A type of cistern barometer in which the level of mercury in the cistern is adjusted to the zero point of the scale before each reading.

An instrument for taking photographs of an image of the sun in monochromatic light.

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 line drawn through points of equal humidity on given surface.

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

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

See foehn.

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.

A device for computing certain psychrometric data, usually the dew point and the relative humidity, from known values of the dry-bulb and wet-bulb temperatures and the atmospheric pressure. One type is the circular slide-rule form and, like the psychromet ...

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

Pertaining to rain, or more broadly, to precipitation.

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.

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.

A line drawn through geographical points where a given seasonal biological event occurs on the same date.

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

Same as precipitation-evaporation ratio.

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 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.

A small balloon whose ascent is followed by a theodolite in order to obtain data for the computation of winds aloft.