山地绿洲边界层特征的数值模拟

使用美国NCAR新版MM5V35非静力平衡模式, 采用三重嵌套的降尺度方法, 通过设计理想的地形和山地绿洲, 模拟研究了山地绿洲环流及边界层特征。山地绿洲的地面感热通量和潜热通量与周围沙漠差异较大, 对形成沙漠绿洲环流有明显贡献。在无山地绿洲的情况下, 地形仅对感热通量有影响, 对潜热通量影响不大。山地绿洲可以使绿洲上空的干冷气流通过下沉气流向下层输送, 在山地绿洲上空形成下沉干冷气流的边界层特征, 它可以抑制由地形形成的向上输送的暖湿气流, 改变地形形成的边界层特征。地形引起的环流是低层复合, 高空辐散。绿洲引起的环流是低空辐散, 高空复合。两种环流呈完全相反的情况。山地绿洲的气候效应可以抑制山地地形的气候效应。

Simulation of the Boundary Layer Characteristics over Oasis Mountaintop

The nonhydrostatic mesoscale atmospheric model MM5 version 3.5 of National Center of Atmospheric Research (NCAR) was used to simulate the local circulation and boundary layer characteristics over an ideal cone mountain. The numerical experiment was done through multiple nesting under two conditions: one is E_(oasis), there is a cone oasis existing atop the hill peak; the other is E_(nooasis), there is no oasis in the research region. The sensitive heat flux and latent heat flux differ much between the mountain atop oasis and surroundings. It plays an obvious role in forcing oasis-desert local thermal circulation. The comparing results show that if there is no oasis on the mountain, the terrain height that affects the sensitive heat flux only, and it does not matter latent heat flux. In E_(oasis), the existing of oasis atop the hill made the cold air over oasis sink with the downward movement, it could restrain the upward movement of warm and moist air caused by the terrain height. Horizontal circulation due to elevation shows convergence at the lower layer; and divergence at the higher layer over ground surface when there is no oasis, while on the contrary it is convergence at the higher layer, and divergence at the lower layer over ground surface when the oasis existing. The climatic effect of mountain atop oasis could restrain the upward movement led by the terrain height.