Improved Wind Environment And Sand Activity Assessment Metho

Aeolian research is mainly concerned with aeolian activity on the surface of planets.Many developing countries in arid or semiarid areas are caught in a dilemma between the threat of sandy desertification and the development of wind energy.Sand-driving winds are momentous for both aeolian research and generating wind energy.Howeve,the estimation for the probability of sand-driving winds has been rarely studied.The ability of the two-parameter Weibull probability distribution function to estimate high wind velocities is questioned and parameters appear to have no practical significance.Sand transport rate is used only for the evaluation of short-term aeolian activities.Drift potential(DP)is an accessible index of evaluating potential sand transport volume by sand-driving winds,but the relationship among annual sand transport volume,DP and wind energy has been rarely studied.Sand-driving winds can be divided into gentle winds and strong winds,but it is hard to distinguish them in practice,and their effects on dune morphology cannot be reflected by DP.This study took the evaluation of the wind velocity probability of sand-driving winds as the starting point.An extended form of two-parameter Weibull probability distribution function based on Lettau-and-Lettau's sand transport rate formula was constructed to improve the evaluation of the probability of sand-driving winds.Based on the multi-year meteorological data from 10 meteorological stations around the Badain Jaran Sand Sea,the wind regime,wind resources and aeolian activities around the sand sea were accurately described and evaluated by using the improved methods(mathematical model),combined with statistical analyses and correlation analyses.The main conclusions were drawn as follows:1.The evaluation of the wind velocity probability of sand-driving winds can be improvedby the constructed function via the Lettau-and-Lettau's sand transport rate formula and the two-parameter Weibull probability distribution function.The modified the Lettau-and-Lettau's sand transport rate formula can accurately evaluate the annual sand transport volume/rate calculated according to sand-driving winds.On these bases,indices such as mean wind velocity and wind power density can be accurately evaluated.According to the distribution of annual sand transport volume,gentle winds and strong winds can be easily and quantitatively distinguished by the wind velocity corresponding to the annual maximum sand transport rate.These methods are simple and applicable to arid or semiarid areas worldwide.2.On the hourly and monthly scales,the scale parameter of the two-parameter Weibull probability distribution function at the height of 10 m can represent the influence of the convection caused by solar radiation on wind velocities.In arid or semiarid regions of the Northern Hemisphere,the shape parameter can characterize the atmospheric stability affected by both the air temperature and the underlying surface properties.This indicates that both the air temperature and the underlying surface properties have influence on the probability distribution of wind velocities.3.The dimensional analysis showed that the actual physical significance of annual mean sand transport rate and annual mean sand transport volume is the mean wind power density lost by sand-driving winds in one year due to sand entrainment and the work on sand entrainment done by sand-driving winds on a unit section area(1m2)in one year,respectively.Aeolian activities have little influence on the wind power density of sand-driving winds at a height of 10 m.The annual mean sand transport volume for each meteorological station can consume 1.36×102-32.30×102 J of wind energy on per unit section area(1 m2).The unit of drift potential is kn3,and the actual physical significance of drift potential is the wind power density.Theoretically,the annual mean drift potential is numerically proportional to the annual wind power density of sand-driving winds and the annual mean sand transport volume,respectively.The proportionality coefficient is affected by the wind velocity probability distribution of sand-driving winds.Hence,the mean drift potential in a period of time cannot accurately represent the mean sand transport rate and sand transport volume in this period.The ratio of the annual maximum drift potential to the annual mean drift potential for each meteorological station was 12.3%on average,and the corresponding wind velocity had little variations and was close to a constant value(10.09 m·s-1 on average).4.On a flat sandy underlying surface,strong winds control the deposition,while gentle winds dominate the sand transport downwinds,namely the erosion.At the wind velocity corresponding to the annual maximum sand transport rate,aeolian activities on a sandy underlying surface reach the erosion-deposition balance.The ratio of the annual maximum sand transport rate to the annual mean sand transport rate for each meteorological station was 11.7%on average.The wind velocity corresponding to the annual maximum sand transport rate is related to the wind velocity probability distribution of sand-driving winds,but the variation was little and close to a constant value(10.89 m·s-1 on average).These indicated that the wind velocity probability distribution of sand-driving winds was not the dominant factor affecting this wind velocity.These results provide a basis for the wind energy development in arid or semiarid areas,improve the understanding of aeolian activities,one of the surface processes,and have a certain implication for sand control engineering.