Equatorward dispersion of a high-latitude volcanic plume and its relation to the Asian summer monsoon: a case study of the Sarychev eruption in 2009

Abstract

Abstract. Tropical volcanic eruptions have been widely studied for their significant contribution to stratospheric aerosol loading and global climate impacts, but the impact of high-latitude volcanic eruptions on the stratospheric aerosol layer is not clear and the pathway of transporting aerosol from high latitudes to the tropical stratosphere is not well understood. In this work, we focus on the high-latitude volcano Sarychev (48.1 • N, 153.2 • E), which erupted in June 2009, and the influence of the Asian summer monsoon (ASM) on the equatorward dispersion of the volcanic plume. First, the sulfur dioxide (SO 2 ) emission time series and plume height of the Sarychev eruption are estimated with SO 2 observations of the Atmospheric Infrared Sounder (AIRS) and a backward trajectory approach using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC). Then, the transport and dispersion of the plume are simulated using the derived SO 2 emission time series. The transport simulations are compared with SO 2 observations from AIRS and validated with aerosol observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The MPTRAC simulations show that about 4 % of the sulfur emissions were transported to the tropical stratosphere within 50 days after the beginning of the eruption, and the plume dispersed towards the tropical tropopause layer (TTL) through isentropic transport above the subtropical jet. The MPTRAC simulations and MIPAS aerosol data both show that between the potential temperature levels of 360 and 400 K, the equatorward transport was primarily driven by anticyclonic Rossby wave breaking enhanced by the ASM in boreal summer. The volcanic plume was entrained along the anticyclone flows and reached the TTL as it was transported southwestwards into the deep tropics downstream of the anticyclone. Further, the ASM anticyclone influenced the pathway of aerosols by isolating an "aerosol hole" inside of the ASM, which was surrounded by aerosol-rich air outside. This transport barrier was best indicated using the potential vorticity gradient approach. Long-term MIPAS aerosol detections show that after entering the TTL, aerosol from the Sarychev eruption remained in the tropical stratosphere for about 10 months and ascended slowly. The ascent speed agreed well with the ascent speed of the water vapor tape recorder. Furthermore, a hypothetical MPTRAC simulation for a wintertime eruption was carried out. It is shown that under winter atmospheric circulations, the equatorward transport of the plume would be suppressed by the strong subtropical jet and weak wave breaking events. In this hypothetical scenario, a high-latitude volcanic eruption would not be able to contribute to the tropical stratospheric aerosol layer.

Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 eruption cloud compared to in situ and satellite observations

“…This indicates broadly similar SO 2 dispersion in the model runs. The spatial and temporal evolution of the plume in our study is consistent with the results of Wu et al (2017), where AIRS data are presented along with results of simulations by a particle dispersion model.…”

MIPAS observations of volcanic sulfate aerosol and sulfur dioxide in the stratosphere

“…We see that the bulk of the aerosol that moves southwards reaches the Equator about 2 to 3 months after the volcanic eruption. To some small extent, this sulfur crosses the Equator and can thereby influence the sulfur loading of the Southern Hemisphere (see also Wu et al, 2017). Generally, similarities in the geographic pattern between Kasatochi in 2008 and Sarychev in 2009 have also been noticed by Haywood et al (2010), caused by the agreement between the season, the injection altitude, and the latitude of the eruptions.…”

“…They further show an "aerosol hole" in the anticyclone, surrounded by aerosol-rich air. Following Wu et al (2017), a strong subtropical jet in combination with weak Rossby wave breaking events would hinder the southward transport of the volcanic plume during winter conditions. Compared to Sarychev, the southward transport of the Kasatochi eruption plume is weaker and initiates at higher altitudes.…”

“…Measurements of the stratospheric optical depth by the Optical Spectrograph and InfraRed Imager System (OSIRIS) onboard Odin also (Bourassa et al, 2012). Wu et al (2017) studied the equatorward dispersion of the Sarychev volcanic plume together with the influence of the Asian summer monsoon on the transport pattern. They find that at 360-400 K potential temperature, the southward transport was primarily caused by anticyclonic Rossby wave breaking, intensified by the Asian summer monsoon during Northern Hemisphere summer.…”

Trajectory errors of different numerical integration schemes diagnosed with the MPTRAC advection module driven by ECMWF operational analyses

“…MPTRAC has been developed to support the analysis of atmospheric transport processes in the free troposphere and stratosphere. In recent studies, it has been used to perform transport simulations for volcanic eruptions and to reconstruct time-and height-resolved emission rates for these events Hoffmann et al, 2016;Wu et al, 2017). An intercomparison of meteorological analyses and MPTRAC trajectory calculations with superpressure balloon observations in the Antarctic lower stratosphere was presented by Hoffmann et al (2017).…”