The$transient$response$of$the$ Southern$Ocean$to$ozone...
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The transient response of the Southern Ocean to ozone depletion in the GFDL ESM2Mc model William Seviour Johns Hopkins University Darryn Waugh, Anand Gnanadesikan, Jordan Thomas FESD Virtual Meeting, 20 November 2015
Transcript of The$transient$response$of$the$ Southern$Ocean$to$ozone...
The transient response of the Southern Ocean to ozone depletion
in the GFDL ESM2Mc model
William SeviourJohns Hopkins University
Darryn Waugh, Anand Gnanadesikan, Jordan Thomas
FESD Virtual Meeting, 20 November 2015
24 Ensemble members run for 48 years each
12 use daily ozone values12 use monthly means of daily values
12 on ‘warm’ start dates12 on ‘cold’ start dates
How does the climate system respond to instantaneously introducing ozone depletion?
How does the climate system respond to instantaneously introducing ozone depletion?
24 Ensemble members run for 48 years each
12 use daily ozone values12 use monthly means of daily values
12 on ‘warm’ start dates12 on ‘cold’ start dates
Ensemble mean SST response
Initial cooling ~0.1 K, for about 30 years
Daily vs. Monthly mean ozone
Atmospheric Response
~50% increase in peak windstress anomaly going from monthly -‐> daily ozone
Consistent with Neely et al. 2014
Position of peak windstress in control simulation
MOC Response
colors: Temp. stratification in control (c.i. 2K)black: MOC anomaly (c.i. 0.5 Sv)
Anomalous overturning circulation ~50% stronger going from monthly -‐> daily ozone
MOC Response
Same contour levels
MITgcm (Ferreira et al., 2014)
Weaker stratification below 100 m in GFDL ESM2Mc.
Stronger cooling over first 100 m.
Transient temperature response
!"#$%&
!' ≈ −𝑤′ !",!-
Agrees with Ferreira et al., 2014
𝑇/012 reaches 0.1K (magnitude of surface cooling) at about 30 years
Transient temperature response
Temperature trend similar despite stronger upwelling. Is upwelling really driving temperature trend?
Heat flux budget: Work in Progress
advection
eddies
column
𝑤2 is positive, but !"!-
2is negative so vertical advection contibution is small
Daily vs. monthly ozone SST (50-‐70S)
Difference in SST response is small relative to differences due to initial conditions.
Warm start vs. Cold start
Role of the initial state
Path of natural (i.e. unforced) variability determined from the autocorrelation of control simulation.
Shaded region = 95% uncertainty of natural variability
Role of the initial state
Natural variability – simulated SST
Similar response relative to natural variability.
Less warming in cold start, but probably not statistically significant.
Role of the initial state
Ferreira et al., 2014
~Similar magnitude
Regional responses
Ross Sea
Weddell Sea
Natural variability larger in Weddell Sea, forced response larger in Ross Sea.
Timescales different (~10 year cooling in Ross Sea, 30 years in Weddell).
Role of the initial state
Natural variability dominates in Weddell Sea, not in Ross Sea
Conclusions
• Two-‐timescale response is reproduced by GFDL ESM2Mc, with ~30 year initial cooling.
• Daily ozone produces stronger windstress anomaly, stronger ocean circulation response, but little temperature difference.
• Response relative to natural variability does not depend strongly on the initial state.
• Natural variability is large relative to response to ozone over much of Southern Ocean, but not the Ross Sea.
• Timescales of response are regionally dependent.
Daily vs Monthly ozone
Sea ice
Sea ice
