Rounded, smooth, globular ‘pouches’ clumped together and hanging underneath the base of a cumulonimbus cloud. They often form on the underside of an anvil and are accompanied by thunderstorms. The name translates to mamma and means ‘mammary cloud’.
One of the 10 characteristic cloud types (or cloud genera) recognised by the International Cloud Atlas. Its name comes from altum (height) and cumulus (heap). It is usually white or grey, and tends to appear as sheets or patches of wavy, rounded masses or rolls.
An instrument used to measure the altitude of an object above a fixed level.
A beautiful illumination effect seen in mountainous regions around sunset, beginning when the sun is around 2º above the horizon. At its most spectacular, snow-covered mountains in the east assume vivid tones of yellow, pink and purple.
Centred near the Aleutian Islands in the North Pacific, this semi-permanent depression is one of the main centres of activity in the atmospheric circulation of the Northern Hemisphere in the winter.
The mixture of gasses that make up the Earth’s atmosphere. Excluding water vapour and dust, the main components of air are nitrogen, oxygen, argon, carbon dioxide, neon, helium, krypton, hydrogen, xenon and ozone.
The process of growth of snow or ice crystals through collision with each other. Without aggregation, the snowman would be extinct.
The study of regions of the atmosphere more than 50km from the Earth, which have different fundamental properties to those found in the lower atmosphere.
A type of fog formed when warm, moist, stable air moves over a far cooler surface. It is most commonly found over cool sea areas in spring and summer, but does occasionally form over land in the winter, especially when the ground is frozen or covered by snow.
Taking its name from the Latin for dawn, aurora is the phenomenon of visible light being emitted by the high atmosphere, caused when charged particles emitted by the sun are deflected by the Earth’s permanent magnetic field. In Britain, aurora usually appears as a grey-white glow on the northern horizon. The terms ‘aurora borealis’ (or northern lights) and ‘aurora australis’ (or southern lights) are applied to the occurrence of aurora in the northern and southern hemispheres respectively.