A series of convection-permitting numerical experiments using the Weather Research and Forecasting Model with different model configurations are performed to investigate physical mechanisms governing convection initiation (CI) at the coast of South China (SC) during a warm-sector heavy rainfall event occurred before the South China Sea (SCS) monsoon onset. The simulation results are more sensitive to initial state from the different reanalysis products than the microphysics schemes, horizontal resolutions, initialization time, and lateral boundary conditions with the variation examined. It is found that the speeds of easterly to southeasterly winds in the boundary layer (BL) over northern SCS determine the strength of horizontal convergence of the warm and moist airflows arriving at the coast. The mid-tropospheric divergence over the west coastal areas of SC and its southwest upstream impact vertical motion of the mid-to-lower tropospheric southwesterly airflows when approaching the coast. Differences in such features of upstream airflows in the experiments lead to distinct temporal evolutions of BL dynamic lifting and temperature stratification in the mid-to-lower levels at the CI location, thus the level of free convection and convective available potential energy. The modeling evidence presented shows that the synoptic dynamic and thermodynamic characteristics of the upstream airflows in BL and mid-to-lower troposphere, with local modulation by the coastal mountains, play important roles in determining the time and location of CI, and the distribution and amount of rainfall. Studies on more cases are needed to gain more general and robust conclusions about physical mechanism governing the warm-sector coastal CI.

中文翻译：

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季风爆发前华南沿海暖区强降雨事件对对流启动的天气影响：数值模拟研究

使用天气研究和预报模型和不同模型配置进行了一系列允许对流数值实验，以研究在之前发生的暖区强降雨事件期间控制华南沿海 (SC) 对流启动 (CI) 的物理机制。南海 (SCS) 季风爆发。与微物理方案、水平分辨率、初始化时间和横向边界条件相比，模拟结果对不同再分析产品的初始状态更加敏感。结果表明，南海北部边界层（BL）的东风到东南风的速度决定了到达海岸的暖湿气流的水平辐合强度。南半球西海岸及其西南上游的对流层中辐散影响对流层中低层西南气流接近海岸时的垂直运动。实验中上游气流的这些特征的差异导致了 CI 位置中低层 BL 动态提升和温度分层的明显时间演变，从而导致自由对流和对流可用势能的水平。所提供的建模证据表明，受沿海山脉的局部调制，BL 和对流层中低层上游气流的天气动力学和热力学特征在确定 CI 的时间和位置以及分布和分布方面起着重要作用。降雨量。