A mercury barometer in which the tube is U-shaped and the upper and lower mercury surfaces have the same diameter.

Same as precipitation- effectiveness index.

A precipitation amount of less than 0.005 inches. Also, the record made by any self-registering instrument.

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

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.

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

The humidity transducinu element in a Diamond-Hinman radiosonde. Also called electrolytic strip.

Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal forms.

A method of winds aloft observation in which the elevation and azimuth angles of a theodolite are read while visually tracking a pilot balloon. Balloon height data is estimated from assumed balloon ascension rates.

Solar radiation of selected wavelengths.

The mean difference between the readings of a given instrument and those of a standard instrument.

A unit of luminance or brightness equal to 1/d candles per foot'.

An instrument which automatically records the measurement of two or more meteorological elements.

A mercury barometer arranged so that the position of the upper or lower meniscus may be measured photographically. In one design the image of the meniscus is formed on a rotating drum covered with sensitized paper so that a continuous record of pressure a ...

Pertaining to rain, or more broadly, to precipitation.

The process of modifying some characteristic of a wave (the carrier) so that it varies in step with the instantaneous value of another wave (the modulating wave) in order to transmit a message. The modified characteristic may be frequency, phase, and/or a ...

The rate of decrease of pressure per unit distance at a fixed time.

Same as water year.

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

Determination of the total amount of snow covering a watershed or a given region. Both depth and water content of the snow may be measured, and the results may be used to predict the amount of water that will be available after melting.