A Roll Cloud Over Uruguay
Credit & Licence: Daniela Mirner Eberl
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, a type of Arcus cloud, is completely detached from their parent cumulonimbus cloud. Pictured above, a roll cloud extends far into the distance in 2009 January above Las Olas Beach in Maldonado, Uruguay.
Fireworks erupted from the sun on May 12 when an X1.7-class solar flare burbled into view. X-class flares are the most intense categorization; the number behind it describes its strength. An X2 is twice as powerful as an X1, and so on.
The image, captured by NASA’s Solar Dynamics Observatory, is a combination of two pictures taken at two different wavelengths of light. (Related: “Solar Storm Heading Toward Earth.”)