Uncertainties in modelling the stratospheric warming following Mt. Pinatubo eruption

In terms of atmospheric impact, the volcanic eruption of Mt. Pinatubo (1991) is the best characterized large eruption on record. We investigate here the stratospheric warming following the Pinatubo eruption derived from SAGE II extinction data including most recent improvements in the processing algorithm and a data filling procedure in the opacity-induced "gap" regions. From these data, which cover wavelengths of 1.024 micrometer and shorter, we derived aerosol size distributions which properly reproduce extinction coefficients at much longer wavelength. 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 dataset in the global chemistry-climate model (CCM) SOCOL leads to exaggerated aerosol-induced stratospheric heating compared to observations, even partly larger 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 arises from deficiencies in the model radiation codes rather than an insufficient observational data basis. Conversely, our approach reduces the infrared absorption in the tropical tropopause region, in better agreement with the post-volcanic temperature record at these altitudes.