Atmospheric water vapor plays an important role in the Earth’s energy balance, in many chemical cycles and in tracing the exchange of air between the upper and lower atmosphere. Water vapor is the most abundant, naturally occurring greenhouse gas and traps outgoing energy in the atmosphere that is radiated from the Earth. Precise measurements of water vapor by SAGE III will provide important contributions to understanding how this process warms the Earth’s atmosphere. Evidence also indicates that water vapor in the upper atmosphere is increasing. This increase is not well understood, but it could affect climate, alter circulation patterns and allow ozone loss in the Arctic to occur more easily. Measurements by SAGE III will provide a crucial new understanding of how water vapor is circulated in the atmosphere and how it is increasing with time.
 

SAGE III
Introduction
Aerosols and volcanic eruptions
Ozone in the upper atmosphere
Water vapor observations
Making measurements at the edge of the Earth

The image above shows the difference in atmospheric water vapor concentrations between January and July. During summer (July in the Northern Hemisphere and January in the Southern) the warmer atmosphere holds more water (red) than during the colder and drier winter. The data were collected by the SAGE II instrument during 1986, 1987, and 1988. (Image courtesy NASA Langley Research Center Atmospheric Sciences Data Center.)

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