dynamical responses to volcanic forcings in climate model simulations
DESCRIPTION
Dynamical responses to volcanic forcings in climate model simulations. DynVar workshop 22.04.13 Matthew Toohey with Kirstin Krüger, Claudia Timmreck, Hauke Schmidt. Motivation. What would happen if a large volcanic eruption occurred tomorrow? - PowerPoint PPT PresentationTRANSCRIPT
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Dynamical responses to volcanic forcings in
climate model simulationsDynVar workshop 22.04.13
Matthew Toohey
with Kirstin Krüger, Claudia Timmreck,
Hauke Schmidt
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• What would happen if a large volcanic eruption occurred tomorrow?
→ Every seasonal to decadal climate forecast made prior to the eruption would become obsolete.
Motivation
Thompson et al. (2012)Thompson et al. (2009)
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Motivation
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“Winter Warming”
Robock and Mao (1992)
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Post-volcanic dynamical anomalies
Baldwin andDunkerton. 2001
Christiansen, 2008
13 eruptions Schmidt et al., 2013
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Stratospheric mechanism
Stenchikov et al. (2002)
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• A number of studies have reported realistic simulation of post-volcanic NH dynamical anomalies (Graf et al., 1993, 1994; Mao and Robock, 1998; Kirchner et al., 1999; Shindell et al., 2001; Rozanov et al., 2002; Stenchikov et al., 2002; Collins, 2004; Shindell et al., 2003, Shindell et al. 2004)
• But multi-model studies (e.g. CMIP, CCMVal-2) have not produced a convincing picture of model behavior.
Model results
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CCMVal-2 post-eruption T anomalies
Ch. 8 in SPARC, CCMVal Report, 2010
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CMIP59 eruptionsn=18
9 eruptions13 models72 members
9 eruptions13 models72 members
4 eruptionsn=8
Driscoll et al. 2012
Sea level Pressure
50 hPaGeopotential height
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CMIP5
Charlton-Perez et al., 2013
Low-topHigh-topERA-interim
CMIP5
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Stratospheric mechanism
Stenchikov et al. (2002)
?
?
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•Why don’t CMIP5 models show strong NH winter vortices (i.e., negative polar cap z50 anomalies) after volcanic eruptions?→Either
1. Response is not real (just chance?)2. Models are flawed3. Implementation of volcanic aerosol forcing is
flawed4. Volcanic aerosol forcing is flawed
The question
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CMIP volcanic forcings
0.4
0.3
0.2
0.1
0
Sato et al. (1990)/GISS/Stenchikov Ammann (2003)/(2007)
• Pinatubo and El Chichon based on SAGE observations
• Recently updated with OSIRIS observations Oct 2001 - present
• Best estimate sulfur mass injection, distributed via parameterized stratospheric transport model
Jan 92
Jul 91Jan 92
Jan 91
Jan 92
Jul 91Jan 92
Jan 91
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• Notes: zonal mean, monthly mean, for pre-satellite era eruptions, spatial distribution of aerosols poorly constrained
CMIP Volcanic forcings
Sato et al. (1990)/GISS/Stenchikov
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• Part 1:• Use MAECHAM5-HAM, a coupled aerosol-climate
model, to simulate the evolution of stratospheric sulfate aerosol after a Pinatubo-like eruption.
• Part 2:• Use MPI-ESM, a high-top CMIP5 model, and replace
the prescribed Pinatubo volcanic forcing from historical simulations with forcing sets built from Part 1.
Experiment
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• MPI-ESM: full Earth System model, with atmosphere, ocean, carbon cycle, vegetation components. • Atmospheric component ECHAM6. • “low resolution” (LR, T63/L47), configuration used here
(no QBO).
• Volcanic aerosols are prescribed• CMIP5 historical simulations use Stenchikov et al.
(1998) forcing data set -> monthly mean, zonal mean aerosol extinction, single scattering albedo, and asymmetry factor
MPI-ESM
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• ECHAM: GCM developed at MPI-M, Hamburg• Middle atmosphere version: 39 vertical levels up to 0.01 hPa (~80 km)• T42 horizontal resolution• Climatological sea surface temperatures, no QBO, no chemistry
• HAM: Aerosol microphysical module• Modified for simulation of stratospheric volcanic aerosols• Models aerosol growth, radiative effects, eventual removal
MAECHAM5-HAM
Inject SO2 at 24 km
Aerosol growthRadiative effects
Aerosol transport via atmospheric
circulation
Transport to troposphere,
rainout!
HAM
ECHAM5SO2→ H2SO4
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Toohey et al (2011, ACP)
MAECHAM5-HAM Pinatubo simulations
• Simulations of 17 Tg eruption, June 15, 15.3°N• Excellent agreement with ERBE TOA SW flux anomalies
observed after Pinatubo eruption. Little to no dependence on eruption longitude.
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Modeled aerosol transport
months after eruption months after eruption
Toohey et al. (2011)
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HAM July eruption simulations: DJF1
Temperature Geopotential height Zonal wind
n=12
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DJF1 z50 anomalies
n=12
July eruptions April, July and October eruptions
n=36
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AOD: July eruption ensemble variability
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Weak and Strong vortex composite AOD
n=12
July eruptions
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Vortex strength ~ AOD gradient?
Polar cap gph anomaly calculated as area mean over 70-90N.AOD gradient at 60N as AOD(60-90N) – AOD(50-60N)
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Vortex strength ~ AOD gradient?
Strong Vortex AOD gradient across vortex
Aerosol heating gradient?
If we want our prescribed aerosols to force a strong vortex, the forcing had better take the form of a strong vortex.
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MPI-ESM Pinatubo forcing experiment
Stenchikov (CMIP5)
HAM weak
HAM strong
r1,r2,r3r4,r5,r6r7,r8,r9
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Aerosol extinction at 550 nmSt
ench
ikov
HA
M w
eak
HA
M s
tron
g
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MPI-ESM: tropical 50 hPa T
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MPI-ESM: DJF1 T and u anomaliesStenchikov HAM weak HAM strong
Tem
pera
ture
(K)
u w
ind
(m/s
)
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MPI-ESM: DJF1 z50 anomalies
Low-topHigh-topERA-interim
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MPI-ESM: DJF1 z50 anomalies
Low-topHigh-topERA-interim
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MPI-ESM: DJF1&2 z50 anomalies
Low-topHigh-topERA-interim
CMIP5
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Aerosol extinction at 550 nmSt
ench
ikov
HA
M w
eak
HA
M s
tron
g
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Arfeuille et al. ACPD 2013
Extinction at 550 nm
August
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• CCMI: Surface Area Densities (SADs), stratospheric heating rates, and radiative properties, based on SAGE_4λ retrievals (Tom Peter and Beiping Luo, ETHZ)
Volcanic forcing, the next generation
• Model-based aerosol reconstructions becoming available for pre-satellite era eruptions.
Tambora: Arfeuille et al. (2013) vs. Crowley (2008)
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• For a CMIP5 historical-style simulation of Pinatubo, we can control the strength of the (ensemble mean) post-eruption NH winter vortex with the aerosol forcing set• Vortex strength ~ AOD gradient across vortex edge
→ Likely that dynamical response to volcanic eruptions can be „improved“ by using different forcing data sets.
→ Future work will show whether new volcanic forcing sets lead to better dynamical responses in climate models.
Conclusions
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Volcanic vs. Anthropogenic forcing