83rd Annual

Tuesday, 11 February 2003
Determination of radiative forcing by dust using surface and satellite measurements
Anand K. Inamdar, University of California/SIO, La Jolla, CA; and M. V. Ramana and V. Ramanathan
Among the tropospheric aerosols (natural and anthropogenic), mineral dust aerosol is known to significantly impact the atmospheric radiation budget. While mineral aerosols play an important role in climate forcing, published studies indicate that there are large uncertainties in the estimation of both shortwave and longwave climate forcing due to dust. Not only we lack a knowledge of the physical and optical properties of these aerosols, but also their spatial and temporal distributions. Further complicating the matters is the relatively short life span of the tropospheric dust aerosols. The most important uncertainty arises from the non-spherical shape of dust particles. In this study we circumvent these issues by obtaining the dust radiative forcing directly from radiation budget observations from the surface and from space.

Arabian Sea during summer months provides an ideal natural location for the study of dust forcing. Studies (Li and Ramanathan, 2002; Ackerman and Cox, 1989) have revealed enhanced levels of aerosol optical depths during the Indian summer monsoon season attributable to dust. These dust particles influence the earth's radiation budget through both direct and indirect effects by means of influencing the cloud nucleation processes and the cloud microphysical properties. The present study represents a first attempt at quantifying the radiative forcing due to dust particles at both the surface and the top of the atmosphere. For the surface, we employ the measurements made at the Kaashidhoo Climate Observatory (KCO) established in the Republic of Maldives as part of the INDOEX campaign. For the top of atmosphere forcing, we use a combination of the AVHRR-retrieved aerosol optical depths and the flux measurements in the shortwave, longwave and window channels made by the CERES (Clouds and the Earth's Radiant Energy System) instrument aboard the TRMM and TERRA satellites.

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