The Sunspot Cycle Influence on Lunar and Solar Daily Geomagnetic Variations

Summary The long-standing question of whether L and S respond similarly to the sunspot cycle is re-examined using a very much more extensive data set than hitherto. The global distribution of the phenomenon is discussed in terms of the coefficients of simple spherical harmonic models, including the first such representation of the changes in S and L from sunspot minimum to maximum. Particular attention is paid to the confidence limits of the results, which indicate that many previously obscure points may be resolved with the present data set. In particular, it is shown that there are significant differences between the response of L and S to sunspot number and that the external currents associated with L do not flow mainly in the E-region as hitherto supposed. It is also shown that the original arguments in favour of the E-region as the location of the external S currents are no longer valid.