Automated Surface Observing System. A network of instrumented weather stations deployed primarily by the National Weather Service to make weather observations without operator involvement.

An anemometer which measures wind speed in terms of the drag which the wind exerts on a solid body. See bridled-cup anemometer, normal-plate anemometer, pendulum anemometer.

Frequency Shift Keying. A form of frequency modulation of a data signal performed by a modem for transmission over dedicated wire or phone lines.

See sea-water thermometer, reversing thermometer.

An instrument for determining the dust content of a sample of air. Also spelled conimeter.

A graphical device used for the determination of the speed of the geostrophic wind from the isobar or contour-line spacing on a synoptic chart.

For a given cloud or cloud laver. the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

A self-recording psychrometer.

Contraction for radiosonde observation.

The inherent imprecision of a given process of measurement, the unpredictable component of repeated independent measurements of the same object under sensibly uniform conditions.

Anemometer whicb measures wind speed by measuring the degree of cooling of a metal wire heated by an electric current. A type of cooling power anemometer.

A faintly-colored circular arc similar to a rainbow but formed on fog layers containing drops whose diameters are 100 microns or less. Also called mistbow, white rainbow.

Programmable Read-Only Memory. Read-only memory which can be programmed by the user using a special hardware programmer.

An instrument which indicates the presence of precipitation. The ombroscope consists of a heated, water-sensitive surface which indicates by mechanical or electrical techniques the occurrence of precipitation.

A hygrometer in which the rotation of the hygrometric element is a function of humidity.

A device for measuring sea-surface waves. It consists of a weighted pole below which a disk is suspended at a depth sufficiently deep for the wave motion associated with deepwater waves to be negligible. The pole will then remain nearly as if anchored to ...

A component of a radiosonde consisting of a series of alternate electrically conducting and insulating strips. As these are scanned by a contact the radiosonde transmits temperature and humidity signals alternately. The contact may be a baroswitch as in t ...

A chronograph used to make a time-record of certain measured meteorological elements. The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed respectively by a contact anemometer, M ...

Determination of the total amount of snow covering a watershed or a given region. Both depth and water content of the snow may be measured, and the results may be used to predict the amount of water that will be available after melting.

The atmospheric pressure computed using station elevation as the reference datum level. Station pressure is usually the base value from which sea level pressure and altimeter setting are determined.