Motional induction in Ganymede's ocean

We investigate the magnetic signature of oceanic circulation in Ganymede's subsurface ocean using kinematic induction modeling. Our approach couples zonal jet flows from rotating thermal convection simulations with magnetic field models incorporating Ganymede's internal dynamo and external contributions from Jupiter.  We solve the induction equation in spherical geometry for deep-ocean (493~km) and shallow-ocean (287~km) scenarios with varying magnetic Reynolds numbers.  Ocean flows generate a predominantly toroidal magnetic field through the omega-effect,
with a weaker poloidal component pervading beyond the conductive ocean layer.  For some, but not all, induction configurations,  analysis  \rv{of the time-averaged Lowes-Mauersberger} spectra  reveals that ocean-induced signals dominate at spherical harmonic degrees $\ell \geq 4$. Deep ocean scenarios with magnetic Reynolds numbers above unity produce surface magnetic signals up to 9~nT. Our results demonstrate that Ganymede's intrinsic magnetic field creates favorable conditions for detecting subsurface ocean dynamics, thus emphasizing the need for low-altitude
orbits for the Juice probe.