SCIENCE AND TECH
Asperatus to Stratus: A Guide to Cloudspotting from the Sky
The earth has a new cloud! How to spot it and more common precipitation formations from the sky
You might know your stratus from your cirrus, but could you spot an undulatus asperatas from your window seat?
Don’t feel despondent if you can’t: The undulatus asperatus (the name is Latin for “agitated waves”) is the first new cloud to be named by scientists since 1951, and it’s one to behold. A dramatic and downright apocalyptic cloud marked by a distinct wave pattern – and a sense of impending doom – the asperatus looks like a tumultuous sea, as viewed from below.
The cloud phenomenon, which forms much like a mammatus cloud and is sheared into wavelike forms like an undulatus, was first identified by an eager cloudspotter in Cedar Rapids, Iowa in 2006, and has since attracted a lot of attention among enthusiasts. In the decade since, Gavin Pretor-Pinney, founder of the UK-based Cloud Appreciation Society, has been campaigning the World Meteorological Organisation to have the formation officially recognized in the annals of cloud science. Finally, on March 23, 2017, World Meteorological Day, the undulatus asperatus became legit, officially entering into the International Cloud Atlas as the “asperitas.”
While catching a glimpse of these relatively rare clouds would make for an Instagram-worthy photo, you certainly wouldn’t want to be in a plane when they’re about. According to weather.com, “They occur when enough atmospheric instability, or rising air, is available to create widespread cloud cover, as well as wind shear and turbulence, which creates the wavy, rough sea-like visual effect.” They would most certainly guarantee a choppy ride.
That said there are other impressive and less intense atmospheric puffs to observe from on high. Here’s a quick guide to help you decipher your cirrostratus from your cumulus congestus – and how much turbulence to expect with each.
The Great Cloudwatcher, Wikimedia Commons
You know those clouds that just drape the sky in an unrelenting blanket of grey? Those are stratus clouds and they typically mean precipitation is on its way.
Low-lying clouds, they occur when moist air gently rises in stable conditions to the point of condensation and can cover hundreds of square kilometres. When they’re very low, that’s when we see fog. Low, dense, dark grey clouds with a more ragged shape (read: rainclouds) are called nimbostratus and deliver steady, persistent rain or snow.
While they’re boring and dreary to look at – and mean you should grab an umbrella – the good news is that they’re not known for causing turbulence.
Turbulence level: low
Alana Sise, Flickr
Clouds that settle in middle latitudes (6,500 to 16,500 feet) are called altostratus and they always carry significant moisture. They’re identified as a thick veil of largely featureless clouds. Altostratus clouds indicate an approaching front and can result in precipitation, if they’re dense enough.
From the ground, altostratus are distinguishable from stratus clouds by their lack of detail. If you can see texture on the clouds, it’s likely stratus; if the cloud is smooth and featureless, it’s likely altostratus.
Puffier clouds in the middle atmosphere are altocumulus. These ones create a more dynamic-looking sky with their large swath of smaller clouds. They don’t tend to produce precipitation or anything more than light turbulence, but if the pattern becomes denser it can signal an approaching front.
Altostratus undulatus are those mid-level clouds with an undulating appearance, the result of wind shear. These clouds don’t produce weather but are a sign of localized moderate turbulence.
Turbulence level: low to moderate
Top: Wikimedia Commons; Bottom: Brocken Inaglory, Wikimedia Commons
Cirrus clouds are those wispy high-level ones that decorate the sky like brushstrokes. Present at altitudes of 16,500 feet or higher, they often signal an approaching frontal system (an area where air masses of different temperatures meet). And weather fronts typically result in precipitation.
The clouds themselves are made of ice crystals since they sit at a point in the atmosphere where the temperature is below freezing.
The pattern of cirrus clouds indicates the stability of the air at altitude. For instance, cirrus uncinus, or clouds with thicker more hook-like wisps (often described as resembling a horse’s tail) are the result of high-speed wind below the level at which ice crystals form, and can be a sign of moderate levels of turbulence at cloud level.
Meanwhile, cirrostratus clouds – a thin even layer that covers the sky – indicate stable air. Conversely, cirrocumulus – that lovely-looking blanket of thin clouds with a pronounced ripple pattern – are the result of air instability at cloud level.
One of the more unique formations of cirrus clouds is called Kelvin-Helmhotlz, which is characterized by wisps that form a distinct wave pattern. They’re caused by wind shear, and rare to see because they dissipate within minutes of forming. While pretty – a cloudspotter’s delight – they result in moderate to severe turbulence at cloud level.
Turbulence level: low to moderate
KairoK, Wikimedia Commons
Pretty white fluffy clouds are technically cumulus clouds. Cumulus, which means “heap” in Latin, are not generally associated with rain – unless there are heaps of them, which can result in localized showers.
Look for them at higher altitudes, starting at 2,000 feet. These clouds are due localized pockets of warm air rising, also known as weak convection, so they’re as tame as they are lovely.
As cumulus clouds get fluffier, denser and taller, however, the story begins to change. Cumulus mediocris are those fluffy clouds that seem taller than they are wider (the thin ones are Cumulus humilis). While they’re the result of weak to moderate convection, which is still pretty stable air, they’re often a sign that cumulus congestus clouds are on the rise.
Cumulus congestus are tall in appearance and can bring with them moderate to heavy showers of rain or snow – which means moderate to heavy turbulence at cloud level.
Turbulence level: mild to moderate, depending on the formation
Михал Орела, via Wikimedia Commons
While technically cumulus clouds, cumulonimbus are in a class of their own when it comes to spotting from the sky. Specifically: you don’t necessarily want to be in the sky when they’re around. While not dangerous, per se, they’re guaranteed to make for a choppy ride.
Cumulonimbus calvus clouds, those big fluffies with a mushrooming top, are seen from 3,000 to 30,000 feet and are caused by powerful convection and atmospheric instability. Calvus clouds always produce some sort of precipitation and the powerful updraft associated with them can produce significant turbulence.
If you happen to spot a cumulonimbus with what looks like an anvil on top, you’re looking at a pileus formation. These clouds are found between 20,000 and 30,000 feet and are a sign of instability in the surrounding air mass. These clouds are a signal of thunderstorms, which cause significant turbulence at cloud level.
Exceptional to look at, cumulonimbus incus are known as the “King of Clouds,” because they’re enormous – in tropical climates they sometimes reach 60,000 feet in height – and tumultuous. Sporting an even more distinct anvil crown, these clouds are harbingers of strong winds, lightning and possible tornadoes. So, yeah, they’re a source of turbulence.
Turbulence level: not for the faint of heart, best observed from the ground
Alf van Beem, Wikimedia Commons