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標題: 密蘇里州上空的捲軸雲 [打印本頁]

作者: charles    時間: 2009-3-27 11:03     標題: 密蘇里州上空的捲軸雲

A Roll Cloud Over Missouri



影像版權與提供: Dan Bush (Missouri Skies)

Explanation:
      What kind of cloud is this? A roll cloud. These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form a cloud. When this happens uniformly along an extended front, a roll cloud may form. Roll clouds may actually have air circulating along the long horizontal axis of the cloud. A roll cloud is not thought to be able to morph into a tornado. Unlike a similar shelf cloud, a roll cloud is completely detached from their parent cumulonimbus cloud. Pictured above, a roll cloud extends far into the distance in the summer of 2005 above Albany, Missouri, USA.

說明:
      這是那一種雲呢?答案是捲軸雲 (roll cloud;或稱弧狀雲),這種罕見的長雲有時會出現在冷鋒前緣。來自往前推進的暴風前緣之下沈下流,會推升前方的溼暖空氣,讓它的溫度低於露點並形成雲。如果這種現象在大範圍冷鋒前緣同時發生時,就會出現這種捲軸雲。在捲軸雲內,氣流有時會沿著捲軸雲的水平軸方向流動。和灘雲 (shelf cloud)最大的差異是,捲軸雲並不會轉變成龍捲風,因為它和造成它的積雨母雲是完全分離的。上面這張2005年夏天在美國.密蘇里州、Albany鎮所拍攝的影像裡,一道捲軸雲向遠方延伸。

資料來源: Scientific American
               Department of Physics, NCKU







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