Abstract
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 ocean-induced 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.
Highlights
The principle of electromagnetic induction due to water flow is long known and was first described by Faraday (1832)
In order to model and simulate ocean-circulation-induced magnetic fields, a 2-D electromagnetic induction model is implemented into the ocean global circulation model Ocean Model for Circulation and Tides (OMCT)
We focused on the question of to what extent spatial and temporal variability in seawater conductivity influences ocean-induced magnetic fields
Summary
The principle of electromagnetic induction due to water flow is long known and was first described by Faraday (1832). Thereby, spatial accumulations of electric charge are formed, leading to the generation of electric currents, which in turn induce secondary magnetic fields. This process is often referred to as “motional induction”. 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.
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