Interdecadal Variability of the Southern Ocean

Hogg, Andrew McC.; Blundell, Jeffrey R.

doi:10.1175/jpo2934.1

Cited by 95 publications

(130 citation statements)

References 42 publications

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“…Meredith and Hogg [16] and Hogg and Blundell [26] used an eddy-resolving ocean model to simulate the response of the ACC to the zonal wind stress and found that there was a lag between the wind stress forcing and the ACC kinetic energy of approximately 2 years, which was consistent with the results of this study. The delayed response is related to the internal variability of the ACC.…”

Section: Discussionsupporting

confidence: 85%

Interannual variability of the Antarctic Circumpolar Current strength based on merged altimeter data

Zhang

Sun

2012

Chin. Sci. Bull.

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Interannual variability of the Antarctic Circumpolar Current (ACC) strength is studied in stream-coordinate with twenty-year Absolute Dynamic Topography data from satellite altimetry. The stream-coordinate projection method separates the ACC from adjacent subtropical and subpolar gyres, enabling consideration of the zonal asymmetry of the ACC rather than assuming that the ACC is a purely zonal flow. It is shown that the ACC strength has large interannual variations with two recent peaks around 2000 and 2009. The interannual variability appears mainly in the Indo-Pacific sector of the Southern Ocean and the strongest signal is located south of Australia. The intensification of the westerly wind in 1998 and 2008 appears to cause the strengthening of the ACC via baroclinic processes. The Antarctic Circumpolar Current (ACC) connects the world's three major ocean basins and is a key element in the global thermohaline circulation. The inter-basin exchange provided by the ACC redistributes heat, salt and other properties in the world's ocean. Therefore, changes in the ACC exert significant influences on the global climate system. Much work has attempted to quantify the transport and variability of the ACC based on hydrography and numerical models. (Figure 1), and therefore zonal transport estimates by previous studies are strongly influenced by adjacent subtropical and subpolar gyres and cannot solely represent the strength of the ACC. Moreover, the data sets used in previous studies are insufficient to map the interannual variability of the ACC, and sampling with a frequency significantly higher than weekly is required to obtain reliable estimates of the ACC variability at interannual periods [8]. Therefore, limited by the in-situ observations and data processing methods, few extant studies give reliable estimates of the interannual variability of the ACC strength. Recently a stream-coordinate method was developed to study the ACC by projecting hydrographic data into a stream function space [7,9]. The method isolates the ACC from its adjacent subtropical and subpolar gyres. It also considers the zonal asymmetry of the ACC path rather than simply assume that the ACC is a purely zonal current. It was found that the baroclinic structure and baroclinic transport of the ACC were very stable. But given a constant volume transport, the ACC strength can still change due to

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Section: Discussionsupporting

confidence: 85%

Interannual variability of the Antarctic Circumpolar Current strength based on merged altimeter data

Zhang

Sun

2012

Chin. Sci. Bull.

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“…However, process-oriented numerical studies have shown that mesoscale eddies may drive chaotic low-frequency fluctuations in the ocean (e.g. Jiang et al, 1995;Spall, 1996;Berloff and McWilliams, 1999;Hogg and Blundell, 2006). One may then hypothesize that both the strong enhancement and (realistic) confinement in eddy-active areas of SLA variabilities at all timescales, and the aforementioned temporal decorrelation, denote the emergence at 1 4…”

Section: Discussionmentioning

confidence: 99%

Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales

et al. 2010

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Abstract. Four global ocean/sea-ice simulations driven by the same realistic 47-year daily atmospheric forcing were performed by the DRAKKAR group at 2 • , 1 • , 1 2• , and 1 4• resolutions. Simulated mean sea-surface heights (MSSH) and sea-level anomalies (SLA) are collocated over the period 1993-2004 onto the AVISO dataset. MSSH fields are compared with an inverse estimate. SLA datasets are filtered and compared over various time and space scales with AVISO regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated bandpassed filtered local SLA timeseries. Beyond the 2 • -1 • transition whose benefits are moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14-180 days) and quasi-annual (5-18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are greatest in the 1 • -1 2• and 1 2• -1 4• transitions, in the 14-180 day range, and within eddy-active mid-and highlatitude regions. In the real ocean, most eddy-active areas areCorrespondence to: T. Penduff (thierry.penduff@legi.grenoble-inp.fr) characterized by a strong SLA variability at all timescales considered here; this localized, broad-banded temporal variability is only captured at 1 4• resolution.

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“…In the following, we list specific differences which may plausibly account for variations in model sensitivity and evaluate their impact: • resolution on a Mercator grid, while MJM13 extends up to 1 6 • resolution. It is well established that improved resolution of eddies moderates the sensitivity of modelled circulation to wind stress [20]; hence, we first consider whether resolution dependence may explain some inter-model differences. However, SH12 gives a higher circumpolar transport and overturning sensitivity than even the 1 2…”

Section: Hypothesesmentioning

confidence: 99%

Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

Hogg

Munday

2014

Phil. Trans. R. Soc. A.

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The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change.

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Interdecadal Variability of the Southern Ocean

Cited by 95 publications

References 42 publications

Interannual variability of the Antarctic Circumpolar Current strength based on merged altimeter data

Interannual variability of the Antarctic Circumpolar Current strength based on merged altimeter data

Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales

Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

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