An instrument for determining the degree of polarization of light. See photopolarimeter.

Line drawn through geographical points recording equal amounts of precipitation during a given time period or for a particular storm.

Radiation with wavelengths greater than 4 microns. (In meteorology, same as infrared radiation.)

Same as recording rain gauge.

A current meter consisting of six conical cups, mounted around a vertical axis, which rotate and generate a signal with each rotation. Tail vanes and a heavy weight stabilize the instrument.

A scale of yellows, greens, and blues for recording the color of sea water, as seen against the white background of a Secchi disk.

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

Diffuse solar radiation which has the same intensity in all directions.

Wind with a speed between 11 and 16 knots (13 and 18 mph); Beaufort scale number 4.

An element that can control current without moving parts, heated filaments, or vacuum gaps.

Moisture contained in the soil above the water table, including water vapor which is present in the soil pores. In some cases this term refers strictly to the humidity contained in the root zone of plants.

Precipitation of very small, white opaque particles of ice, fairly flat or elongated, with diameters less than 1 mm. The solid equivalent of drizzle.

A set of rules or conventions used to standardize data transfer between devices.

Snow shower, particularly of a very light and brief nature.

Same as rain gauge.

The processing of the form or mode of a signal so as to make it intelligible to, or compatible with, a given device.

A recording siphon barometer.

Atmospheric layer throughout which there is no change of temperature with height, i.e. a zero lapse rate.

Contraction for pilot balloon observation.

A local variation in the wind direction or speed. This condition can present danger to aircraft, especially at landing, when a sudden shift from headwind to tailwind can cause a rapid loss of airspeed and lift.