Dispersion of the volcanic sulfate cloud from a Mount Pinatubo–like eruption

Abstract

[1] We use the GEOS-5 general circulation model to simulate the transport of the volcanic cloud from an eruption similar to the 1991 eruption of Mount Pinatubo. The simulated aerosol optical thickness and transport of the volcanic cloud are in good agreement with observations of the actual Pinatubo eruption from the Stratospheric Aerosol and Gas Experiment II (SAGE II) and the Advanced Very High Resolution Radiometer (AVHRR) and with vertical profiles of sulfur dioxide observed by the Microwave Limb Sounder (MLS). We tested the importance of initial conditions corresponding to the specific meteorological situation at the time of the eruption by comparing results when GEOS-5 is initialized using Modern Era Retrospective Analyses for Research and Applications (MERRA) reanalysis fields with results when it is initialized from an existing model run. We found no significant difference in the transport of the cloud. We show how the inclusion of the interaction between volcanic sulfate aerosol and radiation is essential for a reliable simulation of the transport of the volcanic cloud. The absorption of longwave radiation by the volcanic sulfate largely induces the rising of the volcanic cloud up to the middle stratosphere and the divergent motion from the latitude of the eruption to the tropics. Our simulations indicate that the cloud is transported to the Northern Hemisphere through a lower stratospheric pathway and to middle and high latitudes of the Southern Hemisphere through a middle stratospheric pathway, centered at about 30 hPa. The direction of the middle stratospheric pathway depends on the season of the eruption.

Aerosol microphysics simulations of the Mt.~Pinatubo eruption with the UM-UKCA composition-climate model

“…However, most have used aerosol schemes that simulate only the evolution of aerosol mass, prescribing a fixed particle size distribution for sedimentation and radiative effects (e.g. Timmreck et al, 1999;Oman et al, 2006;Aquila et al, 2012). However, sizeresolved stratospheric aerosol modules which include microphysical processes such as new particle formation, coagulation and condensation have also been developed.…”

The Role of Volcanic Activity in Climate and Global Change

“…Another approach, which potentially could shed light on the physical mechanisms governing the development of volcanic plumes and help to resolve some of the problems, is based on GCM simulations interactively accounting for the development of the stratospheric volcanic aerosol layer [45][46][47][48][49][50]. p0075 Timmreck et al [49], Oman et al [48] and Aquila et al [45] used so-called 'bulk' aerosol models when they calculated SO 2 to sulphate conversion and tracked their bulk concentration.…”

“…[130][131][132]). Therefore, understanding of all aspects of stratospheric aerosol microphysics [133], impact on chemical composition [134,135] of the stratosphere, stratospheric circulation [45,136], and tropospheric climate [137][138][139], which we gain from investigating climate consequences of volcanic eruptions, could be and should be employed for a feasibility assessment of solar geoengineering schemes. The analogy of geoengineering with volcanic eruptions is not complete as it is assumed that the geoengineered stratospheric aerosol layer will provide a quasi-permanent radiative forcing unlike sporadic volcanic forcing.…”

“…it showed that on their way to the pole a significant amount of volcanic aerosols are deposited in the midlatitude storm tracks [51], despite the widespread belief that they mostly subside to the pole troposphere in the downward brunches of the Brewer-Dobson circulation. Aquila et al [45], in the NASA GEOS-5 GCM, specifically studied the effect of aerosol radiative feedback on dispersion of the aerosol cloud after the Pinatubo eruption. Their simulations exhibited quite realistic features although underestimated transport of the aerosol plume into the southern hemisphere.…”

“…p0075 Timmreck et al [49], Oman et al [48] and Aquila et al [45] used so-called 'bulk' aerosol models when they calculated SO 2 to sulphate conversion and tracked their bulk concentration. The aerosol size distributions were prescribed and optical properties were precalculated.…”