SQ CURRENTS IN A 3-DIMENSIONAL IONOSPHERE

Calculations are made of Sq currents on the assumption that they are caused by electromotive forces produced by tidal winds at the base of an ionosphere that extends upwards to considerable heights, and has some of the features of the conductivity distribution of the actual ionosphere. It is shown that the current flow is nearly horizontal throughout the region of importance and that the 'layer equations' are therefore approximately true. The strictly horizontal part of the current flow is not, however, non-divergent and it is not possible to define a current function for it. The calculated currents are divided into two parts, one of which has a field below the ionosphere, while the other does not. The significance of this fact is considered in relation to the interpretation of analyses of observations of Sq variations. © 1969.