The element directly responsive to the value of the measured variable.

The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

A metallic element of atomic weight 200.6 1, unique (for metals) in that it remains liquid under all but very extreme temperatures.

Wind with a speed between 48 and 55 knots (55 and 63 mph), Beaufort scale number 10.

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

See gain.

See gust and peak gust.

Any meteorological instrument, such as a radiosonde, in which the recording apparatus is located at some distance from the measuring apparatus.

Dihydrogen oxide, molecular formula H2O.

In general, the transformation of data from a "raw" form to some useable form. In meteorology, this often refers to the conversion of the observed value of an element to the value which it would theoretically have at some selected or standard level. The m ...

A wave disturbance in airflow due to some barrier in the flow. i.e. a hill or mountain.

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.

The total infrared radiation emitted from the earth's surface. To be carefully distinguished from atmospheric radiation, effective terrestrial radiation, and insolation.

Rate of wind movement in distance per unit time.

The maximum distance, usually horizontally, at which a given object or light source is just visible under particular conditions of transmittance and background luminance.

The total of direct solar radiation and diffuse sky radiation received by a unit horizontal surface. Global radiation is measured by pyranometers.

The ratio of the output of an instrument to the input value, i.e. a rain gauge with a sensitivity of 1 tip per 0.01"

A mercury barometer which measures atmospheric pressure by weighing the mercury in the column or cistern.

A weakly colored lunar halo identical in form and optical origin to the solar parhelion.

The actual time during which physical events take place.