That temperature at which, in a specified latitude, the reading of a particular barometer requires no temperature or latitude correction.

A pressure-plate anemometer consisting of a plate which is free to swing about a horizontal axis in its own plane above its center of gravity. The angular deflection of the plate is a function of the wind speed. This instrument is not used for station mea ...

Of equal or constant pressure, with respect to either space or time.

A rainbow formed by light rays which have been reflected from an extended water surface. Not to be confused with a reflected rainbow whose image may be seen in a still body of water. The center of a reflection rainbow is at the same elevation as the sun b ...

The lowest temperature that can be obtained on a wet-bulb thermometer in any given sample of air. Obtained by evaporation of water (or ice) from the muslin wick. Used in computing dew point and relative humidity.

A series of Nansen-bottle water samples and associated temperature observations resulting from one release of a messenger.

A recording magnetometer.

A component of a radiosonde consisting of a series of alternate electrically conducting and insulating strips. As these are scanned by a contact the radiosonde transmits temperature and humidity signals alternately. The contact may be a baroswitch as in t ...

A pyrheliometer of the thermoelectric type. Radiation is allowed to fall on two concentric silver rings, the outer covered with magnesium oxide and the inner covered with lamp black. A system of thermocouples (thermopile) is used to measure the temperatur ...

A common type of liquid-inglass thermometer, used, in meteorology, in psychrometers and as a maximum thermometer.

A combination cup anemometer and pressure-plate anemometer, consisting of an array of cups about a vertical axis of rotation, the free rotation of which is restricted by a suitable spring arrangement.

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

Downward-facing pyranometer used for measuring reflected solar radiation.

The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

A protocol similar to RS232 which permits data interchange on multidrop networks of up to 32 nodes using a single twisted pair cable. In order for this protocol to be used, each device on a network must have some level of intelligence in order establish o ...

A measurement of atmospheric conditions aloft, above the effective range of a surface weather observation. Elements evaluated include temperature, humidity, pressure, wind speed, and wind direction.

Determined by weighing a special type of wooden stick that has been exposed in the woods, its weight being proportional to its contained water.

Any source of radiant energy, especially electromagnetic energy.

A thin metal disc partially evacuated of air used to measure atmospheric pressure by measuring its expansion and contraction.

A self-recording instrument used on aircraft for the simultaneous recording of atmospheric pressure, temperature, and humidity.