Tag: The Cloud Appreciation Society

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.

What nature makes up!

A suitable postscript to yesterday’s post.

Yesterday, I wrote a post under the title of You couldn’t make it up! It featured a recent essay Pregnant Silence from George Monbiot about the consequences and implications of the widespread consumption of meat and dairy products.

Now look at this example of what nature does make up.

Nov-2015-com

A Sunset with Searchlights

You know those glorious fingers of sunlight that sometimes burst out from behind clouds? They’re called ‘crepuscular rays’, they form when light and shadow are rendered visible by haze in the atmosphere and these photographed by Alli Bush over Fort Collins, Colorado, US, are the Cloud of the Month for November.

The haze giving rise to crepuscular rays can be due to the air being filled with fine particles such as sand, dust or pollen. Or it can result from a delicate mist of water droplets – plentiful enough to scatter the sunlight but too scarce to show up as a cloud. The scattering is the important bit. Since we only see light that shines directly into our eyes, rays of sunlight shining in other directions are not visible unless they encounter something that scatters light towards us. Think of shining a torch beam on a clear night. The light only appears where it strikes a surface such as the ground. But on a foggy night, the full torch beam shows up because some light is also scattered towards us by the droplets of fog in the air it passes through. This is why a hazy sky renders rays of sunlight visible.

The other requisite for crepuscular rays besides haze is something to cast the shadows. Most commonly it is a cloud blocking the sunlight that creates the regions of light and shadow we see in the sky. But the crepuscular rays in Alli’s photograph are cast not by clouds but by the peaks of the Rocky Mountains. The rays fan outwards because they are coming towards the camera. In fact, the Sun’s rays are actually pretty much parallel by the time they reach Earth. They only appear to spread out like this because of the effect of perspective. It is just like looking down the length of train tracks. Even though they are parallel, they appear to spread outwards the nearer they are. Only when the sun is high in the sky so that its rays are pointing more directly downwards do crespuscular rays look parallel.

Crepuscular rays over Fort Collins, Colorado, US © Alli Bush.

The photograph comes from the website of The Cloud Appreciation Society of which I am a lowly member. Thus it was that in my in-box yesterday was their latest newsletter. In that newsletter there was the following stunning film, described thus:

This month, we were sent an amazing film of storms over Arizona, US. It was made by Davo Laninga, Cloud Appreciation Society Member No 1,095. You can learn a lot about how storms develop by watching time-lapse videos. Well done, Davo, for this stunning example, showing the monumental power that drives our atmosphere.

Do drop in to Dave’s website and admire his incredible photographs and videos.

And enjoy this:

Puts things back into perspective, doesn’t it!