Uncertainties of Ocean Tide Models for Electromagnetic Inversion Studies

Abstract: The semi-diurnal lunar M2 ocean tide signal as detected by satellite magnetometers is increasingly inverted for electrical properties of the upper mantle, e.g., the mantle's conductance. During the inversion, ocean tidal models are used to generate reference tidal electromagnetic signals. Subsequently, the modeled and the observed signals are compared. Since the tidal models are considered error free, model-observation discrepancies are only projected onto the EM induction part of the modeling, e.g., the mantle's conductance. Our study tests the assumption of error-free tidal models. We analyze the uncertainties in the oceanic tidal models from an electromagnetic point of view. The study provides errors for respective electromagnetic inversion studies. At satellite height, the differences between purely hydrodynamic tidal models reach up to 2nT, i.e., over 100% of the local M2 signal. Assimilative tidal models show smaller differences of up to 0.1nT, which in some locations still corresponds to over 30% of the M2 signal.