Weird Cloud Atlas: a collection of spectacular cloud formations
A skier looks at a lenticular cloud, Mauna Kea, Hawaii, US. Lenticular clouds are popular with UFO believers because they often look like flying saucers. The lens-shaped clouds form at high altitude and are usually formed when moist air passes over a mountain range and is heated adiabatically (that is, without any transference of heat energy) as it descends. The cloud pattern depends upon the wind speed and the shape of the mountains. A constant wind may produce clouds which are stable and remain virtually stationary in the sky for long periods.
Cumulonimbus cloud over western Africa near the Senegal-Mali border. Cumulonimbus clouds rise vertically until they hit a natural barrier, known as the tropopause, and then flatten out. Cumulonimbus clouds usually herald the onset of a severe storm. In this image, which was taken from the International Space Station (ISS), several cumulonimbus towers are seen underneath the main cloud, casting a large shadow on the land below..
Mammatus clouds over northeast South Dakota, . US. Mammatus, also known as mammatocumulus (meaning mammary cloud or breast cloud), is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. They can produce some dramatic and unusual patterns on the sky and are also associated with severe storms.
Sonic boom cloud created by an American F/A-18 Hornet over the Pacific Ocean. This fighter jet is not flying through a cloud, rather, it created the cloud by accelerating towards the speed of sound (768mph). As the aircraft moves through the air, an area of low pressure forms behind it. When the pressure of this air parcel falls below the vapour pressure of gaseous water, the water in the air condenses to form the cloud.
Tornadic supercell thunderstorm over a plain in Mycroft, Wyoming, US. Supercell thunderstorms rotate with immense energy, causing a strong updraft and severe weather, including tornadoes, hail, heavy rain, lightning and heavy winds. Inside these severe long-lived storms the wind speed and direction changes with height. This produces a strong rotating updraft of warm air (a mesocyclone) as well as a separate downdraft of cold air. Around a third of supercells produce tornadoes and are termed tornadic.
Pileus cloud above the Sarychev volcano as it erupts, Kuril Islands, Russia. Pileus clouds, also called scarf or cap clouds, are small clouds that form on top of a bigger cloud. In this photo a pileus cloud (centre) has formed above a cloud of volcanic ash from the Sarychev volcano. A large plume of smoke, steam and ash is erupting from the volcano while pyroclastic flow of denser ash descends the volcano sides. The picture was taken by astronauts aboard the International Space Station. Note too the ring of non-cloudy air surrounding the volcano that is thought to have been caused by the eruption.
Steam ring being blown from the Bocca Nuova vent of Mount Etna, Sicily. Steam rings are generated when a pulse of steam is ejected from a near-cylindrical volcanic vent. The steam in the centre of the pulse is propelled by thermal forces, whereas the steam at the edge of the ring suffers drag from the surrounding air. This results in an annular rotation, which in the correct conditions can become stable over a span of a few minutes and produce a steam ring. The process is similar to blowing smoke rings.
Noctilucent clouds are crystals of ice hanging around 80 kilometres high in the atmosphere that catch the light of the sun long after it has set on the horizon. Natural nacreous clouds occur at altitudes of 20-25 kilometres. The cloud in this image was formed from the exhaust of a missile launched from a distant firing range.
Sunlit contrail over South Wales. This image shows a vapour trail left by an aircraft lit by the sun below – so that it appears to be a fiery meteor.
Shelf cloud, Minnesota, USA. When seen from the ground shelf clouds appear as low, wedge-shaped clouds and are usually associated with severe thunderstorms.
Jetstream cirrus clouds the Sahara Desert, Egypt. The jetstream is a high-altitude, fast-moving air current a few thousand kilometres in length.
Altocumulus undulatus clouds, Abruzzo National Park, Italy. This cloud formation consists of parallel bands of cumulus clouds. It occurs when a layer of altocumulus cloud is affected by wind shear.
Lightning strikes the ground from a supercell thunderstorm. Supercell thunderstorms rotate with immense energy, causing a strong updraft and severe weather, including tornadoes, hail, heavy rain, lightning and heavy winds.
Another lenticular, or UFO, cloud.
Actinoform clouds are seen from space. These large cloud formations form ray-like patterns over hundreds of kilometres. They are associated with drizzle and gloomy weather.
Gravity wave clouds over the Gulf of Mexico, Texas, US. Gravity clouds are distinctive ripple-like clouds that usually form over the ocean. The ripples are caused by the movement of a high pressure area and its cold front. Dense air is pushed upwards into the less dense air above it, forming the crest of the wave. Gravity pulls the dense air back down, forming the trough. This image was taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Aqua satellite.
Von Karman cloud vortices above Alexander Selkirk Island, Chile. These clouds look like they have had a hole punched through them. In fact they are naturally occurring vortices crafted by wind patterns on the clouds. In this image these cloud vortices (swirls down left) have been caused by the peak of Alexander Selkirk Island (bottom left) disrupting wind-blown clouds. This image was captured by the Enhanced Thematic Mapper Plus (ETM ) sensor on NASA’s Landsat 7 satellite.
Lightning illuminates clouds above Monument Peak, Arizona, US. Lightning is an electrical discharge caused by the accumulation of electrical charge on clouds.
Vapour spout. This type of weak localised vortex may occur over water near a lava flow that has reached the coast. Lava pouring into the sea boils the water, causing local cloud formation (top left), and raises the temperature of the surrounding water. If wind blowing around the area creates a rotating air mass, this rotation in combination with strong updrafts from the heated sea surface and the saturated atmosphere from the clouds can create a funnel of air. The reduced pressure within the funnel may draw in some of the water vapour from the nearby clouds to form a vapour spout.
Supercell just north of Grand Island, Nebraska, US
Flying saucer or Lenticular cloud
Cirrus clouds are generally characterised by thin, wispy strands, giving them their name from the Latin word ‘cirrus’, which mean a ringlet or curling lock of hair. Cirrus clouds generally appear white or light grey in colour. They form when water vapour undergoes deposition at altitudes above 5,000m (16,500 ft) in temperate regions and above 6,100m (20,000 ft) in tropical regions. They often arrive in advance of bad weather systems or tropical cyclones and so often indicate that the weather conditions may soon deteriorate.