IGCSE Geography

Weather

The state of the atmosphere at a particular place and time.

Climate

Generally prevailing weather conditions of a region averaged over a at least 30 years.

Maximum-minimum thermometer

Meteorological instrument to measure maximum and minimum temperature (AKA Six's thermometer).

Temperature range

Numerical difference between the minimum and maximum values of temperature. Can be measured as diurnal or annual.

Diurnal range

Refers to difference between daily maximum and daily minimum temperatures.

Mean temperature

The average between the maximum and the minimum temperature.

Isotherms

A line on a map connecting points having the same temperature.

Precipitation

Any form of moisture which falls to the earth. This includes rain, snow, hail and sleet.

Rain gauge

Instrument used to measure precipitation.

Isohyets

A line drawn on a weather map connecting points that receive equal amounts of precipitation.

Wet bulb - dry bulb thermometer

Instrument to measure relative humidity (AKA hygrometer).

Relative humidity

The percentage of water vapor in the air compared to the maximum amount the air could hold at that temperature.

Dew point

Temperature at which air is saturated and condensation forms.

Air pressure

The force exerted on a surface by the air above it as gravity pulls it to Earth.

Barometer

Instrument for measuring air pressure.

Barograph

A barometer that records its readings on a moving chart.

Millibars (Mb)

The unit for air pressure.

Isobars

Lines joining places on the map that have the same air pressure.

Anemometer

Instrument for measuring wind speed.

Wind rose

Graph for displaying information on wind direction.

Prevailing wind

The dominant wind in an area.

Wind vane

Meteorological instrument to measure wind direction.

Sunshine recorder

Instrument used to record hours of sunshine.

Stevenson screen

A standard shelter for meteorological instruments.

Cumulus

Low level; puffy clouds with flat bottoms and rounded tops. These clouds don't indicate rain. Large rising clouds (cumulus congestus) may indicate an approaching storm.

Stratus

Low level; low, flat, layered clouds which often cover the sky and don't bring significant rain.

Stratocumulus

Low level; Layers of cumulus clouds.

Nimbostratus

Low level; dark stratus clouds that bring rain.

Altocumulus

Middle-layer cumulus.

Altostratus

Middle-layer stratus.

Cirrus

High level; often feather like, usually above 5,000 meters, made of ice crystals.

Cirrocumulus

High level; High, thin clouds forming ripples.

Cirrostratus

High level; thin layers of ice which usually cover the sky and form halos around the sun or moon; usually indicate increasing cloudiness.

Cumulonimbus

Large, tall clouds that bring rain; the top of anvil shaped , found from low to high.

Contrails

Thin trails of ice forming from cooled airplane exhaust.

Fog

Clouds near the surface.

Oktas

The extent of cloud cover, estimated by the eye and expressed in eighths.