The measurement and computation of wind speeds and directions at various levels above the surface of the earth. Methods include pilot balloon observations, rabals, rawin or rawinsonde observations, radar tracking, or acoustic sounding.

An inert gas. A colorless, monatomic element which is found to occur in dry air to the extent of only 0.000524 percent by volume. Helium is very light, having a molecular weight of only 4.003 and specific gravity referred to air of 0.138. Because helium i ...

Old snow that has become granular and compacted as a result of melting and refreezing.

A unit of luminous flux. The lumen is equal to the luminous flux radiated into a unit solid angle (steradian) from a small source having a luminous intensity of one candle. An ideal source possessing an intensity of one candle in every direction would rad ...

An instrument of the aspiration condenser type which measures the concentration and mobility of small ions.

A unit of luminous intensity of a light source.

Same as balloon cover.

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

The size of the area comprising a watershed or river basin. Also called catchment area.

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

Winds which, over a small area, differ from those which would be appropriate to the general pressure distribution.

See evaporative opportunity.

An instrument which measures the transmissivity of the atmosphere between two points for the determination of visual range.

The temperature at which all three phases of a substance can exist in equilibrium. This temperature occurs at only one pressure. The triple-point of water is 273.16 K and is the basis of the Kelvin scale.

Sir Napier Shaw's name for the approximate absolute temperature scale,

In general, any self-recording instrument carried aloft by any means to obtain meteorological data.

The general term for dry atmospheric suspensoids, including dust, haze, smoke. and sand. Compare to hydrometeor.

A chronograph used to make a time-record of certain measured meteorological elements. The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed respectively by a contact anemometer, M ...

A wind blowing in a direction opposite to the heading of a moving object, thus opposing the object's intended progress; the opposite of a tailwind.

Name sometimes given to a transmissometer.