Instrument which measures and records the amount of evaporation over time.

The flux of visible radiation, so weighted as to account for the manner in which the response of the human eye varies with the Wavelength of radiation. The basic unit for luminous flux is the lumen,

A graphical representation of a frequency distribution. The range of the variable is divided into class intervals for which the frequency of occurrence is represented by a rectangular column. The height of the column is proportional to the frequency of ob ...

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

Forecasting weather by the use of numerical models, run on high speed computers. Most of the NWP for the National Weather Service is done at the National Centers for Environmental Prediction (NCEP).

The ratio of the actual amount of water evaporated into the atmosphere to the evaporative power. Also called relative evaporation.

A transducer which converts electromagnetic radiation in the infrared, visible, and ultraviolet regions into electrical quantities such as voltage, current, or resistance. Also called photo cell.

An instrument designed to measure the effect of sunlight on evaporation from plant foliage. It consists of a porous clay atmometer whose surface has been blackened so that it absorbs radiant energy.

The length of air flow past a wind vane required for the vane to respond to 50 percent of a step change in wind direction. Expressed in feet or meters and calculated from delay time times wind tunnel speed.

Wind with a speed between 56 and 63 knots (64 and 72 mph); Beaufort scale number 11.

Wind with a speed between 41 and 47 knots (47 and 54 mph); Beaufort scale number 9.

An instrument which measures the instantaneous rate at which rain is falling on a given surface. Also called a rate-of-rainfall gauge.

Similar to the spectroheliograph, but used for visual instead of photographic purposes.

A form of psychrometer with wet-bulb and dry-bulb thermometers mounted on opposite sides of a specialty designed graph of the psychrometric tables. It is so arranged that the intersections of two curves determined by the wet-bulb and dry-bulb readings -yi ...

A type of pressure-tube anemometer, named after the inventor.

The difference between the air temperature and the dew-point. Also called dew-point deficit, dew-point depression.

An instrument designed to record the duration of sunshine at a given location without regard to intensity. See Campbell- Stokes recorder, Jordan sunshine recorder, Marvin sunshine recorder, Pers sunshine recorder.

The closeness of agreement among a number of consecutive output values measuring the same input value under the same operating conditions, approaching from the same direction. Usually measured as nonrepeatability but expressed as repeatability, a percenta ...

An aneroid barograph designed to record atmospheric pressure variations of very small magnitude.

Frequency Shift Keying. A form of frequency modulation of a data signal performed by a modem for transmission over dedicated wire or phone lines.