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Fahrenheit |
Temperature scale designed by the German scientist Gabriel Fahrenheit in 1709, based upon water freezing at 32 degrees Fahrenheit and water boiling at 212 degrees Fahrenheit under standard atmospheric pressure. Compare with centigrade. |
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false color |
A color imaging process which produces an image of a color that does not correspond to the true or natural color of the scene (as seen by our eyes). |
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far infrared |
Electromagnetic radiation, longer than the thermal infrared, with wavelengths between about 25 and 1000 micrometers. See electromagnetic spectrum. |
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fault line |
A fracture in rock along which one side has moved with respect to the other. See Putting Earthquakes in Their Place |
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feedback mechanisms |
Factors which increase or amplify (positive feedback) or decrease (negative feedback) the rate of a process. An example of positive climatic feedback is the ice-albedo feedback. |
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FEMA |
U.S. Federal Emergency Management Agency. |
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field |
The set of influences (electricity, magnetism, gravity) that extend throughout space. |
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field of view |
The range of angles that are scanned or sensed by a system or instrument, measured in degrees of arc. |
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flood plain |
The nearly flat portion of a river (stream) valley adjacent to the river (stream) channel; it is built by sediment deposited during floods and is covered by water during a flood. |
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fluorocarbons |
Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons and related compounds (also know as ozone depleting substances). |
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flux |
the measure of the flow of some quantity per unit area per unit time
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fog |
A cloud on the ground. |
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food chain |
A sequence of organisms, each of which uses the next lower member of the sequence as a food source. |
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force |
Any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body. |
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fossil |
Hardened remains or traces of plant or animal life from a previous geological period preserved in the Earth's crust. |
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fossil fuel |
Any hydrocarbon deposit that can be burned for heat or power, such as petroleum, coal, and natural gas. |
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Fraction of Photosynthetically Active Radiation (FPAR) |
Radiation between 400 and 700 nm used by the green canopy in the photosynthetic process. |
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free radicals |
Atomic or molecular species with unpaired electrons or an otherwise open shell configuration, usually very reactive. Specific to atmospheric chemistry, free radicals are: short-lived, highly reactive, intermediate species produced by dissociation of the source molecules by solar ultraviolet radiation or by reactions with other stratospheric constituents. Free radicals are the key to intermediate species in many important stratosphericchain reactions in which an ozone molecule is destroyed and the radical is regenerated. See ozone |
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frequency (F) |
Number of cycles and parts of cycles completed per second. F=1/T, where T is the length of one cycle in seconds. |
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front |
A boundary between two different air masses. The difference between two air masses sometimes is unnoticeable. But when the colliding air masses have very different temperatures and amounts of water in them, turbulent weather can erupt.
A cold front occurs when a cold air mass moves into an area occupied by a warmer air mass. Moving at an average speed of about 20 mph, the heavier cold air moves in a wedge shape along the ground. Cold fronts bring lower temperatures and can create narrow bands of violent thunderstorms. In North America, cold fronts form on the eastern edges of high pressure systems.
A warm front occurs when a warm air mass moves into an area occupied by a colder air mass. The warm air is lighter, so it flows up the slope of the cold air below it. Warm fronts usually form on the eastern sides of low pressure systems, create wide areas of clouds and rain, and move at an average speed of 15 mph.
When a cold front follows and then overtakes a warm front (warm fronts move more slowly than cold fronts) lifting the warm air off the ground, an occluded front forms. |
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frost |
Ice crystals formed by deposition of water vapor on a relatively cold surface. |
