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

Mamma: the Silly-Season Clouds

Gloriously arresting cloudscapes are, of course, always good news. But when this particularly dramatic formation of mamma clouds* appeared over the UK during August – the holiday season when newsrooms are desperate for something to report – the cloud made the national headlines (The Sun, The Daily Mail, The BBC).

Most meteorology books will tell you that the name of these pendulous cloud features is the Latin for ‘udders’, but few ever agree on what actually makes mamma clouds appear. Why? Because no one really has a clue. ‘Relatively little is known about the formation mechanisms of [mamma],’ stated a 2005 study of them in the Journal of the Atmospheric Sciences (see here). As much as anything, this is because it is very hard to predict when and where they will show up, making it a challenge to be in the right place at the right time to study them.

What we do know is that these pouches can form below of a number of different types of cloud, but the more dramatic examples show up on the underside of the spreading anvil of Cumulonimbus thunder clouds (e.g. see here). Each individual pouch is typically one to three km across and, while they tend to be associated with powerful and dramatic storm clouds, they don’t actually forecast severe weather. This is because mamma generally form at the back, rather than the front, of moving Cumulonimbus clouds. By the time you see them, the storm cloud is already heading off to make news elsewhere.

* Also known as mammatus.

Photographed over St Albans, U.K © Vanessa Sonnabend. See this photo in the Cloud Gallery here.

Take Your Partners…

We are used to the swirling masses of cloud on those satellite photographs of storm systems. As the winds flow in towards the centre of the storm, they develop into an enormous rotating pattern simply because they are passing around the surface of a rotating sphere – the Earth. The spin of our planet causes storms to rotate in different directions in the Northern and Southern Hemispheres: they go anti-clockwise in the north and clockwise in the south.

Cloudspotters might therefore assume that the swirling pattern of clouds in this fine photo, taken from a plane off the coast of Alaska, is just such a storm system. They would, however, be wrong, for these aren’t the deep, furious Cumulonimbus clouds that form the cells of a storm. They are in fact just shallow, innocuous clouds, known as Altocumulus. Nor is this pattern spinning on account of the Earth’s rotation. The cloudy swirl here is due to something much more localised: an island in the path of the wind.

Anyone who has contemplated the undulating surface of a babbling stream will know that, as the current parts to flow around a small stone, it can develop a succession of tiny eddies. Each of these swirls, known as ‘Kármán Vortices’, rotates the opposite way from its neighbours. Lined up in a beautiful procession of weaving curls, they look dancers in a Scottish reel.

Exactly the same Kármán Vortices can form on a much, much larger scale within the atmosphere, as winds part to pass around an island rising from the sea. This month’s photograph is in fact a rare record of one such atmospheric vortex, in which the winds spin with gay abandon in an island’s wake. The dance would, of course, be invisible were it not for the Altocumulus clouds. They can never resist the wind’s energetic embrace, and so follow every graceful twirl of its Highland dance in the sky.

Photographed over the Cook Inlet, southwest of Anchorage, Alaska, US © Barbara Bundy. See this photo in the Cloud Gallery here.

The Arc of Many Names

The ‘summertime halo’, the ‘fire rainbow’, the ‘circumhorizon’ or the ‘circumhorizontal arc’… Whichever of its names you decide call it, this enormous, rare, pastel-coloured optical effect will only appear up in the sky when several different factors happen to occur at the same moment.

Firstly, there needs to be the right sort of cloud around, for this is one of the many ‘halo phenomena’ that can only appear as the light shines through ice-crystal clouds, such as this fine Cirrus. The sun also has to be high in the sky (hence the ‘summertime’ name); in fact, it needs to be at least 58° above the horizon (hence the ‘horizon’ name).

In order to refract the high sunlight in the right way, the ice crystals that make up the Cirrus cloud must be shaped like microscopic hexagonal plates. They must also be aligned more or less horizontally (hence the ‘horizontal’ name), for the colours are formed as light rays enter the clear crystals through a vertical side face and exit through their flat bases. So long as the crystals don’t wobble too much in the wind, the 90˚ inclination of these two sides results in pure rainbow-like colours. When the crystal alignment is just right, the entire cirrus cloud shines like a flaming rainbow (hence the ‘rainbow’ name, even though it is not, of course, a rainbow at all).

While most halos can be observed over any parts of the planet, this one is generally found only in those countries that lie below 55° latitude. North and south of this, the sun never rises above 57.8° in the sky. (That said, you might still be able to see the summertime halo in higher-latitude countries so long as you manage to climb a high mountain just as all the other requirements happened to coincide.)

Another example of the summertime halo was spotted by 11-year-old cloudspotter, Hugo, and can be seen in the gallery pages here.

Not only does this rare phenomenon have more than its fair share of names, it is also very beautiful. So while we are at it, why don’t we also start calling it the ‘beautiful arc’, the ‘arc of lovely colours’ and the ‘really rather delightful-looking halo’?

Photographed over Fort Worden State Park, Port Townsend, Washington, USA © Russ Hendricks. See this photo in the Cloud Gallery here and here.

Some like it Hot

There is a strong northwesterly wind that blows across New Zealand’s South Island which is said to have a disturbing effect on the local population.

The Nor’wester, as it is known, sends temperatures soaring as it sweeps across the Canterbury Plains and has been statistically linked to increases in suicide and domestic violence. Some people feel elated when the dry, hot air hits, but most feel depressed, irritable and drained of energy.

However The Nor’wester also brings with it one of the rarities of the skies, a cloud with its own name. The Nor’west Arch is a distinctive altocumulus formation which partly takes its name from the wind that hurries it along and partly from its shape, because it appears as an arch of high white cloud in an otherwise clear blue sky. It is also often referred to as the Canterbury Arch.

This weather pattern is peculiar to the South Island’s east coast. Warm moist air from over the Tasman Sea is pushed up by the Southern Alps, causing it to cool rapidly, and much of the moisture is dumped on the west coast. As the air passes over the alps, the water vapour remaining becomes visible in a band of cloud over the mountains at the top of each wave of air. To a viewer on the eastern side, this appears as an arch of cloud.

The standing wave of The Nor’west Arch is caused by the moisture condensing and becoming visible towards the top of the wave and then evaporating again as the air descends to the trough of the wave.

Let’s hope this impressive sight helps lift the depression caused by the fiery blasts that accompany it.

The Nor’west Arch spotted by Peter Rees over South Island, New Zealand.

Where Were You Brought Up?

The Cumulonimbus could never be called a refined cloud. It is the beast of the lower atmosphere: roaring with deafening thunder; spitting shards of lightning and hailstones; whipping up twisting tornadoes and spawning dramatic cloud features, such as the udder-shaped mammatus clouds, cigar-shaped roll clouds and, well, wall-shaped wall clouds. Sometimes, the Cumulonimbus also produces something called a ‘microburst’, which is best thought of as a cloud sneeze. Don’t be deceived by the ‘micro’ part: the sneeze of a Cumulonimbus is anything but restrained.

A microburst is a very localized column of air – up to 2.5 miles (4km) across – which shoots earthwards from the base of the cloud, spreading outwards with violent force upon reaching the ground. With gusting speeds of up to 150 mph, these winds can damage buildings, fell trees, and have been known to cause aviation crashes.

Much like human sneezes, microbursts can be either dry or wet. They do however last rather longer than ours: between 5 and 15 minutes. Along with chilly winds, the wet varieties produce sudden downpours. These can be quite heavy: enough to give you a cold, should you be in the firing line without the right clothing. Could the Cumulonimbus not muffle its vulgar microbursts? Presumably, no one has ever had the courage to try and teach this beast of the atmosphere any manners.

Photographed over Long Island, in The Bahamas © Dene Georgelin. See this photo in the Cloud Gallery here.