Weather Glossary : A

Acid Rain: Rain that is more acidic than normal precipitation because water vapour has condensed on to particles of sulphate or nitrogen oxide.
Adiabatic: Changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or descends in the atmosphere, with no exchange of heat with the surrounding air.
Advection: The transfer of heat by the horizontal movement of air or water, such as a warm wind or ocean current.
Advection Fog: Fog caused by the condensation of water vapour when warm, moist air crosses cold ground or sea.
Air: A naturally occurring mixture of gases, chiefly nitrogen and oxygen with small amounts of argon, carbon dioxide, and water vapour. Air also usually contains dust and pollen.
Air Mass: A large body of air with the fairly uniform temperature and humidity of its source region.
Air Pressure: The weight of the atmosphere pressing down on the Earth's surface. The effect is caused by gravity. Also called 'atmospheric pressure'.
Albedo: The measure of the reflectivity of a surface.
Anabatic: Rising, as when air moves up a hillside.
Anemometer: An instrument for measuring the force and speed of wind.
Angular Momentum: The energy of motion of a spinning body or mass of air or water. Its value depends on the mass of the body, its radius of spin, and its rate of spin.
Angular Velocity: The rate at which a spinning body, such as a planet, rotates. The Earth rotates at 15 degrees per hour, which is its angular velocity.
Anticyclone: A large area of high atmospheric pressure, characterised by outward-spiralling winds - a "high".
Atmosphere: A layer of gases surrounding a planet - on the Earth, chiefly made up of the gases Oxygen, Hydrogen and Nitrogen.
Atmospheric Pressure: The weight of the atmosphere pressing down on the Earth's surface. The effect is caused by gravity. Also called 'air pressure'.
Atoms: The smallest parts of an element - such as hydrogen or oxygen.