Date: February 19, 2008
Time: 10:30am
Location: NIA, Rm 137
Additional Information: Webstream

Measuring the water vapor distribution in the atmosphere is quite difficult as the upwelling signal from the lower atmosphere can easily mask the signal from the upper atmosphere.  Since water vapor is a greenhouse gas it is important to have good knowledge of the concentration profile if the contributions of different gases to global warming are to be determined.  The Odin satellite that was launched on February 20, 2001, includes two instruments.  A sub-millimeter radiometer (SMR) that resolves the line shape associated with a spectral emission to provide altitude information of the emitting species.  The second instrument is an optical spectrograph infra red imager system (OSIRIS) that provides observations of both the airglow and the scattered sunlight limb spectra, over the wavelength range 280 – 810 nm, as well as limb images of the oxygen infrared atmospheric band and the OH Meinel band airglow.  Although the recorded spectra only have a 1 nm resolution it is possible to use these measurements together with models to determine the mesospheric water vapor profile.  Around 82 km altitude the water vapor is converted to ice and causes polar mesospheric clouds (PMC) that can be identified in the OSIRIS measurements.  The OSIRIS measurements also include the oxygen atmospheric A-, B- and g- band signatures that provide information on the atmospheric temperature profile.  These temperature determinations are possible in both the presence and absence of PMCs, which are unambiguously identified by OSIRIS.  In this presentation the variability of the atmospheric temperature profile observed with OSIRIS and the temperature in the vicinity of PMCs are discussed.  When the spectrograph measurements are combined with the oxygen infrared atmospheric band airglow emission, which serves as a proxy for the ozone content, it is possible to compare the distribution of water vapour, ozone and temperature in the vicinity of PMCs.  It is hoped to show that the capabilities of global remote sensing using scattered sunlight, as on Odin, is only limited by the imagination of the researcher.