Earlier this week, Kjetil O. Småge was sitting in his office in Bodø when he suddenly noticed the clouds outside the window. – They moved and changed all the time. To the north it looked like an arctic landscape, says Småge. Amazed by the phenomenon, he took out his mobile phone and started taking pictures. – I have never seen this before. Photo: Kjetil O. Småge The cloud has similarities to the surface of the sea on a stormy day and is actually called Altokumutus Andulatus Asperatus. – It can have slightly different types of appearance. But the name means “turbulent sea” and it is quite descriptive. That’s according to meteorologist on duty Pernille Borander at the Meteorological Institute. Several things have to happen for an “upset sea” cloud to occur, explains meteorologist Pernille Borander. Photo: Magne Velle/Meteorological Institute The same physical rules govern both in the sea and in the air. But in the ocean there are water droplets and in the atmosphere there is water vapour. – We get the same waves – only that it is in the form of clouds and not in the sea. It is a fascinating phenomenon and it can look very violent. Often appears in the summer The cloud is often formed when strong winds hit the surface of the clouds. Unsettled air at altitude has the same effect as when wind creates waves on the surface of the sea. Here the wind creates waves on the clouds. The Washington Post writes that stability in the low or middle layers of the atmosphere causes water vapor to settle in horizontal layers. When strong winds from several directions blow against the water vapor, the cloud bends and moves like a wave across the sky. Have you seen an Asperitassky before? Asperitus clouds often appear in the summer just before heavy thunderstorms and showers. – We get pictures like this from time to time, but it is one of the rarer cloud types. Several things must fall into place for it to form. We have no statistics on how often they appear. The Newest Cloud Although clouds have been around since the dawn of time (or, at least for the past 12 billion years), the Asperitus Cloud was not recognized until recently. In the late 2000s, the Cloud Appreciation Society fought to have Asperitus classified as a cloud type of its own. In order to be approved as a new type of cloud, the conditions that create the cloud had to be documented. – First you have to know what conditions form these clouds. It took some time, explains Borander. Asperitus clouds go under the category Altokumutus which is a main category for medium high and thick clouds. – They have a greater extent upwards in the air than downwards and are a bit like round balls in the air, according to the meteorologist. When the weather conditions were documented, the World Meteorological Organization (WMO) was encouraged to include Asperitus in the so-called Cloud Atlas. – When you managed to sort out why these clouds turn out exactly the way they do – you could set them down as a separate Altokumutus cloud. In the 2017 edition of Cloud Atlas, the Asperitus cloud was finally on the list. And that as the first new cloud in 60 years. The WMO divides all types of clouds into ten main categories: Feather clouds Mackerel clouds Veil clouds Rukle clouds Stratus clouds Precipitation cloud layers Gusset clouds Fog clouds Cumulus clouds Thunder clouds There are approximately 100 varieties and combinations within the various main categories. The asperitus cloud is a variant that often occurs in connection with cumulonimbus clouds and cumulus clouds. Look up! With so many different cloud types, it can be good to look up at the sky once in a while. If you’re lucky, you might see an Asperitussky, or one of these:
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Kjetil got to see rare Asperitus clouds: – Looked like an arctic landscape – news Nordland
