A hydrometeor consisting of an aggregate of microscopic and more-or-less hygroscopic water droplets suspended in the atmosphere. It reduces visibility to a lesser extent than fog. The relative humidity of mist is often less than 95 percent.

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 liquid-in-glass thermometer which uses an organic substance such as alcohol as the thermometer liquid. This type of thermometer has a low freezing point and a high coefficient of expansion. It is less accurate, however, than a mercury thermometer.

One of several constant-pressure levels in the atmosphere for which a complete evaluation of data derived from upper air observations is required.

A balloon having a detachable tail which is released when the balloon has undergone a predetermined expansion. It thus serves to measure approximately the density of the atmosphere at the point of release.

A graduated scale placed in a position so that the stage of a stream may be read directly from it. Staff gauges may be placed on bridge piers or pilings, etc., or placed on specially constructed supports.

The value of the quantity measured, as indicated or otherwise provided by a measuring instrument.

An elongated area of relatively high pressure. Usually associated with and most clearly identified as an area of maximum anticyclonic curvature of the wind flow. The opposite of a trough.

A feeble oscillatory disturbance of the earth's crust, detectable only by very sensitive seismographs. Certain types of microseisms seem to be closely correlated with pressure disturbances. See microbarm.

The upward force produced by the gas in a balloon. It is equal to the free lift plus the weight of the balloon and the attached equipment.

An area of low barometric pressure, with its attendant system of winds. Also called a depression or cyclone.

A colorless and odorless gaseous element. The lightest and apparently the most abundant chemical element in the universe. However, it is found only in trace quantities in the observable portion of our atmosphere, only about 0.00005 percent by volume of dr ...

A term used to describe a sensor (or sensors), the associated transducer(s), and the data readout or recording device.

A thermometer, invented by James Six in 1782, which simultaneously indicates the maximum and minimum temperatures attained during a given interval of time. A U-tube min/max thermometer

A type of wind vane having a split or V-shaped tail. The apex orients itself to the direction of the wind.

Name sometimes used in place of pyranometer as a generic term.

Thermometer for measuring the temperature in the soil at different depths.

Precipitation of white, opaque, spherical or conical ice particles that are crisp and easily crushed and that have diameters of 2 to 5 mm.

A measure, proposed by Angstrom, of the precipitation effectiveness of a region.

Particle on which the freezing of water occurs.