Iridescent Lenticular clouds over Mount Rainier

This month’s image shows the beautiful effect that can result from the sunlight shining through thin parts of a cloud where the tiny droplets or ice crystals all have similar sizes. The sunlight can be ‘diffracted’ as it passes around the miniscule particles. The result is that it is split into different wavelengths, which appear as the colours of the rainbow. This optical effect is called iridescence or irisation and tends to appear at the fringes of clouds. This fantastic example, captured by Ryan Verwest, shows iridescence in lenticular clouds, and was spotted over Mount Rainier, Washington, US.
Photograph © Ryan Verwest.

Classic Cirrus

This month’s image was spotted over South Carolina, US.
© Photograph Betty Owen.

A sunset over Mount Rainier

Mount Rainier’s shadow being cast onto the clouds above makes it look like it is erupting. The dramatic light effect was spotted over Washington, US.
Photograph © Nick Lippert.

Cap clouds over the volcano brothers

The cloud-capped twin volcano brothers, Nevados de Payachata. The one with the crater at the top is the Parinacota volcano. The other is the Pomerape volcano. Location Bolivia, near the border of Chile.
Photograph © Alexandre Militao.

A Singer Serenading the Sunset

Well, at least, it looks like one to us. Spotted over Valona, Albania.
Photograph © Maurizio Barbieri.

Noctilucents over Edmonton

This month’s fantastic display of noctilucent clouds was spotted over Edmonton, Alberta, Canada.
Photograph © Hayley Dunning.

A Light Show over Bangkok

This month’s electric display was spotted over Bangkok, Thailand.
Photograph © Sitthivet Santikarn.

Minnesota Mammatus

The mammatus clouds that are this month’s pinups appeared below a storm rolling in at sunset over Lino Lakes, Minnesota, US.
Photograph © Jackie Zeleznikar.

A Stroke of Colours

This month’s rainbow pinup was spotted over Alcalá de Henares, Spain.
Photograph © Adolfo Garcia-Marin.

Rays and Shadows

These crepuscular rays and cloud shadows bursting out from around some Cumulus clouds were spotted over Bergamo, Italy.
Photograph © Fulvio Crotti Spreafico.

Racing The Roll Cloud

This fantastic example of a roll cloud was spotted between Sydney and Marimbula during the Rolex Sydney Hobart Race 2010/2011.
Photograph © Carlo Borlenghi/Rolex.

Faces in the Mammatus

Can you see them? Faces or no faces, we feel these dramatic mammatus clouds forming on a Cumulonimbus storm cloud over Douglas Bay, the Isle of Man, UK, are worthy winners of the title ‘Cloud of the Month’.
Photograph © Patricia Tutt.

A Cloudspotting Dog

We always like to see cloudspotting pets, which is why our Cloud of the Month for this month features Bella Pumpkin, the cloudspotting dog, gazing up at a Cumulonimbus over Skiddaw and Bassenthwaite Lake, Cumbria, UK.
Photograph © Heidi Bailey.

Contrail Creatures

This month’s image was spotted on a flight from Dublin to Spain, and do the contrails look to anyone else like, a Snake exiting stage left and a Frog leaping out of frame, top right?.

Photograph © John Gale.

Storm Front Surprise

This month’s cloud is known as an arcus, or shelf cloud, which sometimes prodrudes from the front base of a Cumulonimbus storm cloud. It was spotted by Eunice Clarke over Turnberry, Ayrshire in Scotland. “It was amazing standing there,” Eunice told us, “I was taking landscape pics on a nice sunny evening, when this strong gusting wind came from nowhere. When I looked behind me, this is what I saw coming towards me.”

© Photograph Eunice Clarke.

A Summer Storm

This month’s cloud is a Cumulonimbus cloud over Italy. Seen from below, it is unleashing ferocious lightning strikes on and around Lake Como.

Photograph © Barbara Mezzera.

The Northern Lights

This month’s image shows the beautiful atmospheric display known as the ‘aurora borealis’. It was given this name by Pierre Gassendi in 1621, after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas. Also known as the northern lights, the display of shifting colours results from the collision of energetic charged particles from solar storms with atoms in the Earth’s high atmosphere. Because of the Earth’s magnetic field, the displays only occur in northern latitudes, like this beautiful example over Denmark.

Photograph © Jesper Grønne.

A Cloud Smile

The most beautiful of halos, officially known as a circumzenithal arc, is created by tiny ice crystals. It is sometimes known as a ‘cloud smile’, and rightly so, it can’t fail to bring joy to any cloudspotter. The delightful example shown here was spotted over Stratford-Upon-Avon, UK.

Photograph © Emma Jukes.

Sunset Lenticularis

The image chosen this month shows a group of U.F.O. lookalikes, namely altocumulus lenticularis clouds, highlighted in a colourful sunset over Fiordland, New Zealand.

© Photograph Shirley Moodie.

On the Wing

This month’s image is a high flying Altocumulus cloud over Southern Spain.

© Photograph Christina Chelmick.

Squall Line

This month’s image taken in Derby, Australia, is a line of severe thunderstorms known as a squall line, they form along or ahead of a cold front.

© Photograph Hans Leenaarts.

Touching the Clouds

This month’s image of Altocumulus stratiformis clouds was taken at Disneyland, Paris. ‘Altocumulus’ are mid-level clumps of cloud that often appear in a layer which, when it is also described as ‘stratiformis’ spreads over the majority of the visible sky.
Photograph © Dawn James.

A Bow from the Air

This month’s image comes from the above the clouds category of our gallery. It is different view of a rainbow from the normal one, and was spotted on a flight above Anglesey, North Wales.

Photograph © John Rowlands.

Diamond Dust over Silvercreek

This month’s image is a true gem, a cloud of Diamond Dust. Early morning temperatures hovering around minus 27 degrees and falling ice crystals, created this varied collection of arcs and halos spotted by Jay Brazel at approx 8,700 feet above a small United States town called Silvercreek in Colorado.

© Photograph Jay Brazel.

Twin Peaks

This month’s image portrays classic Altocumulus Lenticularis forming as cap clouds over Mount Lidgbird and Mount Gower on the south east coast of Australia. Photograph taken from Lord Howe Island.

© Photograph Matthew Brennan.

Looking Down at The Clouds

As any angler will tell you, sitting in front of still water can give you a different perspective on the sky – one that allows you to look up at the clouds without straining your neck. And when the expanse of water is large, it can act like an enormous mirror that reflects huge areas of the sky, like this glorious Altocumulus sunset over southern Australia.

Perhaps the most dramatic example of water mirroring the sky is found on the Salar de Uyuni in Bolivia. This is the world’s largest region of salt flats, and is situated in the Andes, at an elevation of over 3,500m. The salt deposits are incredibly level and become flooded at certain times of the year to be covered in just an inch or two of water. Too shallow to develop any waves, the reflections appear to double the sky.

But you don’t have to cross the world to enjoy the pleasures of cloud reflections. Watch the clouds in any pond or slow river when the day is still, and you will see them sway dreamily with the water’s undulations, as if dancing to a music only they can hear.

© Photograph Heather Hartkamp.

Numbers in the Clouds

Every now and then, someone sends us a cloud in the shape of a number. This month, for instance, it is a Cirrus cloud in the shape of the number three.

In fact, number three is the most common. We’ve also had threes in from Palm Desert, California, Uppsala, Sweden, Margate, UK. There have been a couple of number twos over Cambridge and Stafford. But only one number one over Mercogliano, Italy, (also photographed by Modestino Carbone, who took the image above). We’ve even had a bunch of zeros, mostly photographs of the same cloud, over Dorset, UK.

But we only ever get low numbers. What’s going on? What about the other digits? Now that the collection is started, we think it’s time we graduated to higher numbers. In fact, we have developed an obsession about completing the set. What about fours? Fives? Someone must have seen a six, a seven… an eight? Most of all, we’re desperate for one of our members to capture the elusive cloud nine.

So please do send us your cloud digits – all will be gratefully received.
Except for threes. We are not interested in is any more of those.

© Photograph Modestino Carbone.

The Poor Man’s Optical Effect

Sun pillars are vertical streaks of light that appear above and below a low Sun as it shines through clouds that contain ice crystals, such as the Altocumulus clouds shown here. At night, they are known as moon pillars.

The optical effect is one of the ones that are collectively described as ‘halo phenomena’, and appears on about 25 days of the year over Europe. Sun pillars are caused by the sunlight reflecting off the surface of the ice crystals. So they are rather like an aerial version of the ‘glitter paths’ that appear below the bright sun on the surface of the sea, but it is the faces of tumbling ice crystals that cause the reflections here, rather than then rippled peaks on the ocean. A pillar extending above the Sun like this fine example, spotted over Lively Ontario, looks brightest when the Sun is just below the horizon.

Most of the other the arcs, rings and spots of light that are called halo phenomena only appear when the clouds’ crystals are optically pure, regularly shaped and neatly aligned. But this is not the case for sun pillars. They are like a poor man’s halo phenomenon, for they appear when cloud crystals aren’t so exquisitely refined. Since the sunlight needs only to glance off a surface of the crystals, they can be rough, irregular and jumbled.

© Photograph Paul Laplante.

Thick and Puffy

Your Turn To Do the Washing Up

The cloud species known as lenticularis is one of our favourite formations — not least because it often has the appearance of a UFO. The cloud’s name comes from the Latin for a ‘lentil’, presumably because no one could work out what the Roman’s would have called a flying saucer.

We like the way that this cloud hovers in place, even though a brisk wind is blowing at the cloud level. The cloud forms when the lower atmosphere is ‘stable’, which means that an airstream passing over raised ground, such as a hill or mountain, tends to rise and dip in a wavelike path. It is rather like the standing waves that hover on the surface of a fast-flowing stream in the lee of a rock. Lenticularis clouds can form downwind from the peak, at the crests of these invisible sanding waves of flowing air*.

But we particularly like it when lenticularis clouds take on the stacked formation, known as a ‘pile d’assiettes’, or ‘stack of plates’ in French, like the handsome Altocumulus lenticularis shown above. This type of stacked lenticularis only appears when the airstream encountering the raised ground consists of alternating moister and drier layers. The cloud droplets form as the moister layers cool upon rising at the crest of the standing wave, but are far less plentiful in the drier layers of air in between. Pile d’assiettes is the only internationally accepted cloud term that is in French rather than Latin.

When the atmosphere in the region is particularly stable, even just a gentle raising of ground level can be enough set up the waves of air that produce lenticularis clouds.

Photograph © John Maltas.

Pump it up

A New Cloud Name?

A few years back, we chose a Cloud of the Month which we didn’t feel very confident about identifying. Since it looks rather like the surface of a choppy sea viewed from below, we gave it the nickname of the ‘Jacques Cousteau cloud’, after the legendary 1970s French diver and ecologist.

But as we started receiving more and more dramatic examples of this cloud formation from members and visitors across the world, we decided that it warranted a more official-sounding name. We looked for a Latin one that would sound at home amongst the official cloud classifications and settled on ‘asperatus’, which is the Latin for ‘roughened up’. The term was used by Classical poets to describe the seas being agitated by strong winds.

We propose that asperatus should be adopted as a new ‘variety’ of cloud, meaning that it is a particular characteristic that appears in one or other of the main cloud types. This would mean that the rough and choppy looking Altocumulus cloud shown above would become known as ‘undulatus asperatus’.

Our proposed new cloud variety shares some similarities with existing formations such as the more regular waves of undulatus clouds and the hanging pouches of mamma clouds, but we feel that this cloud is different enough from them to be classified as a variety of its own – or a ‘supplementary feature’, if you want to be precise about it.

Who knows whether asperatus will eventually be accepted as an official variety? If it ever is, we will celebrate with a snorkelling holiday.

Asperatus over Schiehallion, Perthshire, Scotland © Ken Prior

By the light of the silvery moon

Every Sundog Has its Day

Cloudspotter Collision Alert

Please Form an Orderly Line

Nature can exhibit surprising displays of order in seemingly chaotic situations: lining up grains of sand into regular, parallel ripples below the ebb and flow of the surf; coordinating bees to form geometric honeycombs as they construct their hives; arranging fair-weather Cumulus clouds into regimented lines, known as ‘cloud streets’, like those in February’s Cloud of The Month.

Orderliness in clouds can seem more surprising than when it is found elsewhere in the natural world. Are clouds not the most disorderly things around, shaped as they are by the unruly motions of the atmosphere? So irregular is their movement that when physicists came up with Chaos Theory in the 1970s, some had been inspired by gazing up at the clouds.

While the particular curls and wisps of these ghosts of the atmosphere are indeed chaotic, the clouds themselves occasionally exhibit quite regimented formations. This tension between order and disorder is surely one reason we find them so intriguing to watch. Some cloudspotters love them for their stubborn refusal to abide by rules. Others, who tend to like to have their CD collections arranged in alphabetical order for easy access, find neat formations such as cloud streets a blessed relief.

Cumulus cloud streets spotted over Amsterdam, Netherlands by Carlos Herrero.

A New Dawn

While they may not know the name, most cloudspotters will be more than familiar with crepuscular rays. These optical effects, caused by the shadows of clouds, are the familiar beams of sunlight that appear to shine down from a hole in a layer of Stratocumulus or burst out in dramatic fashion from behind a Cumulus, as is the case in January’s The Cloud of the Month, above.

Crepuscular rays appear when the path of sunlight is made visible by atmospheric water droplets too scarce to appear as cloud, but plentiful enough to noticeably scatter the light. Like fingers through a torch beam in a smoky room, the shadows caused by the clouds provide edges to the path of the light, making the rays appear as sunbeams. These rays seem to radiate outwards from behind the cloud, in spite of the fact that they are actually almost parallel. Like like railway tracks approaching from the horizon, the effect is due to perspective.

The rays that form when the Sun is high in the sky often look like they are pointing downwards, especially when they break through a hole in a cloud layer (see here, for example). But when the Sun is low on the horizon, they invariably point upwards. They look like the fingers of a hand outstretched, waving to the day that is departing, or welcoming the one that’s just arrived.

Crepuscular rays spotted over Puesta, Mexico by Fabian Gonzalez.

During the longer autumn and winter nights, the ground has more time cool than at other times of the year. This is particularly the case when it is a starry night, devoid of cloud cover, for the ground loses (or ‘radiates’) its heat out to space much more readily without any blanket of clouds to keep it in. When such a situation coincides with no more than the slightest breeze of moist air, conditions are ideal for the formation of ‘radiation fog’.

Shadow Play