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題 名 | 臺灣北部午後對流閃電與綜觀氣流風向之關係=The Relation between Afternoon Convective Lightning and Direction of Prevailing Flow in Northern Taiwan |
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作 者 | 戴志輝; 林得恩; 賴世運; | 書刊名 | 大氣科學 |
卷 期 | 36:3 2008.09[民97.09] |
頁 次 | 頁179-196 |
分類號 | 328.71 |
關鍵詞 | 雲中閃電; 雲間閃電; 雲對地閃電; 整合型閃電偵測系統; TLDS; Intra-cloud discharge; Inter-cloud discharge; Cloud to ground discharge; Total lightning detection system; |
語 文 | 中文(Chinese) |
中文摘要 | 午後對流之生成、移動及演變是中小尺度天氣現象,無論是主觀或模式客觀預報,目前台灣地區都沒有預報度可言。過去研究指出,地形阻擋對盛行氣流的動力效應,除了在背風面造成局部合流之外,相對於地形的風向變化,也會使局部合流的位置改變;而在作業經驗中,午後對流經常出現的位置,也往往與相對於中央山脈的盛行風向相關。本文分析2004至06年間臺灣電力公司「整合型閃電偵測系統(Total Lightning Detection System, TLDS)」的雲中、雲間及雲對地閃電資料,並應用過去研究中被強調的局部動力因素,以探討臺灣北部夏季午後對流閃電與綜觀氣流風向之間的關係。資料分析結果顯示:(一)午後對流閃電日數以雪山山脈左側、高度約海拔500公尺的山坡最多;(二)午後對流閃電日數在七、八月份最多、九月份最少;(三)在本文所定義的午後對流個案中,雖然部份個案的雲對地閃電次數極少,甚至不曾出現雲對地閃電,但仍然伴隨大量的雲中與雲間閃電,這個現象說明了在討論與對流相關的議題時,一併分析雲中及雲間閃電的重要性;(四)午後對流閃電經常發生的位置,在五至九月間有隨季節逐漸沿著雪山山脈左側向西南轉移的特徵;(五)925 hPa盛行偏南風時,雪山山脈左側是有利於午後對流閃電出現的位置,進一步分析風向,在925 hPa盛行西南風,且500 hPa的導引風爲西南風時,午後對流閃電多半分布在121.4°E以東,當925 hPa盛行東南風,且500 hPa的導引風爲東南風時,午後對流閃電多半分布在121.4°E以西。 |
英文摘要 | The generation, movement, and evolution of afternoon convections are poorly predicted. Previous research has pointed out that the direction of prevailing flow opposite to the topography can affect the location of local confluence on the downstream slope. From operational experience, the location where afternoon convection appears is usually also related to the wind direction opposite to the central mountain range. This research utilizes 2004~2006 measurements from Taipower's Total Lightning Detection System (TLDS), which provides intra- and inter-cloud discharge (IC) as well as cloud-to-ground discharge (CG). Based on local dynamical factors emphasized in past studies, the present analysis probes the relation between summertime (May~September) afternoon convective lightning in Northern Taiwan and the direction of prevailing flow. The results show: (1) The number of days in which afternoon convective lightning took place over the slopes with elevation of ~500 m on the left hand side of Snow Mountain occurred most frequently; (2) Afternoon convective lightning was found in the most (least) days in July+August (September); (3) Some cases with afternoon convection were associated with few or no CG but a large number of IC, underscoring the importance of considering inter- and intra-cloud lightning when examining convection; (4) By a) dividing Northern Taiwan into two equal-area regions with 121.4 °E as the boundary and b) calculating the average normalized lightning percentage can provide information on the varying location of afternoon convective lightning, which shifted towards the southwest, along the left side slopes of Snow Mountain as time progressed during the period from May to September; (5) When southerly flow was prevalent in 925 hPa, the left side slopes of Snow Mountains were favored as locations for afternoon convective lightning to take place. When 925 hPa flow was southwesterly and 500 hPa steering winds were southwesterly, afternoon convective lightning was mostly found east of 121.4°E In contrast, when the predominant 925 hPa flow was southeasterly and 500 hPa steering winds were southeasterly, afternoon convective lightning was mostly found west of 121.4°E. |
本系統中英文摘要資訊取自各篇刊載內容。