In aviation terminology, route or terminal weather conditions of sufficiently low visibility to require the operation of aircraft under instrument flight rules.

A temperature scale on which the freezing point of water equals 32

A numbering system using a base number of 16 and including the ten decimal digits (0 to 9) along with six alpha digits (A to F). Thus. a digit is available to represent each of the possible values of a 4-bit binary digit.

Pertaining to the action or effect of the wind. Derived from the name of the Greek god of the winds, Aeolus.

A thermometer with a muslin-covered bulb which is moistened. used to measure wet-bulb temperature.

The true freezing point of water. The temperature at which a mixture of air-saturated pure water and pure ice may exist in equilibrium at a pressure of one standard atmosphere.

See mote.

A thermometer based upon the principle that the velocity of a sound wave is a function of the temperature of the medium through which it passes. Sonic thermometers possess very short time-constants and eliminate radiation error.

The component of the radiosonde which includes the modulating blocking oscillator and the radiofrequency carrier oscillator.

The measuring, transmitting, receiving, and indicating apparatus for obtaining the value of a quantity at a distance.

A unit of energy equal to 101 ergs or to 0.2389 calories.

A small balloon used to determine the height of the cloud base. The height can be computed from the ascent velocity of the balloon and the time required for its disappearance into the cloud.

A general name for instruments which detect the presence of (but do not necessarily measure) small electrical charges by electrostatic means. Compare to electrometer.

A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.

The center of an area of high pressure, usually accompanied by anticyclonic and outward wind flow. Also known as an anticyclone.

An absolute instrument developed by K. Angstrom for the measurement of direct solar radiation. The radiation receiver station consists of two identical manganin strips whose temperatures are measured by attached thermocouples. One of the strips is shaded, ...

Infrared radiation emitted by or being propagated through the atmosphere.

Overflowing by water of the normal confines of a stream or other body of water, or accumulation of water by drainage over areas which are not normally submerged.

A form of data transmission in which the bits of each character are sent one at a time along a single communication path. Compare to parallel data transmission.

A photometer that measures the received intensity of a distance tight source.