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

A thermograph in which ventilation is provided by a suction fan.

A scale with the ice point at zero degrees and the boiling point of water at 80 degrees, with pressure of one atmosphere.

A clock-driven instrument mounting which automatically and continuously points in the direction of the sun. It is used with a pyrheliometera,hen continuous direct solar radiation measurements are required.

An instrument resulting from the combination of a thermograph and a hygrograph and furnishing, on the same chart, simultaneous time recording of ambient temperature and humidity.

Ice crystal deposits formed by sublimation (conversion of water vapor directly to ice) when temperature and dew point are below freezing.

The standard deviation of a sufficiently large number of measurements of the same quantity by the same instrument or method. The non-correctable part of the inaccuracy of an instrument, it represents the limit of measurement precision. The uncertainty of ...

The value of the quantity measured, as indicated or otherwise provided by a measuring instrument.

A type of hygrometer which measures the water vapor content of the atmosphere by means of the absorption of vapor by a hygroscopic chemical.

The statement that the viscosity of air is independent of the density of air.

The level at which ice crystals and snowflakes melt as they descend through the atmosphere.

A thermometer whose sensitive element has been made to resemble a black body by covering it with lamp black. The thermometer is placed in an evacuated transparent chamber which is maintained at a constant temperature. The instrument responds to insolation ...

An instrument for measuring the pressure of the atmosphere. The two principle types are aneroid and mercurial.

A balloon having a detachable tail which is released when the balloon has undergone a predetermined expansion. It thus serves to measure approximately the density of the atmosphere at the point of release.

A device for measuring the height of tide. It may be simply a graduated staff in a sheltered location where visual observations can be made, or it may consist of an elaborate recording instrument (sometimes called a marigraph) making a continuous graphic ...

Atmospheric layer throughout which there is no change of temperature with height, i.e. a zero lapse rate.

The water volume within a specified portion of a stream channel.

Difference between the temperatures of the dry-bulb and the wet-bulb thermometers of a psychrometer.

Same as atmometer.

A temperature scale with the ice point at 273 degrees and boiling point of water at 373 degrees. It is intended to approximate the Kelvin temperature scale with sufficient accuracy for many sciences, notably meteorology.