The modelling of the toroidal magnetic field induced by tidal ocean circulation

Dostál, J.; Martinec, Z.; Thomas, Maik

doi:10.1111/j.1365-246x.2012.05407.x

Cited by 16 publications

(10 citation statements)

References 25 publications

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“…The primary toroidal ocean-induced magnetic signals are not considered in this study, since these are confined to the oceans and cannot be measured from the outside. Nevertheless, the toroidal component couples with the large conductivity contrasts between the oceans and continents, which leads to the generation of secondary poloidal magnetic signals along the oceanic shorelines (Dostal et al, 2012;Szuts, 2010). In this study, only the primary poloidally induced magnetic signatures are considered that directly originate from large-scale ocean global circulation and that can be recorded at both sea surface and satellite altitude.…”

Section: Electromagnetic Induction Modelmentioning

confidence: 99%

“…With the advance in computational power, ocean models and data have been used in studies to estimate motionally induced magnetic signals. Stephenson and Bryan (1992), Tyler et al (1997) and Manoj et al (2006) focused on motional induction due to global ocean circulation, while Tyler et al (2003), Kuvshinov et al (2006), Dostal et al (2012) and Schnepf et al (2014) discussed the modelling and observation of electromagnetic fields due to ocean tides. Flosadóttir et al (1997) and Vivier et al (2004) investigated electromagnetic fields on a regional scale, focusing on the North Atlantic circulation and the Antarctic Circumpolar Current.…”

Section: Introductionmentioning

confidence: 99%

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Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

2016

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Abstract. Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As seawater flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for ocean-induced magnetic fields, a realistic consideration of seawater conductivity is often neglected and the effect on the variability of the oceaninduced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model ocean-induced magnetic signals but also to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in seawater conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global seawater conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in seawater conductivity prove to be a key factor for the variability of the ocean-induced magnetic field. However, temporal variations of seawater conductivity only marginally affect the magnetic signal.

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Section: Electromagnetic Induction Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

2016

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“…The model calculates the radial component of the primary ocean‐induced poloidal magnetic field, which is generated by the large‐scale horizontal ocean circulation and emitted outside of the ocean. The primary toroidal ocean‐induced magnetic field component [ Chave , ] and secondary poloidal magnetic signals near continental borders [ Szuts , ; Dostal et al ., ] are not considered in this model.…”

Section: Methodsmentioning

confidence: 99%

Utilizing oceanic electromagnetic induction to constrain an ocean general circulation model: A data assimilation twin experiment

Irrgang

Saynisch

Thomas

2017

J Adv Model Earth Syst

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Satellite observations of the magnetic field induced by the general ocean circulation could provide new constraints on global oceanic water and heat transports. This opportunity is investigated in a model‐based twin experiment by assimilating synthetic satellite observations of the ocean‐induced magnetic field into a global ocean model. The general circulation of the world ocean is simulated over the period of 1 month. Idealized daily observations are generated from this simulation by calculating the ocean‐induced magnetic field at 450 km altitude and disturbing these global fields with error estimates. Utilizing an ensemble Kalman filter, the observations are assimilated into the same ocean model with a different initial state and different atmospheric forcing. Compared to a reference simulation without data assimilation, the corrected ocean‐induced magnetic field is improved throughout the whole simulation period and over large regions. The global RMS differences of the ocean‐induced magnetic field are reduced by up to 17%. Local improvements show values up to 54%. RMS differences of the depth‐integrated zonal and meridional ocean velocities are improved by up to 7% globally, and up to 50% locally. False corrections of the ocean model state are identified in the South Pacific Ocean and are linked to a deficient estimation of the ocean model error covariance matrices. Most Kalman filter induced changes in the ocean velocities extend from the sea surface down to the deep ocean. Allowing the Kalman filter to correct the wind stress forcing of the ocean model is essential for a successful assimilation.

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“…The OMCT is used in several studies [e.g., Dobslaw and Thomas , ; Dostal et al ., ; Dobslaw et al ., ; Saynisch et al ., ; Irrgang et al ., ] and is considered to realistically resolve the main features of ocean global circulation. In the current configuration, the OMCT does not resolve small‐scale features, which also affect motional induction in the ocean [e.g., Lilley et al ., ].…”

Section: Methodsmentioning

confidence: 99%

“…The modeling of motional induction due to ocean circulation (global and regional) is investigated by, e.g., Stephenson and Bryan [1992], Flosad ottir et al [1997], Tyler et al [1997], Vivier et al [2004], and Manoj et al [2006]. In further studies, motional induction due to tidal motion is addressed, e.g., by Tyler et al [2003], Maus and Kuvshinov [2004], Kuvshinov et al [2006], Dostal et al [2012], Schnepf et al [2014Schnepf et al [ , 2015, and Sabaka et al [2015]. Irrgang et al [2016] investigate the influence of spatial and temporal variations of seawater conductivity on motional induction due to ocean circulation.…”

Section: Introductionmentioning

confidence: 99%

Ensemble simulations of the magnetic field induced by global ocean circulation: Estimating the uncertainty

2016

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The modeling of the ocean global circulation induced magnetic field is affected by various uncertainties that originate from errors in the input data and from the model itself. The amount of aggregated uncertainties and their effect on the modeling of electromagnetic induction in the ocean is unknown. For many applications, however, the knowledge of uncertainties in the modeling is essential. To investigate the uncertainty in the modeling of motional induction at the sea surface, simulation experiments are performed on the basis of different error scenarios and error covariance matrices. For these error scenarios, ensembles of an ocean general circulation model and an electromagnetic induction model are generated. This ensemble‐based approach allows to estimate both the spatial distribution and temporal variation of the uncertainty in the ocean‐induced magnetic field. The largest uncertainty in the ocean‐induced magnetic field occurs in the area of the Antarctic Circumpolar Current. Local maxima reach values of up to 0.7 nT. The estimated global annual mean uncertainty in the ocean‐induced magnetic field ranges from 0.1 to 0.4 nT. The relative amount of uncertainty reaches up to 30% of the signal strength with largest values in regions in the northern hemisphere. The major source of uncertainty is found to be introduced by wind stress from the atmospheric forcing of the ocean model. In addition, the temporal evolution of the uncertainty in the induced magnetic field shows distinct seasonal variations. Specific regions are identified which are robust with respect to the introduced uncertainties.

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The modelling of the toroidal magnetic field induced by tidal ocean circulation

Cited by 16 publications

References 25 publications

Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

Utilizing oceanic electromagnetic induction to constrain an ocean general circulation model: A data assimilation twin experiment

Ensemble simulations of the magnetic field induced by global ocean circulation: Estimating the uncertainty

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