HR: 1330h
AN: A13A-14 [Abstracts]
TI: On the Negative Brightness Temperature Differences Observed by Satellites Above Thick Ice Clouds in the Tropics.
AU: * Chepfer, H
EM: chepfer@lmd.polytechnique.fr
AF: LMD/IPSL, Ecole Polytechnique, Palaiseau, France
AU: Chiriaco, M
EM: chiriaco@lmd.polytechnique.fr
AF: LMD/IPSL, Ecole Polytechnique, Palaiseau, France
AU: Dubuisson, P
EM: dub@mren2.univ-littoral.fr
AF: ELICO, Universit‚ du Littoral, Wimereux, France
AU: Minnis, P
EM: p.minnis@nasa.gov
AF: LaRC/NASA, MS 420, Hampton, United States
AU: Riviere, E
EM: riviere@cnrs-orleans.fr
AF: LPC, 3A Av. de la recherche scientifique, Orleans, France
AB:
Negative brightness temperature differences (BTD) between 10.5 and 12 ŸYm have been observed frequently from satellites or
aircraft imageur above thick ice clouds in the tropics. Those negative BTD reach typically -1 to -3 K, and can not be
reproduced in radiative transfer computations using reasonable ice cloud optical properties, or changing humidity and
temperature profiles in standard composition of tropical atmosphere. The spatial structure of the negative BTD signature as
seen by satellite and their high frequency in low latitudes seem to indicate that they are associated to tropopause
overshoots. Different scenarios assuming that tropical convection introduces -or allows the formation of- molecules absorbing at 10.5 ŸYm in the tropical tropopause layer have been examined in order to understand the negative BTD. Increasing the
concentration of the absorbing molecules (O3, CO2, HNO3, NO2, etcK) above a thick ice cloud in the tropical tropopause layer allows to reproduce negative BTD in radiative transfer computations. In order to estimate the potential validity of this
explanation, and determine which molecule is effectively involved in the process, the theoretical increases in the molecule
concentration deduced from radiative transfer computation are compared to concentrations found in the literature deduced from observations and chemistry models.
DE: 0320 Cloud physics and chemistry
DE: 0365 Troposphere--composition and chemistry
DE: 3360 Remote sensing
DE: 3362 Stratosphere/troposphere interactions
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly