Environmental Engineering Reference
In-Depth Information
310
305
50˚ N
300
295
290
0˚ N
285
280
275
50˚ S
270
Bulk aerosol model with
prescribed size distribution
1.46 Gt/year SO
2
(for 10 years)
265
0
1
2
3
4
5
6
7
8
9
10
Years after eruption begins
Figure 20.3 Zonal mean surface temperature during a prolonged Siberian Traps
explosive eruption, with 1.46 Gt/year SO
2
release (corresponding to 240 km
3
/year
erupted volume).This simulation uses a prescribed aerosol size distribution that is
inaccurate for sulfur release of this magnitude (Pinto
et al
.,
1989
; Timmreck
et al
.,
2010
); the magnitude of cooling in the simulation is therefore unrealistically severe.
However, the asymmetric pattern of cooling, with larger temperature decreases in the
northern hemisphere, should still be valid. Ablack andwhite version of this
gure will
appear in some formats.
For the colour version, please refer to the plate section
.
latitude
-
around 60
N (Cocks and Torsvik,
2007
)
-
with several implications for
sulfur aerosols. The high-latitude tropopause dips to an annual mean altitude of
10 km, versus 18 km at the equator (Grise
et al
.,
2010
); as a result, high-latitude
eruption plumes are more likely to breach the tropopause (Stothers
et al
.,
1986
).
The climate effects of high-latitude eruptions are asymmetric (Oman
et al
.,
2005
),
because the patterns of stratospheric circulation largely con
ne aerosols from high-
latitude eruptions to the hemisphere of origin. Because of downward transport in
the polar vortex, the residence time of stratospheric sulfur injected near the poles is
signi
cantly shorter than that of sulfur injected in the tropics (Hamill
et al
.,
1997
).
Our bulk aerosol simulations allow us to track volcanogenic sulfate in the
atmosphere, though with many of the relevant aerosol physics greatly simpli
ed
or neglected. Because of this simpli
cation, the radiative effects of large sulfur
emissions are vulnerable to signi
cant overestimation. While our simulations may
overestimate the magnitude of sulfur-induced cooling, they do reveal the geo-
graphic pattern of climate change. As expected, our simulations of a Siberian Traps
pyroclastic eruption (illustrated in
Figure 20.3
) show a much stronger decrease in
temperature in the northern hemisphere than in the southern hemisphere. Timm-
reck
et al
.(
2010
)
find that during the 74 ka Toba super-eruption, equatorial release
