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Influence of Arctic Sea Ice Loss in Autumn Compared to That in Winter on the Atmospheric Circulation
Russell Blackport
James Screen
University of Exeter
PAMIP Workshop 26th June 2019
Blackport, R., & Screen, J. A. (2019).Geophysical Research Letters, https://doi.org/10.1029/2018GL081469
Background
• Winter circulation response to projected year-round sea ice loss in coupled models consistent across models and protocols
Screen et al. 2018
Question: To what extent is the winter circulation response driven by autumn sea ice loss?
• Relevant for understanding physical mechanisms as well as for seasonal prediction
• Observed correlations indicate winter response may be driven by Autumn sea ice
• Previously addressed in an AGCM (Sun et al. 2015), but ocean coupling may provide additional mechanisms for lagged response
Model Experiments• HadGEM2-ES model with 1.25° latitude by 1.875° longitude resolution
• 4 ensembles (400 realizations x 5 years):• Present day control: 2008-2012 RCP8.5 forcing
• ‘2C’: 2036-2040 RCP8.5 forcing (target for sea ice loss ensembles)
• ‘2Cice’: As in control, but sea ice albedo modified to achieve year-round sea ice loss similar to ‘2C’ ensemble. Cold deep snow albedo: 0.80 -> 0.05, Snow-free ice albedo: 0.61 -> 0.66
• ‘2CiceASO’: As in control, but sea ice albedo modified to achieve Autumn sea ice loss similar to ‘2C’ ensemble. Cold deep snow albedo: 0.80 -> 0.88, Snow-free ice albedo: 0.61 -> 0.10
Sea Ice Response
Autumn sea ice loss
Year-round sea ice loss
Surface Air Temperature Response
Year-round sea ice loss
Surface Air Temperature Response
Autumn sea ice loss
Year-round sea ice loss
• In response to autumn ice loss, high-latitude warming persists into winter despite little change in SIC/SIE
Zonal Wind Response
Year-round sea ice loss
Zonal Wind Response
Autumn sea ice loss
Year-round sea ice loss
• Winter circulation response not seen in response to sea ice loss in autumn
U700 Response
Autumn sea ice loss
Year-round sea ice loss
Sea Level Pressure Response
Autumn sea ice loss
Year-round sea ice loss
Polar Cap Height Response
Autumn sea ice loss
Year-round sea ice loss
• We find a winter circulation response to year-round sea ice loss similar to previous coupled model experiments
• These are not seen in response to reduced sea ice extent only in autumn
• Our results suggest winter circulation response seen in models is primarily driven by winter sea ice loss
Conclusions
• Only one model used – conclusions could be model dependant
• Pan-Arctic sea ice vs regional sea ice loss
• Are the responses to autumn and winter sea ice loss additive?
• Could test these with additional experiments using PAMIP forcing fields
Caveats and Future Work
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