 |
 |
| January Map | July Map |
Water vapor is the dominant greenhouse gas in our atmosphere. The
greenhouse effect of water vapor is enhanced at high altitudes, where the
air is significantly colder than the ground, and increases rapidly as the
temperature contrast grows. As a result, the small fraction of 5-10% of
water molecules above 500 hPa altitude produces half the total greenhouse
effect of the atmosphere. The height at which atmospheric pressure is 500
hPa roughly divides in half the atmosphere vertically, half the mass of
air being above and half below that height.
AIRS, The Atmospheric Infrared Sounder, can look at distinct levels of the
atmosphere. This pair of maps show the average distribution of water vapor
from 500 millibars, approximately 14,000 feet in altitude, to the top of
the atmosphere. The shift of water vapor towards the northern hemisphere
from January to July is apparent. Note that this layer is also much drier
than the atmosphere as a whole. This map is also significant because it's
the first of its kind. AIRS is the first instrument with the ability to
isolate water vapor content to layers of the atmosphere.
The Atmospheric Infrared Sounder (AIRS) in conjunction with the Advanced
Microwave Sounding Unit (AMSU) sense emitted infrared and microwave
radiation from the Earth to provide a three-dimensional look at Earth's weather
and climate. Working in tandem, the two instruments can make simultaneous
observations all the way down to the Earth's surface, even in the presence of
heavy clouds. With more than 2,000 channels sensing different regions of the
atmosphere, the system creates a global, 3-D map of atmospheric temperature
and humidity, cloud amounts and heights, greenhouse gas concentrations, and
many other atmospheric phenomena. The AIRS and AMSU fly onboard NASA's
Aqua spacecraft and are managed by the Jet Propulsion Laboratory, Pasadena,
California, under contract to NASA. JPL is a division of the California Institute of
Technology in Pasadena.
The AIRS Public Web site can be found at http://airs.jpl.nasa.gov.
