Abbreviation for Instrument Flight Rules, but commonly used to refer to the weather and/or flight conditions to which these rules apply, i.e. low visibility.

A common type of terrestrial scintillation; shimmering over a hot surface (such as a roadway) on a quiet, cloudless. summer day.

An absolute pyhrliometer, developed by C.G. Abbott, in which the radiation-sensing element is a blackened water-calorimeter.

The older name for the Celsius temperature scale. Officially abandoned by international agreement in 1948, but still in common use.

The height of the cloud base above the local terrain.

A unit measure of electrical conduction. The facility with which a substance conducts electricity, as represented by the current density per unit electrical-potential gradient in the direction of flow. Electrical conductivity is the reciprocal of electric ...

A combination cup anemometer and pressure-plate anemometer, consisting of an array of cups about a vertical axis of rotation, the free rotation of which is restricted by a suitable spring arrangement.

A set of electrical conductors, often on a backplane, that carry data and power signals among the various components of a computer.

A mercury barometer designed for use aboard ship. The instrument is of the fixed-cistern type (see Kew barometer). The mercury tube is constructed with a wide bore for its upper portion and with a capillary bore for its lower portion. This is done to incr ...

An instrument for measuring angles of inclination. Used in conjunction with a ceiling light to measure cloud height at night.

A definite portion of a stream channel, commonly taken between two gauging stations, but may be taken between any two specified points.

Temperature of equilibrium between the liquid and vapor phases of a substance at a given pressure.

A clock-driven instrument mounting which automatically and continuously points in the direction of the sun. It is used with a pyrheliometera,hen continuous direct solar radiation measurements are required.

An instrument which determines the black-body temperature of a substance by measuring its thermal radiation.

Turbulence encountered by aircraft when flying through air space devoid of clouds. Thermals and wind shear are the main causes.

Air in motion relative to the surface of the earth. Almost exclusively used to denote the horizontal component.

An increase in the central pressure of a pressure system; opposite of a deepening. More commonly applied to a low rather than a high.

Any device or instrument for measuring salinity, especially one based on electrical conductivity methods.

A graphical device used for the determination of the speed of the geostrophic wind from the isobar or contour-line spacing on a synoptic chart.

A hypothetical "body" whose surface absorbs no electromagnetic radiation of any wavelength. An idealization exactly opposite to that of the black body. In nature, no true white bodies are known. Moist white pigments exhibiting high reflectivity for visibl ...