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  • Look! Up in the sky! It's a new kind of cloud - #Asperitas

    Looking up, you might be thinking you're under a roiling, stormy sea.

    But what you're looking at is a unique and breathtaking meteorological phenomenon. And today, World Meteorological Day, it's being officially recognized: asperitas cloud.
    This is how the new edition of the International Cloud Atlas describes it, in almost poetic form:
    "Asperitas is characterized by localized waves in the cloud base, either smooth or dappled with smaller features, sometimes descending into sharp points, as if viewing a roughened sea surface from below."

    What's in a name?

    Asperitas comes from the Latin word for roughness.
    In 2006, the Cloud Appreciation Society, a group of weather enthusiasts based in the UK, received the first images of the distinctive cloud from Cedar Rapids, Iowa. A few years later, they proposed the cloud be included in the atlas. That would be a huge coup since the atlas is widely used to train meteorologists from the time it was first published in the late 19th century.
    "When we know the name of something, we began to know it in a different way and when we began to know it, we began to care about it," Gavin Pretor-Pinney said at a World Meteorological Day ceremony in Geneva.

     A big deal

    Adding a new cloud type is rare. The World Meteorological Organization had not updated the atlas in 30 years, until now.
    "It is a classic example of citizen science, in which observations by the general public, enabled by the technology of smartphones and the Internet, have influenced the development this most official of classification systems," a news release on the Society's website reads.

    View image on Twitter
    Alongside the striking cloud formations, a few other classifications have been added to the new edition. Some of them are "volutus," a roll cloud, "contrail," a vapour trail that is sometimes produces by airplanes and more common phenomena like rainbows, halos and hailstones, according to the foreword of the atlas.


    Asperitas (formerly known as Undulatus asperatus) is a cloud formation first popularized and proposed as a type of cloud in 2009 by Gavin Pretor-Pinney of the Cloud Appreciation Society. Added to the International Cloud Atlas in March of 2017, it is the first cloud formation added since cirrus intortus in 1951. The name translates approximately as "roughness".

    The clouds are closely related to undulatus clouds. Although they appear dark and storm-like, they almost always dissipate without a storm forming . The ominous-looking clouds have been particularly common in the Plains states of the United States, often during the morning or midday hours following convective thunderstorm activity. As of June 2009 the Royal Meteorological Society is gathering evidence of the type of weather patterns in which asperitas clouds appear, so as to study how they form and decide whether they are distinct from other undulatus clouds.

    History of observations

    Margaret LeMone, a cloud expert with the National Center for Atmospheric Research has taken photos of asperatus clouds for 30 years, and considers it in her own words, a new cloud type.

    On June 20, 2006 Jane Wiggins took a picture of asperatus clouds from the window of a downtown office building in Cedar Rapids, Iowa. In March 2009, Chad Hedstroom took a picture of asperatus clouds from his car near Greenville Ave in Dallas, Texas. Soon after taking it, Wiggins sent her Cedar Rapids image to the Cloud Appreciation Society, which displayed it on its image gallery. Wiggins' photograph was posted on the National Geographic website on June 4, 2009. On July 23, 2013, Janet Salsman photographed them along the South Shore of Nova Scotia, Canada. On October 28, 2013, an Asperitas cloud layer formed over Tuscaloosa, Alabama. On July 7, 2014 asperatus clouds in Lincoln, Nebraska, have been caught on tape by Alex Schueth. One of the most dramatic formations was captured by Witta Priester in New Zealand in 2005. The photo was posted by NASA as the Astronomy Picture of the Day and shows great detail, partly because sunlight illuminates the undulating clouds from the side.

    Since 2006, many similar cloud formations have been contributed to the gallery, and in 2009 Gavin Pretor-Pinney, founder of The Cloud Appreciation Society, began working with the Royal Meteorological Society to promote the cloud type as an entirely new type in and of itself.

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