Twelve-hour real-time and synchronous measurements of the three-dimensional components of the near-surface turbulence at four heights(8,16,32 and 47 m)during a dust storm are obtained by sonic anemometers for the first time.The experimental results show that(1)the mean vertical velocities at all four heights have considerably positive values during the dust storm,illustrating a strong upward flow near the surface;(2)during the dust storm,the mean vertical velocity is higher at 8 m than at 16 and 32 m,implying that the convection is stronger at 8 m than at the other two heights;and(3)when the longitudinal velocity is a maximum,the mean of the vertical components of wind velocities at 8 m is a minimum and the standard deviation is a maximum,which reveals weaker vertical convection during the period of greatest dust storm intensity,while the turbulence intensity contrarily increases,which may result in more entrainment of surface dust.The analysis results also show that the standard deviations of the longitudinal and vertical velocities increase as the mean inflow velocity increases,but the standard deviation of the lateral velocity is hardly affected by the mean inflow velocity.Based on the calculated skewness and kurtosis of the longitudinal,vertical and lateral velocities every 20 min at different heights,it is seen that all three components obviously fluctuate with height,which further indicates the importance of performing real-time and synchronous measurements at different heights near the surface during a dust storm so as to reveal the three-dimensional turbulence structure accurately.
Windblown sand flux and dune field evolving toward the oasis have been a common ecological and environmental threat confronted by many countries.Meanwhile,it is also a kind of complex dynamical process involving multiple temporal and spatial scales which is still out of accurate description through current field observations.Available models and reliable quantitative simulations are of significant value to predict the spreading rate of desertification and provide an optimal design for sand prevention.This paper presents a 'triple-jump' method to realize quantitative simulations to the formation and evolution of an aeolian dune field from an arbitrary initial configuration.Simulated results achieve a satisfactory agreement with observations qualitatively and quantitatively,which also reveal the characteristics and dynamical behaviors of dunes and dune field.Such a paradigm is of a good level of generality,which provides an exploratory probe into the subject of multi-scale physics.
Xiaojing Zheng a) Key Laboratory of Mechanics on Western Disaster & Environment,Ministry of Education,Lanzhou 730000,China
