Atmospheric solar tides and their electrodynamic effects—I. The global Sq current system

Abstract

This paper is Part I of a study dealing with the electrodynamic consequences of solar tides in the E-region of the Earth's atmosphere. The major result to emerge from Part I is that E-region dynamo action of combined diurnal and semidiurnal winds consistent with measurements is found to account for the S q variations in ground magnetic data, without having to resort to electric fields of plasmaspheric origin as suggested in the recent literature. Real discrepancies on the order of 20% in amplitude and 1 to 2 h in phase still exist between the data and the present theoretical model. The model couples a global thin-shell dynamo solution which takes into account the vertical structure of the winds with a full three-dimensional model of the equatorial electrojet. Part I is primarily concerned with the classical thin-shell global solution, whereas Part II deals solely with the equatorial electrojet; however, the equatorial magnetic variations to be presented here are taken from Part II. Previous global dynamo models have utilized winds which are shown to be unrealistic by recent measurements and dissipative tidal theory, and do not include the important effects of vertical current flow at the magnetic equator. Inclusion of vertical current effects, which are discussed in detail in Part II, relaxes the need for E-region diurnal wind speeds as large as those required by previous workers to reproduce the S q current system. Computed vertical structures of the S q currents explain some puzzling features of the few midlatitude rocket magnetometer measurements that are available. The joule heating by S q currents is comparable to solar EUV heating above 60°N, but contributes negligibly to the total heat budget of the thermosphere.