Lowest altitude in the atmosphere over a given location at which the air temperature is 0

An instrument for determining the degree of polarization of light. See photopolarimeter.

Wind with a speed between 28 and 33 knots (32 and 38 mph); Beaufort scale number 7.

That stage, on a fixed river gauge, at which overflow of the natural banks of the stream begins to cause damage in any portion of the reach for which the gauge is used as an index.

An instrument for measuring the relative speed of a fluid. It consists of a concentric pipe arrangement in which the inner pipe is open at one end and the outer pipe is perforated and closed at both ends. Each pipe is connected to a manometer. The unit is ...

A rain gauge which is placed under trees or foliage to determine the rainfall in that location. By comparing this catch with that from a rain gauge set in the open. the amount of rainfall which has been intercepted by foliage can be determined.

A line drawn through all points on a map having the same amount of cloudiness.

See foehn.

Pertaining to rain, or more broadly, to precipitation.

By international agreement, a period during which greatly increased observation of world-wide geophysical phenomena is undertaken through the co-operative effort of participating nations. July 1957-December 1958 was the first such year. However, precedent ...

A precipitation amount of less than 0.005 inches. Also, the record made by any self-registering instrument.

A line drawn through points of equal humidity on given surface.

Same as precipitation-evaporation ratio.

A line drawn through geographical points having the same duration of sunshine (or other function of solar radiation) during a given interval of time.

Determination of the total amount of snow covering a watershed or a given region. Both depth and water content of the snow may be measured, and the results may be used to predict the amount of water that will be available after melting.

Wind with a speed between 11 and 16 knots (13 and 18 mph); Beaufort scale number 4.

Line drawn through geographical points recording equal amounts of precipitation during a given time period or for a particular storm.

An instrument used to measure the water vapor content of the air. A type of hygrometer. It consists of a wet-bulb and a dry-bulb thermometer. See aspiration psychrometer, Assmann psychrometer. hygrodeik, sling psychrometer.

The boundary between the troposphere and stratosphere, usually characterized by an abrupt change in lapse rate. Its height varies from 10 to 20 km. Regions above the tropopause have greater atmospheric stability than regions below.

The most common of the principal rainbow phenomena, which appears as an arc of about 42