An instrument for taking photographs of an image of the sun in monochromatic light.

The change in barometric pressure within a specified period of time (typically 3 hours for meteorological observations).

A box-like structure designed to protect certain meteorological instruments from exposure to direct sunlight, precipitation, and condensation, while at the same time providing adequate ventilation. Instrument shelters are painted white, have louvered side ...

A unit of energy per unit area commonly employed in radiation theory. Equal to one gram-calorie per square centimeter.

Ragged low clouds, usually stratus fractus. Most often applied when such clouds are moving rapidly beneath a layer of nimbostratus.

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

A general term for atmospheric water in any of its forms, i.e. clouds, fog, hail, ice crystals, rain.

An instrument which automatically determines the size distribution of raindrops.

An optical instrument which consists of a sighting telescope mounted so that it is free to rotate around horizontal and vertical axes, with graduated scales so that the angles of rotation may be measured. Used to observe the motion of a pilot balloon.

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

A calorimetric radiation instrument of historic interest used for the measurement of outgoing heat radiation from the earth during an interval of time. The time integration is performed by allowing the radiation to fall on an uninsulated vessel containing ...

A measure of the relative power, or of the relative values of two flux densities, especially of sound intensities and radar power densities. The decibel is derived from the less frequently used unit, the bel, named in honor of Alexander Graham Bell.

A hygrometer in which the rotation of the hygrometric element is a function of humidity.

The condition of the atmosphere when the amount of water vapor present is the maximum possible at the existing temperature.

Force wind-Wind with a speed above 64 knots (73 mph); Beaufort scale numbers 12 through 17.

A momentary decrease in the speed of the wind.

A thermoelectric thermometer used for measuring air temperature. The name is derived from the fact that the reference thermocouple is placed in an insulated bottle.

The source of illumination for an antenna reflector. Also called antenna feed.

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.

Downward scattered and reflected solar radiation, coming from the whole hemisphere with the exception of the solid angle of the sun's disc on a surface perpendicular to the axis of this cone.