分层气流条件下地形降水的二维理想数值试验

利用WRF v3.5中尺度数值模式,在条件不稳定层结下,针对分层气流(基本气流风速和大气湿浮力频率呈二层均匀分布)过山时,地形对降水的影响进行了多组二维理想数值试验,以研究不同高度、尺度山脉和不同方向基本气流对降水形态和分布的影响。模拟结果表明,地形重力波触发对流是地形降水的主要机制之一,地形波的特征(波长、振幅)和传播均受到地形和基本气流的影响,其中,强基本气流流经高而陡峭的山脉时,更容易在其背风坡捕捉到重力波,地形降水呈现多种模态,反之亦然;当改变基本气流与山脉交角时,主要通过影响地形强迫抬升速度、基流对波动稳定性发展来进一步影响地形降水的强度和分布。

Two-dimensional idealized numerical experiments on the orographic rainfall with a stratified flow over mountain

By using Weather Research and Forecast model (WRF v.3.5), a series of two-dimensional numerical experiments were carried out under the conditionally unstable stratification to investigate the effect of different height, wide terrain and basic air currents of different directions on the rainfall mode and distribution, when the stratified air currents (uniform distribution of the two layer currents with different wind velocity and wet buoyancy frequency) flow over a terrain. Results show that the terrain gravity wave is the main mechanism to trigger the convection, and the features (amplitude and wavelength) and propagation of the terrain gravity wave are affected by the terrain and environmental flow. When the strong air currents flow over the high and steep mountain, it is easier to recognize the gravity wave located in the lee side of mountain, and a number of types of precipitation modes can be detected, or vice versa. The strength and distribution of rainfall depend on the angle between air currents and mountains because of changes in forced uplift rate and wave stability.