梅雨期臺灣地區中範圍天氣之分析與預報

Meso-scale Weather Analysis and Forecasting during the Plum-rain Season in the Taiwan Area

王崇岳(Griffith C. Y. Wang)

《大氣科學》 5卷1期 (1978/05) Pp. 15-25

摘要

應用地面流線圖分析法分析梅雨期臺灣區天氣圖，發現臺灣之東南方近海有一中範圍氣旋，臺灣中部有一中範圍反氣旋環流，臺灣南部沿海有一中性氣流場，該氣流場擴張軸附近之輻合區時有雷胞存在；如500mb面槽前之上昇氣流場與該區重疊，則有暴雨發生之可能；若反氣旋氣流場範圍擴大，則臺灣中、南部之雷雨可望終止。西南氣流場內雷胞內、外之環流型態與牛頓模式顯有差別，於此已詳予闡明，雷胞移動之方向與牛頓模式相同。850mb面高度與時間連續圖可表示一地氣壓波之波幅與週期；如以桃園、東港850mb面高度同時填繪，可研判臺灣上空東西向低層氣流之強度，均有助於梅雨期天氣之預報。

並列摘要

During the transit season from spring to summer the polar front moves back and forth over South China with frequent rainshowers or thunderstorms in the Taiwan area. Intense thundery rainshowers with a 24-hour rainfall over 100mm are at times associated with minor waves forming along the quasi-stationary front or within a strong southwest flow. In this season and summer pressure gradients are flat over Taiwan. The method of surface streamline analysis is highly recommended to replace the pressure analysis. The former one can indicate certain peculiarities not easily discernible from pressure patterns. Based on charts of surface streamline analysis the following phenomena are discussed:1. Meso-scale anticyclone and cycloneIn the southwest flow, due to the blocking effect of the Central Mountain Range, a mesocyclone is normally observed over the area off-shore of Taitung, along the eastern coast of Taiwan; while a meso-anticyclone is located over the CentraI Taiwan. The intensity of the ”Taiwan Meso-anticyclone” is highly important to thunderstorm activities over Taiwan.2. Locations of the CB formation are separated into 3 categories:(1) Along the windward side of the Central Mountain Range,(2) Along the quasi-stationary polar front, and(3) In the area of convergence of the southwest flow. The life of this type of CBs is much longer than any other types.3. In the southwest flow the circulation within and without a CB is different from Newton's model (1963), which is applicable to CBs forming in the area of strong westerly winds aloft (over 25,000ft). The CB model in the south west flow is presented herein.4. Westerly trough at 500mb is the triggering mechanism that provides sufficient ventilation for CBs to prolong the life of a sufficiently large and vigorous system.5. Finally a 850mb height-time continuity chart is recommended for weather forecasting. In this chart the pressure wave is clearly shown by daily 850mb heights. Whenever the current height is below the climatological mean value, both the frontaI activity and weather within the southwesterly flow are much active than any other times except at Taipei, where heavy afternoon (thermal) thunderstorms frequently occur at the stage of pressure increase from low to high and the current 850mb height is higher than the corresponding climatological mean value.