美国拉什莫尔山上空的乳状云
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Mammatus Clouds over Mount Rushmore
Image Credit & Copyright: Laure Mattuzzi
Explanation: What’s that below those strange clouds? Presidents. If you look closely, you may recognize the heads of four former US Presidents carved into famous Mount Rushmore in South Dakota, USA. More obvious in the featured image are the unusual mammatus clouds that passed briefly overhead. Both were captured together by a surprised tourist with a quick camera in early September. Unlike normal flat-bottomed clouds which form when moist and calm air plateaus rise and cool, bumpy mammatus clouds form as icy and turbulent air pockets sink and heat up. Such turbulent air is frequently accompanied by a thunderstorm. Each mammatus lobe spans about one kilometer. The greater mountain is known to native Lakota Sioux as Six Grandfathers, deities responsible for the directions north, south, east, west, up, and down.
Tomorrow’s picture: an almost great conjunction
美国拉什莫尔山上空的乳状云
影像提供与版权: Laure Mattuzzi
说明: 这些怪云的下方有什么？数位美国总统。如果你细瞧，或许能认出它们是美国南塔可达州拉什莫尔山上，4位前任美国总统的人头石雕。这张主题影像，则是九月初当时发现这片奇景的一位游客用简易相机所记录，其中更显眼的是短暂出现在上空的乳状云。一般常见的云是平底的，这是因为潮湿的空气缓缓上升时，会在特定温度和高度凝结成云。不过当带冰晶的湍动气胞沉降和升温时，就会形成一团团宽约1公里的凹凸不平乳状云。拉什莫尔山所在的山脉，拉可塔苏族印地安人称之为六祖父山，分别是掌管北、南、东、西、上与下六个方位的神祇。
明日的图片: an almost great conjunction
