A photometric unit of illuminance or illumination equal to one lumen per square meter

A set of weekly colored rainbow arcs sometimes discernable inside a primary rainbow.

Similar to the spectroheliograph, but used for visual instead of photographic purposes.

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

The part of a measuring instrument which responds directly to changes in the environment.

Electromagnetic radiation of shorter wavelength than visible radiation but longer than x-rays, between 0.02 and 0.4 micron (200 and 4000 angstrom).

The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface. In terms of the hydrologic cycle, the ...

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

A technique for making winds aloft observations in which two theodolites located at either end of a baseline follow the ascent of a pilot balloon. Synchronous measurements of the elevation and azimuth angles of the balloon. taken at periodic intervals, pe ...

For a given cloud or cloud laver. the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

An ice coating with a consistency intermediate between glaze and rime.

Same as luminous intensity.

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

An instrument used for measuring the specific gravity of a liquid.

The transducer of any hygrometer, i.e. that part of a hygrometer that quantitatively "senses" atmospheric water vapor.

A small, limited-capacity central processing unit contained entirely on one semiconductor chip.

In Jeffreys' classification, a wind for which the pressure force exactly balances the viscous force, in which the vertical transfers of momentum predominate.

A thin metal disc partially evacuated of air used to measure atmospheric pressure by measuring its expansion and contraction.

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 ...

The minimum temperature shown by a minimum thermometer exposed in an open situation with its bulb at the level of the tops of the grass blades of short turf.