Ice crystal deposits formed by sublimation (conversion of water vapor directly to ice) when temperature and dew point are below freezing.

Water vapor content of the air. See absolute humidity, dew point, mixing ratio, relative humidity, specific humidity.

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

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.

An instrument which measures the rate of evapotranspiration. It consists of a vegetation soil tank so designed that all water added to the tank and all water left after evapotranspiration can be measured.

A momentary decrease in the speed of the wind.

A transducer which converts electromagnetic radiation in the infrared, visible, and ultraviolet regions into electrical quantities such as voltage, current, or resistance. Also called photo cell.

In meteorology, an area of low pressure; a low or trough.

An aviation weather forecast for a specific flight.

Wind with a speed between 41 and 47 knots (47 and 54 mph); Beaufort scale number 9.

The portion of the precipitation on the land which ultimately reaches the streams. especially the water from rain or melted snow that flows over the surface.

The maximum deviation of any points from a straight line drawn as a "best fit" through the calibration points of an instrument with a linear response curve. Usually expressed as a percentage of full- scale range.

Same as dew-point hygrometer.

The elevation of the water surface in a stream as measured by a river gauge with reference to some arbitrarily selected zero datum.

check chamber-A chamber use to check the sensing elements of radiosonde equipment.

The audio-frequency signal transmitted by the Diamond-Hinman radiosonde when the baroswitch pen passes each fifteenth contact of the commutator, up to a number determined by the design of the commutator, and each fifth contact thereafter. This signal is t ...

An anemometer in which the sensor rotation is transmitted to a mechanical counter which directly integrates the air movement past the sensor. Used to determine total air passage (wind run). Average wind speed can be calculated from the difference between ...

Any emission of light at temperatures below that required for incandescence.

The rate of decrease of temperature with height when unsaturated air is lifted adiabatically (without exchange of heat with its surroundings). The decrease is due to expansion as the air is lifted to a lower pressure.

The volume of liquid water evaporated per unit area in unit time. usually measured as the depth of liquid water lost per unit time from the whole area.