美国威斯康辛州上空的卷轴云

2023年8月20日

A Roll Cloud Over Wisconsin
Credit: Megan Hanrahan (Pierre cb), Wikipedia

Explanation: What kind of cloud is this? A type of arcus cloud called 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 here, a roll cloud extends far into the distance as a storm approaches in 2007 in Racine, Wisconsin, USA.

Tomorrow’s picture: comet unknown

美国威斯康辛州上空的卷轴云
影像提供: Megan Hanrahan (Pierre cb), Wikipedia

说明: 这是那一种云啊？此为一种称为卷轴云的弧状云，在冷锋前缘偶而会出现这种罕见的长云。当往前推进的暴风前缘之下冲流，抬升了前方的暖湿空气，让它的温度低于露点时就会凝结成云。如果这种现象在大范围的冷锋前缘同时发生，就有可能形成这种卷轴云。而在卷轴云内，气流有时真的会沿着水平轴方向流动。滚轴云和外观相近的滩云之的最大差异在于：卷轴云不会转变成龙卷风，因为它与积云母云是完全分离的。在上面这张摄于2007年的照片里，随着暴风系统逼近美国威斯康辛州的拉辛市，一道卷轴云绵延伸向远方。 （arcus cloud 弧状云; roll cloud 卷轴云; shelf cloud 滩云; cumulonimbus cloud 积云）

明日的图片: comet unknown