Earth Science Chapter 12

Meteorology Unit
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Weather
The current state of the atmosphere.
Climate
The average weather of a particular area over a long time; 10 years or more.
Air Mass
Large body of air that takes on the characteristics of the area over which it forms; can be described by its stability, temperature, and humidity.
Maritime
A air mass that forms over water.
Continental
An air mass that forms over land.
Arctic
An air mass that develops in latitudes above 60 degrees North or South.
Polar
An air mass that forms in latitudes ranging from 30 degrees to 60 degrees.
Tropical
An air mass that forms in latitudes ranging from 0 degrees to 30 degrees North or South of the Equator.
Front
Boundary between two air masses of differing densities and characteristics.
Cold Front
When cold dense air replaces warm moist air and forces the warm air to rise up along a steep front. Clouds, showers, and the occasional thunderstorm are associated with cold fronts as well as drops in temperature after a cold front moves through a region.
Warm Front
When warm air displaces cold air causing a gradual rise of air. These fronts are characterized by a great amount of cloudiness and precipitation.
Stationary Front
When two air masses meet and they stall; nothing happens. This happens when differences between air masses are small and rarely weather events are produced out of these fronts. If precipitation and clouds do form, they are similar in nature to those produced by a warm front.
Occluded Front
When a cold air mass is moving so quickly that it overtakes a warm front; precipitation is common on both sides of a occluded front.
High Pressure
An area where air is diverging, going away from, a center or sinking; this moves in a clockwise direction in the northern hemisphere. This system is associated with clear skies and fair weather.
Low Pressure
An area where air is converging, coming toward, to rise; this moves in a counterclockwise direction in the northern hemisphere. This system is associated with clouds and precipitation.
Source Region
Region over which an air mass forms.
** Example: The source region for a Maritime Tropical air mass might be the Gulf of Mexico.
Air Mass Modification
It is the change in humidity or temperature of an air mass as it moves away from its source region.

Humidity: An air mass becomes more humid if it moves over an ocean, and drier if it moves over land.

Temperature: An air mass becomes warmer if it moves towards the equator, and colder if it moves towards the poles.
Station Model
Use of symbols to record the weather data for a particular site at a particular time.
Isopleths
Lines that connect points of equal or constant values.
(Iso is same, like an isoceles triangle.)
Isobars
Lines on a map drawn through all points having the same atmospheric pressure
Isotherms
Lines that connect points that have the same temperature
Heat Budget
The distribution of heat energy to maintain average conditions across Earth; this movement of heat produces weather.
Infrared Radiation
Detects differences in thermal energy, which are used to map either cloud cover or surface temps. It helps meteorologists to determine the temp. of a cloud.
Intertropical Convergence Zone (ICTZ)
Low pressure zone caused by the trade winds converging near the equator, resulting in rising air, many clouds, lots of rain - hot & humid. While air rises in the ITCZ, the surface winds are very weak - the Doldrums.
Jet Stream
High-altitude, narrow, westerly wind band that occurs above large temperature contrasts and can flow as fast as 185 km/h.
Polar Easterlies
A global wind system that lies between 60 degrees latitude and the poles and characterized by very cold air.
Prevailing Westerlies
A global wind system that lies between 30 and 60 degrees north and south latitude where surface air moves toward the poles in an easterly direction.
Coriolis Effect
The deflection of air to the right above the Equator and to the left below the Equator that is caused by the Earth's rotation. This combines with the heat imbalances found on Earth to create the trade winds, polar easterlies, and prevailing westerlies.
Trade winds
A global wind system that flows at 30 degrees north and south latitude, where air sinks, warms, and returns to the Equator in a westerly direction.
Doppler Effect
Radar used to measure the speed or movement of precipitation. Speed is determined by a change in wave frequency that occurs in energy, such as sound or light, as the energy moves toward or away from an observer. (Example: pitch of train horn changes as it passes.)