November is proving to be a good month for cloud spotters. Most recently, strange-looking formations over Cape Town, South Africa precipitated a flurry of UFO-themed headlines, but the past two weeks or so have brought us cool cloud sightings from all corners of the globe.

 1. UFO clouds – Cape Town, South Africa

Let's start with Cape Town's UFO invasion. It might look more like science fiction than fact, but these "lenticular" clouds, also known as UFO clouds or cloud-ships, are a very real phenomenon. They form when moist air passes over large objects such as buildings, bridges, or, in this case, Cape Town's famous Table Mountain. If the temperature is low enough on the other side, that moisture will condense, forming the large saucers. 

2. Skypunch clouds – Victoria, Australia  

Fallstreak -cloud _2015_11_10
Image: Imgur

This rare formation generated its own UFO buzz when photographer David Barton snapped it in the skies over eastern Victoria recently. Skypunch clouds (or "fallstreak holes") are circular gaps that form in a cloud layer. This only happens when the water in the cloud is supercooled, but not yet frozen. If something disturbs this supercooled water, for example a plane's propellers, it can trigger ice crystals to form in the mix. This sets off a chain reaction that causes any water droplets surrounding the ice to evaporate, leaving the hole behind. 

3. Shelf clouds – Sydney, Australia 

When this ominous cloud moved in on Sydney late last week, it unleashed some pretty blustery weather. Menacing in appearance, shelf clouds aren't actually dangerous, but they do typically come hitched to the leading edge of a thunderstorm. What you're seeing here is the boundary between the storm's updraft and downdraft. Fun fact: When a shelf cloud passes overhead, you'll feel an abrupt shift in wind direction!

4. Kelvin-Helmholtz clouds – Colorado, US  

Spotted over a ski resort in the Colorado town of Breckenridge, these bizarre clouds are formed when different layers of air move at different velocities. Because the upper layers of air are moving at higher speeds, they will often "scoop" the top of the cloud into wave-like structures. Much of the turbulence you feel in an airplane is caused by formations like these.

5. Wave clouds – North Carolina & New Zealand 

Linville Gorge Autumn Asperatus - FEEL FREE TO SHARE!My plans changed for my Autumn 2015 trek into the Linville Gorge,...

Posted by Cathy Price Nature Photography on Thursday, November 5, 2015

And speaking of waves, these watery formations are officially known as asperatus clouds. The top image was snapped in mountains of western North Carolina late last month (the other one, from back in 2005, shows the skies over Canterbury in New Zealand). The name loosely translates to "agitated waves", but just what causes them is still a bit of a mystery. Because they seem to have vertical elements moving through them, some have proposed that these might be an entirely new classification of cloud. That would make asperatus clouds the only addition since 1951.

6. Night shining clouds – Xinjiang, China

Snapshots of this eerie-looking phenomenon popped up on Chinese social media platform Weibo recently. One possibility is that you're looking at what's called a noctilucent cloud. Every so often, people at high altitudes catch a glimpse of these shimmering bodies, which form in the mesosphere up to 50 miles (80 kilometres) above the Earth’s surface. They’re are thought to be made of ice crystals, which catch and reflect sunlight. 

7. Sulphur clouds – Venus

Image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. Oxford

And one from beyond our planet, for good measure. The European Space Agency recently released beautiful images of swirling sulphur clouds to mark a decade since its Venus Express spacecraft left Earth. These vortexes on Venus are created when warm air from the equator rises and spirals out towards the poles. Venus's atmosphere is composed mostly of carbon dioxide, but the planet is also wrapped in a thick cloud of sulphur. These gasses make Venus hot ... really hot – sometimes over 840°F (449°C) at the surface. 


Top header image: Jono Hey, Flickr