Board that holds graph paper on which is plotted information obtained from a pilot-balloon observation.

Conditions to which a device is subjected, not including the variable measured by the device. See normal operating conditions, reference operating conditions.

A mercury barometer which measures atmospheric pressure by weighing the mercury in the column or cistern.

Same as luminous intensity.

A weakly colored lunar halo identical in form and optical origin to the solar parhelion.

Clouds which cover between 6/10 and 9/10 of the sky. See Sky Terminology.

Same as aneroid barometer. Holostelic means wholly made of solids, while aneroid means devoid of liquid.

Of equal or constant pressure, with respect to either space or time.

In general, any self-recording instrument carried aloft by any means to obtain meteorological data.

An instrument of the aspiration condenser type which measures the concentration and mobility of small ions.

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 cover which fits over a large inflated balloon to facilitate handling in high or gusty winds.

Same as contact anemometer.

A counterclockwise change in wind direction. Backing winds with height are indicative of cold air advection (CAA).

Any and all forms of water particles, liquid or solid, that fall from the atmosphere and reach the ground.

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.

Same as wave pole.

A fixed-length group of bits representing the large data element handled as a unit by a computer. Word length is determined by the capacity of the CPU registers.

The algebraic difference between the upper and lower limits of the measuring range of an instrument, i.e. a thermometer with a range of -35 to 50

A unit that represents one degree of deviation from a reference point in the mean daily outdoor temperature (usually 65