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
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 hig...
Main Authors: | , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-11-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/17/13439/2017/acp-17-13439-2017.pdf |
Summary: | 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<sub>2</sub>) emission time series and plume
height of the Sarychev eruption are estimated with SO<sub>2</sub> 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<sub>2</sub> emission time series. The transport
simulations are compared with SO<sub>2</sub> 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 <q>aerosol
hole</q> 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. |
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ISSN: | 1680-7316 1680-7324 |