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.

Negative Vorticity Advection.

A systematic observational error due to the characteristics of the observer. The uncertainty in a reading made by an observer may be acertained by a statistical analysis of his or her readings.

Precipitation of very small, white opaque particles of ice, fairly flat or elongated, with diameters less than 1 mm. The solid equivalent of drizzle.

A small anemometer with flat vanes which indicates the number of linear feet or meters of air which have passed the instrument during its exposure.

A device for computing certain psychrometric data, usually the dew point and the relative humidity, from known values of the dry-bulb and wet-bulb temperatures and the atmospheric pressure. One type is the circular slide-rule form and, like the psychromet ...

An atmospheric phenomenon, other than clouds, which obscures a portion of the sky from the point of observation. Also called obscuration.

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

An approximation to the complete equations describing atmospheric motion in which only the terms most important for the growth and decay of synoptic scale extratropical weather systems (i.e., the large areas of high and low pressure seen on weather maps) ...

Same as atmospheric pressure.

Apparatus using the combined simultaneous action of a bimetallic thermometer and a hair hygrometer to move a needle in front of a divided scale. fts construction permits dew point variations to be indicated approximately.

A radiosonde whose carrier wave is modulated by audio-frequency signals whose frequency is controlled by the sensing elements of the instrument.

A hypothetical temperature characterized by a complete absence of heat and defined as 0 K, -273.15 C, or -459.67 F.

Same as water year.

A general term for instruments which sample atmospheric suspensoids by impaction. Same as impactometer.

A balloon-borne instrument for the simultaneous measurement and transmission of meteorological data. It includes transducers for the measurement of pressure, temperature, and humidity; a modulator for the conversion of the output of the transducers to a q ...

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, ...

The wind speed and direction at various levels in the atmosphere above the level reached by surface weather observations.

A temperature scale with the ice point at 273 degrees and boiling point of water at 373 degrees. It is intended to approximate the Kelvin temperature scale with sufficient accuracy for many sciences, notably meteorology.