摘要 本研究主要探討2017年6月2日至3日的梅雨鋒面個案。此個案鋒面影響台灣約2天，並為台灣帶來劇烈降雨。鋒面在6月2日凌晨至清晨近乎停滯在台灣北方26°N附近，6月2日上午快速移動至嘉義地區又停滯。在此期間高層配置幾乎不變，因此影響低層鋒面移動的物理機制值得討論。在本篇研究中，主要利用渦度方程及鋒生方程，利用ERA-Interim再分析資料對於925 hPa等壓面之鋒面移動及發展進行討論。由相對渦度最大值定義鋒面位置。鋒生方程使用相當位溫水平梯度大小為判斷鋒生之物理量。根據渦度趨勢方程及鋒生方程的分析，分項探討台灣海峽鋒面移動趨勢的主要影響因子， 鋒面的移動可分為兩段時期。第一個停滯期(6月2日00-06 Z)，由於鋒面冷/暖側，有強勁東北/西南風，及西南風帶來之水氣，有利鋒面北側大陸沿岸鋒生，加上台灣地形阻擋，使鋒面被限制在台灣北方海面。在第二個停滯期(6月2日12 Z-18 Z)，鋒面停滯在24°N，此時由於大陸東南方低壓環流的發展，西南風逐漸增強，使得冷空氣不易向南推進，鋒面因此停滯。渦度方程與鋒生方程診斷結果顯示，當鋒面在台灣海峽移動時，水平平流項為主要貢獻項，當鋒面停滯時水平平流貢獻量小，同時有較明顯的鋒生發展趨勢，在鋒面接近台灣時渦度變化及鋒生作用呈現區域差異性，使得鋒面帶上之鋒生趨勢不同步，受地形阻擋之地形噴流在鋒面兩側發展，同時加強鋒面附近之梯度加強鋒生，加上地形阻擋，使得第一個停滯期鋒面移速緩慢。而當鋒面往南移動，由於鋒面北方冷空氣層變薄，加上受到大陸東南低壓環流影響，西南風增強，鋒面之風切特性逐漸變成低壓環流之西南風主導，此時渦度趨勢往北發展且與風場之輻合區重疊，另一方面，鋒生趨勢減弱許多。顯示此時的鋒面特性逐漸減弱，風切特性僅存在於更低層大氣，冷空氣持續往南移動但梯度減弱。;Abstract This study focuses on the Mei-Yu front movement during 2-3 June, 2017. In this case, the front affected Taiwan about 2 days, and cause heavy rainfall. The front was almost stationary nearly 26°N in the morning of June 2, then moved quickly to 24 °N in the afternoon of June 2, and then stopped again. The synoptic environment of up-level is almost unchanged during June 2-3, so the movement and development of the low-level front is worth discussing. The vorticity equation and frontogenesis function have been applied to analysis the tendency of front movement and discuss which term contribute most. These two equations both show when the front moves, the horizontal advection term contribute the most. When the front moves slowly the horizontal advection term contribute less and the local tendency of frontogenesis tend to develop along the frontal zone. During the first time period, the front move to the north coast area of Taiwan and then stopped nearly 26°N (0000-0600 UTC 2 June), and the wind at the cold/warm side near front was the strongest in this case. The strong wind shear and moisture flux from southwest flow provide favorable conditions for convection development near the front. The local tendency of frontogenesis developing on the coast north area of front limited the front move south. In the second time period (1200 UTC 2 June-0000 UTC 3 June), the front was stationary nearby 24°N. The southwesterly wind gradually increased in accompanied with the developing low pressure, and resulted in moisture flus increased. The local tendency of frontogenesis developed near front and the front wasn’t continuously move south. And the moisture transform from southwest flow is a factor needed to be noticed during a slow-moving Mei-Yu front affecting Taiwan.
