宜蘭地區梅雨季鋒後大豪雨之中尺度特徵探討

Characteristics of the Mesoscale Features of an Extremely Heavy Rainfall Event Occurring after the Frontal Passage during Mei-yu Season in Yi-Lan

陳泰然(George Tai-Jen Chen) ； 王子軒(Tzy-Shyuan Wang) ； 黃心怡(Shin-Yi Huang)

《大氣科學》 40卷4期 (2012/12) Pp. 407-426

摘要

本文利用中央氣象局高時空解析度之自動雨量站觀測資料及ECMWF1.125°×1.125°經緯度網格資料，針對2001年5月28日在宜蘭地區發生且出現多測站大豪雨之梅雨季鋒後型個案，進行中尺度分析，探討鋒後東北季風影響下，地形影響之局部環流日夜變化及其在該地區降雨時空分布所扮演之角色，以進一步了解東部地區梅雨季鋒後豪雨發生機制。結果顯示，除了有利對流發展之綜觀環境條件外，局部環流亦扮演重要角色。蘭陽平原與鄰近地區之地形複雜，西北邊有雪山山脈而南邊有中央山脈，蘭陽溪將兩個主要山脈分開，使梅雨季大尺度環境氣流與熱力驅動之局部環流在此區有活躍之交互作用，在該區降雨時空分布上扮演重要角色。中尺度分析結果顯示，白天（1200-1800 LST）為各地豪雨出現時段，由海上而來之東風氣流與局部環流上坡風/海風結合並受地形舉升激發對流發展。夜晚（2100-2400 LST）位於山區下坡風影響之古魯測站最大降雨強度，主要乃因鋒面北退使海上東風氣流增強，且受下坡風與地形舉升效應增強而來。此外，結果亦顯示蘭陽溪上游兩側山坡之局部環流，均非單純僅受該山脈熱力驅動，亦可受鄰近較強局部環流驅動使原有之熱力環流轉向；礁溪以南之蘭陽平原的局部環流，可因鋒後東北季風與地形交互作用，使海風延後發展。

關鍵字

梅雨季 ； 鋒後大豪雨 ； 局部環流 ； 地形舉升

並列摘要

Observational data with high spatial and temporal resolution from the Central Weather Bureau and ECMWF 1.125°×1.125° grid data were used to study extremely heavy rain event occurring at multiple stations in Yi-Lan for the post-frontal case during the Mei-yu season on May 28, 2001. Mesoscale analysis was carried out to investigate the diurnal variation of the local circulation impacted by the topography and its role in the time-space distribution of the precipitation in this region under the influence of the post-frontal northeast monsoon. The main purpose of this study is to better understand the mechanism of post-frontal extremely heavy rainfall during the Mei-yu season in the eastern Taiwan.The results showed that in addition to the synoptic environment conditions favorable for the development of the convection, the local circulation also played an important role. The topography of Lan-Yang Plain and its vicinity was very complicate - the Snow Mountain Range being in the northwest and the Central Mountain Range in the southwest, which were separated by the Lan-Yang River. Large-scale environmental flow in the Mei-yu season and local circulation driven by diurnal heating/cooling had active interactions, thus playing an important role on the time-space distribution of the precipitation in this region.The mesoscale analysis showed that the daytime (1200-1800 LST) was the time period of heavy rainfall occurred in each place. The airflow of east wind from the sea combined with the upslope wind/sea breeze of the local circulation and was lifted by topography, thus activating the development of convection. In the night (2100-2400 LST) the maximum intensity of precipitation under the influence of downslope wind in Gu-Lu station was mainly due to both the intensification of the airflow of the east wind over the sea caused by the northward retreat of the front and the downslope wind and topographical lifting effect.Besides, the results also showed that the local circulation of both mountainsides in the upriver region of the Lan-Yang River was not driven solely by the thermal forcing of the individual mountain range. It could also be driven by vicinal stronger local circulation to change the direction of original thermal circulation. Because of the interaction between the post-frontal northeast monsoon wind and the topography, the local circulation of the Lan-Yang Plain to the south of Jiao-Si could postpone the development of the sea breeze.

並列關鍵字

Mei-yu Season ； Post-frontal Extremely Heavy Rainfall ； Local Circulation ； Topographical Liftinga