Abstract: Field experiments show that the airflow strength varies with wind directions on the surface of simple linear dunes.The airflow directions are similar with that Tsoar(1983) suggested,but the airflow shows some characteristics of the secondary flow in the lee side of the dune.The sand flux at the stoss slope foot is much higher than that at the lee side foot of dunes when the airflow directions are perpendicular with the dune trend.In comparison there are slight divergences of sand flux on both sides of dunes when the airflow directions are deflective with the dune trend.It is one of the main mechanisms for linear dunes maintaining their morphology in the dynamic processes.The sand flux within sand-flowing boundary layer has not near relation with wind velocity because of the variations of wind directions and landforms.The particle sizes of sands transported by wind have some divergences with that of the underlaying materials.The mean grain size of the sands being transported is smaller than that of the underlaying materials under the controlling of the medium-low wind activities.In generally,the sand transportation on the surfaces of dunes is a stochastic process.Under the controlling of two dominant wind directions the simple linear dunes are accumulated and elongated.The sand-drifting winds in east direction are responsible for much of sand transportation than that in west direction do,so there are lateral migration for the simple linear dunes.The lateral migration of the simple linear dunes,time scale of the dune formation,and the other factors result in the development of the compound/complex linear dunes.

Key words: linear dune, morphodynamic process, Taklimakan Desert