Parameterization of Spatio-temporal Patterns of Volcanic Aerosol Induced Stratospheric Optical Depth and its Climate Radiative Forcing

Jürgen Grieser and Christian-D. Schönwiese
Department of Meteorology and Geophysics, University of Frankfurt,
P.O. Box 11 19 32, 60054 Frankfurt, Germany

Abstract:

Explosive volcanism is known to have a large impact on climate. Thus, in order to understand past climate variability, volcanic forcing has to be considered. For the most recent explosive volcanic eruptions instrumental data of stratospheric aerosol optical depth are available. For early eruptions only index values with no or only crude spatial and seasonal resolution do exist. To estimate the spatio-temporal patterns of aerosol induced optical depth of the atmosphere due to any known strong volcanic eruption, we introduce a stratospheric aerosol distribution parameterization using recent information about stratospheric transport phenomena as well as date, location, and strength of an eruption. Using this parameterization, observed time series of stratospheric aerosol optical depth can be reproduced with reasonable accuracy. To investigate volcanic climate forcing, we introduce a radiation transfer parameterization which takes into account the undisturbed seasonal and latitudinal pattern of radiation uptake as well as the extension of a ray path in a spherical layer. Thus, spatio-temporal patterns of volcanic climate forcing for any known volcanic eruption can be estimated, too.