Air Mass: large body of air that has the same properties as the surface over which it develops

Albedo: fraction of solar radiation that is reflected back to space

Anemometer: instrument used to measure wind speed

Antarctic Circle: located at 66.5 ºS latitude

Arctic Circle: located at 66.5 ºN latitude

Barometer: instrument used to measure air pressure

Climate: average weather of an area over a period of 30+ years

Climatologist: scientist that studies climate

Dew Point: temperature to which air must be cooled to be saturated

Front: boundary between 2 air masses

Greenhouse Effect: natural warming of the atmosphere that occurs when certain gases absorb re-emitted radiation

Greenhouse Gases: atmospheric gases that contribute to Earth's greenhouse effect; include carbon dioxide, methane, water vapor, and nitrogen oxides

Global Warming: global rise in temperatures, caused primarily by an enhancement of Earth's natural greenhouse effect

Humidity: the amount of water vapor held in the air

Hurricanes: tropical, cyclonic storms that produce winds that travel at 120-240 km per hour

Hygrometer: instrument used to measure humidity

North Pole: located at 90 ºN latitude

Precipitation: water falling from clouds

Relative Humidity: percentage of moisture in the air

Revolution: amount of time it takes Earth to complete one trip around the sun; 365 days

Rotation: amount of time it takes Earth to complete one spin on its axis; 24 hours

Saturated: when air contains as much moisture as it can possibly hold; relative humidity is 100%

South Pole: located at 90 ºS latitude

Supercells: most powerful thunderstorms; required for tornado formation

Tropic of Cancer: located at 23.5 ºN latitude

Tropic of Capricorn: located at 23.5 ºS latitude

Vortices: spinning columns of air

Weather: describes present state of the atmosphere and current conditions.