the southern ocean: a frontier for satellite altimetrysummary • southern ocean: historically...
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The Southern Ocean: A Frontier forSatellite Altimetry
Sarah Gille
Scripps Institution of Oceanography
and Department of Mechanical and
Aerospace Engineering
UCSD, La Jolla, CA
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In situ observations: Sparse prior to floats
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The ACC: connector and barrier
Dynamic Topography Potential Temperature and Isopycnals
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Southern Ocean Overturning
Speer et al., 2004; Olbers et al., 2004
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Global Wind Energy Input: Concentrated in SouthernOcean
Huang et al, Deep Sea Res., 2006
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Ocean Uptake of Carbon
Caldeira and Duffy, Science, 2003
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Deciphering sea surface height anomalies
Strategies
• Use an independent mean dynamic to-pography
• Study variability of geostrophic currentsonly
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Ocean Currents and Altimetry
Geostrophic balance:
fv =1
ρ
∂p
∂x= g
∂η
∂x
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Locating the ACC: Mean plus anomaly
Gille, JGR, 1994
• Frontal width: 44 km• Meandering amplitude: 75 km• (For comparison, microwave
SST suggest PF meanderingamplitude: approx 120 km(Dong et al., 2006)
• TOPEX results largely inagreement with Geosat
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Altimetric “Mean” Field
retains
small-scale
structure but
inaccurate for
large-scale.
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Updated Mean: GRACE, surface drifters, etc.
Niiler andMaximenko
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Multiple Filamented Jets
Sokolov and Rintoul, 2007
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Bathymetry and the Polar Front Variability
(Dong et al., JPO, 2006)
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Latitudinal shift in ACC?
Southern Annular Mode intensifica-tion implies poleward shift in wind.
Poleward shift in wind implies pole-ward shift in ACC (at least on sometime scales; Dong et al., JPO, 2006)
φPF ∝ φτ
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Latitudinal shift in ACC?
ACC displacement is top-to-bottom. (Sokolov and Rintoul,2003)
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Latitudinal shift in ACC?Sparse hydrographicrecord indicates ACChas warmed at alldepth levels over last50 years.
In ACC below 200 mdepth, ∼95% of profiletrend explained as pole-ward migration of cur-rent at 1◦ latitude/35years.(Gille, 2008, J. Climatein press)
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Summary
• Southern Ocean: historicallyundersampled, climatically im-portant, experienced substantialwarming over last 50+ years.
• Altimetry has exposed complexfilamented nature of AntarcticCircumpolar Current.
• Regional changes in SouthernOcean consistent with migra-tion of ACC fronts, driven bychanges in latitude of wind forc-ing.
• Extended record from T/P, Ja-son, and Jason-2 should enablefull unraveling of ACC frontal re-sponse to climatic shifts in wind.