Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 1: Sensitivity to the modes of atmospheric circulation and boundary conditions

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 conCorrespondence to: M. A. Thomas (manu.thomas@zmaw.de) sistently 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.

Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with airborne TiO<sub>2</sub> particles and its implication for stratospheric particle injection

“…However, the nudging has those feedbacks implicitly included for the volcanic aerosol case, which may or may not be a valid and good-enough assumption for TiO 2 . Interactive feedbacks could also contribute to chemistry changes through factors such as the modification of the Quasi-Biennial Oscillation (Telford et al, 2009), strengthening of polar vortices (Thomas et al, 2009), and increasing uplift (Rosenfield et al, 1997). Our description of the aerosol particles is also simple; obviously particles with uniform radii distributed as the products of the Pinatubo eruption would be impossible to obtain.…”

Reassessment of causes of ozone column variability following the eruption of Mount Pinatubo using a nudged CCM

“…Pinatubo. This may be due to impacts of the eruption on the QBO, such as phase-locking, as seen by Thomas et al (2009b) and others.…”

“…It modulates the tropical up-welling and extra-tropical wave propagation, both affecting ozone concentrations (Baldwin et al, 2001). The heating of the lower stratosphere by the aerosols produced by Pinatubo affected the QBO, "locking" the phase of the QBO for several months (Thomas et al, 2009b). The years 1991 and 1992 had pronounced El Niño conditions as indicated by the multivariate ENSO index (Wolter and Timlin, 1993).…”

Initial fate of fine ash and sulfur from large volcanic eruptions

“…The impact of sulfuric aerosols on climate after a volcanic eruption has been comprehensively studied, but in General Circulation models (GCMs) mainly aerosol bulk models assuming a fixed aerosol partition (Oman et al, 2006;Timmreck et al, 1999Timmreck et al, , 2003 or a prescribed aerosol distribution e.g. (Stenchikov et al, 1998;Kirchner et al, 1999;Thomas et al, 2009) was used so far. The simulations presented here are different to previous GCM studies because they include Correspondence to: U.…”