2025年8月17日
Asperitas Clouds Over New Zealand
Image Credit & Copyright: Witta Priester
Explanation: What kind of clouds are these? Although their cause is presently unknown, such unusual atmospheric structures, as menacing as they might seem, do not appear to be harbingers of meteorological doom. Formally recognized as a distinct cloud type only last year, asperitas clouds can be stunning in appearance, unusual in occurrence, and are relatively unstudied. Whereas most low cloud decks are flat bottomed, asperitas clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperitas clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn — a type of dry downward wind that flows off mountains. Clouds from such a wind called the Canterbury arch stream toward the east coast of New Zealand’s South Island. The featured image, taken above Hanmer Springs in Canterbury, New Zealand in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side.
Tomorrow’s picture: working spiral
新西兰上空的糙面云
影像提供与版权: Witta Priester
说明: 这什么云呢？这种具有不寻常结构、外观颇为凶恶的云种，其成因目前不明，但咸信并非恶劣天气的前兆。近几年才确认是新云种的罕见糙面云（Asperitas Clouds），外观颇让人惊艳，但相对少有研究。相较于大多数云种的底部是平坦的，糙面云的底部有明显的垂直结构。因此专家推测糙面云可能与某些云种相关，像是形成于山区附近的荚状云、与雷暴系统有关的乳状云、或出现在背山面沿着山坡往下吹的干热焚风。而发生在新西兰南岛东岸的焚风，则另有西北云弧 （Canterbury arch streams）之称。在这张2005年摄于新西兰 坎特伯雷区汉默泉镇的主题影像里，这团糙面云由于受到阳光侧照，其云层结构变得格外鲜明。
明日的图片: working spiral
