Companion to the wet-bulb thermometer in a psychrometer. Used to measure ambient air temperature.

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

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

A faintly-colored circular arc similar to a rainbow but formed on fog layers containing drops whose diameters are 100 microns or less. Also called mistbow, white rainbow.

Quantitative Precipitation Forecast.

A device that combines several separate communications signals into one and outputs them on a single line.

See radar theodolite, radio direction-finder.

A type of cooling-power anemometer based upon the principle that the time constant of a thermometer is a function of its ventilation.

An instrument for measuring the ultraviolet in solar and sky radiation.

An instrument which automatically determines the size distribution of raindrops.

Anemometer which generates an electrical contact output with a frequency proportional to wind speed.

Not a linear function of the relevant variables.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

Thermometer in which the difference in the rates of expansion with temperature of a liquid and its receptacle is used as a measure of the temperature. The liquid used may be ethyl alcohol, toluene, petroleum, or mercury.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

Name applied to a class of instruments which measure the liquid content of the atmosphere.

The unit of speed in the nautical system; one nautical mile per hour. It is equal to 1.1508 statute miles per hour or 0.5144 meters per second.

The difference between downward and upward (total) radiation; net flux of all radiation.

The wind speed and direction at various levels in the atmosphere above the level reached by surface weather observations.

Wind with a speed between 4 and 6 knots (4 and 7 mph), Beaufort scale number 2.