The convective systems are major producers of high-impact weather, yet the convective-scale dynamics leading to development of extreme rainstorms on monsoon coasts (South China) are poorly understood. Using the advanced coupled model WRF Chem-MOSAIC, this study reasonably simulates the thermodynamic conditions and inhomogeneous near-surface PM2.5 during the Guangzhou "May 7" record-breaking rainfall event, as well as the dynamical and microphysical features of two extreme hourly rainfall-producing storms with contrasted convective intensities, respectively. Two modes of the storms’ rapid self-organizing development are unraveled based on detailed modeling through applying the air vertical momentum equation.

Storm1 of strong convective intensity develops in an “effective buoyancy dominantly driving mode”, in which a deep layer of inflow air with high convective available potential energy (CAPE) from South China Sea is lifted by a convectively generated shallow cold pool. The upward motion is accelerated by strong effective buoyancy forcing, resulting in intense updrafts that propagate upward through local advection to above the melting level, with some contribution from the dynamic vertical pressure perturbation forcing below 3 km. Under a condition of decreased CAPE in the boundary layer by nocturnal radiative cooling, Storm2 is formed as a convective region merges with a convective cell to the south and develops in a “dynamic and buoyancy jointly driving mode”. The local southerlies below 3 km are strengthened by the convective updrafts and interact with the overturning outflow from the lower-topped Storm2, pushing the inflow upward via the vertical twisting acceleration. Meanwhile, the rear low-level descending air enhances the cold pool and its near-surface northerly, which converges with the strengthened near-storm southerly to form strong horizontal convergences centered at 300 m, pushing the near-surface moist air upward through the vertical extension. The intensified updrafts further enhance the southerly water vapor flux and the condensation latent heating, increasing the effective buoyancy.

极端降水风暴,自组织发展模态,动力结构,华南沿海,区域地球系统模式