A hydrometeor consisting of a visible aggregate of minute water and/or ice particles in the atmosphere above the earth's surface. Cloud differs from fog only in that the latter is, by definition, in contact with the earth's surface.

The condition of the atmosphere when the amount of water vapor present is the maximum possible at the existing temperature.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

The temperature at which an object gives out as much radiation as it receives from its surroundings.

In Jeffreys' classification, a wind for which the pressure force exactly balances the viscous force, in which the vertical transfers of momentum predominate.

A method of upper air observation consisting of an evaluation of the wind speed and direction, temperature, pressure, and humidity aloft by means of a balloon-borne radiosonde tracked by radar or a radio theodolite.

An atmometer which uses a filter paper disc as the evaporating element. The amount of water evaporated through the paper is read at the graduated tube reservoir.

The process by which water in plants is transferred as water vapor to the atmosphere. Also, the amount of water so transferred.

An instrument used to measure changes in the level of the water in an evaporation pan. The gauge is normally placed in a Stillwell and adjusted so that the point of the hook just breaks the water surface. The change in water level is read on the attached ...

An instrument used for measuring the specific gravity of a liquid.

Anemometer which measures wind speed by the speed of rotation of 3 or 4 hemispherical or conical cups, each fixed to the end of a horizontal arm projecting from a vertical axis. See condenser-discharge anemometer, contact anemometer. Compare to bridled-cu ...

See Koschmieder's law.

The indicating part of an instrument. For example, the hand of a watch or the meniscus of a mercury column.

Rate of wind movement in distance per unit time.

A computed characteristic of a particular river basin, expressed as the time difference between the time-center of mass of rainfall and the time-center of mass of resulting runoff.

The process by which small particles suspended in a medium of a different refractive index diffuse a portion of the incident radiation in all directions. In scattering no energy transformation results, only a change in the spatial distribution of the radi ...

Temperarure at which a liquid solidifies under any given set of conditions. It may or may not be the same as the melting point or the more rigidly defined true freezing point or (for water) ice point.

Wind with a speed between 28 and 55 knots (32 and 63 mph); Beaufort scale numbers 7 through 10.

A systematic observational error due to the characteristics of the observer. The uncertainty in a reading made by an observer may be acertained by a statistical analysis of his or her readings.

A local variation of the wind vector or any of its components in a given direction.