The lunar daily geomagnetic variation and its dependence on sunspot number

A detailed spherical harmonic model of the lunar daily geomagnetic variation, L, is presented and discussed. This model, which is based on a vastly greater data-set than hitherto, is compared to an earlier model of the solar daily geomagnetic variation, S, which is based on the same data. The dependence of L on sunspot number, as measured by the Wolf ratio, is found to be less than that of S by a factor of 2. It is confirmed that the dependence of S, L and E-region conductivity with sunspot cycle differ significantly from one another, casting doubt on that region as the principal location for the L and S dynamo currents. (C) 2014 Elsevier Ltd. All rights reserved.