Numerical study on mountain waves generated by a two-dimensional mountain and their effect on the transport of Yellow Sand

We have studied the effect of ground topography, focusing on mountain waves, on the transport of Yellow Sand by two-dimensional numerical simulation. An advection-diffusion equation for scalar concentration is solved to simulate the transport of Yellow Sand. Two different models are employed: the first is a one-layer model in which the density gradient is constant in the entire domain, and the other is a two-layer model in which the density gradient changes at an altitude of I I km. In the both models stream lines at high altitude descend greatly toward the ground along the lee side of the mountain as the atmospheric stability increases. However, in the two-layer model, trapped mountain waves become stronger than those in the one-layer model, and rotors are also generated on the ground. These become stronger for larger mountain width, and the scalar concentration rapidly diffuses there. It is found that the ground scalar concentrations for the two-layer model are generally much larger, especially in the rotors, compared with those in the one-layer model.