A unit of illuminance or illumination equal to one lumen per foot'. This is the illuminance provided by a light source of one candle at a distance of one foot.

meter-An instrument for measuring the transmissivity of the atmosphere; a type of transmissometer. It consists of a constant- intensity collimated light source located at a suitable distance from a photoelectric cell. Variation in the turbidity of the atm ...

An elongated area of relatively low atmospheric pressure. Usually associated with and most clearly identified as an area of maximum cyclonic curvature of the wind flow. The opposite of a ridge.

A tube designed to measure the rate of flow of fluids. It consists of a tube having a constriction or throat at its midsection. The difference between the pressure measured at the inlet and at the throat is a function of the fluid velocity. Compare to Pit ...

A general term for atmospheric water in any of its forms, i.e. clouds, fog, hail, ice crystals, rain.

See aneroid capsule.

A term used to describe a sensor (or sensors), the associated transducer(s), and the data readout or recording device.

The record obtained from a bolometer.

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 photometric unit of illuminance or illumination equal to one lumen per square meter

The play or loose motion in an instrument due to the clearance existing between mechanically contacting parts.

A sudden, significant increase in station pressure.

Technically, the temperature registered by the dry-bulb thermometer of a psychrometer. However, it is identical with the temperature of the air and may also be used in that sense.

The water portion of the earth as distinguished from the solid part, called the lithosphere, and from the gaseous outer envelope, called the atmosphere.

The total of direct solar radiation and diffuse sky radiation received by a unit horizontal surface. Global radiation is measured by pyranometers.

Overflowing by water of the normal confines of a stream or other body of water, or accumulation of water by drainage over areas which are not normally submerged.

See standard atmosphere.

A line drawn through geographical points where a given seasonal biological event occurs on the same date.

In meteorology, a deflecting force acting on a body in motion and resulting from the earth's rotation. It deflects air currents to the right in the northern hemisphere and to the left in the southern hemisphere, thus having an effect on wind direction.

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 ...