Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

White, Antony; Heinson, Graham

doi:10.5636/jgg.46.1067

Cited by 10 publications

(7 citation statements)

References 39 publications

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“…The general southward orientation of the arrows at all three Anchor‐mag sites is consistent with the ‘coast effect’ caused by the body of seawater in the Great Australian Bight and Southern Ocean. In fact, while the coast effect of South Australia has been observed by seafloor instruments (White & Heinson 1994), the present results are the first observations (perhaps anywhere?) of the coast effect at the sea surface.…”

Section: Floating Magnetometers Anchored Off the Eyre Peninsula Sosupporting

confidence: 66%

Induction arrows from offshore floating magnetometers using land reference data

Hitchman

Lilley

Milligan

2000

Geophysical Journal International

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S U M M A RY Induction arrows are a traditional output of magnetovariational experiments, and represent transfer functions used quantitatively in the inversion of geomagnetic depth sounding data to give Earth electrical conductivity structure. In this paper, a technique is tested in which`total-¢eld' variations are combined with horizontal-¢eld data recorded simultaneously at remote stations in order to derive induction arrows. The method is ¢rst demonstrated using total-¢eld data recorded on land by an aeromagnetic base station, and then applied to data obtained from magnetometers £oated o¡shore on the sea surface. The £oating magnetometers were deployed in two con¢gurations: one tethered to the sea£oor; the second free-£oating.

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Section: Floating Magnetometers Anchored Off the Eyre Peninsula Sosupporting

confidence: 66%

Induction arrows from offshore floating magnetometers using land reference data

Hitchman

Lilley

Milligan

2000

Geophysical Journal International

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“…The scale of this uncertainty is illustrated on Fig. 11 graph of White and Heinson's (1994) model (shown stippled); changes in conductivity of two orders of magnitude can be made without affecting their data fit.…”

Section: Discussionmentioning

confidence: 99%

“…Likewise, we have no information for the Southern Ocean (although F. E. M. Lilley is currently undertaking one such study). However, White and Heinson (1994) have followed earlier GDS work by Polatayko (1978, 1985) to obtain an electrical conductivity profile for the continental-ocean boundary of South Australia (using a transect of stations going from the land to just beyond the continental shelf south of station PTA in our Fig. 1).…”

Section: Discussionmentioning

confidence: 99%

“…Models for the middle of the Tasman Sea (Ferguson, Lilley, and Filloux, 1991) are shown by the bold stepped dashed line (site TP3) and the stepped thin line (site TP4). WH(1994) is the result of White and Heinson (1994) that was based on a transect of the GDS stations across the continent-ocean boundary of South Australia. HL(1993) is the profile obtained by Heinson and Lilley (1993) from a re-analysis of the Tasman sea data.…”

Section: Discussionmentioning

confidence: 99%

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Quiet-day ionospheric currents and their application to upper mantle conductivity in Australia

et al. 2014

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This study concerns the use of selected geomagnetic field records to establish the 1990 quiet-day current system (Sq) for Australia and to use the ionospheric current source of Sq for a determination of the Earth's deep electrical conductivity. The primary data set came from a chain of eight, three-component magnetometer stations that was operated along a north-south line in central Australia. Additional records, necessary for boundary conditions, were added to the data set. A regional spherical harmonic analysis (SHA) allowed the separation of the internal and external field contributions to the Sq variations. Mapping of the equivalent ionospheric current from the external field showed that the Sq contour focus passed near the -30° geomagnetic latitude of central Australia with a 5°l atitude variation between winter and summer and a corresponding change from about 80 to 200 kA in strength. A special transfer function allowed the computation of an equivalent conductivity-depth profile of central Australia from the paired external and internal coefficients of the SHA. A regression line through the conductivity estimates gives a profile that starts at 0.025 S/m for a depth of 130 km, rising gradually to about 0.045 S/m at 250 km, then steepens to 0.11 S/m at 360 km and rises moderately to 0.13 S/m at 470 km near the base of the upper mantle. No data were obtained through the mantle transition zone. Computations gave 0.18 S/m in the region of 800 km depth. Previous conductivity models for the upper mantle beneath central Australia, although less specific in values, are consistent with our profile. At depths greater than 500 km, the regression profile is in agreement with the conductivity distribution beneath the Tasman Sea determined from seafloor magnetotellurics, although both measurements lack high resolution at such depths.

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“…The origins of these instruments lie in designs described by White (1979) and Chamalaun & Walker (1982). With various successive improvements, the instruments have been used to record seafloor data in a range of experiments, such as EMSLAB-Group (1988) and White & Heinson (1994). For the Southern ocean magnetometer experiment (SOMEx) deployments each magnetometer was packed into the space available inside a standard acoustic-release glass sphere, without compromising the acoustic release facility.…”

Section: S E a F L O O R I N S T Ru M E N Tat I O N A N D O B S E Rvamentioning

confidence: 99%

Seeking a seafloor magnetic signal from the Antarctic circumpolar current

Lilley¹,

White²,

Heinson³

et al. 2004

Geophysical Journal International

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S U M M A R YMotional electromagnetic induction by ocean currents is a basic phenomenon of geophysics, with application to the monitoring of ocean transport. One of Earth's strongest ocean currents is the Antarctic circumpolar current (ACC). This paper explores the magnetic signals that should be generated by the ACC, and reports an experiment in which a magnetometer recorded natural variations of Earth's magnetic field on the floor of the Southern ocean for some five months in 1996. Magnetometer records from Kingston, Tasmania, and from Macquarie Island give reference information concerning magnetic storms and substorms. The instrument was sited in the region of the major oceanographic subantarctic flux and dynamics experiment (SAFDE), where the ACC passes south of Tasmania, between the major topographic features of the South Tasman rise and the Australia-Antarctica spreading ridge. The SAFDE records give comprehensive control on the actual ocean current flow at the time of the magnetic recording, and allow a magnetic signal to be predicted, in terms of the seafloor conductance. The seafloor conductance for the area is however low, and the amplitude of the predicted signal is low. The seafloor observations confirm that the signal is weak against the effects of ionospheric signals.In future experiments, the choice of sites with thicker seafloor sedimentation would increase the ACC magnetic signal to be observed.The magnetometer measurements have a result relevant for the SAFDE, in confirming that the correction of electric data for seafloor conductance is small. There is also the result for seafloor magnetic observatories for which motional induction effects are unwanted, that such an observatory can operate even under the ACC, and be substantially protected from motional induction effects by low seafloor conductance.

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Two-Dimensional Electrical Conductivity Structure across the Southern Coastline of Australia.

Cited by 10 publications

References 39 publications

Induction arrows from offshore floating magnetometers using land reference data

Induction arrows from offshore floating magnetometers using land reference data

Quiet-day ionospheric currents and their application to upper mantle conductivity in Australia

Seeking a seafloor magnetic signal from the Antarctic circumpolar current

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