aksu,however the angle of Yutian-Qiemo is little.The monthly circulation of DP in 2007 had a huge discrepancy,only in May being30%,which average circulation of DP was –10 800 VU/km.In May,showed the same North-South discrepancy as the circulation in 2007.The expansion area extends westward to the Pishan section from Yutian-Hetian,while the vicinity of Qiemo changed from expansion trend to contraction trend in Qiemo-Ruoqiang section.Unlike in May,the desert expansion trend in February showed an east-west difference division between Luntai and Cele.There was almost no change in the northwest,but an obvious contraction trend in the Korle type section in the east of the desert.The circulation of DP of a strong sand-dust storm,which took place from May 7 to10 in 2007,was – 3 403 VU/km(about nine times as much as it in February).During this period,the desert still showed a contraction trend.The area with strong sandstorm activity in the northern part of the desert showed a clear contraction trend,and there was a significant expansion with an average circulation of –100 473 VU/km around Cele in the southern area. |
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