An element that can control current without moving parts, heated filaments, or vacuum gaps.

Binary Coded Decimal. A coding system in which each decimal digit from 0 to 9 is represented by a 4-digit binary number.

An instrument which measures the effective terrestrial radiation. See Angstrom pyrgeometer.

A rotation anemometer in which the axis of rotation is horizontal. The instrument has either flat vanes (as in the air meter) or helicoidal vanes (as in the propeller anemometer). The relation between wind speed and angular rotation is almost linear.

A photometric unit of illuminance or illumination equal to one lumen per square meter

The length of fluid flow (gas or liquid) past a sensor required for the sensor to respond to 63.2% of a step change in speed. Expressed in feet or meters. For anemometers, this value is calculated from time constant times wind tunnel speed.

Same as constant-level balloon.

Same as fogbow.

The upper surface of a column of liquid.

Root Mean Square. This notation is used frequently with error analysis. In that context, it is the square root of the arithmetic mean of the squares of the deviations of the individual calibration points from the theoretical or ideal response.

Radiation with wavelengths greater than 4 microns. (In meteorology, same as infrared radiation.)

A rain gauge which automatically records the amount of precipitation collected, as a function of time.

Instrument for measuring the intensity of radiant energy. Its principle is based on the variation of electrical resistance, with the incoming radiation, of one or both the metallic strips which the instrument comprises.

Precipitation composed of balls or irregular lumps of ice with diameters between 5 and 50 mm.

A protocol similar to RS232 which makes use of differential transmission to provide high speed data transmission over significantly longer distances.

The difference between amounts of precipitation and runoff for a given storm. It is that portion of the precipitation that remains in the basin as soil moisture, surface storage, ground water, etc.

A set of weekly colored rainbow arcs sometimes discernable inside a primary rainbow.

The cardinal points of the compass, i.e. north, south, east, west.

An atmometer consisting of a porous porcelain or ceramic container connected to a calibrated reservoir filled with distilled water. Evaporation is determined by the depletion of water in the reservoir.

The unit of acceleration in the centimeter-gram-second system of units, equal to one cm per sec2. Commonly used in gravimetry.