A local variation in the wind direction or speed. This condition can present danger to aircraft, especially at landing, when a sudden shift from headwind to tailwind can cause a rapid loss of airspeed and lift.

Instrument for measuring the mean intensity of glo global solar radiation (direct and diffuse) near the earth's surface in a specified time interval.

A momentary decrease in the speed of the wind.

A unit of luminous flux. The lumen is equal to the luminous flux radiated into a unit solid angle (steradian) from a small source having a luminous intensity of one candle. An ideal source possessing an intensity of one candle in every direction would rad ...

A measure of the intrinsic luminous intensity emitted by a source in a given direction. Luminance is a measure only of light. The comparable term for electromagnetic radiation in general is radiance.

Any emission of light at temperatures below that required for incandescence.

The flux of visible radiation, so weighted as to account for the manner in which the response of the human eye varies with the Wavelength of radiation. The basic unit for luminous flux is the lumen,

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.

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

Name applied to a class of instruments which measure the liquid content of the atmosphere.

The direction, with respect to magnetic north, from which the wind is blowing. Distinguish from true wind direction.

A cup anemometer with its shaft mechanically coupled to a magneto.

A recording magnetometer.

General name for an instrument which measures the earth's magnetic field intensity.

An instrument for measuring the pressure of gases and vapors. A mercury barometer is a type of manometer.

In folklore, a name for wind.

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 ...

A rainbow seen in the spray of the ocean. It is optically the same phenomenon as the ordinary rainbow.

See sea-water thermometer, reversing thermometer.

A sunshine recorder of the type in which the time scale is supplied by a chronograph. It consists of two bulbs, one of which is blackened, which communicate through a glass tube of small diameter. The tube is partially filled with mercury and contains two ...