Instrument for measuring the depth of water from precipitation that is assumed to be distributed over a horizontal, impervious surface and not subject to evaporation.

An instrument designed to measure the effect of sunlight on evaporation from plant foliage. It consists of a porous clay atmometer whose surface has been blackened so that it absorbs radiant energy.

A calorimetric radiation instrument of historic interest used for the measurement of outgoing heat radiation from the earth during an interval of time. The time integration is performed by allowing the radiation to fall on an uninsulated vessel containing ...

A rainbow seen in the spray of the ocean. It is optically the same phenomenon as the ordinary rainbow.

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

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

Forecasting weather by the use of numerical models, run on high speed computers. Most of the NWP for the National Weather Service is done at the National Centers for Environmental Prediction (NCEP).

The direction, with respect to true north, from which the wind is blowing. Distinguish from magnetic wind direction. In all standard upper-air and surface weather observations, it is true wind direction that is reported.

A wind scale adapted by the U.S. Forest Service for use in the forested areas of the northern Rocky Mountains (NRM). It is an adaptation of the Beaufort wind scale. The difference between these two scales lies in the specification of the visual effects of ...

A balloon used to carry a radiosonde aloft, considerably larger than pilot balloons or ceiling balloons.

The component of the radiosonde which includes the modulating blocking oscillator and the radiofrequency carrier oscillator.

Precipitation composed of liquid water drops more than 0.5 mm in diameter, failing in relatively straight, but not necessarily vertical, paths. Compare to drizzle.

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

An instrument which automatically records the voltage applied to it, as a function of time.

The difference between the input quantity applied to a measuring instrument and the output quantity indicated by the instrument. The inaccuracy of an instrument is equal to the sum of its instrument error and its uncertainty.

The temperature registered by a thermometer with its bulb at the level of the tops of the grass blades in short turf.

A device that combines several separate communications signals into one and outputs them on a single line.

A cylinder installed in a body of water or an evaporation pan to hold a sensor, such as a float to measure water level or a hook gage. The stillwell is constructed so that there is free movement of water in and out of it, and it therefore provides a repre ...

See ceilometer.

A hydrometeor consisting of a visible aggregate of minute water droplets suspended in the atmosphere near the earth's surface. Fog differs from cloud only in that the base of fog is at the earth's surface while clouds are above the surface.