UV Aerosol Indices from SCIAMACHY: introducing the SCattering Index (SCI) Max Planck Institute for Chemistry, Mainz, Germany
Received: 27 April 2009 – Published in Atmos. Chem. Phys. Discuss.: 19 June 2009 Abstract. The Absorbing Aerosol Index (AAI) is a useful tool for detecting aerosols
that absorb UV radiation – especially in cases where other aerosol
retrievals fail, such as over bright surfaces (e.g. desert) and in the
presence of clouds. The AAI does not, however, consider contributions from
scattering (hardly absorbing) aerosols and clouds: they cause negative AAI
values and are usually disregarded. In this paper, we demonstrate the use of
the AAI's negative counterpart, the SCattering Index (SCI) to detect
scattering aerosols. Consideration of the full UV Aerosol Index scale is of
importance if the Aerosol Index is to be used for the quantification of
aerosol absorption in the future.
Revised: 07 December 2009 – Accepted: 09 December 2009 – Published: 21 December 2009
Maps of seasonally averaged SCI show significantly enhanced values in summer
in Southeast USA and Southeast Asia, pointing to a high production of
scattering aerosols (presumably mainly sulphate aerosols and secondary
organic aerosols) in this season. The application of a cloud filter makes
the presence of scattering aerosols even more clear. Radiative transfer
calculations were performed to investigate the sensitivity of AAI and SCI to
cloud parameters, and it is demonstrated that clouds cause significant SCI,
in some special cases even small AAI values. The results from cloud
modelling imply that cloud effects need to be taken into account when AAI
and SCI are used in a quantitative manner.
The paper concludes with a comparison of aerosol parameters from AERONET and
our Aerosol Indices (AAI and SCI) from SCIAMACHY, where reasonable agreement
was found for six AERONET stations in Southeast USA, Southeast Asia, and
Africa. These findings corroborate the suitability of SCI as a tool to
detect scattering aerosols.
Citation: Penning de Vries, M. J. M., Beirle, S., and Wagner, T.: UV Aerosol Indices from SCIAMACHY: introducing the SCattering Index (SCI), Atmos. Chem. Phys., 9, 9555-9567, doi:10.5194/acp-9-9555-2009, 2009.