Federal Aviation Administration.

The difference between the true value of some quantity and its observed value. Every observation is subject to certain errors. Systematic errors affect the whole of a series of observations in nearly the same way. For example, the scale of an instrument m ...

Physical equipment used in data processing. Compare to firmware, software.

The minimum temperature shown by a minimum thermometer exposed in an open situation with its bulb at the level of the tops of the grass blades of short turf.

See approximate absolute temperature scale, Celsius temperature scale, centigrade temperature scale, Fahrenheit temperature scale, Kelvin temperature scale, Rankine temperature scale, Reaumur temperature scale,

Solar radiation of selected wavelengths.

A measure, proposed by Angstrom, of the precipitation effectiveness of a region.

The inherent imprecision of a given process of measurement, the unpredictable component of repeated independent measurements of the same object under sensibly uniform conditions.

In a system of moist air, the ratio of the mass of water vapor to the total volume of the system. Usually expressed as grams per cubic meter (g/m3).

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

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

Hygrometer in which the dew (frost) point is determined by observing the temperature of an artificially cooled surface at the moment at which dew (frost) first appears on it.

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 ...

The maximum rate at which precipitation can pass through the surface into the soil, for a given soil in a given condition.

A cylinder installed in a body of water or an evaporation pan to hold a sensor, such as a float to measure water level or a hook gage. The stillwell is constructed so that there is free movement of water in and out of it, and it therefore provides a repre ...

Electromagnetic radiation lying in the wavelength interval between 0.8 micron and I millimeter. At the lower limit of this interval, the infrared radiation spectrum is bounded by visible radiation, while on its upper limit it is bounded by microwave radia ...

A fixed support for mounting maximum and minimum thermometers of the liquid-in-glass type. The support holds the thermometers at the correct operating attitude and also permits their rotation for resetting when desired.

Wind with a speed between 48 and 55 knots (55 and 63 mph), Beaufort scale number 10.

The correctable part of the inaccuracy of an instrument.

A liquid-in-glass or liquid-in-metal thermometer using mercury as the liquid.