Abstract
Abstract. The eruption of Mt. Pinatubo in the Philippines in June 1991 was one of the strongest volcanic eruptions in the 20th century and this well observed eruption can serve as an important case study to understand the subsequent weather and climate changes. In this paper, the most comprehensive simulations to date of the climate impact of Mt. Pinatubo eruption are carried out with prescribed volcanic aerosols including observed SSTs, QBO and volcanically induced ozone anomalies. This is also the first attempt to include all the known factors for the simulation of such an experiment. Here, the climate response is evaluated under different boundary conditions including one at a time, thereby, investigating the radiative and dynamical responses to individual and combined forcings by observed SSTs, QBO and volcanic effects. Two ensembles of ten members each, for unperturbed and volcanically perturbed conditions were carried out using the middle atmosphere configuration of ECHAM5 general circulation model. Our results show that the simulated climate response that may arise solely from aerosol forcing in lower stratospheric temperature is insensitive to the boundary conditions in the tropics and does not show some observed features such as the temperature signature of the QBO phases. Also, statistically significant positive anomalies in the high latitudes in NH winter of 1991/92 seen in our model simulations with prescribed observed SST and QBO phases as boundary conditions are consistent with the observations. To simulate realistically the lower stratospheric temperature response, one must include all the known factors. The pure QBO and ocean signatures in lower stratospheric temperature are simulated consistently with earlier studies. The indirect effect of the volcanic aerosols manifested as the winter warming pattern is not simulated in the ensemble mean of the experiments. Our analysis also shows that the response to El Niño conditions is very strong in the model and that it partially masks the effects due to volcanic forcing.
Highlights
Large volcanic eruptions and their subsequent climate responses are relatively short-lived perturbations to the climate system
The Pinatubo volcanic plume reached a maximum height of 40 km (Lynch and Stephens, 1996; Holasek et al, 1996), with the bulk of aerosol centered around 25 km
Our analysis shows that the El Nino-Southern Oscillation (ENSO) signal is dominating and partly masks the effects due to volcanic forcing
Summary
Large volcanic eruptions and their subsequent climate responses are relatively short-lived perturbations to the climate system. They provide an excellent opportunity to understand the response of the climate system to a global radiative forcing and to assess the ability of our climate models to simulate such large perturbations. The SO2 injected into the stratosphere by explosive volcanic eruptions is chemically transformed to sulfate aerosols and in the case of Mt. Pinatubo eruption, encircled the globe in a month (McCormick and Veiga, 1992; Long and Stowe, 1994). Sulfate aerosol particles are purely scattering in the visible part of the solar spectrum, scattering the incoming solar radiation partially back to space, resulting in cooling of the Earth surface.
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