Spatial inhomogeneity of synoptic-induced precipitation in a region of steep topographic relief

The topography plays an essential role in initiation and development on precipitating clouds, therefore has a profound effect on the ultimate spatial distributions of precipitation. This study investigates the fine-scale characteristics of synoptic-induced precipitation over Southwest China, a region characterized by a sequence of steep mountains aligned roughly north-south. Based on the convection-permitting simulation for a realistic case, the results show that the model successfully reproduces the observed precipitation, which is induced by a low-level shear line over Southwest China. The spatial distribution of precipitation over three small-scale mountains (named as M1, M2 and M3 from east to west) exhibits distinct inhomogeneity. The precipitation is notably enhanced on the leeward slope of M1, the high-altitude area of M2, as well as the windward slope of M3, which is driven by the steep topography relief, through exerting dominant influences on the local atmospheric circulations. Further results of the high-resolution experiment shows that the thermal instabilities and topographic lifting over the high-altitude ridges are beneficial to the enhanced precipitation. In addition, the small-scale vortex generated on the leeward slope of M1, as well as the convergence zones established over M2 and the windward slope of M3, dynamically contribute to the intensification of precipitation over these three small-scale mountains. In sensitivity simulation with the terrain height of M2 reduced to the comparable height as the other two mountains, the enhanced precipitation decreases significantly over M2. The dynamic blocking effect of M2 on airflow is weakened, leading to the maximum precipitation over M3 moving to its mountaintop.