A balloon-borne instrument for the simultaneous measurement and transmission of meteorological data. It includes transducers for the measurement of pressure, temperature, and humidity; a modulator for the conversion of the output of the transducers to a q ...

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

Rate of wind movement in distance per unit time.

Generally, an instrument designed to measure or estimate the blueness of the sky. See Linke-scale.

The mass density of a parcel of air expressed in units of mass per volume.

An instrument for recording global solar radiation.

Generally, a measure of the departure of the mean daily temperature from a given standard, one degree day for each degree (

Water vapor content of the air. See absolute humidity, dew point, mixing ratio, relative humidity, specific humidity.

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.

Temperature assumed by an unsaturated air parcel when brought adiabatically to a standard pressure (1,000 mb).

Of or pertaining to the air, atmosphere, or aviation. Also, same as antenna.

A device which surrounds a rain gauge and acts to maintain horizontal flow in the vicinity of the funnel so that the catch will not be influenced by eddies generated near the gauge. See Alter shield, Nipher shield, Wild fence.

The mean difference between the readings of a given instrument and those of a standard instrument.

A thermometer. the sensitive element of which consists of two metal strips which have different coefficients of expansion and are brazed together. The distortions of the system in response to temperature variations are used as a measure of temperature. It ...

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.

A liquid-in-glass thermometer which uses an organic substance such as alcohol as the thermometer liquid. This type of thermometer has a low freezing point and a high coefficient of expansion. It is less accurate, however, than a mercury thermometer.

A captive balloon used to maintain meteorological equipment aloft at approximately a constant height. The kytoon is streamlined and combines the aerodynamic properties of a balloon and a kite.

A vector term which includes both wind speed and wind direction.

Emission or transfer of energy in the form of electromagnetic waves or particles.

The amount of sky covered or concealed by clouds or obscuring phenomena. It is reported in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky. The following classifications are used in aviation weather observat ...