HR: 10:50h
AN: A12A-02    [Abstracts]
TI: The Discovery of Polar Stratospheric Clouds by SAM II
AU: Poole, L R
EM: l.r.poole@larc.nasa.gov
AF: Science Applications International Corporation, One Enterprise Parkway, Suite 300, Hampton, VA 23666 United States
AU: * McCormick, M P
EM: pat.mccormick@hamptonu.edu
AF: Hampton University, Center for Atmospheric Sciences, 23 Tyler Street, Hampton, VA 23668 United States
AB: Until the advent of spaceborne observations, clouds were thought to occur very rarely in the extremely dry stratosphere. This view changed dramatically following the launch of the Stratospheric Aerosol Measurement (SAM) II instrument on the Nimbus 7 spacecraft in October 1978. SAM II was a single channel solar photometer designed to measure stratospheric aerosol extinction profiles at a wavelength of 1.0 micron at latitudes from 64-80 degrees in both hemispheres. An analysis of SAM II data from the Arctic for January 1979 revealed a number of profiles in which the extinction was 1-2 orders of magnitude larger than expected. Careful study showed that these large extinction values were not artifacts, but were indeed due to dramatic reductions in the amount of solar radiance reaching the instrument. Further analyses showed that these so-called polar stratospheric clouds (PSCs) were observed only when the local stratospheric temperature was very low (185-200 K). The interest in PSCs was primarily academic until the discovery of the Antarctic ozone hole in 1985, which was quickly followed by studies associating this ozone depletion with the release of active chlorine through heterogeneous chemical reactions catalyzed by PSC particles. A large body of research over the ensuing two decades has firmly established this link. In this paper, we will recount the serendipitous discovery of PSCs in SAM II data more than 25 years ago and highlight other advances in our understanding of PSCs that have stemmed from spaceborne observations.
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere: composition and chemistry
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005