A faint, curved halo―sometimes called a mock sun―that appears opposite to, and at the same elevation as, the real sun. It is a rare phenomenon, the cause of which remains hotly debated.
Anti-trades, also known as countertrades, are winds in the upper atmosphere which blow above and in the opposite direction to the trade winds.
An exception to the fine weather usually associated with anticyclones, anticyclonic gloom results from stratus or stratocumulus clouds forming in the moist air below the system, often trapping pollution from towns and cities below.
The process of growth of snow or ice crystals through collision with each other. Without aggregation, the snowman would be extinct.
A weather system with higher pressure in the centre than in its surroundings. An anticyclone is characterised on a weather chart by completely closed isobars, roughly circular in form, spreading out from the central high pressure area. The presence of an anticyclone system usually results in fine, cloudless weather.
A form of barometer invented by Lucien Vidie in 1843. In its simplest form it consists of a small capsule made from a beryllium and copper alloy, which is exhausted of air. Small changes in external pressure cause the capsule to expand or contract.
An instrument for determining the speed of the wind. Its name is derived from the Greek word anemos, meaning wind.
A local wind that blows up a slope heated by sunshine.
One of the 10 characteristic cloud types (or cloud genera) recognised by the International Cloud Atlas. Its name comes from altum (height) and stratus (spread out). It appears as a greyish or bluish sheet of cloud, partly or totally covering the sky, but with parts sufficiently thin to at least vaguely reveal the sun.
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.
