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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 Bitz 1 and Lorenzo Polvani 2 1 Atmospheric Sciences, University of Washington 2 Applied Physics and Applied Mathematics and Earth and Environmental Sciences, Columbia University

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Antarctic Climate Response to Ozone Depletion in a Fine Resolution Ocean Climate Mode

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  1. Antarctic Climate Response to Ozone Depletion in a Fine Resolution Ocean Climate Mode by Cecilia Bitz1 and Lorenzo Polvani2 1Atmospheric Sciences, University of Washington 2Applied 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

  2. How have increased westerlies influenced sea ice? Antarctic Million Square Kilometers Arctic

  3. Turner et al 2009

  4. Simulated Surface Currents and Sea Ice Extent Around Antarctica 0.1 degree Simulation 1 degree Simulation 0 10 20 30 40 50 60 Current Speed in cm/s for randomly chosen October

  5. Weddell Sea

  6. How does Earth’s Climate Respond to Ozone Depletion? Ozone Depletion Stratospheric Cooling Polar Vortex Spins up Stratospheric Cooling Surface Westerlies Strengthen Around Antarctica

  7. Simulations using Community Climate System Model • Version 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 ice • Fine – 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.

  8. DJF Atmospheric Zonal-Mean Response to Depleting Ozone wind change (color) mean wind (contour lines) Temperature change 7.5 °C °C m/s latitude latitude Low Resolution Sensitivity of Temperature and Winds is about 15-20% greater

  9. Annual Mean Surface Air Temperature Response to Ozone Loss 0.1° Simulations 1° Simulations

  10. Annual Mean Sea Ice Concentration Response to Ozone Loss 0.1° Simulations 1° Simulations

  11. Surface westerly winds blow on the Southern Ocean Heat exits ocean near Antarctica and enters on northern edge of ACC heat in heat out dimes.ucsd.edu

  12. Ocean Temperature Response to Ozone Depletion for Mar. to Nov. (about the same annually) 0.1° Simulations 1° Simulations Color contour interval is 0.1 deg Celsius Fine resolution ocean has a weaker response

  13. Normal Sea Ice Mass Balance Ice transport AA Sea ice net growth net melting

  14. Sea Ice Mass Balance Response to ozone loss Ice transport flux is REDUCED AA Sea ice growth decreases here melting increases here Less growth/more melt in pack ice is the reason the ice concentration declines with ozone loss

  15. Horizontal Heat Transport by the Ocean in PetaWatts (1015 W) In Fine Resolution Simulation Mean Total Eddies Latitude (plus gyres)

  16. Northward Ocean Heat Transport Response to Ozone Loss Total 0.1° Simulations 1° Simulations Mean Eddies Latitude Latitude The low resolution model has a larger, albeit modest, increase in poleward eddy heat flux, while the high resolution model has almost no change

  17. 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.

  18. Annual Mean Ocean Surface Heat Flux Response to Ozone Loss 0.1° Simulations 1° Simulations 10 6 2 -2 -6 -10 W m-2 less insulation with reduced ice more SW absorption with reduced ice and low clouds

  19. Northward Ocean & Atmospheric Heat Transport Response to Ozone Loss 0.1° Simulations 1° Simulations Ocean Ocean Atmosphere Atmosphere Latitude Latitude The atmospheric heat transport change is as large as the ocean’s south of 65S, compensation is poor

  20. Normal Sea Ice Mass Balance Ice transport AA Sea ice net growth net melting ice concentration tendency % day-1 thermodynamics dynamics

  21. 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° Simulations 1° Simulations Moderate ACC shift in Atlantic and Indian sectors. ACC increases by about 2 Sv (from ~170 Sv) at both resolutions

  22. Annual Mean SST Response to depleting ozone 0.1° Simulations 1° Simulations °C 0.5 0 -0.5 40S 50S 60S 70S 40S 50S 60S 70S 0 20 50 0 20 50 O3 ramped O3 fixed O3 ramped O3 fixed time (years) time (years)

  23. Schematic of the Overturning Circulation from Marshall and Speer (2012) heat in heat out westerly Ozone depletion speeds up westerlies, Ekman response is to move ocean waters northward, causing surface cooling near Antarctica. But sucking up causes upwelling, which …

  24. Annual Mean Global MOC response 1° Simulations 0.1° Simulations ~2Sv ~1Sv Sv Latitude Latitude includes parameterized eddy-effect Contour Interval is 0.5 Sv

  25. Annual Mean, Zonal Mean Sea Ice Concentration Response to Ozone Loss Concentration change % 1° Simulations 0.1° Simulations

  26. DJF Lowest Level Zonal Wind Speed Response to depleting ozone 0.1° Simulations 1° Simulations m/s Low level zonal wind response is significantly larger in low resolution model

  27. Annual Zonal Mean Ocean Temperature Response to Ozone Loss 0.1° Simulations 1° Simulations Depth - m Antarctica Antarctica °C Latitude

  28. Annual Zonal Mean Ocean Temperature Response to Ozone Loss 0.1° Simulations 1° Simulations Depth - m Antarctica Antarctica °C Latitude Upward Heat Transport Change across 45 m depth Strengthened meridional overturning circulation brings CDW up W m-2 0.1° Simulations 1° Simulations

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