air mass
a large volume of air defined by its temperature and water vapor content.
air pressure
the force per unit area exerted by the weight of air above a surface.
albedo
the ratio of the amount of radiation reflected by a body to the amount of light that shines on it.
atmosphere
the gases surrounding the Earth.
aurora bands
of light in the atmosphere caused by charged solar particles following the Earth's magnetic lines of force.
barometer
a device for measuring air pressure.
climate
the weather in a location averaged over a period of time.
conduction
the transfer of thermal energy between neighboring molecules in a substance due to a temperature difference.
convection currents
currents in air and water that are caused by differences in temperature. In air, cooler air moves downward, while warmer air rises. The warm air usually cools in the cooler, higher sections of the atmosphere and begins to return back down. Local breezes,
Coriolis effect
the deflective effect of the Earth's rotation (to the right in the Northern Hemisphere and to the left in the Southern Hemisphere) on all free-moving objects, including the atmosphere and oceans.
cyclone
a rapid inward circulation of air masses over ocean masses about a low-pressure center; circles counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. dew point the temperature at which the water vapor in the air becomes sat
doldrums
a belt of calms and light winds between the northern and southern trade winds of the Atlantic and Pacific oceans.
El Ni�o
a warming of the ocean surface off the western coast of South America that occurs every 4 to 12 years when upwelling of cold, nutrient-rich water does not occur. Results in die-offs of plankton and fish, affects Pacific jet stream winds, and alters storm
eye
(hurricane) a zone of weak winds that exists in the center of the swirling vortex of a hurricane or typhoon.
Ferrell cell
an atmospheric cell lying between the polar cell and the Hadley cell. Transfers warm air to high latitudes and shifts cold air back to the subtropics, where it is warmed.
Hadley cell
a circulation pattern that dominates the tropical atmosphere with rising poleward motion near the equator, descending motion in the subtropics, and motion toward the equator near the surface.
horse latitudes
subtropic latitudes between 30� and 35� both north and south. The region receives little precipitation and has variable winds mixed with calm.
hurricane
also known as a typhoon. A severe tropical cyclone that starts in the equatorial regions of the Atlantic Ocean, Caribbean Sea, or eastern regions of the Pacific Ocean and is usually associated with heavy rains and winds.
insolation
a measure of solar radiation energy received on a given surface area in a given time.
jet stream
a high-speed, high-altitude airstream blowing from west to east near the top of the troposphere. It has important effects on the formation of weather fronts.
La Ni�a
an upwelling of cooler-than-normal water to the ocean surface off the western coast of South America; normally occurs every 4 to 12 years affecting Pacific and other weather patterns.
latitude
distance in degrees north or south of the equator; i.e., 0� at the equator to 90� (N and S) at the poles.
leeward
the direction in which the wind is blowing.
longitude
imaginary lines drawn through the north and south poles that are used to measure distance east and west. Greenwich England, is designated as 0.
mesosphere
the atmospheric layer between the stratosphere and the thermosphere, situated at an altitude of approximately 50 to 80 kilometers, in which temperature decreases with increasing altitude.
monsoon
a seasonal wind in southern Asia that blows from the southwest and brings rain in summer.
orographic lifting
occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain.
polar cell
a weak circulation pattern in the high-latitude troposphere characterized by ascending motion in the subpolar latitudes (50�-70�), descending motion over the pole, poleward motion aloft, and equatorward motion near the surface.
rain shadow
an area of land that receives reduced precipitation due to proximity to a mountain range. The mountains block the passage of rain-producing weather systems, casting a "shadow" of dryness behind them.
relative humidity
the ratio (expressed as a percentage) of the amount of water in the air at a given temperature to the maximum amount it could hold at that temperature.
stratosphere
the region of the uppermost atmosphere where temperature increases along with the altitude due to the absorption of solar UV radiation by ozone.
temperature inversion
an increase in temperature with height above the Earth's surface which is a reversal of the normal pattern.
thermosphere (ionosphere)
the upper layer of the atmosphere, above 50 miles (80 km) from the Earth's surface. It is extremely hot due to absorption of radiation by gases.
tornado
a localized and violently destructive windstorm generally produced by solar heating of the land and characterized by a funnelshaped cloud extending toward the ground. Characteristics: diameters in the hundreds of meters, produced from a single convective
trade winds
the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere. The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere.
typhoon
a tropical cyclone occurring in the western Pacific or Indian oceans.
weather
a set of all the phenomena occurring in a given atmosphere at a given time.
westerlies
the prevailing winds in the middle latitudes between 35� and 65� latitude, blowing from the high-pressure area in the horse latitudes toward the poles.
wind chill
based on the rate of heat loss from exposed skin caused by the combined effects of wind and cold.
wind shear
the difference in wind speed and direction over a relatively short distance in the atmosphere.
windward
the direction from which the wind is coming.