雙相機攝影法推估對流雲發展高度與對流特徵－以2017年夏季北台灣午後對流個案為例

The Characteristic Study on Convective Cloud by Stereo Photogrammetric Method-Afternoon Convective Cases at Northern Taiwan, 2017

黃彧珉(Yu-Min Huang) ； 林博雄(Po-Hsiung Lin)

《大氣科學》 48卷2期 (2020/12) Pp. 173-204

https://doi.org/10.3966/025400022020124802002

摘要

熱帶地區的對流發展是由三種對流雲所組成，其中介於淺對流與深對流之間的濃積雲在深淺對流轉換中扮演了重要的角色。近年來已出現許多相關研究，不過對於濃積雲的發展高度仍然缺乏明確客觀的界定。雙相機攝影測量是一種利用兩台相機來測量物體於三度空間位置的技術，這樣的觀測技術除了有很高的空間、時間解析度，對於觀測對流雲尚未產生降雨，並且變化快速的時期也很有幫助。本研究利用此觀測技術在桃園濱海架設兩台自動化相機朝北台灣山區方向進行觀測，並利用地面山脈與夜空恆星來取得影像的方位角與仰角，計算出2017年6月到9月發生午後對流時的對流雲頂高度。最後選出四天在時間與發展高度觀測最完整的個案進行觀測結果分析，包括分析每個高度區間的垂直上升速度、垂直上升加速度與雲頂寬度，嘗試分析出濃積雲與深對流的差異。分析結果顯示，並沒有發現明顯抑制濃積雲發展的穩定層，整體而言對流雲在最高雲頂高度持續上升的過程中，雲頂減速的程度會越來越明顯，雲頂寬度則是越來越寬；特別的是，最高雲頂高度發展到8－9公里時，對流雲頂的減速程度會明顯變小，雲頂寬度也是明顯變小。

關鍵字

濃積雲 ； 午後對流 ； 攝影測量 ； 雲頂高度 ； 垂直速度

並列摘要

Tropical convective cloud has been observed to contain three cloud modes. Cumulus congestus clouds between cumulus and deep convection plays an important role in the transition from shallow to deep convection. Many related studies have improved the understanding of cumulus congestus, but there is still lack of clear and objective definition of its cloud top height. Stereo-photogrammetry is a technique that uses two cameras to measure the position of an object in three-dimensional coordinates. In addition to its high spatial and temporal resolution, this observing technique is very helpful for observing rainless or rapidly changing convection. This research uses this technique to set up two automated cameras at Taoyuan coastal toward mountian, and use the mountains and stars in the image to obtain the azimuth and elevation to calculate cloud top height of afternoon convection in northern Taiwan from June to September 2017. Five of the most complete and clearest cases are selected to analysis. And analyzes the vertical velocity, vertical acceleration and cloud top width of each altitude level to find the difference between cumulus congestus and deep convection. The results indicate that there is no obviously stable layer. When convective cloud develops upwards, the vertical acceleration will decelerate with height and suddenly increase until it reaching 8-9 km, and then keep decelerate with height; the width of cloud top is exactly the opposite of the acceleration change with height; the vertical velocity tends to increase steadily with height below 8- 9 km.

並列關鍵字

cumulus congestus ； afternoon convection ； stereo-photogrammetry ； cloud top height ； vertical velocity