On the possible perturbation of stratospheric dynamics due to Pinatubo aerosols

Summary The injection of a large amount of SO₂ in the tropical lower stratosphere following the eruption of Mt. Pinatubo (15.1^oN, 120.4^oE; June 15, 1991) can produce a not negligible perturbation in the stratospheric dynamics. Sulfate aerosols formed by nucleation of H₂SO₄ vapour, which is in turn produced from the SO₂ plume, are responsible for a net heating of the order of 0.15K/day in the equatorial stratosphere, located where the thickest portion of the aerosol cloud is found. As shown by recent satellite data, this diabatic perturbation is responsible for a temperature increase of the order of (2÷3) K at 30m bar during the summer and fall of 1991, that is similar to what found for the 1982 eruption of El Chichón. In this work we use a stratospheric three-dimensional model to investigate the dynamical response of the middle atmosphere to this diabatic forcing. Few months after the eruption, change in the diabatic circulation larger than 10% is found in the lower stratosphere, along with a stronger planetary wave activity during the 1991/92 winter season. This supports some conclusions of a recent investigation by Dunkerton and Delisi on the effects of the 1982 eruption of El Chichón and is shown to have a substantial effect on trace species transport, comparable to that associated to the Quasi-Biennal Oscillation (QBO).