每年5月底至6月，臺灣經常受到滯留的梅雨鋒面影響，有利於大雨事件發生。臺灣區域豪雨觀測與預報實驗（TAHOPE）於2022年5月至8月期間進行，旨在提升對極端降雨事件的瞭解與預報能力。本研究使用快速更新的四維變分分析系統（IBM_VDRAS）探討於TAHOPE第一次密集觀測期間（IOP#1），2022年5月26日造成臺灣中部數小時極端降雨的中尺度對流系統（MCS）。透過同化臺灣西部七部雷達的觀測資料，該系統產生了高時空解析度的分析場，幾乎涵蓋整個MCS事件。當梅雨鋒面位於臺灣北方海面上，伴隨鋒前臺灣中部上空強勁的低層噴流（LLJ）輸送豐沛水氣，促使MCS持續發展與增強。隨著西南氣流減弱與水氣減少，梅雨鋒面逐步南移至臺灣上空，局地條件轉趨不利，導致MCS向南移動並規模縮小。此長時間MCS事件中，對流胞多次在不同但相近的上游位置被觸發，向下游傳播並與先前的對流胞合併，呈現典型的後造型對流特徵。本研究進一步探討影響MCS的多重尺度因素。結果顯示，西南氣流受南部山脈阻擋產生向北的水平氣壓梯度力，驅動低層噴流（LLJ）。此外，北邊的梅雨鋒面與東邊的地形阻擋MCS的移動，使之長時間滯留在中部地區。;From late May to June, Taiwan is frequently affected by the quasi-stationary Mei-Yu front, which provides favorable conditions for torrential rainfall. The Taiwan-Area Heavy Rain Observation and Prediction Experiment (TAHOPE) was conducted from May to August 2022 to enhance the understanding and forecasting of extreme rainfall events in Taiwan. A mesoscale convective system (MCS) was investigated, which produced extreme rainfall over central Taiwan (CT) for several hours on 26 May during Intensive Observation Period #1 (IOP#1) of the TAHOPE, using a rapid-update 4DVar analysis system (IBM_VDRAS). High-spatiotemporal analysis fields were generated by assimilating observed data from seven radars across western Taiwan, covering the entire MCS event. When the Mei-Yu front was positioned to the north and a strong southwesterly low-level jet (LLJ) over CT transported abundant moisture, it was supportive for the widespread convective development and sustaining the MCS. As the southwesterly flow weakened with reduced moisture, the Mei-Yu front began moving southward and the local conditions became unfavorable, thereby shifting the MCS southward and causing it to become smaller in scale. Several convective cells were repeatedly triggered at nearby upstream locations, propagated downstream over the same area, and merged with preceding ones downstream, suggesting a back-building system. Multi-scale factors influencing the MCS are further examined. Our results reveal that the LLJ was driven by a local northward horizontal pressure gradient force generated as the southwesterly flow impinged upon the southern mountain range. Meanwhile, the MCS was blocked by both the Mei-Yu front to the north and the mountainous terrain to the east, causing it to remain quasi-stationary over CT for an extended period.
