Pressure surface (geopotential height) in the troposphere equivalent to about 18,000 feet above sea level. Level of the atmosphere at which half the mass of the atmosphere lies above and half below, as measured in pressure units. This area is important for understanding surface weather, upper air storms tend to be steered in the direction of the winds at this level and are highly correlated with surface weather.
- Browse Related Terms: 500 hPa, 500 mb, Constant Pressure Chart, Engineer's Level, Extraterrestrial Radiation, Isobaric Chart, Isoheight, Lithometeor, Precision, REP, Station pressure, Theodolite, Tides, Upper-air Weather Chart