Estimating ocean tide model uncertainties for electromagnetic inversion studies

Abstract

Abstract. Over a decade ago the semidiurnal lunar M2 ocean tide was identified in CHAMP satellite magnetometer data. Since then and especially since the launch of the satellite mission Swarm, electromagnetic tidal observations from satellites are used increasingly to infer electric properties of the upper mantle. In most of these inversions, ocean tidal models are used to generate oceanic tidal electromagnetic signals via electromagnetic induction. The modelled signals are subsequently compared to the satellite observations. During the inversion, since the tidal models are considered error free, discrepancies between forward 5 models and observations are projected only onto the induction part of the modelling, e.g., Earth's conductivity distribution. Our study analyses uncertainties in oceanic tidal models from an electromagnetic point of view. Velocities from hydrodynamic and assimilative tidal models are converted into tidal electromagnetic signals and compared. Respective uncertainties are estimated.The studies main goal is to provide errors for electromagnetic inversion studies. At satellite height, the differences between the hydrodynamic tidal models are found to reach up to 2 nT, i.e., over 100% of the local M2 signal. Assimilative tidal models 10 show smaller differences of up to 0.1 nT which in some locations still corresponds to over 30% of the M2 signal.

High‐Resolution Numerical Modeling of Barotropic Global Ocean Tides for Satellite Gravimetry

“…Signatures of ocean tidal dynamics are omnipresent in oceanographic and geodetic observations taken either on the ground or from space. This includes periodic variations in ocean currents registered by moored instruments or acoustic tomography (Dushaw et al., 1997; Luyten & Stommel, 1991; Ray, 2001) as well as by induced secondary magnetic fields (Maus & Kuvshinov, 2004; Saynisch et al., 2018), sea surface height changes measured from tide gauges and satellite altimetry (Doodson, 1928; Schrama & Ray, 1994), and global bottom pressure variations from pelagic pressure recorders and gravimetric satellite missions (Wiese et al., 2016). More recently, even tiny variations in sea surface temperature (Hsu et al., 2020) and tropical precipitation observations (Kohyama & Wallace, 2016) were related to ocean tidal dynamics.…”

On the Approximation of Spatial Structures of Global Tidal Magnetic Field Models

“…While, e.g., Saynisch et al (2018) compared forward models for the M2 tidal magnetic field based on different tidal models, we aim at illustrating the effect of the involved trial functions on the possible extraction of the tidal 15 magnetic field from satellite data in the first place. The indicated residuals for the synthetic examples show that the use of the presented adapted physics based trial functions could have a detectable effect for the extraction of such signals in satellite data.…”

Phase Changes of Electromagnetic Oceanic Tidal Signals

“…Especially since the launch of the Swarm satellite magnetometers (Friis‐Christensen et al, ), the number of EMOTS‐related studies is ever growing. Alone in the last few years, many papers studying or using EMOTS were published (Grayver & Olsen, ; Guzavina et al, , ; Petereit et al, , ; Šachl et al, ; Schnepf et al, ; Saynisch et al, ; Velimsky et al, ). EMOTS are used to infer information about the Earth's lithosphere and mantle (Guzavina et al, ; Grayver et al, ; Kuvshinov et al, ; Schnepf et al, ).…”

“…Likewise, EMOTS are proposed to infer information about the oceans (Irrgang et al, ; Petereit et al, ; Saynisch et al, , ). In addition, EMOTS influence on other EM observations, and EMOTS errors are important topics (Guzavina et al, ; Saynisch et al, ; Schnepf et al, , ). Most of the mentioned studies focus only on the amplitudes of EMOTS and their sensitivities.…”