Pyrheliometer based on the comparison of the heating of two identical metal strips, one exposed to radiation, the other to a joule effect.

See standard atmosphere.

Upwarddirected solar radiation, reflected by the earth's surface and the atmosphere.

An instrument used for measuring geometric angles. See radio direction-finder.

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

An absolute temperature scale with the degree of the Fahrenheit scale and the zero point of the Kelvin scale. The freezing point of water equals 491.69

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

An instrument for measuring differences of electric potential.

That horizontal wind velocity at which the Coriolis acceleration exactly balances the horizontal pressure force. It is directed along contour lines or isobars.

The array of indicating marks and figure in relation to which the position of an index is observed, i.e. a scale plate on a recorder.

A device, similar to a potometer, for measuring transpiration, consisting of a vessel containing soil in which one or more plants are rooted and sealed so that water can escape only by transpiration from the plant.

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

A fabric cone attached to a metal ring and used to indicate wind direction. often at airfields.

A special type of radar target, usually a comer reflector, tied beneath a free balloon and designed to be an efficient reflector of radio energy.

The stage on a fixed river gauge at which it is necessary to begin issuing warnings or river forecasts if adequate precautionary measures are to be taken before flood stage is reached.

A curve showing the variation of temperature with height in the free air. See lapse rate.

A tube designed to measure the rate of flow of fluids. It consists of a tube having a constriction or throat at its midsection. The difference between the pressure measured at the inlet and at the throat is a function of the fluid velocity. Compare to Pit ...

A motorlike device containing a rotor and a stator and capable of converting an angular position into an electrical signal, or an electrical signal into an angular position. When several synchros are correctly connected, all of the rotors will align thems ...

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

A refraction phenomenon similar to a parahelion, but occurring generally at a distance of 120