3-D modelling of the magnetic fields due to ocean tidal flow

Recently Tyler et al. (2003) demonstrated that the magnetic fields generated by the lunar semidiurnal (M-2) ocean flow can be clearly identified in magnetic satellite observations. They compared their numerical simulations of magnetic fields due to the M-2 tide with CHAMP observations and found close agreement between observations and predictions. Their three-dimensional (3-D) conductivity model consists of a surface thin shell of variable conductance and an insulating mantle underneath. Some discrepancies between observations and predictions have been addressed to the absence of a coupling between the surface shell and the mantle. Here we performed model studies of the magnetic signals due to ocean tidal flow in order to answer the following questions. (1) How does the inclusion of a conducting mantle affect the magnetic signals of the M, tide at CHAMP altitude? (2) Are magnetic signals from other tidal components detectable at CHAMP altitude? (3) What amplitude has the magnetic M-2 tide at Orsted altitude? The 3-D conductivity model that we consider incorporates a thin shell and either a radially symmetric or a 3-D mantle underneath. Our model studies demonstrate that including a conducting mantle yields significant changes of the magnetic M-2 oceanic signals. with peak-to-peak values at CHAMP altitude of order 3 nT. The magnetic signals due to other prominent ocean tidal modes (like K-1 and O-1) are below 0.5 nT at CHAMP altitude. The M-2 peak-to-peak magnetic signal at Orsted altitude is of order 1 nT.