Jet Propulsion Labratory

AIRS Maps In Motion

Water Vapor at 500 Millibars

This map shows AIRS observations of the amount of water vapor present in the atmospheric layer positioned at 500 millibar air pressure, which occurs at roughly 18,000 feet (5,500 m). Approximately half the mass of Earth's atmosphere is below this level, and half is above. This level is often used to represent upper level flow conditions because the level is well above the effects of topography and friction and the level is below the region in the upper troposphere where the air flow may experience strong accelerations and decelerations when in the vicinity of the upper jet streams. Since many weather systems tend to follow the wind flow at this level, this level is often considered to symbolize the steering level of these systems.