Retrieving Antarctic Cloud Phase in 1996 and 1997 from the Interferometric Monitor of Greenhouse Gases (IMG)

The polarity of the southern annular mode (SAM) has changed from being generally negative in the 1970s to more positive values over the last decade. Different generations of satellite data can be used to retrieve cloud phase, which can be correlated with the polarity of the SAM over this time period. Cloud phase retrievals over Antarctica are possible from the Infrared Interferometer Sounder (IRIS), launched in 1970, and the Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI), both currently in operation. Between these time periods, the Interferometric Monitor for greenhouse Gases (IMG) operated aboard the polar-orbiting Advanced Earth Observing Satellite (ADEOS) from October 1996 through June 1997. The IMG measured upwelling infrared radiance at the top of the atmosphere from 3.3 to 14 micron at fine spectral resolution (0.1 inverse centimeter). The subset of spectra at latitudes below 75 degrees south over Antarctica has been selected. The IMG data have been corrected for ambiguities in the instrumental phase and for noise bursts to produce high quality, calibrated radiance spectra. Preliminary work on retrieving cloud phase from this dataset is presented. The best set of frequencies to use for cloud phase retrieval over Antarctica is investigated through simulations of upwelling radiance, for a variety of different clouds and atmospheric profiles.