Compact Glossary of Meteorological Terms

Response value The wind velocity at which the cup or the wind vane starts to move.
Barometer General term for the device measuring the atmospheric pressure.
Barometric pressure Pascal [Pa] = Newton per square meter [N/m2]; 1hPa=1mbar; 1 bar=105Pa
Beaufort Classification for certain wind velocity ranges:

bft m/s bft m/s bft m/s bft m/s bft m/s bft m/s
0 0-0.2 1 0.3-1.5 2 1.6-3.3 3 3.4-5.4 4 5.5-7.9 5 8.0-10.7
6 10.8-13.8 7 13.9-17.1 8 17.2-20.7 9 20.8-24.4 10 24.5-28.4 11 28.5-32.6
12 32.7-36.9 13 37.0-41.4 14 41.5-46.1 15 46.2-50.9 16 51.0-56.0 17 56.1-61.2

Damping ratio Measure for the damping of wind vanes. It is the ratio of successive damped deflection amplitudes
(e.g. 3rd to 1st amplitude) in one direction.
Distance constant Is the distance that has been passed by the wind and which is reached when, after a sudden change of the wind velocity, the velocity has reached 63% of the final value.
Gray code One step digital code used for the wind direction.
Altitude formula Mathematical reduction of the barometric air pressure to a reference altitude, at minimum to sea level (QFF). Example: with each altitude increase of 8m the pressure decreases by approximately 1hPa.
Detection limit The lowest value of the wind velocity and wind direction where a stable measured value is established.
Normal pressure The barometric normal pressure (1013.25hPa) that, according to DIN ISO 2533, serves as base value for the ´high pressure´ and ´low pressure´ data.
QFE The atmospheric pressure that has been reduced to the elevation of an airport runway.
QFF Designation used in aviation for the barometric air pressure that has been reduced to sea level (0m). Also serves as a common base for the barometric air pressure comparison of different weather stations with different elevations of the stations and it is the base for the presentation of the isobars in weather maps.
QNH Designation commonly used in aviation for the barometric air pressure, which has to be entered into an altimeter as an initial value so the altimeter can indicate the altitude above sea level.
Altitude of station The local elevation regarding the installation of the measuring station incl. the barometer above sea level.
Variation The range in which the wind direction has been changing within the preceding 10 minutes (acc. to ICAO).
Wind velocity Usual practical units: 1m/s = 3.6km/h = 1.9455knots
Wind direction Specification of which direction the wind comes from. The specification is based on a clockwise setup starting from North to East (90°), South (180°) and West (270°) to North (360°).
Wind travel Is the distance travelled by the wind during a certain period.