本研究以中央氣象署於預報作業使用之對流監測平台系統(System for Convection Analysis and Nowcasting, SCAN)提供的歷史對流胞及冰雹預警資訊為基礎，結合由民眾或新聞媒體所記錄下來的歷史冰雹目擊事件，針對臺灣近年夏季冰雹的即時預警狀況進行統整評估。分析資料方面，為能涵蓋臺灣南北地區之事件，故分別選用五分山雷達、七股雷達作為北部與南部地區的資料來源。統計結果顯示，臺灣夏季冰雹多發生於弱綜觀天氣條件的下午時段，且實際目擊的冰雹尺寸平均值小於現行預警門檻。冰雹相應對流胞的持續時間比一般夏季對流更長，其中又以較低海拔的七股雷達訊號更完整。然而，更高的雷達掃描時間解析度，使五分山雷達的預警表現明顯更好。整體而言，過去SCAN系統於臺灣冰雹事件發生前可提供的預警時間多在15分鐘以內，核心問題則包含(一)部分目擊事件未成功預警以及(二)現有系統假警報過多二者。本研究針對上述情況，分別提供(一)以冰雹目擊個案特徵統計結果下修預警門檻與(二)以臺灣探空資料修正SCAN系統背景預設之環境0℃、-20℃高度等改善建議。

This study is based on the historical storm cell and hail warning information provided by the System for Convection Analysis and Nowcasting (SCAN), which is utilized by the Central Weather Bureau (CWB) for operational forecasting. By combining hail records from recent years as reported in the news, the real-time early warning capabilities for Taiwan's summer hail can be integrated and improved. In terms of the analysis data, Wu-Fan San (RCWF) and Chi-Gu (RCCG) were selected as radar data sources to cover events in the northern and southern regions, respectively. The results indicate that most of the events occur in the afternoon during weak synoptic weather conditions, and the size of witnessed hail is mostly below the warning threshold. Hailstorms have a longer duration compared to general summer storm cells, and the RCCG at lower altitudes provides a more complete signal. However, the higher time resolution of the radar scan gives RCWF a significantly better early warning performance. In summary, SCAN can provide a lead time of approximately 15 minutes for hail warnings, but two major issues are identified: (1) some hail events were not detected by the SCAN system, and (2) there are too many false alarms. This research proposes two solutions: (1) lowering the warning threshold based on the statistical analysis of hail reports, and (2) correcting the default value of the SCAN system using sounding data from Taiwan to address these problems.