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

Abstract

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

Tidal transports from satellite observations of earth’s magnetic field

“…Nonetheless, so far it is useful to include the CHAMP data into the assimilation since it results in a slight reduction of the posterior SH variance which enables the assimilation to start already at a lower level of prior variance when Swarm data becomes available in 2013. Furthermore, during the model development we noticed a high sensitivity towards the ionospheric component of our model 13 , cf. (not shown).…”

“…Second, to calculate EM signals from the tidal electric current density, we use x3dg with the tidal frequencies from Table 1 and by employing a commonly used background conductance environment. The conductance environment (cf., 13 , 36 ) consists of superposed 2D horizontal layers of sediments 8 , 18 and oceans 47 over the vertical 1D mantle conductivity profile of Grayver et al 12 . To estimate the influence of the mantle, we incorporate also the 1D Püthe et al 27 mantle conductivity profile.…”

“…Using oceanic EM signals to infer information about the ocean itself, e.g., ocean transports, temperature, salinity or electric conductivity is very much desired 14 , 25 , 33 , 39 , 49 . However, respective studies either heavily rely on numerical ocean models 13 , 48 , or are limited to very local measurements 20 , 26 , 38 , 44 . All studies report on high uncertainties due to the incorporated models or EM noise from non-oceanic sources.…”

Exploration and Application of Marine Magnetic Field Information Based on Ocean Measurement Technology

“…Whether it is a superpower, a traditional maritime power, or a coastal developing country, they all consider developing and managing the ocean as an important national policy, and strive to build a navy and develop maritime power to obtain the maximum ocean benefits. After efforts in recent years, China's marine magnetic field measurement technology has made significant progress in multiple research and application fields, with its applications specifically reflected in both marine engineering and military fields [4].…”