February 2nd. In American folklore, a day that is popularly supposed to provide the key to the weather for the remainder of the winter. Specifically, if the ground-hog upon emerging from its hole casts a shadow, it will return underground, thereby forebod ...

A unit of luminance (or brightness) equal to 1/6 candles per square centimeter.

The stage, on a fixed river gauge, corresponding to the top of the lowest banks within the reach for which the gauge is used as an index. Compare to flood stage.

variable audio-modulated radiosonde developed at the Bureau of Standards and used by the United States weather services.

A small pointer extending downward from the top of the cistern of a Fortin barometer. The level of the mercury in the cistern is adjusted so that it just comes in contact with the end of the pointer, thus setting the zero of the barometric scale.

Very generally, any moving- stream of air. It has no particular technical connotation.

General term for an instrument which records the vertical electric current in the atmosphere.

A method of winds aloft observation in which the elevation and azimuth angles of a theodolite are read while visually tracking a pilot balloon. Balloon height data is estimated from assumed balloon ascension rates.

The record of a barograph.

A hygrometer which determines the amount of precipitable moisture in a given region of the atmosphere by measuring attenuation of radiant energy caused by the absorption bands of water vapor.

The length of air flow past a wind vane required for the vane to respond to 50 percent of a step change in wind direction. Expressed in feet or meters and calculated from delay time times wind tunnel speed.

The state of the weather with respect to its effect upon the kindling and spreading of forest fires.

An instrument for measuring differences of electric potential.

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

A direct-vision nephoscope constructed in the following manner: A grid-work of bars is mounted horizontally on the end of a vertical column and made free to rotate about the vertical axis. The observer rotates the grid and adjusts his or her position unti ...

A graphical representation of a frequency distribution. The range of the variable is divided into class intervals for which the frequency of occurrence is represented by a rectangular column. The height of the column is proportional to the frequency of ob ...

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

A recording weight barometer.

A vector term which includes both wind speed and wind direction.

A polarimeter utilizing a Wollaston prism as a polarizer and a Nicol prism as an analyzer.