重力流冷锋及其受地形的影响

GRAVITY CURRENT FRONTS AND THEIR INTERACTION WITH OROGRAPHY

中文关键词:  重力流  冷锋  地形影响

英文关键词:Gracity-current  Cold front  Orographic influence

中文摘要:

      建立了一个二维非静力平衡模式,通过坐标变换的方法使得模式低层有较高的分辨率.对重力流的模拟结果显示;本模式模拟出的重力流冷锋主要特征,如抬高的头部、头部较强的上升运动以及等位温线密集带与实际大气观测很一致.此外,模式还成功地模拟出了重力流头部后面底层的高速潜流层.应用模拟结果与理论结果对重力流的移动速度进行了对比分析.当考虑地形时,重力流在山前受阻,其头部比不考虑地形时高,且产生了向上游传播的“涌浪”;重力流过山后其头部降低,位温梯度减弱,头部后面的水平速度减小.此外,还对非静力平衡与静力平衡条件下重力流的差异进行了分析讨论.

英文摘要:

      A two-dimensional,nonhydrostatic model with a vertical transformed coordinate to improve the resolution in the lower level is designed to study gravety-current vividly.The results indicated that the nonhydrostatic model provided a successful simulation of the gracity-current,especially in the neutrally stable case.The simulated high head with large vertical velocity of gravity-current, the large velocity of underrun and the dense isentropes in the front are closely consistent with those observed.The speed of gravitycurrent in the model is compared with analytical solution (Benjamin.1968).When the orography is included in the model. gravity-current is greatly retarded on the upwind side of the mountain.Conssquently, the gravity-current head in the orography case is much higher than the no-mountain case.An additional bore is triggered and propagates to the upstream direction.As the gravity-current passes over the mountain,its head becomes lower and the gradient of isentropes in front becomes weaken.The differences between hydrostatic and nonhydrostatic simulations are also analyzed.