| 摘要: | 本研究以2016~2020年暖季(5~9月)的資料進行台灣中部區域午後對流環境特徵的統計分析，並考慮不同綜觀風場的影響，以暖季盛行風場東北風(NE)、東風(EE)、東南風(SE)、南風(SS)與西南風(SW)，分別進行午後對流日(afternoon thunderstorm day, TSA)及非午後對流日(non-afternoon thunderstorm day , noTSA)的環境場分析；以兩者間的差異探討午後對流發生前的環境特徵及可用於預報的環境因子，可提供未來中部區域的午後對流預報的參考。本研究使用的資料有00UTC的馬公站探空資料與歐洲氣象中心提供的ERA5再分析資料以進行綜觀場分析，以及利用中央氣象局地面測站資料，檢視地面環境場在時序上的變化，探討中部區域午後對流的環境特性。
研究結果顯示，中層副熱帶高壓位置明顯影響中部地區的午後對流的生成環境，太平洋高壓脊位置越往西伸南偏，台灣環境越趨於穩定，而當台灣位於副高邊緣，則會使台灣有相對較高的環境不穩定度。各綜觀風場下有無午後對流間差異明顯的高度不同，但受綜觀風場的風向與強弱影響，有午後對流日(TSA)於中低層都有較暖濕的環境條件，導致對流抑制位能減少，只需受較少的外力作用，即可達自由對流高度發展對流系統，再加上較大的對流可用位能與可降水量，使TSA有相當利於對流發展之環境條件，而近地表海風的水氣傳輸作用，則能把水氣傳送至內陸區域，當熱力作用充足時，更容易成雲降水，而受綜觀風場影響的向岸風會產生南北偏轉的情形，造成降水熱區位置改變，說明降水熱區與地表風場受到地形影響的位置具有高度相關。
;This study focus on the warm season (May-September) from 2016 to 2020 in recent years to conduct a statistical analysis of the characteristics of the afternoon thunderstorm environment in the central region of Taiwan. This study discuss the impact of different wind fields on the development of afternoon thunderstorms. The northeast wind (NE), east wind (EE), southeast wind (SE), south wind (SS), and southwest wind (SW) prevail in the warm season, respectively on afternoon thunderstorm days (TSA) and non-afternoon thunderstorm days (noTSA). Based on the differences between TSA and noTSA, we conducted environmental field analysis to discussed the environmental characteristics before the occurrence of afternoon thunderstorms and the environmental factors that can be used for forecasting. We hope this study could be benefit to future afternoon convective forecasting in central Taiwan. In this study we use the sounding data from the Magong Station with 00UTC and the ERA5 reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) to conduct a comprehensive weather types analysis, as well as the data from the ground station of the Central Weather Bureau (CWB), to examine the temporal and spatial changes of the surface environmental field, and to explore the afternoon thunderstorms environmental characteristics in the central Taiwan.
The results of the study show that the location of the mid-subtropical high will affect the occurrence of afternoon convection. The more the high-pressure ridge extends to the west and the south, the environment in Taiwan tends to be more stable. When Taiwan is on the edge of subtropical high pressure, Taiwan′s environmental instability will be relatively high. Under different synoptic wind fields, the height of the obvious difference in temperature and humidity fields is not the same but affected by the wind direction and intensity of the wind field. The lower and middle environmental conditions of the TSA are warmer and humid, resulting in lower convective inhibition and less external force can reach the level of free convection. Coupled with larger convective available potential energy and precipitable water, makes TSA quite conducive to the development of convective environmental conditions. Near-surface sea breeze transports water vapor, which can be transported to inland areas. When the thermal effect is sufficient, it is easier to turn into clouds and precipitation, and the onshore wind will split into north or south due to the terrain effects on synoptic wind field, resulting in changes in the location of the precipitation hot zone. It shows that the precipitation hot zone is highly related to the influence of terrain effects on the prevailing surface wind field. |
