A very strange cloud!

The endless fascination of the clouds in the sky.

Wherever one is in the world there’s something that will always offer delight, interest and a bit of a weather forecast as a bonus. I’m speaking of clouds.

I have written about clouds before in this place but the reason that I just have to share another post about clouds with you is this image:

garysmith-zippercontrailIt is from The Cloud Appreciation Society’s November newsletter and I’m taking the liberty of sharing the particular news item with you.

cloud-of-month-nov2016November 2016

A Mystery in the Clouds

Earlier this month, a peculiar ring appeared in the clouds over Warwickshire, England. James Tromans, who photographed the formation, asked what might have caused it. Clearly, this was time for some cloud detective work.

The ring was actually more of a curve, or a ‘U’, as there was no other half to it. It appeared to consist of regular lumps, or lobes, hanging down from the underside of a cloud layer. We wondered if this layer was an Altostratus, but off in the distance to the right of the image there appeared to be showers, like those produced by a storm cloud. This suggested that the cloud layer might in fact have been part of the huge canopy that spreads out at the top of a Cumulonimbus storm cloud.

Sometimes, to the rear of a storm, lobes of cloud known as

1. Could ‘mamma’ be involved? Spotted over Wilton, Wiltshire, UK, by William Saberton,
1. Could ‘mamma’ be involved? Spotted over Wilton, Wiltshire, UK, by William Saberton,

mamma can be seen

hanging from the underside of the canopy (see image 1). There certainly was a general appearance of mamma in the cloud layer. But could some of these mamma cloud lobes have arranged themselves into this strange, regular curved formation? It seemed unlikely.

There was something decidedly unnatural about the cloud’s appearance – as if it were man-made. Then it occurred to us that the photograph was looking towards Coventry Airport. Might this cloud effect have been in some way caused by an aircraft?

As planes fly through clouds made of ‘supercooled’ water droplets, they can encourage these extremely cold droplets to freeze and fall below, leaving behind a gap, known  as a dissipation trail, or ‘distrail’. Such formations are often seen in

2. Or was it to do with an aircraft ‘distrail’, like this spotted over Newcastle, Australia, by Jillian De Martin (Member 12801)?
2. Or was it to do with an aircraft ‘distrail’, like this spotted over Newcastle, Australia, by Jillian De Martin (Member 12801)?

straight lines where planes ascend or descend through the cloud. But they can also appear in circular shapes when one is flying in a holding pattern as it waits to land (see image 2). James’s cloud wasn’t quite a distrail, but we felt we were getting close.

It was then that we recognised the regular spacing of the lobes. These sometimes appear below aircraft condensation trails (see image 3). They are caused by the interaction between the two swirling vortices produced by the wings. As these rotate in opposite directions in the wake of an aircraft, the two turbulent flows interact and combine to form a periodic pattern of turbulent downdrafts. In the right conditions, they appear as lobes hanging below the condensation trail.

3. The clue was in the turbulence lobes that can appear hanging from an aircraft contrail. You can see these in this strip of contrail spotted over the Smokey Mountains, US, by Gary Smith.
3. The clue was in the turbulence lobes that can appear hanging from an aircraft contrail. You can see these in this strip of contrail spotted over the Smokey Mountains, US, by Gary Smith.

This explained the formation. It was caused by an aircraft, which happened to be flying just above the base of the cloud layer as it turned in a holding pattern above the nearby airport. The plane’s condensation trail was hidden within the cloud layer, but the lobes of cloud descending below it, caused by the turbulence from its wings, appeared extending below the layer.

Phew! With that cleared up, we could finally relax once more.

Turbulence lobes beneath the contrail of an aircraft in holding pattern over Hampton Lucy, Warwickshire, UK, by James Tromans.

ooOOoo

 How very interesting and hope I’m not the only one to think so.

10 thoughts on “A very strange cloud!

  1. Wow! I don’t know which is more surprising, the explanation of the cloud formation or the fact that there is a Cloud Appreciation Society! I happen to live in Chicago on the lakefront, so I have a ringside seat as it were to a wonderful ‘cloud show’ nearly every day. I thought I was the only person who cared about cloud formations except for forecasting weather. I shoot iPhone pics several days a week of cloud formations I see riding my bike along the lake. Thanks for a very enlightening post!

    1. Tony, my love of cloud-watching goes back more than 30 years to when I was introduced to gliding, or sail-planing in American speak. Where we live here in Merlin, OR, with mountains all around us there are wonderful clouds to observe. Love the mental image of you on your bike riding by the lake.

      1. I am very fortunate. I live in downtown Chicago yet I have the lakefront out my window and the ducks, squirrels, rabbits, etc. running around all over. The best of both worlds.

  2. Funny how I immediately thought of aircraft when I looked at your picture, Paul. Weather, clouds, etc are fascinating to me. Thanks for the share. Although the one photo from the UK might have people thinking that 👽made it, LOL.

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