Geography Class 8

Weather

The condition of the atmosphere at a specific time and place including temperature wind precipitation and cloud cover.

Climate

The long term average pattern of weather in a region over many years.

Air Pressure

The force exerted by the weight of air molecules in the atmosphere.

High Pressure System (Anticyclone)

An area where air pressure is higher than surrounding areas causing sinking air and generally clear calm weather.

Low Pressure System (Depression)

An area where air pressure is lower than surrounding areas causing rising air clouds and precipitation.

Millibar

A unit used to measure air pressure equal to one thousandth of a bar.

Isobar

An imaginary line on a weather map connecting points of equal atmospheric pressure.

Pressure Gradient

The difference in air pressure between two areas which causes wind to move.

Wind

The movement of air from areas of high pressure to areas of low pressure.

Clockwise Rotation (Northern Hemisphere)

The direction air circulates around a high pressure system in the Northern Hemisphere.

Counterclockwise Rotation (Northern Hemisphere)

The direction air circulates around a low pressure system in the Northern Hemisphere.

Convergence

When wind patterns collide and force air upward often leading to storms.

Warm Front

A boundary where warm air advances and rises over colder air usually bringing steady rain.

Cold Front

A boundary where cold air advances and pushes under warm air often bringing sudden heavy rain and storms.

Occluded Front

A front formed when a cold front overtakes a warm front creating a mix of warm and cold front characteristics.

Veer

When wind direction shifts clockwise often associated with a passing warm front.

Condensation

The process by which water vapor cools and changes into liquid droplets forming clouds.

Precipitation

Any form of water that falls from clouds including rain snow sleet or hail.

Cumulonimbus Clouds

Tall dense storm clouds that produce heavy rain thunderstorms and sometimes tornadoes.

Depression Life Cycle Birth Stage

The stage when warm and cold air masses first meet and begin to interact.

Depression Life Cycle Maturity Stage

The stage when a storm is strongest and an occluded front often forms.

Depression Life Cycle Decay Stage

The stage when temperature differences equalize and the storm weakens.

Sea Breeze

A daytime wind that blows from water toward land because land heats faster than water.

Land Breeze

A nighttime wind that blows from land toward water because land cools faster than water.

Trade Winds

Steady winds that blow toward the equator from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere.

Polar Easterlies

Winds near the poles that blow toward the equator and are deflected by Earths rotation.

Coriolis Effect

The apparent deflection of moving air caused by Earths rotation.

Equilibrium

The state reached when air pressure differences balance and wind movement decreases.

Radiation Cooling

The loss of heat from Earths surface at night under clear skies often causing frost.

Humidity

The amount of water vapor present in the air.