A measure of the relative power, or of the relative values of two flux densities, especially of sound intensities and radar power densities. The decibel is derived from the less frequently used unit, the bel, named in honor of Alexander Graham Bell.

A decrease in the central pressure of a pressure system. Usually applied to a low rather than to a high.

A thermometer using transducing elements which deform with temperature. Examples are the bimetallic thermometer and the Bourdon tube type of thennometer.

Generally, a measure of the departure of the mean daily temperature from a given standard, one degree day for each degree (

As used by the U.S. Army Corps of Engineers, the departure (in

A unit that represents one degree of deviation from a reference point in the mean daily outdoor temperature (usually 65

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 difference between temperature measurements taken at two significant levels above the ground. Temperatures at 10 and 40 meters are commonly used.

In meteorology, an area of low pressure; a low or trough.


Water condensed onto objects at or near the ground, due to the fact that their temperatures have fallen below the dew point temperature of the surrounding air, but not below freezing.

An Instrument used to determine dew point.

The temperature to which a sample of air must be cooled, while the mixing ratio and barometric pressure remain constant, in order to attain saturation by water vapor. When this temperature is below O

Same as dew-point hygrometer.

Hygrometer in which the dew (frost) point is determined by observing the temperature of an artificially cooled surface at the moment at which dew (frost) first appears on it.

The difference between the air temperature and the dew-point. Also called dew-point deficit, dew-point depression.

Thermodynamic change of state of a system in which there is transfer of heat across the boundaries of the system. Compare to adiabatic process.

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

Downward scattered and reflected solar radiation, coming from the whole hemisphere with the exception of the solid angle of the sun's disc on a surface perpendicular to the axis of this cone.

A hygrometer based upon the diffusion of water vapor through a porous membrane.

Pertaining to measurements or devices in which the output vanes in discrete steps, i.e. on-off or pulse signals. Compare to analog.