恆春落山風之分析研究一、現象分析

Study of the Hengchun Fall Wind Phenomenon I. Analysis of the Phenomenon

洪秀雄(Siu-Shuang Hong) ； 胡仲英(Chung-Ying Hu)

《大氣科學》 18卷3期 (1990/09) Pp. 171-191

摘要

每年十月至翌年三、四月間，恆春半島地面時有狂風怒號，有時持續二、三小時，有時十天、半月不停息。地面陣風大時甚至超過秒速20公尺，漫天風沙滾滾狂飆。由於風是越山而過，有如空氣由山頂直落而下般，這種現象俗稱「落山風」。本研究就能收集到的地面資料、探空資料等作較完整的統計與分析，以了解此現象之眞相，並指出過去認識之謬失，再借助理論之輔助提出正確之解釋，並進而探尋其預報因子。本文僅牽涉資料分析的部份。結果顯示恆春落山風只有在東北風或北北東風時才會發生，可見氣流必須跨越恆春半島，並非氣流繞山而成。落山風發生前也不一定有顯著天氣現象，與寒潮暴發並無直接關聯。探空資料顯示落山風發生時一定有臨界層存在於2至3.5公里間，而且臨界層處之里查遜數小於或接近一。

關鍵字

恆春落山風 ； 內重力波 ； 理查遜數 ； 臨界層

並列摘要

There are strong gusty surface winds over the Hengchun Peninsula every year from October till March-April the next year. The gusts sometimes lasted for only 2-3 hours, but some other times persisted for several days or even weeks. The strong surface wind can exceed 30 m/s. It brings dusts into the sky and soars and sweeps over the west coast of the Hengchun Peninsula. The air rushes down the mountain slope, just as falling down from the mountain top. Therefore the phenomenon is coined ”fall wind” by the folks.The research collected abundant local surface data as well as sounding data on the upstream side of the peninsula. Analyses ere done to reveal the truth of the phenomenon. The results and statistics toppled the existing subjective theories. And a comprehensive new theory, assisted by a numerical model simulation, is proposed to explain the mechanism of the phenomenon. Based on the new theory, certain criteria can be identified for the purpose of forcasting the onset of the fall wind.This is the first part of the results, focusing on phenomenology and the relationship between surface gusts and vertical structure of the atmosphere. It was found that the fall wind occurred only when the flow was north-easterly or north-north-easterly, meaning that the air flowed over the ridge but not around the peninsula. No significant synoptic patterns were relevant with the phenomenon. There were no direct relationship between the fall wind phenomenon and the cold surge. The upstream sounding data showed that there were critical level (with respect to the mountain wave) existed in the neighborhood of 1.5 to 3.5 km aloft and the Richardson number there is less than or near to 1.

並列關鍵字

fall wind ； internal gravity waves ； Richardson number ； critical level