Global Climate Models(8)

Sophisticated computer models of the atmosphere and oceans that attempt to include all the processes known to affect climate.

Global measurement(1)

All of the activities required to specify a global variable. such as ozone. These activities range from data acquisition to the generation of a data-analysis product. and include estimates of the uncertainties in that product. A global measurement often will consist of a combination of observations from a spacecraft instrument (required for global coverage) and measurements in situ (needed to provide reference points for long-term accuracy).

Global positioning system (GPS)(1)

A system consisting of 25 satellites in 6 orbital planes at 20.000 km altitude with 12 hr periods. used to provide highly precise position. velocity and time information to users anywhere on Earth or in its neighborhood at any time.

Global variables(1)

Functions of space and time that describe the large-scale state and evolution of the Earth system. The Earth system's geosphere. hydrosphere. atmosphere. and biosphere and their components are. or potentially are. global variables.

Global Warming(3)

Certain natural and human-produced gases prevent the sun's energy from escaping back to space leading to an overall rise in the temperature of the Earth's atmosphere.


Colored rings that appear around the shadow of an object.


See Snow pellets

Green flash(6)

A small. green color that occasionally appears on the upper part of the sun as it rises or sets.

Greenhouse Effect(3)

The atmosphere allows solar radiation to reach the earth relatively easily. The atmosphere absorbs the infrared radiation emitted by the Earth's surface and radiates it back to the Earth in much the same way a greenhouse traps heat as the sun's rays pass through the glass. and the heat generated does not pass back through the glass. The 'greenhouse effect' causes the surface of the Earth to be much warmer that it would be without the atmosphere 60�F). Without the greenhouse effect. life as we know it might not exist on Earth.

Greenhouse Gas(3)

Certain gases. such as water vapor. carbon dioxide. and methane. that more effectively trap heat affecting the Earth's surface temperature.

Greenwich Mean Time (GMT)(3)

Explain when we would use this relative to satellite images. GMT is the global standard for time that was established in 1884 when delegates from 27 nations met in Washington. DC for the Meridian Conference and agreed on a system basically the same as that now in use. Civilian designations are typically three letter abbreviations (e.g. EST) for most time zones. Military designations use each letter of the alphabet (except 'J') and are known by their phonetic equivalent. For example. Greenwich Mean Time (civilian) or Z = Zulu (military and aviation). Universal Time Coordinated (UTC) has been substituted for GMT.

Ground fog(6)

See Radiation fog.

Growing degree-day(6)

A form of the degree-day used as a guide for crop planting and for estimating crop maturity dates.

Growing season(6)

The number of days between the last spring freeze date and the first fall freeze date.

Gulf stream(1)

A warm. swift ocean current that flows along the coast of the Eastern United States and makes Ireland. Great Britain. and the Scandinavian countries warmer than they would be otherwise.


A dust or sandstorm that forms as cold downdrafts from a thunderstorm turbulently lift dust and sand into the air.


Solid precipitation in the form of chunks or balls of ice with diameters greater than 5 mm. The stones fall from cumulonimbus clouds.


Transparent or partially opaque particles of ice that range in size from that of a pea to that of golf balls.

Hair hygrometer(6)

An instrument used to monitor relative humidity by measuring the changes in the length of human hair that accompany humidity variations.


Rings or arcs that encircle the sun or moon when seen through an ice crystal cloud or a sky filled with falling ice crystals. Halos are produced by refraction of light.


Fine dry or wet dust or salt particles dispersed through a portion of the atmosphere. Individually these are not visible but cumulatively they will diminish visibility.

Heat balance(1)

The equilibrium existing between the radiation received and emitted by a planetary system.

Heat capacity(6)

The ratio of the heat absorbed (or released) by a system to the corresponding temperature rise (or fall).

Heat index ((HI))(6)

An index that combines air temperature and relative humidity to determine an apparent temperature-how hot it actually feels.

Heat lightning(6)

Distant lightning that illuminates the sky but is too far away for its thunder to be heard.

Heat of fusion(6)

Heat released when water changes phase from liquid to solid. 80 calories per gram.

Heat of melting(6)

Heat required to change the phase of water from solid to liquid. 80 calories per gram.


A form of energy transferred between systems by virtue of their temperature differences.

Heating degree-day(6)

A form of the degree-day used as an index for fuel consumption. Needed on days when average air temperature falls below 69�F (18�C). computed by subtracting the day's average temperature from 65�F.


A faint white ring surrounding the shadow of an observer's head on a dew-covered lawn.


The atmosphere above 80 km (50 mi) where gases are stratified. with concentrations of the heavier gases decreasing more rapidly with altitude than concentrations of the lighter gases.

High inversion fog(6)

A fog that lifts above the surface but does not completely dissipate because of a strong inversion (usually subsidence) that exists above the fog layer.

Highland climate(6)

Complex pattern of climate conditions associated with mountains. Highland climates are characterized by large differences that occur over short distances.

Historical Flood(6)

Flood events documented by human observation but recorded prior to the development of systematic streamflow measurements.


Fernlike crystals of ice that form by deposition of water vapor on twigs. tree branches. and other vegetation.


The atmosphere up to 80 km (50 mi) in which the proportionality of principal gaseous constituents. such as oxygen and nitrogen. is constant.

Humid continental climate(6)

A relatively severe climate characteristic of broad continents in the middle latitudes between approximately 40-50� north latitude. This climate is not found in the southern hemisphere. where the middle latitudes are dominated by the oceans.

Humid Subtropical Climate(6)

A climate generally located on the eastern side of a continent and characterized by hot. sultry summers and cool winters.


See Cyclone.


An instrument that provides a continuous trace of relative humidity with time.

Hydrologic cycle(5)

The process of evaporation. vertical and horizontal transport of vapor. condensation. precipitation. and the flow of water from continents to oceans. It is a major factor in determining climate through its influence on surface vegetation. the clouds. snow and ice. and soil moisture. The hydrologic cycle is responsible for 25-30% of the mid-latitudes' heat transport from the equatorial to polar regions. See The Water Cycle.


The scientific study of precipitation. evaporation. distribution. and effects of water on the Earth's surface. in the soil and rocks. and in the atmosphere.


An instrument designed to measure the air's water vapor content. The sensing part of the instrument can be hair (hair hygrometer). a plate coated with carbon (electrical hygrometer). or an infrared sensor (infrared hygrometer).


The deterioration in one's mental and physical condition brought on by a rapid lowering of human body temperature.

Ice Age(2)

Period during which polar ice extends to much lower latitudes than normal.

Ice Cap Climate(6)

A climate that has no monthly means above freezing and supports no vegetative cover except in a few scattered high mountain areas. This climate. with its perpetual ice and snow. is confined largely to the ice sheets of Greenland and Antarctica.

Ice core(1)

A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice. scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.

Ice fog(6)

A type of fog composed of tiny suspended ice particles that forms at very low temperatures.

Ice nuclei(6)

Particles that act as nuclei for the formation of ice crystals in the atmosphere.

Ice pellets(6)

See Sleet
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Americans’ health, security and economic wellbeing are tied to climate and weather. Every day, we see communities grappling with environmental challenges due to unusual or extreme events related to climate and weather.