Abstract
Abstract. In terms of atmospheric impact, the volcanic eruption of Mt. Pinatubo (1991) is the best characterized large eruption on record. We investigate here the model-derived stratospheric warming following the Pinatubo eruption as derived from SAGE II extinction data including recent improvements in the processing algorithm. This method, termed SAGE_4λ, makes use of the four wavelengths (385, 452, 525 and 1024 nm) of the SAGE II data when available, and uses a data-filling procedure in the opacity-induced "gap" regions. Using SAGE_4λ, we derived aerosol size distributions that properly reproduce extinction coefficients also at much longer wavelengths. This provides a good basis for calculating the absorption of terrestrial infrared radiation and the resulting stratospheric heating. However, we also show that the use of this data set in a global chemistry–climate model (CCM) still leads to stronger aerosol-induced stratospheric heating than observed, with temperatures partly even higher than the already too high values found by many models in recent general circulation model (GCM) and CCM intercomparisons. This suggests that the overestimation of the stratospheric warming after the Pinatubo eruption may not be ascribed to an insufficient observational database but instead to using outdated data sets, to deficiencies in the implementation of the forcing data, or to radiative or dynamical model artifacts. Conversely, the SAGE_4λ approach reduces the infrared absorption in the tropical tropopause region, resulting in a significantly better agreement with the post-volcanic temperature record at these altitudes.
Highlights
The most recent large tropical volcanic eruption was that of Mt
The chemistry–climate model (CCM) SOCOL, which participated in CCMval-2, was forced by a data set based on SAGE II measurements
The third is the approach described by Schraner et al (2008) using SAGE_ASAP and deriving the surface area densities and effective radii based on a principal component analysis using four wavelengths of SAGE II (Thomason et al, 1997b) and assuming a fixed distribution width
Summary
The most recent large tropical volcanic eruption was that of Mt. Pinatubo in June 1991 in the Philippines (15◦ N). The data set of Stenchikov et al (1998) provides directly calculated heating rates for modeling studies, while the Sato et al (1993) “GISS” data set consists of optical depth data for 0.5 μm wavelength and effective radii in 4 different altitude ranges and 24 latitude bands derived from SAGE II data. The CCM SOCOL, which participated in CCMval-2, was forced by a data set based on SAGE II measurements All these methods produce large differences in the volcanic aerosol optical properties, making it difficult to compare these models against each other. It must be noted that uncertainties in observed/modeled tropopause height may lead climate models to discard part of the heating rates below the tropopause, not representing fully the stratospheric forcing of a given aerosol data set
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