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

The rate of decrease of pressure per unit distance at a fixed time.

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.

See foehn.

A mercury barometer arranged so that the position of the upper or lower meniscus may be measured photographically. In one design the image of the meniscus is formed on a rotating drum covered with sensitized paper so that a continuous record of pressure a ...

Same as precipitation-evaporation ratio.

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

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.

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

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

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.

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

A thermometer based upon the principle that the velocity of a sound wave is a function of the temperature of the medium through which it passes. Sonic thermometers possess very short time-constants and eliminate radiation error.

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

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

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

Same as recording rain gauge.

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

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.