8-year climatology of dust aerosol in the infrared with HIRS

8-year climatology of dust aerosol in the infrared with HIRS
Clémence Pierangelo, Alain Chédin, Raymond Armante, Claudia Stubenrauch,
and Soumia Serrar
Laboratoire de Météorologie Dynamique / IPSL
Ecole Polytechnique
The last report from the Intergovernmental Panel on Climate Change (IPCC, 2001) pointed out that
aerosols are one of the major sources of uncertainty in the climate system. Since then, many studies
have been conducted, most of them focusing on the solar spectrum. Yet, the closure of the Earth
radiative balance also needs knowledge of the aerosol effect on terrestrial and atmospheric infrared
radiation. This is why we focus here on remote sensing of aerosol at infrared wavelengths.
We show that it is possible to build an aerosol index over sea using HIRS observations. The algorithm
is based on a regression using the brightness temperatures of HIRS channel 8 (11.1 µm) and 10 (8.3
µm) and the sea surface temperature retrieved from TOVS. Great care has been put into
discrimination between aerosols and possibly remaining low altitude clouds.
Here, we present daily and monthly results over the ocean in the tropics, for the period 1987-1995,
both for day-time and night-time observations. Validation with in-situ and satellite retrievals are
presently being conducted; moreover, emphasis will be put on the comparison between visible and
infrared products.
The global coverage of HIRS, the availability of 25 years of observations and the ability to monitor
aerosols both during day and night open the way to a very promising archive of mineral aerosol
products in the infrared.