Short-term climatic impact of the 1991 volcanic eruption of Mt. Pinatubo and effects on atmospheric tracers

Abstract

Abstract. Large explosive volcanic eruptions are capable of injecting considerable amounts of particles and sulphur gases (mostly sulphur dioxide) above the tropopause, causing increases in the stratospheric aerosol optical depth that may be even larger than one order of magnitude. The efolding particle lifetime in the stratosphere is much longer than in the troposphere (one year versus a few days) so that climatic perturbations in a timeframe of a few years are produced after major volcanic eruptions. A climate-chemistry coupled model is used here to study the dynamical effects of the radiative forcing due to stratospheric aerosols formed after the June, 1991 cataclysmic eruption of Mt. Pinatubo in the Philippines. It is shown that the dynamical perturbation is twofold: (a) the stratospheric mean meridional circulation is affected by local aerosol radiative heating (mostly located in the tropical lower stratosphere); (b) the planetary wave propagation in the mid-to high-latitude lower stratosphere is altered as a consequence of decreasing atmospheric stability due to the climatic perturbation. Dynamical results of the climate model are compared with available observations; a discussion is made regarding the similarities with the dynamical regime of the easterly phase of the equatorial quasi-biennial oscillation. Major findings of this study are: (a) radiatively forced changes in the stratospheric circulation during the first two years after the eruption may, to a large extent, explain the observed trend decline of long-lived greenhouse gases (CH 4 and N 2 O, in particular); (b) the dynamical perturbation helps explain why simple photochemical studies of the ozone trends during 1991-1993 generally fail in reproducing the satellite observed feature consisting of a 2% additional global ozone depletion during 1993 with respect to 1992. In both cases we conclude that an increase in the mid-to high-latitude downward flux at the tropopause is the key factor for explaining the behaviour of these atmospheric tracers during 1991/92.

The impact of volcanic aerosol on the Northern Hemisphere stratospheric polar vortex: mechanisms and sensitivity to forcing structure

“…However, given the fact that maximum anomalous tropical upwelling occurs at and above the location of maximum aerosol radiative heating in the tropics, it seems possible that there is also a diabatic component to the anomalous residual circulation, forced directly by the aerosol radiative heating, as suggested by previous studies (e.g. Aquila et al, 2013;Pitari and Mancini, 2002).…”

“…Post volcanic-eruption enhancement of the stratospheric residual circulation (or Brewer-Dobson circulation) has been suggested based on previous model studies (Pitari and Mancini, 2002;Pitari, 1993). Graf et al (2007) assessed the observational record and found evidence of increased winter stratospheric wave activity after three eruptions (Agung, El Chichón and Pinatubo).…”

Stratospheric Aerosols from Major Volcanic Eruptions: A Composition-Climate Model Study of the Aerosol Cloud Dispersal and e-folding Time

“…Pinatubo (June 1991) may help explain the observed declining growth rate of long-lived greenhouse gases (as CH 4 and N 2 O) [11][12][13][14], as a result of the increased mid-to high-latitude stratospheric downward fluxes. Since the stratosphere contains lower CH 4 and N 2 O mixing ratios, a decline in the observed trends could result from a higher degree of exchange between the stratosphere and the troposphere [15]. Other important processes that may have affected the tropospheric abundance of CH 4 after the Pinatubo eruption are: (a) the surface cooling, with tropospheric water vapor decrease as a response, followed by a decrease in OH and a longer CH 4 lifetime; (b) Changes in OH resulting from the perturbed tropospheric UV budget, due to additional aerosol scattering and stratospheric ozone changes; (c) Increase of sulfate aerosol surface area density (SAD) in the mid-upper troposphere, thus enhancing heterogeneous chemistry with a decrease of tropospheric NO x and OH.…”

The climatic effects of the direct injection of water vapour into the stratosphere by large volcanic eruptions

“…Previous studies have suggested possible inventories of stratospheric water vapour (hence SWV) resulting from volcanic eruptions; between 10 Mt from magma (Pitari and Mancini, 2002) to 540 Mt from magma and entrainment into the Plinian column from the atmosphere (Dartevelle et al, 2002) from Pinatubo's eruption in 1991. However, satellite observations of SWV in the months following the eruption imply a maximum value of 100-150 Mt up to that time (Nedoluha et al, 1998).…”