Weather Glossary

  • Acid rain

    Rain that is more acidic than normal because water vapour has condensed on to particles of sulphate or nitrogen oxide.

  • Advection

    The transfer of some property (e.g. temperature or moisture) by the horizontal movement of air or water, such as wind or ocean current.

  • Advection fog

    Fog caused by the condensation of water vapour when warm, moist air crosses cold ground or sea.

  • Aerosol

    A suspension of microscopic liquid and solid particles in the atmosphere for at least a few hours. Can be natural or anthropogenic (man-made).

  • Air

    A naturally occurring mixture of gases, chiefly nitrogen and oxygen with small amounts of argon, carbon dioxide and water vapour- we sometimes call this our atmosphere

  • Airmass

    A large area of air which has similar temperature and humidity characteristics.

  • Air pressure

    The weight of the atmosphere pressing down on the Earth’s surface as a result of gravity.

  • Altitude

    The height of the something above sea level. It is usually measured in feet or metres. Sea level is an altitude of 0 m.

  • Anemometer

    An instrument for measuring the speed of wind

  • Anticyclone

    A large are of high atmospheric pressure, characterised by outward-spiralling winds- a ‘high’. In the northern hemisphere winds rotate around an anticyclone in a clockwise direction.

  • Atmosphere

    A layer of air which covers the earth.

  • Barometer

    An instrument for measuring atmospheric pressure

  • Beaufort scale

    A scale that indicates wind speed by the effect wind has on familiar objects.

  • Biofuel

    Any fuel (liquid, solid or gas) produced from organic matter (matter from animals or plants).

  • Black ice

    Transparent ice forms when liquid water freezes on the ground

  • Blizzard

    Blowing snow reduces surface visibility. There are low temperatures, strong winds and heavy snow.

  • Celsius

    A scale of temperature based on one introduced in 1742 by Celsius, a Swedish astronomer and physicist, who divided the interval between the freezing and boiling points of water into 100 parts. The present system, where the freezing point is marked 0 and the boiling point is marked as 100, was introduced by Christin Lyons in 1743.

  • Climate

    The long term (often taken as 30 years) average weather pattern of a region.

  • Cloud

    A structure formed in the atmosphere by condensed water vapour.

  • Cold front

    The boundary between two different air masses where the cold air pushes the warm air out of way and brings colder weather.

  • Condensation

    The process by which water vapour becomes liquid water.

  • Conduction

    The process of heat transfer through materials by molecular motion.

  • Convection

    The process of heat transfer through fluids by means of rising currents.

  • Coriolis force

    An effect caused by the Earth’s rotation, which causes winds and currents to follow a curved path across the Earth’s surface- to the right in the northern hemisphere, to the left in the southern hemisphere.

  • Cyclone

    A large area of low atmospheric pressure, characterised by inward-spiralling wind often called a ‘low’ or a ‘depression’. Also the name used for a hurricane in the Indian Ocean and Western Pacific.

  • Depression

    A low-pressure weather system.

  • Dew

    Liquid water that has condensed on to objects at or near the Earth’s surface.

  • Dew point

    The temperature below which water droplets can form in the air.

  • Downburst

    A strong downdraught of short duration produced by some thunderstorms.

  • Drizzle

    Very small droplets of liquid precipitation.

  • Evaporation

    The process where liquid water turns into vapour (e.g. a rain puddle may evaporate into water vapour when the sun comes out). It is the opposite of condensation.

  • Eye

    Centre of a hurricane

  • Fahrenheit

    A scale of temperature introduced in about 1709 by the German Physicist, Fahrenheit, who was the first to use mercury as a thermometric substance.  Primary fixed points were the temperatures of a mixture of common salt and ice and the temperature of the human body; with reference to these the freezing point of water was marked 32 degree and the boiling point of water was marked 212 degrees.

  • Fog

    Water droplets in the air that reduce visibility to less than 1000m (1100 yards).

  • Front

    The boundary between two air masses.

  • Frost

    White ice crystals deposited on the surface of objects that have a temperature below the freezing point of water.

  • Global warming

    The increase in global mean temperature,  linked to the artificial increase in greenhouse gas concentrations.

  • Greenhouse gases

    Gases which absorb some of the outgoing radiation from Earth and re-emit it back down towards Earth.

  • Hail

    Pieces of hard, solid ice falling from clouds.

  • Hemisphere

    One half of a sphere. The term is usually applied to regions north or south of the equator or east or west of the Prime (Greenwich) meridian.

  • High

    Also known as an anticyclone- an area of high pressure with a system of winds rotating outwards. This usually means dry weather.

  • Humidity

    The amount of water vapour in the air. May be absolute or relative.

  • Hurricane

    A tropical revolving storm with sustained wind speeds of more than 118km/h (73mph). It is called a hurricane in the North Atlantic, but in other parts of the world it is known as a typhoon or tropical cyclone.

  • Isobar

    A line on a map or chart that links points of equal atmospheric pressure.

  • Jet stream

    A strong, high level wind that can reach speeds in excess of 320km/h (200mph) – it is usually around 5-10km (3-6 miles) above the ground.

  • Katabatic wind

    A wind which blows down a slope.

  • Latitude

    Position on the Earth’s surface north or south of the equator.

  • Lee

    The side of a mountain, hillside or island what is facing away from the prevailing wind.

  • Lightning

    Discharge of static electricity in the atmosphere, usually between the ground and a storm cloud.

  • Longitude

    Position on the Earth’s surface east or west of the Greenwich (prime) meridian.

  • Low

    Also called a depression- this region of low pressure can mean wet weather- it is the opposite of high pressure or anticyclone.

  • Meteorologist

    Someone who makes a scientific study of weather, weather processes and/or the climate.

  • Meteorology

    The science of the atmosphere- meteorology embraces both weather and climate and is concerned with all aspects of the Earth’s atmosphere (and those of the planets) and with the interaction between the atmosphere and the surface. The term was first used by Aristotle.

  • Millibar

    Unit for measuring air pressure. Now a hectoPascal (hPa) is the standard unit for pressure.

  • Monsoon

    The seasonal shift in wind direction that brings alternate very wet and very dry seasons to India and much of South-East Asia and other regions.

  • Occluded front

    The combination of  warm and cold fronts as a cold front overtakes a warm front. The front develops during the later stage of the life cycle of a frontal depression and is so called because of the associated occluding (shutting off) the warm air from the Earth’s surface.

  • Precipitation

    Moisture that is released from the atmosphere as rain, drizzle, hail, sleet or snow.

  • Radiation

    Process by which energy travels across space.

  • Rainbow

    A rainbow appears when sunlight shines through water droplets in the air. White light is made of seven colours. As the light shines through the water droplets the light is bent. The different colours of light bend by different amounts, so they separate and become visible.

  • Sea-level

    The normal level of high tide, used as a baseline for measuring height or depth.

  • Snowline

    The vertical limit of snow lying on mountain side throughout the year.

  • Synoptic chart

    A map showing large-scale weather patterns in an area at a given time.

  • Temperature:

    The heat content of the air.

  • Thunder

    Sound caused by intense heating of the air by lightning.

  • Typhoon

    A name of Chinese origin, meaning ‘great wind’ applied to the intense tropical cyclones which occur in the western Pacific Ocean. They are the same as the hurricanes  of the Atlantic Ocean and the cyclones of the Bay of Bengal.

  • Warm front

    The boundary between two different air masses where warm air pushes cold air away to bring warmer weather.

  • Water vapour

    Water in its gas form. The proportion of water vapour in the air varies with time and place. The dominant greenhouse gas.

  • Weather

    The state of the atmosphere (with regard to wind strength and direction, temperature, precipitation and pressure) at a specific time and place.