A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.

A unit of luminance or brightness equal to 1/d candles per foot'.

An instrument which automatically records the measurement of two or more meteorological elements.

Graduated fixed stake used in regions of abundant snowfall to facilitate the measurement of snow depth.

Same as geostrophic wind level.

An instrument for taking photographs of an image of the sun in monochromatic light.

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

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

A small balloon whose ascent is followed by a theodolite in order to obtain data for the computation of winds aloft.

Apparatus from which the nature and time of precipitation may be determined.

Same as precipitation-evaporation ratio.

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

A unit of mass numerically equal to the molecular weight of the substance. The gram-mote or gram-molecule is the mass in grams numerically equal to the molecular weight, i.e. a gram-mole of oxygen is 32 grams.

Temperature assumed by an unsaturated air parcel when brought adiabatically to a standard pressure (1,000 mb).

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

A reversing thermometer which is encased in a strong glass outer shell that protects it against hydrostatic pressure. Compare to unprotected thermometer.

The length of fluid flow (gas or liquid) past a sensor required for the sensor to respond to 63.2% of a step change in speed. Expressed in feet or meters. For anemometers, this value is calculated from time constant times wind tunnel speed.

modulated radiosonde-A radiosonde which transmits the indications of the meteorological sensing elements in the form of pulses spaced in time. The meteorological data are evaluated from the intervals between the pulses. Also called timeinterval radiosonde ...

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.

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