climatology and meteorology

middle-level clouds

clouds composed of ice crystals and water droplets in the middle region of the atmosphere, from 2,000 - 6,000 meters (6,500 to 23,000 feet); includes altocumulus, altostratus, nimbostratus, and portions of cumulus and cumulonimbus clouds.

microwave sensors

in terms of wavelength, microwaves range from 1 millimeter to 1 meter, and are much longer than the shorter visible (0.38-0.78 micrometer) wavelengths; these longer wavelengths allow microwave energy to penetrate through clouds; because these sensors measure microwave energy, they do not rely on sunlight for illumination so they can acquire images regardless of time of day; can be either passive or active; passive sensors detect and record naturally upwelling microwave energy emitted from objects; active sensors generate their own beam of energy, generally with an antenna, which then detects the returned energy patterns (backscatter) that indicate the presence of features and their position relative to the sensor; radar (radio detection and ranging) was an original active microwave sensor that became widely operational with the onset of World War II.


study of the atmosphere and its phenomena, including its structure, properties, and physical processes.

mass balance

the difference between accumulation and ablation on a glacier; usually calculated on an annual basis.

luminous pillars

white or sometimes reddish vertical streaks of light extending from above and below the sun; they are caused by light reflected off the mirror-like surfaces of ice; most commonly seen at sunrise and sunset.


general term for dry atmospheric suspensoids, including dust, haze, smoke and sand.

latent heat of fusion

the amount of heat required to cause a change of phase from solid to liquid, or the heat released when the phase change is from liquid to solid; in the case of melting snow, the phase change from ice to water requires a significant amount of heat—160 times that required to raise the temperature of the same amount of ice by just 1 degree Celsius; until the required amount of heat is supplied to completely melt all of the ice being considered, no further increase in temperature will occur.

large-scale atmospheric processes

atmospheric processes with a representative scale (large-scale) of 10,000 kilometers (6,200 miles); in meteorology, it is a scale in which the curve of the earth is not negligible; the large-scale atmospheric flows are essentially nearly hydrostatic, nearly geostrophic and wave-like in appearance; they exist mainly in response to the latitudinal differences in radiative heating, to the particular value of the coriolis force and to the spatial distribution of the oceans and continents.

lapse rate

the rate of change of any meteorological element with height.

land sky

the relatively dark appearance of the underside of a cloud layer when it is over land that is not snow covered; this term is used largely in polar regions with reference to the sky map; land sky is brighter than water sky, but is much darker than ice blink or snow blink.


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