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暖季台灣中北部午後連續對流的氣候特徵研究

Climatological Characteristics of the Warm Season Afternoon Convection over Northern and Central Taiwan under Weak Synoptic Forcings

摘要


本文利用民航局桃園國際機場C波段都卜勒雷達回波資料,依午後對流日發生之連續性,將1999-2006年5-8月暖季弱綜觀環境條件下台灣中北部177個午後對流個案,分爲單一日、連二日、連三日、連四日及連五日(暨以上)五種類型,探討其氣候特徵。另外,利用歐洲中期天氣預報中心(European Centre for Medium-Range Weather Forecasts; ECMWF)格點資料與中央氣象局板橋探空資料,合成分析各類型綜觀天氣形勢並探討大氣環境與午後對流時空分布的關係。 結果顯示,各類型初生期對流主要分布在台北盆地的南方與雪山山脈西側山坡與高山上,成熟期對流發生頻率明顯增加,尤其在中台灣的台中與南投山坡上發生頻率增加特別顯著,唯中台灣午後對流有較北台灣延後發展特性。由初生期到成熟期的頻率分布顯示,對流在北台灣有向西向雪山山脈西側地形緩坡移動發展之勢,而中台灣則有向東向中央山脈西側山坡移動發展之勢。此外,亦發現不同類型午後對流最大頻率出現時間,不論初生期與成熟期或中台灣與北台灣,均有其相同與相異之處。 綜觀環境條件分析顯示,在副熱帶太平洋高壓脊影響下,綜觀尺度之環流微弱且大氣具有足夠對流可用位能,由局部環流主宰午後對流發展,其持續日數應爲多重環境條件之綜合結果而非單一因子可決定,唯若要有連續午後對流發展,前一日在台灣附近有低壓槽與低壓中心之出現,使風場與水氣傳送更有利大氣不穩度與CAPE之恢復似爲重要條件。

並列摘要


C-band Doppler radar data at Taoyuan International Airport of CAA in the period of May-August 1999-2006 were used to identified the afternoon convection over northern and central Taiwan under weak synoptic forcing. Climatological characteristics of different types of convection with different continuous occurrence feature were investigated for the selected 177 cases. Grid data of European Centre for Medium-Range Weather Forecasts (ECMWF) and rawinsonde data at Panchio station of the Central Weather Bureau were used to study the influence of synoptic circulations and environment conditions on the spatial and temporal distributions of afternoon convection. Results showed that convection occurred mainly over the Taipei Basin and western slope and top of the Snow Mountain Range (SMR) at initial stage. Convection frequency increased significantly at matured stage, particularly over central Taiwan near Taichung and mountain slope of Nantou. Also, time of the development of afternoon convection over central Taiwan tended to lag behind as compared to that occurred over northern Taiwan. Frequency distribution at initial and mature stages indicated that convection tended to move and develop westward towards the gentle slope of the SMR over northern Taiwan. Whereas over central Taiwan, convection tended to move and develop eastward towards the western slope of the Central Mountain Range. In addition, it was found that there were some similarities and differences for the occurrence time of maximum frequency of convection among all convection types, no matter the initial or mature stage as well as northern or central Taiwan was concerned. Synoptic circulations and environment conditions suggested that local circulations control the development of afternoon convection under the weak synoptic forcing of subtropical high pressure ridge with sufficient convective available potential energy in the environment. The continuous occurrence of afternoon convection was not determined by any single factor but depended on the combination of multiple environment conditions. It was found that the necessary condition for the continuous occurrence of convection was the existence of a low pressure trough or a low center in the vicinity of Taiwan such that the wind field and water vapor transport were favorable for the recovery of instability and convective available potential energy in the atmospheric environment.

被引用紀錄


孔令鈞 (2011). 一個更普遍用於半經典理論研究化學反應動態學的絕熱勢能曲線 [master's thesis, National Chiao Tung University]. Airiti Library. https://doi.org/10.6842%2fNCTU.2011.01153
歐安祥(2010)。台灣北部夏季午後降雨機制與地形影響之探討〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-1610201315203239

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