A circumpolar gravest empirical mode for the Southern Ocean hydrography

Sun, Chenglin; Watts, D. Randolph

doi:10.1029/2000jc900112

Cited by 94 publications

(102 citation statements)

References 16 publications

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“…The vertical distributions of temperature and salinity are represented as functions of SSDH, as performed in the Antarctic Circumpolar Current region by Sun and Watts (2001) and Swart et al (2010), in the North Pacific western subarctic gyre region by Nagano et al (2016), and in other regions. Through the linear relationship between SSDH and SSH, the vertical hydrographic distributions can be inferred by altimetric SSH.…”

Section: Introductionmentioning

confidence: 99%

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

et al. 2016

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Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30 • N, 145 • E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993-2012. The volume transport-weighted temperature (T I ) is strongly dependent on the season. The anomaly of T I from the mean seasonal variation, whose standard deviation is 0.14 • C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0 − 25.5σ θ . The anomaly of T I was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of T I had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in T I affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer.

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Section: Introductionmentioning

confidence: 99%

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

et al. 2016

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“…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.…”

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confidence: 99%

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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“…In order to test this possibility, we have turned to sea surface temperature (SST) gradients. These are not always indicative of surface currents, but the fact that the ACC is to first order an equivalent barotropic flow (Killworth, 1992;Killworth and Hughes, 2002) means that temperature at any depth does tend to be a good proxy for the dy-15 namic topography in this region (Sun and Watts 2001). In order to calculate a mean SST gradient, we have used merged infra-red and microwave satellite data from the Mersea Odyssea project, downloaded from ftp://ftp.ifremer.fr/ifremer/medspiration/data/l4hrsstfnd/eurdac/glob/odyssea.…”

Section: Interpretation Of Low Kurtosis Regionsmentioning

confidence: 99%

Identification of jets and mixing barriers from sea level and vorticity measurements using simple statistics

Hughes¹,

Thompson²,

Wilson³

2010

Ocean Modelling

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The probability density functions (PDFs) of sea level and geostrophic relative vorticity are examined using satellite altimeter data. It is shown that departures from a Gaussian distribution can generally be represented by two functions, and that the spatial distribution of these two functions is closely linked to the skewness and kurtosis of the PDF. The patterns indicate that strong jets tend to be identified by a zero contour in skewness coinciding with a low value of kurtosis. A simple model of the statistics of a meandering frontal region is presented which reproduces these features. Comparisons with mean currents and sea surface temperature gradients confirm the identification of these features as jets, and confirm the existence of several Southern Ocean jets unresolved by drifter data. Diagnostics from a range of idealized eddying model simulations show that there is a strong, simple relationship between kurtosis of potential vorticity and effective diffusivity. This suggests that kurtosis may provide a simple method of mapping mixing barriers in the ocean.

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A circumpolar gravest empirical mode for the Southern Ocean hydrography

Cited by 94 publications

References 16 publications

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

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

Identification of jets and mixing barriers from sea level and vorticity measurements using simple statistics

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