Strong winds concentrated within a narrow band in the atmosphere. The jet stream often "steers" surface features such as front and low pressure systems.

The maximum distance along the runway at which the runway lights are visible to a pilot at touchdown. Runway visual range may be determined by an observer located at the end of the runway, facing in the direction of landing, or by means of a transmissomet ...

A curve showing the variation of temperature with height in the free air. See lapse rate.

Precipitation composed of liquid water drops more than 0.5 mm in diameter, failing in relatively straight, but not necessarily vertical, paths. Compare to drizzle.

A sunshine recorder of the type in which the time scale is supplied by a chronograph. It consists of two bulbs, one of which is blackened, which communicate through a glass tube of small diameter. The tube is partially filled with mercury and contains two ...

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.

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 ...

An empirical curve relating stream discharge or stage at a point on a stream to discharge or stage at one or more upstream points and, possibly. to other parameters. Also called stage relation.

A hygrometer in which the sensitive element is a strand or strands of human hair, the length of which is a function of the relative humidity of the air.

Operation mode of a communication circuit in which one end can only transmit and the other end can only receive.

The length of air flow past a wind vane required for the vane to respond to 50 percent of a step change in wind direction. Expressed in feet or meters and calculated from delay time times wind tunnel speed.

The audio-frequency signal transmitted by the Diamond-Hinman radiosonde when the baroswitch pen passes each fifteenth contact of the commutator, up to a number determined by the design of the commutator, and each fifth contact thereafter. This signal is t ...

A measure of the degree to which the weather or climate of a region is favorable to the process of evaporation. Usually considered to be the rate of evaporation. under existing atmospheric conditions, from a surface of water which is chemically pure and h ...

The depth below which the ground is saturated with water. No water table exists if the ground water is confined by an overlying impermeable stratum, as in the case of artesian ground water.

A small balloon, loaded with ballast and inflated so that it will explode at a predetermined altitude, which is attached to a larger balloon.

That portion of the atmosphere which is above the lower troposphere. Generally applied to levels above 850 mb.

Routine broadcast of meteorological information for aircraft in flight.

Any source of radiant energy, especially electromagnetic energy.

An instrument for collecting liquid water from the atmosphere.

Frozen or partly frozen rain.