Asperitas: These new-found rare clouds do not bring rainfall 

Clouds look scary at times, and ominous too, especially before a storm. One eerie-looking, beautiful, yet frightful cloud formation that has been recently documented is asperitas. If you ever see clouds that look like rippling waves, you have probably seen asperitas. When viewed from the ground, they look like a rough sea surface as the structures resembling waves form on the underside. Formed at an altitude of 4000-10000 ft above the sea level, these clouds are often seen across the Great Plains of the United States of America, including Montana, Wyoming, North Dakota, South Dakota, Nebraska, Oklahoma, Kansas, Colorado, New Mexico and Texas. Here is all about this new-found cloud formation.  

How are asperitas clouds formed? 
There are two basic explanations to how the asperitas clouds form. According to one theory, they are created when another set of rare clouds, known as mammatus, fall into those regions of the sky where the direction of the wind changes with height, creating a wave-like motion. These clouds, with a bulge or pouch-like appearance, hang from the base of other clouds.  

The other theory is that gravity waves cause them. We often overlook that the atmosphere is fluid because we cannot see it, but it is. Therefore, all the characteristics that apply to fluids apply to the atmosphere too. So, there is a possibility of waves existing in the atmosphere! Unless they pass through a layer of cloud, they are usually undetectable.  

When this happens, the pressure surface that the cloud layer is ‘stuck to’ can be bent and twisted. Did you have a hard time imagining that? Let’s make it easier for you. It would be like adding water to a fish aquarium and then shaking it. Its surface will develop waves that resemble gravity waves in the atmosphere. 

These gravity waves frequently form during intense thunderstorms when strong air currents create a ripple-like motion. When several waves from different origins travelling in various directions pass through a region, their motions combine to create a chaotic displacement pattern. It would be like whipping a blanket up and down with four people holding the various ends. As a result, the Asperitas clouds are formed. Atmospheric conditions must be unstable to generate a wavy cloud foundation like that of asperitas. 

Clouds without rain  
Yes, you read that right. These clouds do not cause rainfall, nor do they lead to bad weather conditions. However, asperitas clouds have been found during thunderstorms. They are visible in comparatively calm weather too. Stormy rain clouds can grow under the same unstable atmospheric conditions needed to form asperitas. So, they may be followed by other clouds that cause rainfall.   

Asperitas become a part of the International Cloud Atlas  
Decades back, cloud watchers first spotted these wave-like mysterious clouds in the sky. They shared snapshots of these unidentified clouds with Gavin Pretor-Pinney, a cloud expert and founder of the Cloud Appreciation Society, UK. Surprised by these new-found entities, Pretor-Pinney urged the UK’s Royal Meteorological Society and the World Meteorological Organization (WMO) to carry out studies on them way back in 2008. After years of research, scientists came to the conclusion that these unclassified were not anything like the existing cloud types. Finally, in March 2017, asperitas clouds were added to the other clouds listed with the WMO’s International Cloud Atlas. It is being used for categorising clouds since 1896.