3.4 Cloud thermodynamic phase over the Antarctic plateau from NASA IRIS data: a baseline for climate change study

Monday, 18 May 2009: 2:15 PM
Capitol Ballroom AB (Madison Concourse Hotel)
Dan Lubin, SIO/Univ. Of California, La Jolla, CA; and V. P. Walden and P. Rowe

The InfraRed Interferometer Sounder (IRIS) was a pioneering Earth remote sensing experiment flown on the NASA Nimbus 4 spacecraft during 1970-71. Until the advent of ADEOS-IMG during the late 1990s, and AIRS in the present decade, IRIS data were the only readily accessible data of their type. IRIS was a Michelson interferometer that measured outgoing longwave radiance in the wavelength range 6.3-25 microns. Although its radiometric quality is noticeably less than that of AIRS and similar contemporary sensors, its wavelength coverage out to 25 microns allows for an interesting study of cloud microphysics over the high Antarctic Plateau. Using the longest wavelengths available with IRIS (but not with AIRS and its contemporaries) in concert with the middle-infrared (10 micron) window, it is possible to retrieve cloud thermodynamic phase with a high degree of confidence. Over Antarctica, the interesting science lies in the frequency of liquid water cloud detection in the extremely cold but pristine atmosphere. Since 1970, several large-scale phenomena have affected Antarctic meteorology, including a shift to a positive index in the Southern Annular Mode (SAM), and an overall climatic warming trend in which was nested a temporary cooling trend over the continental interior. Retrievals from IRIS can serve as a baseline from which one can study contemporary changes in cloud microphysics, moisture advection, and ultimately precipitation and ice mass balance changes over the Antarctic continent.
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