2022年TAHOPE期間兩場梅雨鋒面個案之比較：探討造成降水特徵差異的物理機制

Abstract

在2022年5月25日至8月10日進行的臺灣區域豪雨觀測與預報實驗(Taiwan-Area Heavy rain Observation and Prediction Experiment, TAHOPE)中，本研究選取了兩道梅雨鋒面個案進行分析，分別對應第一次特別觀測期(Special Observation Period 1, SOP1)與第三次密集觀測期(Intensive Observation Period 3, IOP3)。儘管於5月25日(SOP1)與6月6日(IOP3)的0700-1900 UTC期間，這兩道梅雨鋒面在臺灣海峽中北部之975 hPa等壓面上具有相當接近的平均位置，但SOP1個案在北臺灣(桃園以北)地區產生的總降水量卻接近IOP3個案的三倍，呈現非常顯著的差異，本研究旨在探討造成此降水差異的可能因素與物理機制。

分析結果顯示，儘管IOP3個案的鋒面斜率、鋒面強度及綜觀尺度的運動學特徵相較於SOP1個案而言均明顯偏強，但SOP1個案具備更有利的熱力條件及中小尺度運動場結構(如：持續性的低層輻合帶，可不斷激發新對流胞)，並伴隨著較顯著的碰撞合併過程、較高的低層液態水含量與可能較高的雲微物理尺度降水效率，這些因素共同促使SOP1個案在北臺灣地區產生明顯高於IOP3個案的總累積雨量，因此鋒面過境時所伴隨的降水多寡可能並非單純由其結構與強度所決定，而是環境水氣含量、中小尺度過程與雲微物理過程綜合作用之下的結果。

During the Taiwan-Area Heavy rain Observation and Prediction Experiment (TAHOPE) conducted from 25 May to 10 August 2022, two Meiyu front cases were selected for investigation in this study, corresponding to Special Observation Period 1 (SOP1) and Intensive Observation Period 3 (IOP3), respectively.

Although the two Meiyu fronts at 975 hPa were similarly positioned over the central to northern Taiwan Strait between 0700 UTC and 1900 UTC on 25 May (the SOP1 case) and 6 June (the IOP3 case), the rainfall totals observed over northern Taiwan (over and north of Taoyuan) in the SOP1 case were nearly three times as much as those in the IOP3 case, showing a highly significant difference. This study aimed to uncover the possible controlling factors and physical mechanisms responsible for this contrast.

Our analysis indicated that although the IOP3 case exhibited a noticeably steeper frontal slope, greater frontal intensity, and stronger synoptic-scale kinematic features, the SOP1 case possessed more favorable thermodynamic conditions and mesoscale-to-convective-scale kinematic structures (e.g., persistent low-level convergence zones repeatedly initiating new convection), along with more pronounced collision-coalescence, higher low-level liquid water content, and potentially greater cloud-microphysics precipitation efficiency. These factors collectively led to substantially higher accumulated rainfall over northern Taiwan in the SOP1 case than in the IOP3 case, suggesting that the amount of precipitation during the frontal passages may not be solely determined by the structure and intensity of the front, but rather by the combined effects of environmental moisture and both mesoscale-to-convective-scale and microphysical processes.