Spatial And Temporal Distribution Characteristics Of Sand Drift Potential In Taklimakan Desert Based On The ‘Fryberger’ Method

Taklimakan Desert is the largest area of China, ranking second in the world of the active desert. Because of the vast area, extreme arid climate and the loose sandy surface of Taklimakan Desert, the activities of blown sand have an important impact on the global material transport and climates. So, many scholars do researches on the intensity of blown sand activity in Taklimakan. Sand drift potential is a useful index for assessing the wind-energy of blown sand, which plays an important role in the formation of aeolian landforms. It is widely used to evaluate the dynamic conditions of the drifting sand activity.The Fryberger method provides a simple and practical model to evaluate the value of drift potential(DP) from measurements of wind velocity. Unfortunately, there is still some doubt about the process of DP calculation, and it would influence the accuracy of DP. Thus, the clarification of some confusion about DP is given with the example calculations of using Fryberger method at the first. Whereas the accuracy of the DP values and its differences between wind velocity-type calculated in Fryberger model are required for each site. Then, the most precise values of DP calculated from the definition-based method are expressed as the reference values(DP*), the annual DPs at the five sites and their components corresponding to each wind class are estimated to compare the different deviations of DP from the DP* distinguished by local sites and wind velocity classes. After that, using the Fryberger method, the spatial and temporal distribution characteristics of sand activity in the desert is to be studied.On the basis of the varied wind data recorded hourly from twenty-one sites in Taklimakan Desert from 2005 to 2007 and Cele site in 2007 to 2013, firstly, the deviations of Fryberger model are estimated. Secondly, using the definition-based method calculated the DP, resultant drift potential(RDP), resultant drift direction(RDD) and the index of the effective wind directional variability(r). The results show:(1) For the types of wind velocity recorded as different time-averaged mean values, it appears that the shorter of the time-interval is, the higher of the wind mean velocity becomes. Because the impact of wind impulse on sand drift has been improved, by which the evaluated DPs are enlarged relatively.(2) In Fryberger model, the representative velocity value corresponding to each wind class is an important factor that directly influences the accuracy of DP calculations. For the annual DPs in the region, it is only the type of Fryberger’s mid-point values that approach to the smallest deviations among the three types of representative velocities, i.e. mid-point values, modified mid-point values, and arithmetical mean values, and it is selected as the best-fit representative values.(3) The best-fit values of the representative velocity not only vary with wind classes, also vary with locations. Here, with the aggregation of best-fit values for each wind class corresponding to each site, the DP calculations have been improved obviously.(4) Taklimakan Desert is in low wind energy environment, the wind regime is with bimodal or unimodal. There are two different prevailing wind directions in the desert, the east is in northeast, while the west is in northwest.(5) There is an interannual variation among RDD, RDP and r, the variation of RDD is the most obviously, and the change of r is so small. All of the calculations corresponding to strong and weak wind seasons of a year have a great differences betwwen the regions.(6) Sand activity in May is so strong, for the desert is divided into five parts by the distribution of DP, high value centers or low value centers are located in the boundries between each two parts. In contrast, sand activity in February is weak, even nearly no sand activity in north and the west edge of the desert, large part of the sand drift potential equals to zero.(7) DP calculations of a strong dust event in the east of the desert are larger than the west.For the north to the south, the south’s DP values are much larger, and the center of the desert is stronger than the edges.