Abstract
Synoptic scale variability of the Southern Ocean wind field in the high-frequency range of barotropic Rossby waves results in transport variations of the Antarctic Circumpolar Current (ACC), which are highly coherent with the bottom pressure field all around the Antarctic continent. The coherence pattern, in contrast to the steady state ACC, is steered by the geostrophic f/h contours passing through Drake Passage and circling closely around the continent. At lower frequencies, with interannual and decadal periods, the correlation with the bottom pressure continues, but baroclinic processes gain importance. For periods exceeding a few years, variations of the ACC transport are in geostrophic balance with the pressure field associated with the baroclinic potential energy stored in the stratification, whereas bottom pressure plays a minor role. The low-frequency variability of the ACC transport is correlated with the baroclinic state variable in the entire Southern Ocean, mediated by baroclinic topographic–planetary Rossby waves that are not bound to f/h contours. To clarify the processes of wave dynamics and pattern correlation, we apply a circulation model with simplified physics (the barotropic–baroclinic-interaction model BARBI) and use two types of wind forcing: the National Centers for Environmental Prediction (NCEP) wind field with integrations spanning three decades and an artificial wind field constructed from the first three empirical orthogonal functions of NCEP combined with a temporal variability according to an autoregressive process. Experiments with this Southern Annular Mode type forcing have been performed for 1,800 years. We analyze the spin-up, trends, and variability of the model runs. Particular emphasis is placed on coherence and correlation patterns between the ACC transport, the wind forcing, the bottom pressure field and the pressure associated with the baroclinic potential energy. A stochastic dynamical model is developed that describes the dominant barotropic and baroclinic processes and represents the spectral properties for a wide range of frequencies, from monthly periods to hundreds of years.
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References
Aoki S (2002) Coherent sea level response to the antarctic oscillation. Geophys Res Lett 29(20):1950, 0094–8276
Borowski D, Gerdes R, Olbers D (2002) Thermohaline and wind forcing of a circumpolar channel with blocked geostrophic contours. J Phys Oceanogr 32:2520–2540
Charney JG, DeVore JG (1979) Multiple flow equilibra in the atmosphere and blocking. J Atmos Sci 36:1205–1216
Cunningham S, Pavic M (2007) Surface geostrophic currents across the Antarctic Circumpolar Current in drake passage from 1992 to 2004. Prog Oceanogr 73:296–310
Cunningham SA, Alderson SG, King BA, Brandon MA (2003) Transport and variability of the Antarctic Circumpolar Current in Drake Passage. J Geophys Res 108: nO. C5, 8084
Gent PR, Large WG, Bryan FO (2001) What sets the mean transport through Drake Passage? J Geophys Res 106: 2693–2712
Gille ST (1999) Evaluating southern ocean response to wind forcing. Physics And Chemistry Of The Earth Part A Solid Earth Geodesy, 24(4):423–428, 1464–1895
Hall A, Visbeck M (2002) Synchronous variability in the southern hemisphere atmosphere, sea ice, and ocean resulting from the annular mode. J Clim 15(21):3043–3057
Hallberg R (1997) Localized coupling between surface- and bottom-intensified flow over topography. J Phys Oceanogr 27:977–998
Hallberg R, Gnanadesikan A (2006) The role of eddies in determining the structure and response of the wind-driven southern hemisphere overturning: results from the Modeling Eddies in the Southern Ocean (MESO) project. J Phys Oceanogr 36:2232–2252
Hasselmann K (1976) Stochastic climate models, part I: theory. Tellus 28:473–485
Hughes CW, Meredith CP (2006) Coherent sea-level fluctuations along the global continental slope. Philos Trans R Soc Lond A 364(1841):885–901, Mathematical Physical And Engineering Sciences
Hughes CW, Meredith MP, Heywood K (1999) Wind driven transport fluctuations through Drake Passage: a southern mode. J Phys Oceanogr 29:1971–1992
Hughes CW, Woodworth PL, Meredith MP, Stepanov V, Whitworth T, Pyne AR (2003) Coherence of antarctic sea levels, southern hemisphere annular mode, and flow through Drake Passage. Geophys Res Lett 30(9): 0094-8276 1464
Lettmann K (2006) Untersuchungen zur Variabilit”at im S”udlichen Ozean mit dem Ozeanzirkulationsmodel BARBI. PhD thesis, University Bremen
Meredith MP, Woodworth PL, Hughes CW, Stepanov V (2004) Changes in the ocean transport through Drake Passage during the 1980s and 1990s, forced by changes in the southern annular mode. Geophys Res Lett 31(21): 0094-8276 L21305
Meredith MP, Vassie JM, Heywood KJ, Spencer R (1996) On the temporal variability of the transport through drake passage. J Geophys Res 101:22485–22494
Olbers D, Eden C (2003) A simplified general circulation model for a baroclinic ocean with topography. part I: theory, waves and wind-driven circulations. J Phys Oceanogr 33:2719–2737
Olbers D, Völker C (1996) Steady states and variability in oceanic zonal flows. In: Anderson DLT, Willebrand J (eds) Decadal climate variability dynamics and predicition. Springer, Berlin, pp 407–443
Olbers D, Borowski D, Völker C, Wolff J-O (2004) The dynamical balance, transport and circulation of the antarctic circumpolar current. Antarct Sci 16(4):439–470
Olbers D, Lettmann K, Wolff J-O (2007) Wave-induced topographic formstress in baroclinic channel flow. Ocean Dyn doi:10.1007/s10236-007-0109-2
Olbers D, Lettmann K, Timmermann R (2006) Six circumpolar currents—on the forcing of the Antarctic Circumpolar Current by wind and mixing. Ocean Dyn 57:12–31. doi:10.1007/s10236-006-0087-9
Rhines P (1977) The dynamics of unsteady currents. In: Goldberg E (ed) The sea, vol VI. Wiley, New York, pp 189–318
Rintoul SR, Hughes C, Olbers D (2001) The Antarctic Circumpolar Current system. In: Siedler G, Church J, Gould J (eds) Ocean circulation and climate. Academic, New York, pp 271–302
Rintoul SR, Sokolov S, Church J (2002) A 6 year record of baroclinic transport variability of the Antarctic circumpolar current at 140 degrees E derived from expendable bathythermograph and altimeter measurements. J Geophys Res 107
Sura P, Gille ST (2003) Interpreting wind-driven southern ocean variability in a stochastic framework. J Mar Res 61(3):313–334, 0022-2402.
Tansley CE, Marshall DP (2001) On the dynamics of wind-driven circumpolar currents. J Phys Oceanogr 31:3258–3273
Thompson DWJ, Wallace JM (2000) Annular modes in the extratropical circulation. Part I: month-to-month variability. J Climate 13(5):1000–1016, 0894–8755
Vivier F, Kelly KA, Harismendy M (2005) Causes of large-scale sea level variations in the Southern Ocean: Analyses of sea level and a barotropic model. J Geophys Res-Oceans, 110(C9):C09014
Völker C (1999) Momentum balance in zonal flows and resonance of baroclinic Rossby waves. J Phys Oceanogr 29: 1666–1681
von Storch H, Zwiers FW (1999) Statistical analysis in climate research. Cambrige Univ. Press
Wearn Jr RB, Baker Jr DJ (1980) Bottom pressure measurements across the Antarctic circumpolar current and their relation to the wind. Deep-Sea Res 27A:875–888
Webb D, de Cuevas B, Coward A (1998) The first main run of the occam global model. Southampton Oceanography Centre, Internal Report SOC, UK (34)
Weijer W, Gille ST (2005) Adjustment of the southern ocean to wind forcing on synoptic time scales. J Phy Oceanogr 35(11):2076–2089, 0022–3670
Whitworth III T, Peterson RG (1985) Volume transport of the Antacrtic circumpolar current from bottom pressure measurements. J Phys Oceanogr 15:810–816
Willebrand J, Philander SGH, Pacanowski RC (1980) The oceanic response to large-scale atmospheric disturbances. J Phys Oceanogr 10(3):411–429
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Olbers, D., Lettmann, K. Barotropic and baroclinic processes in the transport variability of the Antarctic Circumpolar Current. Ocean Dynamics 57, 559–578 (2007). https://doi.org/10.1007/s10236-007-0126-1
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DOI: https://doi.org/10.1007/s10236-007-0126-1