Regional radiative impact of volcanic aerosol from the 2009 eruption of Mt. Redoubt School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
24 Apr 2012
Received: 09 August 2011 – Published in Atmos. Chem. Phys. Discuss.: 27 September 2011 Abstract. High northern latitude eruptions have the potential to release volcanic
aerosol into the Arctic environment, perturbing the Arctic's climate system.
We present assessments of shortwave (SW), longwave (LW) and net direct
aerosol radiative forcing efficiencies and atmospheric heating/cooling rates
caused by volcanic aerosol from the 2009 eruption of Mt. Redoubt by
performing radiative transfer modeling constrained by NASA A-Train satellite
data. The optical properties of volcanic aerosol were calculated by
introducing a compositionally resolved microphysical model developed for both
ash and sulfates. Two compositions of volcanic aerosol were considered in
order to examine a fresh, ash rich plume and an older, ash poor plume.
Optical models were incorporated into a modified version of the SBDART
radiative transfer model. Our results indicate that environmental conditions,
such as surface albedo and solar zenith angle (SZA), can influence the sign
and the magnitude of the radiative forcing at the top of the atmosphere (TOA)
and at the surface and the magnitude of the forcing in the aerosol layer. We
find that a fresh, thin plume (~2.5–7 km) at an AOD (550 nm) range of
0.18–0.58 and SZA = 55° over snow cools the surface and warms the
TOA, but the opposite effect is seen for TOA by the same layer over ocean.
The layer over snow also warms by 64 W m−2AOD−1 more than the
same plume over seawater. The layer over snow at SZA = 75° warms
the TOA 96 W m−2AOD−1 less than it would at SZA = 55°
over snow, and there is instead warming at the surface. We also find that
plume aging can alter the magnitude of the radiative forcing. An aged plume
over snow at SZA = 55° would warm the TOA and layer by 146 and
143 W m−2AOD−1 less than the fresh plume, while the aging plume
cools the surface 3 W m−2AOD−1 more. Comparing results for the
thin plume to those for a thick plume (~3–20 km), we find that the
fresh, thick plume with AOD(550 nm) = 3, over seawater, and
SZA = 55° heats the upper part of the plume in the SW
~28 K day−1 more and cools in the LW by ~6.3 K day−1
more than a fresh, thin plume under the same environmental conditions. We
compare our assessments with those reported for other aerosols typical to the
Arctic environment (smoke from wildfires, Arctic haze, and dust) to
demonstrate the importance of volcanic aerosols.
Revised: 24 February 2012 – Accepted: 26 March 2012 – Published: 24 April 2012
Citation: Young, C. L., Sokolik, I. N., and Dufek, J.: Regional radiative impact of volcanic aerosol from the 2009 eruption of Mt. Redoubt, Atmos. Chem. Phys., 12, 3699-3715, doi:10.5194/acp-12-3699-2012, 2012.