climatology and meteorology

thawing index

the cumulative number of degree-days above 0 degrees Celsius for a given time period.


a substance dispersed throughout another substance; also called suspended phase.

surface temperature

the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 - 2.0 meters (5.0 - 6.6 feet) above ground; also called air temperature.


the condition which occurs in the atmosphere when the relative humidity is greater than 100%.


the condition when a liquid remains in the liquid state even through its temperature is below its freezing point.


the transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase.


a principal low-level cloud type (cloud genus) in the form of a low-altitude, light to dark gray cloud layer with a rather uniform base; generally diffuse and dull; this cloud formation has little structure and looks like fog, except that it is above the ground, stratus does not usually produce precipitation, but when it does occur, it is in the form of minute particles, such as drizzle, ice crystals, or fine snow grains.


a layer of the Earth’s atmosphere, between the troposphere and mesosphere, that is stratified in temperature such that cooler layers are closer to the Earth’s surface, and warmer layers are higher up (opposite the pattern of the troposphere near the Earth’s surface); situated between about 10 to 50 kilometers (6 to 31 miles) in altitude above the surface of the moderate latitudes; at the poles, it starts at about 8 km in altitude; composition is basically the same as that of the lower atmosphere, with the addition of ozone.


the boundary layer between the stratosphere and the mesosphere at about 50 to 55 kilometers (31 to 34 miles).


a principal low-level cloud type (cloud genus), predominantly stratiform, in the form of relatively low gray and/or whitish layer, sheet or patch; its elements are often arranged in bands or rolls that lie across the wind; light rain, snow, or sleet may fall from stratocumulus.


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