| Popis: |
In this study, a set of idealized three-dimensional numerical simulations with mesoscale models are designed to study the impacts of vertical wind shear upon the topographically convective precipitation based on the mesoscale features of topography in the middle-lower reaches of the Yangtze River and the main characteristics of vertical wind shear during the rainstorm processes. It is found that the dry airstream will split, flow around and flow upward when encountering a barrier under a condition of Fr ≈ 1. The topographically generated gravity waves propagate in horizontal and vertical directions with different wave amplitude and vertical velocity in the upslope, the lee, the upstream and downstream of the barrier, respectively. Under moist conditionally unstable atmosphere with Fr > 1, there are mainly three convective precipitation modes, that is, a quasi-stationary convective precipitation in the upslope and the leeside mountain foot, respectively, and a moving convective precipitation in the downstream. It is also found that the circular vertical wind shear (wind direction changing with height) not only influences the moving direction of topographical convective precipitation in the downstream, but also affects the intensity and spatial distribution of heavy convective precipitation in the upslope and the leeside mountain foot. The linear vertical wind shear (wind direction not changing with height) mainly impacts the intensity and moving speed of topographical convective precipitation. The topographical convective precipitation systems propagate to the right (left) when the wind veering (backing) with height. The vertical wind shear impacts the topographical convective precipitation distribution by a way of altering the structure and propagation of topographical gravity waves, and changs the formation, moving direction and speed of convective systems, where the vertical wind shear in the middle-lower level exerts an important influence. |
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