The impact of the ozone hole on the Antarctic surface...
Transcript of The impact of the ozone hole on the Antarctic surface...
The impact of the ozone hole on
the Antarctic surface energy budget
G.Chiodo¹, L.Polvani¹ and M.Previdi²
1.Applied Physics and Applied Mathematics, Columbia University, NY
2.Lamont Doherty Observatory, Columbia University, NY
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-Poleward shift of the tropospheric Jet (SAM increase)
-Year-round loss of sea-ice around Antarctica
Polvani et al 2011
Bitz and Polvani 2012
The impact of the ozone depletion on
Southern Hem. Climate is well known
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Cooling over E-Antarctica, and warming of Peninsula (SAM-driven,
…so “indirectly” induced.)
What is the (direct) radiative effect of ozone depletion?
Thompson and Solomon, 2002
Did ozone depletion have an impact on
Antarctic climate?
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Direct (radiative) impact of ozone depletion
Ramanathan and Dickinson, JAS 1979
Ramaswamy et al, NAT 1991
-Cooling of the troposphere mostly
due to reduced downward LW
emission, but surface warming due
to increased SW heating.
-Solar forcing change from idealized O3
forcing offset by reduced LW emission
resulting from stratospheric adjustment.
-What is the impact of a realistic O3 forcing in a comprehensive
GCMs, with dynamic ocean and land ice? 4
Experiments with WACCM4 and CAM5-LE
WACCM: 6 members with O3 depletion (“historical”)vs 6 members without (“fixedODS”)
CAM5-LE: 8 members with imposed O3 depletion from WACCM (“historical”) vs 8
members with O3 fixed at 1960 levels (“fixO3”)
400
300
200
100
1960 1970 1980 1990 2000
DU
Column ozone (SON)
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Clear-sky downward SW radiation
WACCM SON CAM5
DJF
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Full-sky downward SW radiation
SON CAM5WACCM
DJF2 W/m² SW-forcing, after clouds are taken into account.
Does O3 depletion warm Antarctica?
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O3-hole effect on SAT
DJF
SONCAM5WACCM
No detectable effect of ozone depletion over Antarctica.
…why?
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GHG-effect only (long term d LW rad increase)
The O3 depletion does not induce decrease in downwelling
LW radiation at surface, so the SW forcing dominates!
LW compensating SW forcing?
Surface downwelling LW radiation (SON) CAM5WACCM
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Why does the SW forcing have no impact
on Antarctic SAT?
-Slight increase in surface albedo in both models compensates
the 2 W/m2 SW forcing, leading to 0-change in net surface SW!
CAM5WACCM Clear-sky albedo (SON)
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Is the surface albedo related to changes in
large-scale snowfall?
Increase in DJF snowfall in WACCM, and to lesser extent, in CAM5.
CAM5 WACCM DJF LS snowfall rate
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Does DJF snowfall affect surface
albedo in other seasons?
-In CAM5, a smaller change in albedo-precip is needed to counter act increased
SW forcing than in WACCM (background albedo is higher).
-Surface albedo in CISM is f(snow age + depth). Since there is no melting
in Antarctic interior, a change in DJF precip can alter albedo all-year round
CAM5WACCM
LS snowfall rate LS snowfall rate
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Conclusions
1) O3 depletion leads to a detectable increase in SW forcing
over Antarctica.
2) The SW forcing is balanced by an increase in large-scale
snowfall, possibly associated with O3-driven SAM increase,
which make Antarctica “brighter”.
3) Without increase in albedo, Antarctica would receive a net
SW forcing of 0.4 W/m² from O3-depletion, which, if
unbalanced and sustained over period of 25 years, could
have significantly altered the Antarctic energy budget.
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Total cloud cover
Disparate long-term trends in clouds in WACCM and CAM5.
In WACCM, increase is mostly due to high-clouds (see Grise et al., 2013)
Increase in SW forcing not related to long-term changes in cloud fraction or
cloud properties! 14
Does O3-hole induce zonal asymmetries in SW-heating?
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Karen Smith, private communication
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10/26/2015
Does O3-hole “cool” E-Antarctica?
McLandress et al., 2011
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Grise et al., 2013 18