#2510 "Singleton Asperitas"

I witnessed these clouds one Tuesday afternoon in early May. It was not windy at the surface but the cloud shapes belied the wind shear and strong winds above the warm frontal inversion. I have witnessed similar formations many times before but I now discover that these beauties have been given a name "asperitas". I thought that I had better paint them as well. Here is that story. 

Apparently, asperitas is a cloud formation first popularized and proposed as a type of cloud in 2009 by Gavin Pretor-Pinney of the Cloud Appreciation Society. Asperitas was added to the International Cloud Atlas as a supplementary feature in March 2017 and it is the first cloud formation added since cirrus intortus in 1951 - before I was even born! 

Asperitas requires a stable layer in the atmosphere and wind shear. It helps if the winds are also strong. The wavelength of the cloud pattern varies directly with the wind speed. A stable layer is when the air actually warms with height which is inverted from the typical atmospheric temperature profile where the air cools with height. This leads to the stable layer being called an "inversion" by meteorologists since the atmospheric profile is inverted from the norm. The greatest stability is created with warm air aloft over a cold surface layer. The waters of the Great Lakes are cold in May after a winter of cooling and snow and ice. Warm air approaching from the Gulf of Mexico also provides moisture for the clouds. The required stable layer is also a warm frontal inversion in this situation. The warm air is referred to as a warm conveyor belt and I have written about that conceptual model many times. The tortured and twisted clouds are actually within the warm conveyor belt and we are looking at the bottom of the warm frontal surface. 

A warming wind creates characteristic wind shear that encourages cyclonic swirls. These cyclonic swirls encourage updrafts and what goes up must also come down. Backward-S shaped deformation zones link these cyclonic swirls. The moisture is spun in this wind shear like yarn. The stable layer of the inversion gets shook like a thermal blanket on the clothes line in a strong wind. The clouds react in the interesting variations of shapes, colours and tones which make asperitas so darn exciting. Rain was on the way. 

On that May day, Jim Montanus posted a picture of the asperitas over Lake Ontario in a FaceBook post to the 1000 Islands River Rats Now and Then Group (21.9K members). "Crazy clouds over Lake Ontario! I have never seen anything like it. Looks like they have tentacles - like an octopus. What would you call them?" The image prompted 322 shares and 207 comments including one from me. I had just written about the interesting science responsible for creating the cloud patterns. 

For this and much more art, click on Pixels. Thank you.