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Sea Ice Extent (How Winds Δ Sea Ice? Turner 2009 (Cooling due to ozone…
Sea Ice Extent
How Winds
Δ Sea Ice?
Turner 2009
Change in winds due to ozone depletion
Cooling due to ozone depletion
since ozone absorbs UV ∴ heating stratosphere
Low pressure trough generated
as cooling modifies air pressure
Westerly winds strengthened over S. Ocean
by pressure anomaly (cooling)
Equatorward Ekman transport strengthened
driving Ekman flux away from Antarctica
Cold surface waters extend further North
∴ freezing & sea ice extends further N
Sea ice response timescales
Varies as f(how model represents ocean upwelling)
i.e. how aggressively upwelling simulated
upwelling =
difficult to model
alters ocean circulation
subject to feedbacks
Theory is viable
Different models show same qualitiative behaviour
Timings differ
btwn models
Ferreira - retreat after 15 years
Sigmond - retreat after 5 years
Short & Long Term Response
Ferreira et al 2015
Modelling response to ozone depletion
idealised 'aquaplanet' - no continents
Fast
(years)
Sea ice advances North
Ekman pumping equatorwards etc
Short term ~ year
Concurs with observed expansion
Slow
(decades)
Warm water upwelling at depth
Sea ice retreats
If Ekman flux imposed for long enough
Authors found 2 phases of response
Sea Ice
Trends
Arctic sea ice = declining
Antarctic sea ice = increased over past 20 years
Antarctic Δ contradicts global warming ? Why?
Westerlies
Effect Nutshell
Westerlies move further N in S Ocean
3.
Sea ice extent moves N
(Colder waters brough further N ∴ sea surface freezes)
Strengthens equatorward Ekman flux
Proposed
Cause Ant Δ
Why Antarctic sea ice increased despite global warming ?
Change in winds due to ozone depletion
Some disagree
Sigmond & Fyfe 2013
Coupled climate models
Modelled effects of
ozone depletion:
Does increase wind stress
2.
Decreased sea ice extent
due to strengthened winds
Contradicts observations...
Two-fold Effect Ozone Depletion
1. Moves equatorward strong core of Westerlies
i.e. latitude @ which Westerlies = most intense
2. Strengthens Westerlies
induces geostrophic circulation in upper atmos around S Pole
low pressure above antarctica
Ozone hole
most ozone depletion = above Antarctica