ATMOS ATLAS-3 INFRARED PROFILE MEASUREMENTS OF CLOUDS IN THE TROPICALAND SUBTROPICAL UPPER TROPOSPHERE/

Vertical profiles of infrared cirrus extinction have been derived from tropical and subtropical upper tropospheric solar occultation spectra . The measurements were recorded by the Atmospheric Trace Molecule Spe ctroscopy (ATMOS) Fourier transform spectrometer during the Atmospheri c Laboratory for Applications and Sciences (ATLAS) 3 shuttle flight in November 1994. The presence of large numbers of small ice crystals is inferred from the appearance of broad extinction features in the 8-12 mu m region. These features were observed near the tropopause and at lower altitudes. Vertical profiles of the ice extinction (km(-1)) in m icrowindows at 831, 957, and 1204 cm(-1) have been retrieved from the spectra and analyzed with a model for randomly oriented spheroidal ice crystals. An area-equivalent spherical radius of 6 mu m is estimated from the smallest ice crystals observed in the 8-12 mu m region. Direc t penetration of clouds into the lower stratosphere is inferred from o bservations of cloud extinction extending from the upper troposphere t o 50 mbar (20 km altitude). Cloud extinction between 3 and 5 mu m show s very little wavelength dependence, at least for the cases observed b y the ATMOS instrument in the tropics and subtropics during ATLAS 3. P ublished by Elsevier Science Ltd.