climatology and meteorology

unstable air

air in which static instability prevails; this condition is determined by the vertical gradients of air temperature and humidity.


the dominant west-to-east motion of the atmosphere, centered over the middle latitudes (35 to 65 degrees latitude) of both hemispheres.

warm low

at a given level in the atmosphere, any low that is generally characterized by warmer air near its center than around its periphery; the opposite of a cold low.


a measure of a fluid’s resistance to flow; can be thought of as a measure of fluid friction.


precipitation that evaporates before reaching the ground.

vapor pressure

the pressure exerted by water vapor molecules in a given volume of air.


instrument used to measure wind direction; also called wind vane.

ultraviolet radiation

electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays; roughly, radiation in the wavelength interval from 10 to 4000 angstroms.


in meteorology, an elongated area of relatively low atmospheric pressure; the opposite of a ridge.


lower part of the atmosphere, extending from the surface up to a height varying from about 7 to 9 kilometers (4.3 to 5.6 miles) at polar regions to approximately 17 kilometers (10.6 miles) in tropics; characterized by decreasing temperature with height, appreciable vertical wind motion, appreciable water vapor content, and weather.


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