Atmospheric water vapor plays an important role in the Earths 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 Earths 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.
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.)