Antarctic Climate Response to Ozone Depletion in a Fine Resolution Ocean Climate Mode
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Transcript of Antarctic Climate Response to Ozone Depletion in a Fine Resolution Ocean Climate Mode
Antarctic Climate Response to Ozone Depletion in a Fine
Resolution Ocean Climate Mode
by Cecilia Bitz1 and Lorenzo Polvani2
1Atmospheric Sciences, University of Washington2Applied Physics and Applied Mathematics and Earth and
Environmental Sciences, Columbia University
with thanks to Jean-François Lamarque, Peter Gent, Frank Bryan, and the Peta-Apps team
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Current Speed in cm/s for randomly chosen October
Simulated Surface Currents and Sea Ice Extent Around Antarctica0.1 degree Simulation1 degree Simulation
Simulations using Community Climate System ModelVersion 3.5 with Ozone Anomaly from SPARC datasets for CMIP5
At two ozone levels:High Ozone (1940s) or “Normal”Low Ozone (1997) or “Most depleted”
At two resolutions:Coarse - 1 degree ocean and sea iceFine – 0.10 degree ocean and sea ice
Four runs in total, each 50 yr long – ramp ozone 20 yr and hold fixed for 30 yr. Results shown are differences of last 30 yr.
Low Resolution Sensitivity of Temperature and Winds is about 15-20% greater
DJF Atmospheric Zonal-MeanResponse to Depleting Ozone
latitude latitude
7.5 °C
°C m/s
Temperature changewind change (color)
mean wind (contour lines)
dimes.ucsd.edu
heat out
heat
in
Surface westerly winds blow on the Southern OceanHeat exits ocean near Antarctica and enters on northern edge of ACC
Ocean Temperature Response to Ozone Depletionfor Mar. to Nov. (about the same annually)
Color contour interval is 0.1 deg Celsius
Fine resolution ocean has a weaker response
0.1° Simulations 1° Simulations
Sea Ice Mass Balance Response to ozone loss
Sea iceAA
Ice transport flux is REDUCED
growthdecreases here
melting increases here
Less growth/more melt in pack ice is the reason the ice concentration declines with ozone loss
Horizontal Heat Transport by the Ocean in PetaWatts (1015 W)
In Fine Resolution Simulation
Total
Mean
Eddies
Latitude(plus gyres)
1° Simulations
Latitude
0.1° Simulations
Latitude
Northward Ocean Heat TransportResponse to Ozone Loss
Total
Mean
Eddies
The low resolution model has a larger, albeit modest, increase in poleward eddy heat flux, while the high resolution model has almost no change
Conclusions
The quasi-equilibrium response to ozone depletion is reduced Antarctic sea ice concentration and warmer surface air temperature (in agreement with Sigmond and Fyfe, 2010; Smith et al, 2012)
The sea ice response is dominated by thermodynamic changes, despite changes to ice motion
Below the surface, the low resolution ocean response is stronger. But on average the SST and sea ice response is about the same.
In the 21st century, ozone will recover and we can expect it to partially offset global warming effects on Antarctic sea ice loss, surface warming, and large-scale oceanic heat transport towards the shelves.
Annual Mean Ocean Surface Heat Flux Response to Ozone Loss
0.1° Simulations1° Simulations10
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2
-2
-6
-10
W m-2
0.1° Simulations
Latitude
1° Simulations
Latitude
Northward Ocean & Atmospheric Heat TransportResponse to Ozone Loss
Ocean
The atmospheric heat transport change is as large as the ocean’s south of 65S, compensation is poor
Atmosphere
Ocean
Atmosphere
Normal Sea Ice Mass Balance
Sea iceAA
Ice transport
net growth net melting
thermodynamics
dynamics
ice concentration tendency % day-1
Sea Surface Height Change from Ozone Loss (change is from solid to dashed colored contours, 50 cm contour interval)
with sea ice extent (heavy black), annual means
0.1° Simulations1° Simulations
Moderate ACC shift in Atlantic and Indian sectors. ACC increases by about 2 Sv (from ~170 Sv) at both resolutions
Annual Mean SST Response to depleting ozone
40S
50S
60S
70S
40S
50S
60S
70S
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-0.5
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time (years) time (years)
O3 ramped O3 fixed O3 ramped O3 fixed
°C0.1° Simulations 1° Simulations
Schematic of the Overturning Circulation from Marshall and Speer (2012)
wes
terly
heat
in
heat
out
Ozone depletion speeds up westerlies, Ekman response is to move ocean waters northward, causing surface cooling near Antarctica. But sucking up causes upwelling, which …
0.1° Simulations
Latitude
~1Sv
1° Simulations
Latitude
~2Sv
Sv
Contour Interval is 0.5 Sv
Annual Mean Global MOC response
includes parameterized eddy-effect
Annual Mean, Zonal Mean Sea Ice Concentration Response to Ozone Loss
0.1° Simulations
1° Simulations
Con
cent
ratio
n ch
ange
%
DJF Lowest Level Zonal Wind Speed Response to depleting ozone
0.1° Simulations 1° Simulations
Low level zonal wind response is significantly larger in low resolution model
m/s
Annual Zonal Mean Ocean Temperature Response to Ozone Loss
Dep
th -
m
Ant
arct
ica
1° Simulations
Latitude°C
Ant
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0.1° Simulations