1. Gravity Waves

Credit:  Mick Petroff

When cold air gets trapped beneath warm air above,  it behaves a bit like bathwater. Because the cold air near the ground is higher in density,  disturbances from wind or topography cause a ripple effect,  sometimes visible in the form of gravity waves.

2. Asperatus Clouds

Credit:  Witta Priester

Asperatus clouds form under the same conditions as gravity waves,  but rather than rippling,  asperatus represent chaotic sloshing.

3. Lenticular Clouds

Credit:  klausbalzano/Flickr

Lenticular clouds are another type of wave cloud,  but they mostly commonly form when air is obstructed by an object,  such as a mountain. These clouds are stationary and can form directly over the obstruction or farther downwind. The phenomenon is similar to rapids on a river,  where water passing over a rock will rise and fall several times over. Occasionally,  they bear a UFO-like appearance.

Pileus clouds or “cap”  clouds are lenticulars cloud that form atop a cumulus or cumulonimbus clouds. Below is a rare photo of a pileus cloud scattering light to produce a rainbow effect.

Credit:  estherhavens.com

4. Mammatus Clouds

Credit:  Craig Lindsay

Mammatus clouds typically form on the underside of thunderstorm anvils. They can form for a variety of reasons but generally represent pockets of moist air falling into drier air below. The most impressive mammatus clouds are often associated with intense supercell thunderstorms.

5. Fallstreak Holes

Credit:  Lisa &  Tony Schultz

Many of the clouds you see have a concentration of super-cooled water droplets. Oddly enough,  water does not freeze automatically at 32 F / 0 C,  and seed crystals are needed to trigger the process. This can occur both naturally and artificially,  with fallstreak holes being a great representation of this phenomenon. This happens when a chain reaction of crystallization sends ice crystals cascading downward,  leaving a hole in the cloud layer.

6. Sprites,  Elves &  Blue Jets

Credit:  University of Alaska Fairbanks

These electrical pulses look a lot different than regular lightning,  and the mythical names are fitting. They occur above intense thunderstorms, and it wasn’t until 1989 that they were caught on camera. That’s for good reason, since they only linger for a few milliseconds,  so count yourself lucky if you ever see these in person.

This video has some of the best footage of blue jets to date.

7. Pyrocumulonimbus

Credit:  Jeremya Greene

Pyrocumulus are distinct by origin. They are fueled by the heat of a volcano or wildfire, and if conditions support thunderstorms, they can grow into pyrocumulonimbus. With wildfires,  these are dangerous since lightning strikes can off a new set of fires –  a nightmare for firefighters. In January 2013,  a pyrocumulonibus cloud grew into a supercell thunderstorm that produced a large and destructive fire tornado.

VIDEO:  Mt Arawang Fire Tornado – 18th January, 2003

Warning:  This video occasionally contains strong language.

8. Shelf Clouds

Credit:  Jason Weingart

Shelf clouds signal a boundary between warm air and air cooled by a thunderstorm. They are also a good indication of strong winds,  and their menacing appearance comes from rushing winds pushing outward from the storm. The actual cloud feature develops as wind plows through the warm air ahead. Well-defined shelf clouds have striated bands,  resembling an alien spaceship. This is due to an area of strong wind shear at the head of an approaching windstorm.

Credit:  Doug Berry

9. Kelvin-Helmholtz Waves

Credit:  Henrik Bondo

Kelvin-Helmholtz waves have the look of a curling ocean wave. They are a consequence of wind shear and are not exclusive to Earth’s atmosphere. Photos revealed the same type of wave formations on Saturn.

Credit:  NASA

10. Sun Dogs

Credit:  Deven Stross

Sun dogs appear as a ring around the sun. They are caused by light refracting off ice crystals suspended in the air and are most commonly seen when the sun shines through a thin layer of cirrus clouds. On very cold days,  an abundance of ice crystal near the ground can make the ring even more pronounced as in the picture above.