On the Use of Satellite Altimetry to Detect Ocean Circulation's Magnetic Signals

Saynisch, Jan; Irrgang, Christopher; Thomas, Maik

doi:10.1002/2017jc013742

Cited by 5 publications

(7 citation statements)

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“…Indeed, ocean tides may supply the most predictable naturally occurring, global‐scale electromagnetic field source on Earth and the predictable phase‐locked astronomical periodicity has been a key element allowing both the successful theoretical modeling of these fields as well as their extraction from satellite magnetic records (Sabaka et al, , ; Tyler et al, ). The study of ocean tidal electromagnetic fields and their use as a sounding source in oceanographic and geophysical studies is currently receiving much attention (Grayver et al, , ; Irrgang et al, , , , ; Sabaka et al, , ; Saynisch et al, , , ; Schnepf, , ; Tyler, ; Velimsky et al, ) due to the unprecedented geomagnetic field coverage coming from the ESA Swarm mission (e.g., Friis‐Christensen et al, ) consisting of three satellites launched in 2013 and expected to continue until 2030.…”

Section: Introductionmentioning

confidence: 99%

“…A recent study of ocean climatology data (Tyler et al, ) suggests that over much of the global ocean, observed conductivity tracks observed temperature and over much of the remainder of the ocean, observed conductivity tracks observed salinity. However, time variations and depth integrals (e.g., Irrgang et al, ; Saynisch et al, ) combined with the nonlinearity of the equation for conductivity complicates the question of whether a linear relationship holds between conductance and OHC. Because of aliasing and sparse sampling of some regions of the ocean, it is possible that the relationship between conductance and OHC is not simply linear.…”

Section: Introductionmentioning

confidence: 99%

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Predictability of Ocean Heat Content From Electrical Conductance

Trossman

Tyler

2019

JGR Oceans

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Ocean heat content (OHC) is a key climate variable that needs to be monitored to know how Earth's energy imbalance is changing, yet observing OHC remains a challenge. The present study examines whether a depth integral of the ocean's electrical conductivity ("conductance"), which may be inferred from both in situ methods and satellite magnetometers over the global ocean, could help monitor OHC. The ocean's electrical conductivity locally depends on temperature, salinity, and pressure, but it is not as well known how the conductance depends on OHC and ocean salt content. By examining the output of an ocean state estimate shown to agree well with observations that have not been assimilated, this study evaluates the fundamental limitations of using perfectly known ocean conductance to predict OHC, rather than the challenges associated with accounting for observational error. It is found that the ocean's conductance and OHC fields are nonlinearly related but nevertheless highly correlated. A statistical framework tends to predict OHC more accurately than ocean salt content from ocean conductance in regions where conductivity is more sensitive to salinity than temperature. The annually (bidecadally) averaged OHC can be predicted from a combination of conductance and depth-averaged conductivity ocean fields to within nearly 0.1% (1%) error globally and even more accurately in many poorly observed (e.g., ice-covered) regions. Practical application of this statistical framework to monitor OHC requires examination of the effect of uncertainties in the observed bathymetry and ocean conductance, which vary with application.Plain Language Summary Seawater's electrical conductivity describes the ocean's ability to conduct electricity, which has an associated magnetic field. It may be possible to get a conductivity averaged over all depths from a combination of satellite observations and our knowledge of the seafloor. Because conductivity depends upon how warm/cold the ocean is, how salty the ocean is, and how deep you are in the ocean, we investigate whether this depth-averaged conductivity can provide us with information about how much heat is in the ocean over different time period lengths. We develop some frameworks for predicting how much heat is in the ocean from the averaged conductivity and find that there is a trade-off between the accuracy of the predictions and the length of the time period over which changes in the amount of heat can be detected in the ocean. We also note that there will be additional uncertainties added when our frameworks are applied to observations. The electrical conductance (i.e., depth integral of conductivity) can of course be obtained by in situ instruments sampling a depth profile of conductivity, but more practical means are also available. As a simple

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Predictability of Ocean Heat Content From Electrical Conductance

Trossman

Tyler

2019

JGR Oceans

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“…Hence, the crucial aspect of the proposed method is to predefine the temporal behavior of the OIMF from circulation. Saynisch et al (2018) already suggested to predict magnetic signals from circulation and to use these proxies for a fit on magnetometer data. Saynisch et al (2018) also pointed out the possibility of constructing the proxy OIMF from independent observations like satellite altimetry.…”

Section: Introductionmentioning

confidence: 99%

On the detectability of the magnetic fields induced by ocean circulation in geomagnetic satellite observations

Hornschild

Baerenzung

Saynisch

et al. 2022

Earth Planets Space

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Due to their sensitivity to conductivity and oceanic transport, magnetic signals caused by the movement of the ocean are a beneficial source of information. Satellite observed tidal-induced magnetic fields have already proven to be helpful to derive Earth’s conductivity or ocean heat content. However, magnetic signals caused by ocean circulation are still unobserved in satellite magnetometer data. We present a novel method to detect these magnetic signals from ocean circulation using an observing system simulation experiment. The introduced approach relies on the assimilation of satellite magnetometer data based on a Kalman filter algorithm. The separation from other magnetic contributions is attained by predicting the temporal behavior of the ocean-induced magnetic field through presumed proxies. We evaluate the proposed method in different test case scenarios. The results demonstrate a possible detectability of the magnetic signal in large parts of the ocean. Furthermore, we point out the crucial dependence on the magnetic signal’s variability and show that our approach is robust to slight spatial and temporal deviations of the presumed proxies. Additionally, we showed that including simple prior spatial constraints could further improve the assimilation results. Our findings indicate an appropriate sensitivity of the detection method for an application outside the presented observing system simulation experiment. Therefore, we finally discussed potential issues and required advances toward the method’s application on original geomagnetic satellite observations. Graphical Abstract

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“…Hz (Schmelz et al, 2011). Also, Kominis et al (2003) have presented an SERF-based atomic magnetometer with a measurement volume 1800 cm 3 and a sensitivity of 0.54 fT / √ Hz.…”

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confidence: 99%

Electromagnetic characteristics of ENSO

et al. 2018

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The motion of electrically conducting sea water through Earth's magnetic field induces secondary electromagnetic fields. Due to its periodicity, the oceanic tidally induced magnetic field is easily distinguishable in magnetic field measurements and therefore detectable. These tidally induced signatures in the electromagnetic fields are also sensitive to changes in oceanic temperature and salinity distributions. We investigate the impact of oceanic heat and salinity changes related to the El Niño-Southern Oscillation (ENSO) on oceanic tidally induced magnetic fields. Synthetic hydrographic data containing characteristic ENSO dynamics have been derived from a coupled ocean-atmosphere simulation covering a period of 50 years. The corresponding tidally induced magnetic signals have been calculated with the 3-D induction solver x3dg. By means of the Oceanic Niño Index (ONI), based on sea surface temperature anomalies, and a corresponding Magnetic Niño Index (MaNI), based on anomalies in the oceanic tidally induced magnetic field at sea level, we demonstrate that evidence of developing ENSO events can be found in the oceanic magnetic fields statistically 4 months earlier than in sea surface temperatures. The analysis of the spatio-temporal progression of the oceanic magnetic field anomalies offers a deeper understanding on the underlying oceanic processes and is used to test and validate the initial findings.

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On the Use of Satellite Altimetry to Detect Ocean Circulation's Magnetic Signals

Cited by 5 publications

References 45 publications

Predictability of Ocean Heat Content From Electrical Conductance

Predictability of Ocean Heat Content From Electrical Conductance

On the detectability of the magnetic fields induced by ocean circulation in geomagnetic satellite observations

Electromagnetic characteristics of ENSO

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