Aerosol direct radiative effect at the top of the atmosphere over cloud free ocean derived from four years of MODIS data L. A. Remer and Y. J. Kaufman Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt MD, USA
Abstract. A four year record of MODIS spaceborne data provides a new measurement tool
to assess the aerosol direct radiative effect at the top of the atmosphere.
MODIS derives the aerosol optical thickness and microphysical properties
from the scattered sunlight at 0.55–2.1 μm. The monthly MODIS data used
here are accumulated measurements across a wide range of view and scattering
angles and represent the aerosol's spectrally resolved angular properties.
We use these data consistently to compute with estimated accuracy of
±0.6 Wm−2 the reflected sunlight by the aerosol over global oceans in
cloud free conditions. The MODIS high spatial resolution (0.5 km) allows
observation of the aerosol impact between clouds that can be missed by other
sensors with larger footprints. We found that over the clear-sky global
ocean the aerosol reflected 5.3±0.6 Wm−2 with an average
radiative efficiency of −49±2 Wm−2 per unit optical thickness. The
seasonal and regional distribution of the aerosol radiative effects are
discussed. The analysis adds a new measurement perspective to a climate
change problem dominated so far by models.
Citation: Remer, L. A. and Kaufman, Y. J.: Aerosol direct radiative effect at the top of the atmosphere over cloud free ocean derived from four years of MODIS data, Atmos. Chem. Phys., 6, 237-253, doi:10.5194/acp-6-237-2006, 2006.