Solar-wind induction and lunar conductivity

A summary review of electromagnetic induction driven in the Moon by the interplanetary magnetic field is given. The point of view developed centers on inversion of Fourier transforms of the magnetic field in the free-stream solar wind (forcing function) and the response on the lunar surface measured by Lunar Surface Magnetometers. Conductivity profiles are shown to depend upon the central angle between the magnetometer given by local time and the incident wave-normal direction. The induction excites at least magnetic dipole and quadrupole “radiation”, but any scattered field is confined to the Moon's interior, save for propagation down the cavity where a TE-mode surface wave is generated. Confinement of the induced field on the sunward hemisphere and near the subsolar point is nearly complete, decreasing to the limbs, while in the diamagnetic cavity downstream of the Moon, partial confinement takes place. Both time and spatial multipoles of the induced field are present in the lunar interior complicating inversion into conductivity profiles. Profiles are reviewed and resolution limits are given and compared to those obtained from transient analysis. Finally a qualitative comparison to conductivity in the Earth is given.