8-year climatology of dust aerosol in the infrared from HIRS
Clémence Pierangelo, Eric Péquignot, Alain Chédin, Raymond Armante, Claudia Stubenrauch, Soumia Serra
Laboratoire de Météorologie Dynamique/IPSL École Polytechnique
XIV International TOVS Study Conference, China, 25-31 May 2005
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 retrieve the infrared optical depth and the altitude of dust aerosol layers over both sea and land using HIRS observations. The algorithm is based on regressions using the brightness temperatures of HIRS channel 8 (11.1 μm), 10 (8.3 μm), 18 (4.0 μm) and the sea surface temperature retrieved from TOVS. The adaptation of the algorithm to continental surfaces uses monthly maps of surface emissivity at the same wavelengths.
Here, we present daily and monthly results in the 40°S-40°N latitude band, for the period 1987-1995. A comparison with Meteosat visible optical depth over the ocean for a case study proves the ability of HIRS to monitor dust event. Climatological monthly results show the main expected features: the Saharan and Arabic deserts as first dust sources, a seasonal cycle with maximum optical depth in summer, a transport of dust at higher altitudes in summer than in winter over the Atlantic Ocean.