A radiosonde which is dropped by parachute from an aircraft for the purpose of obtaining soundings of the atmosphere below.

A line of equal or constant temperature.

Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal forms.

The study of waters (including oceans, lakes, and rivers) embracing either: (a) their physical characteristics, from the standpoint of the oceanographer or limnologist; or (b) the elements affecting safe navigation, from the point of view of the mariner. ...

The temperature at which the liquid and solid forms of a substance may exist in equilibrium at a given pressure (usually one standard atmosphere). The true freezing point of water is known as the ice point.

The lowest value of a measured quality at which a sensor meets its accuracy specification.

The actual lifting force of an inflated balloon, usually expressed in grams.

An instrument for measuring the intensity of light or the relative intensity of a pair of lights. Also called an illuminometer. If the instrument is designed to measure the intensity of light as a function of wavelength, it is called a spectrophotometer. ...

An evaporation pan in which the evaporation is measured from water in a pan floating in a larger body of water.

A buoyant balloon rising freely in the atmosphere, as opposed to a captive balloon.

A systematic summary of the terms (inflow, outflow, and storage) of the storage equation as applied to the computation of soil-moisture changes, ground-water changes, etc. An evaluation of the hydrologic balance of an area. Also called basin accounting, w ...

The time required for an instrument to register a designated percentage (frequently 90%) of a step change in the variable being measured.

In aviation terminology, route or terminal weather conditions of sufficiently low visibility to require the operation of aircraft under instrument flight rules.

Very small precipitation drops (diameters less than 0.5 mm) that appear to float with air currents while falling in an irregular path. Unlike fog droplets, drizzle falls to the ground.

By international agreement, a period during which greatly increased observation of world-wide geophysical phenomena is undertaken through the co-operative effort of participating nations. July 1957-December 1958 was the first such year. However, precedent ...

An instrument for measuring the relative speed of a fluid. It consists of a concentric pipe arrangement in which the inner pipe is open at one end and the outer pipe is perforated and closed at both ends. Each pipe is connected to a manometer. The unit is ...

A type of cistern barometer in which the level of mercury in the cistern is adjusted to the zero point of the scale before each reading.

A thermometer, invented by James Six in 1782, which simultaneously indicates the maximum and minimum temperatures attained during a given interval of time. A U-tube min/max thermometer

Any and all forms of water particles, liquid or solid, that fall from the atmosphere and reach the ground.

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