The South Atlantic in the Fine-Resolution Antarctic Model

Stevens, David P.; Thompson, S. R.

doi:10.1007/s00585-994-0826-5

Cited by 11 publications

(4 citation statements)

References 14 publications

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“…From the above analysis, a temporal variability of the contribution of the PF branch 2, either from the LCDW layer or through intermittent UCDW or AAIW supply, is a potential cause for such variations. Model simulations have shown that there is a high correlation between the transport of the Falkland Current and that of the Antarctic Circumpolar Current in Drake Passage (Stevens and Thompson 1994). Our results suggest that a time-dependent supply of the Falkland Current by the PF northbound branch could be a link between the transport variability in the passage and that of the boundary current.…”

Section: A Supply To the Falkland Currentmentioning

confidence: 56%

The Antarctic Circumpolar Current between the Falkland Islands and South Georgia

Arhan¹,

Garabato²,

Heywood³

et al. 2002

J. Phys. Oceanogr.

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Hydrographic and lowered acoustic Doppler current profiler data along a line from the Falkland Islands to South Georgia via the Maurice Ewing Bank are used to estimate the flow of circumpolar water into the Argentine Basin, and to study the interaction of the Antarctic Circumpolar Current with the Falkland Plateau. The estimated net transport of 129 21 Sv (Sv 10 6 m 3 s 1) across the section is shared between three major current bands. One is associated with the Subantarctic Front (SAF; 52 6 Sv), and the other two with branches of the Polar Front (PF) over the sill of the Falkland Plateau (44 9 Sv) and in the northwestern Georgia Basin (45 9 Sv). The latter includes a local reinforcement (20 Sv) by a deep anticyclonic recirculation around the Maurice Ewing Bank. While the classical hydrographic signature of the PF stands out in this eastbound branch, it is less distinguishable in the northbound branch over the plateau. Other circulation features are a southward entrainment of diluted North Atlantic Deep Water from the Argentine Basin over the eastern part of the Falkland Plateau, and an abyssal anticyclonic flow in the western Georgia Basin, opposite to what was generally assumed. The different behavior of the SAF and PF at the Falkland Plateau (no structural modification of the former and partitioning of the latter) is attributed to the PF being deeper than the sill depth on the upstream side of the plateau, unlike the SAF. It is suggested that the partitioning takes place at a location where the 2500-m and 3000-m isobaths diverge at the southern edge of the plateau. The western branch of the PF crosses the plateau at a distance of 250 km to the east of the SAF. Comparison with a section across the Falkland Current farther downstream shows that its deep part subsequently joins the SAF on the northern side of the plateau where the 2000-3000 m isobaths converge in the steep Falkland Escarpment. The result of this two-stage bathymetric effect is a net transfer of at least 10 Sv from the PF to the SAF at the crossing of the Falkland Plateau.

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Section: A Supply To the Falkland Currentmentioning

confidence: 56%

The Antarctic Circumpolar Current between the Falkland Islands and South Georgia

Arhan¹,

Garabato²,

Heywood³

et al. 2002

J. Phys. Oceanogr.

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“…In this depth range the ACC carries roughly 50% of its total eastward heat transport. Most of it leaves the South Atlantic again while crossing the section at 20øE eastward (Figure 14, middle While the inflow in the upper ocean is often confirmed in observations [Gordon, 1986, Garzoli andGordon, 1996] and other models [Stevens and Thompson, 1994]…”

Section: Pathway Of the Nadw Compensating Flowmentioning

confidence: 99%

Mean circulation and transports in the South Atlantic Ocean: Combining model and drifter data

Stutzer¹,

Krauß²

1998

J. Geophys. Res.

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Abstract. Numerical experiments with a medium-resolution primitive equation model of the South Atlantic mean circulation are described. The results from the standard model realization indicate that the model succeeds in representing the large-scale transport and circulation features. However, a comparison with a velocity field derived from surface drifter data reveals discrepancies of the modeled velocities from the observations in magnitude as well as direction of the flow field. In order to diminish the model deviations from the data, an attempt is made to couple the model to the observations through a simple data assimilation technique. The assimilated model succeeds in improving the subtropical gyre circulation. Only a minor effect on the basin-scale integrated quantities is observed. However, the density field may be deformed as a response to the assimilation of velocity data without simultaneously adapting a corresponding density structure. The influence of the disturbance of the density structure is most prominent at the edges of the observed data set, which does not cover the entire model domain, and is confined to the upper ocean and balanced above the thermocline. We calculated a meridional heat transport that is generally in accordance with estimates from other sources. The analysis of heat and salt fluxes suggests that the model features both the so-called "warm water path" and "cold water path" in closing the global thermohaline circulation. While heat is mainly imported in surface and thermocline waters with the Agulhas Current around South Africa, it is the Antarctic Intermediate Water that compensates for more than 50% of the salt loss by the outflowing North Atlantic Deep Water.

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“…Although the passage is located near to the highest latitude of T/P, the tracks are far from being completely zonal. The descending (essentially NW to SE) passes are of particular interest as they cross, rather than graze, the main part of the current as it flows with a northerly component through the passage [Nowloen and Clifford, 1982;Nowlin and Klinck, 1986;Gille, 1994;Stevens and Thompson, 1994]. The descending passes also provide a near connection between two pairs of coastal gauges: Port Stanley (Falkland Islands/Malvinas) and Signy (South Orkney Islands) on the eastern side of the passage and Diego Ramirez (Chilean coast) and Espcranza (Antarctic Peninsula) on the western-central side.…”

Section: Topex/poseidon Altimetrymentioning

confidence: 99%

A test of the ability of TOPEX/POSEIDON to monitor flows through the Drake Passage

Woodworth¹,

Vassie²,

Hughes³

et al. 1996

J. Geophys. Res.

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TOPEX/POSEIDON (T/P) altimeter data from the Drake Passage (DP) area of the Southern Ocean, near to the highest latitudes accessible by the satellite, are found to agree as well, in general, to data from an extensive set of in situ instrumentation as has been observed for other parts of the ocean. Root-mean-square (rms) differences between subsurface pressures (SSP) measured by altimetry and bottom pressures (BP) measured by in situ devices are approximately 2 mbar in the northern DP and 4 mbar in the south, after application of a 20-day low-pass filter. Two mbar accuracy would suggest that altimetry could be capable of providing useful additional information on Antarctic Circumpolar Current (ACC) transport fluctuations through the DP on seasonal and interannual timescales. The larger rms differences on what is considered to be the more important southern side are explainable in terms of baroclinic variability at the southern end of the World Ocean Circulation Experiment (WOCE) SR1 section. The first WOCE conductivity-temperature-depth data sets from SR1 have confirmed the existence of a major baroclinic "eddy feature" in the south, which could account to a great extent for the larger rms values. Better southern DP locations could possibly have been chosen for WOCE. However, further recent in situ measurements from other locations near to the DP have shown that the southern DP ACC-related signals in SSP or BP are only slightly larger than T/P accuracy, which suggests that, as yet, they cannot be adequately monitored by means of altimetry alone, whichever location is chosen. Even if the altimetric and in situ observations were perfect, would they provide information directly relatable to transport variability through the passage? This question has been studied by means of Fine-Resolution Antarctic Model (FRAM) numerical modeling investigations which have demonstrated the complexity of the correlation between the variability in DP transport and SSP (or sea level). Within FRAM, northern SSP (or BP) variations are virtually uncorrelated with transport fluctuations, and the modelling has confirmed the importance of southern measurements, as inferred from in situ measurements over a decade ago. It is evident that, for the foreseeable future, an extensive set of in situ instrumentation will be required, in addition to the altimetry, if further insight into circulation in this part of the Southern Ocean is to be obtained. This paper has two main objectives. The first one is concerned with verifying that high T/P accuracy is also obtained in the DP area by comparison of the altimetry to sea level, or proxy sea level, data from coastal tide gauges, deep-sea bottom pressure recorders (BPRs), and inverted echo sounders (IESs).It is clear that all devices, either in situ or altimetric, should provide compatible scientific results and that any differences should be understood as far as possible. A related objective is concerned with asking if the altimetric accuracies are "good enough," compared to the in situ values, for perf...

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The South Atlantic in the Fine-Resolution Antarctic Model

Cited by 11 publications

References 14 publications

The Antarctic Circumpolar Current between the Falkland Islands and South Georgia

The Antarctic Circumpolar Current between the Falkland Islands and South Georgia

Mean circulation and transports in the South Atlantic Ocean: Combining model and drifter data

A test of the ability of TOPEX/POSEIDON to monitor flows through the Drake Passage

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