天秤掃過 浪災重創蘭嶼 史上最慘 - 颱風討論
By Tracy
at 2012-08-30T10:04
at 2012-08-30T10:04
Table of Contents
推 IMBALLGOD :中颱出17級風 是因為本身地形嗎 08/28 19:38
推 lembertlin :很前面的推文中，有大大提到是地形因素沒錯 08/28 19:47
推 zzcb :有點好奇 用中心附近十分鐘平均風速衡量颱風強度來看 08/29 09:12
→ zzcb :蘭嶼的實測 天秤的強度不知是否被低估 雖然我也覺得 08/29 09:13
→ zzcb :中度颱風下限還滿合理的~ 08/29 09:14
→ zzcb :也許算是定義颱風強度的瑕疵? 反觀布拉萬是強烈颱風 08/29 09:15
→ zzcb :實測卻沒有那麼猛烈 08/29 09:15
這次蘭嶼出現全面性的強陣風，地形因素可能較為其次
蘭嶼比較常見強陣風的原因是颱風氣流繞山時，因為中央山脈地勢高會阻擋氣流過山
而恆春半島地勢較低，使得氣流在通過時會加速產生"噴流"
如CWB的這張概念圖 http://ppt.cc/c41M 東南部外海(地形下游)的氣流會加速
所以常常有強度不強的颱風通過台灣附近時，蘭嶼也會吹出強陣風
(當然測站地勢比較高也會影響)
但這次天秤的狀況可能比較不同
颱風的切向風風速主要取決於氣壓梯度力 (其實所有風速皆是)
因此近中心風速強弱 取決於近中心的氣壓梯度有多大 而不是中心氣壓有多低
天秤颱風23日下午還在123E附近 中心氣壓945 hPa假設是正確
蘭嶼的海平面氣壓999.4 hPa 北邊的與那國島和宮古島甚至都在1000 hPa之上
http://ppt.cc/7-tl (風標右上紅字是氣壓的十位數/個位數和小數)
短短的150公里距離 氣壓差將近50 hPa 可以預期天秤近中心的氣壓梯度有多大
天秤近中心扎實的程度應該是這幾年侵台颱風都沒有的
可以相比的也許是桃芝 但登陸地的秀姑巒溪口附近沒有測站~
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颱風
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