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
1
-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
2
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?
3
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)
5
Clear-sky downward SW radiation
WACCM SON CAM5
DJF
6
Full-sky downward SW radiation
SON CAM5WACCM
DJF2 W/m² SW-forcing, after clouds are taken into account.
Does O3 depletion warm Antarctica?
7
O3-hole effect on SAT
DJF
SONCAM5WACCM
No detectable effect of ozone depletion over Antarctica.
…why?
8
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
9
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)
10
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
11
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
12
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.
13
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?
15
Karen Smith, private communication
16
10/26/2015
Does O3-hole “cool” E-Antarctica?
McLandress et al., 2011
17
Grise et al., 2013 18
