Weather forecasts rely on data from satellites – and often images which don’t look particularly spectacular can yield important data about the physical processes in the atmosphere at different times. Some instruments aboard satellites can show phenomena that would not normally be visible to the human eye. When it comes to clouds, we can see a lot from space.
Weather forecasts rely on data from satellites - and often images which don't look particularly spectacular can yield important data about the physical processes in the atmosphere at different times. Some instruments aboard satellites can show phenomena that would not normally be visible to the human eye. When it comes to clouds, we can see a lot from space.
1. Cumulonimbus clouds
Thunderstorms develop when warm parcels of air rise through the atmosphere. As a parcel of air rises, it meets cooler air, causing the moisture it carries to condense into cloud. The rising air is stopped by an abrupt rise in temperature at the bottom of the stratosphere and the cloud spreads out to form the anvil shape associated with the top of a thunderstorm.
The development of anvil clouds, which can be 40,000 feet off the ground and higher, can be seen in satellite imagery. If the part of the storm where the air is rising, the updraft, is particularly strong, clouds may break through the anvil.
2. Overshooting top
A powerful storm updraft can break through the anvil cloud to create a dome-like shape called an “overshooting top” - which you can see bubbling through the anvil in this image from Meteosat showing a storm over the Czech Republic on 25 June 2006. Overshooting tops can be short-lived phenomena or can last for a long time with a violent storm such as a supercell. The presence of an overshooting top can indicate that the storm is more likely to produce severe weather on the ground.
3. Cirrus clouds
Cirrus clouds are wispy, high altitude clouds made up of ice crystals. They can be seen clearly in this image taken over Algeria in May 2003. They are often partly translucent.
4. Cloud streets
Fluffy cumulus clouds can form cloud streets – seen in this image as parallel lines of cloud. The clouds form this way along the line of low-level wind. They can sometimes be seen from the ground, but stand out much more clearly in satellite images.
5. Gravity waves
The atmosphere is not the same through all of its layers. Gravity waves are created when moist air encounters areas of uneven air density. An example of gravity waves can be seen towards the bottom of this image, taken above the island of Corsica by Meteosat 8 in December 2006. Clouds form when the air rises and cools, and dissipate again as the air falls and warms up. Unlike cloud streets, gravity wave clouds form perpendicular to the direction of low-level winds. They are not gravitational waves, which are part of Einstein’s theory of general relativity.
Condensation trails (or contrails) appear high in the sky as a cirrus-type cloud in the wake of an aeroplane. The trails are not always obvious in visible light images, but stand out over Spain in this infrared image from Meteosat. Contrails form because of the interaction of the hot exhaust from the aircraft engine with the surrounding air. The formation of contrails depends on the temperature and level of moisture in the air, and they can remain in the sky for several hours after the aircraft has passed.
Dissipation trails (or distrails) are also related to aircraft. They appear as holes or blank strips in an area of cloud. These trails form in supercooled clouds – meaning an environment where the temperature is below freezing but water is still liquid. The exhaust gases from the aircraft’s engines, and the disruption to the air from the plane passing through, can allow the supercooled water to turn into ice crystals and drop out of the cloud – leaving the gap we see from space.
8. Small scale vortex
A water vapour vortex also appears as a strange gap in the satellite image, but forms in a different way. In the northern hemisphere, this hole in the water vapour is related to a low pressure system and has moist air moving clockwise around the centre. The gap arises because of drier air injected from the stratosphere. A water vapour vortex can last for several days. For more information on this image, click here.
Fog is defined by how much it reduces visibility, and it can cause a lot of disruption to transport. Fog forms when the air is saturated – it can hold no more water at its current temperature – so water droplets condense. Air can start to cool for a variety of reasons, including because the sun has set, or because it encounters lower temperatures beneath it (such as warmer air moving over the sea, or moving over lying snow).
10. Tropical storms
Observations from space have transformed our understanding of tropical storms, the strongest of which are known as typhoons, cyclones, and hurricanes, depending on where they are. These storms form over water warmer than 25C and can grow to enormous sizes.
Before satellites, it was much more difficult to tell if one of these storms was approaching. Now the development and future track of a storm can be predicted in advance using a combination of ground-based and space-based observations, feeding computer models.
These storms have very low atmospheric pressure - lowest at the centre, and through the combination of low pressure, high wind and tides can cause huge storm surges when they eventually hit land. The central eye and swirling cloud patterns make these storms very distinctive from space, but while they can be beautiful, forecasters and emergency managers work hard to try to avoid deaths and injuries along their paths.
Coastal areas of Queensland were evacuated before Cyclone Yasi, pictured above, made landfall.