A type of modulation in which the frequency of a continuous radio carrier wave is varied in accordance with the properties of a second (modulating) wave.

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

A wave resulting from the action of wind on a water surface.

An instrument which automatically determines the size distribution of raindrops.

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

Old snow that has become granular and compacted as a result of melting and refreezing.

An instrument which measures the transmissivity of the atmosphere between two points for the determination of visual range.

A temperature-sensing element which converts thermal energy directly into electrical energy. In its basic form it consists of two dissimilar metallic conductors connected in a closed loop. Each junction forms a thermocouple. If one thermocouple is maintai ...

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 time required for an instrument to register a designated percentage (frequently 90%) of a step change in the variable being measured.

A type of photoelectric photometer used to measure high-altitude winds on the assumption that stellar scintillation is caused by atmospheric inhomogeneities being carried along by wind near the tropopause level.

Operation mode of a communication circuit in which one end can only transmit and the other end can only receive.

A buoyant balloon rising freely in the atmosphere, as opposed to a captive balloon.

A hygrometer in which the sensitive element is a strand or strands of human hair, the length of which is a function of the relative humidity of the air.

A sudden brief increase in the speed of the wind, followed by a lull or slackening. Compare to peak gust.

A wind blowing in a direction perpendicular to the course of a moving object.

The temperature to which a sample of air must be cooled, while the mixing ratio and barometric pressure remain constant, in order to attain saturation by water vapor. When this temperature is below O

A c.g.s. (centimeter-gram-second) unit of mass. Originally defined as the mass of 1 cubic centimeter of water at 4

See wind vane.

Any source of radiant energy, especially electromagnetic energy.