An instrument used to measure the water vapor content of the air. A type of hygrometer. It consists of a wet-bulb and a dry-bulb thermometer. See aspiration psychrometer, Assmann psychrometer. hygrodeik, sling psychrometer.

A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.

A line drawn through points of equal humidity on given surface.

A small balloon whose ascent is followed by a theodolite in order to obtain data for the computation of winds aloft.

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 ...

Line drawn through geographical points recording equal amounts of precipitation during a given time period or for a particular storm.

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

The boundary between the troposphere and stratosphere, usually characterized by an abrupt change in lapse rate. Its height varies from 10 to 20 km. Regions above the tropopause have greater atmospheric stability than regions below.

A unit of mass numerically equal to the molecular weight of the substance. The gram-mote or gram-molecule is the mass in grams numerically equal to the molecular weight, i.e. a gram-mole of oxygen is 32 grams.

The length of fluid flow (gas or liquid) past a sensor required for the sensor to respond to 63.2% of a step change in speed. Expressed in feet or meters. For anemometers, this value is calculated from time constant times wind tunnel speed.

The rate of decrease of pressure per unit distance at a fixed time.

A scale of yellows, greens, and blues for recording the color of sea water, as seen against the white background of a Secchi disk.

A line drawn through geographical points where a given seasonal biological event occurs on the same date.

Same as recording rain gauge.

Graduated fixed stake used in regions of abundant snowfall to facilitate the measurement of snow depth.

An instrument for determining the degree of polarization of light. See photopolarimeter.

An instrument for studying, or examining substances in, polarized light. See Savant polariscope.

Generally, the relative states of inflow, outflow, and storage of moisture over a given area of earth's surface.

Amount of solar radiation incident, per unit area and time, on a surface which is perpendicular to the radiation and is situated at the outer limit of the atmosphere, the earth being at its mean distance from the sun. It equals approximately 2.00 ly/ min ...

A current meter consisting of six conical cups, mounted around a vertical axis, which rotate and generate a signal with each rotation. Tail vanes and a heavy weight stabilize the instrument.