Surface signatures of meridional currents in the equatorial electrojet

Abstract

The requirement that the surface magnetic field linked with the equatorial electrojet (EEJ) should be curl free is used to demonstrate that the electrojet has to have variations in the declination (<i>D</i>) component with well defined diurnal and latitudinal structures and an amplitude of around 5-10% of the electrrojet strength. Data from the standard magnetic observatories in the Indian sector are used to identify the predicted signature of the electrojet-associated <i>D</i> variations. The pattern of time variations deduced from the data shows enhancement with respect to the theoretically predicted values in the afternoon sector, but the signatures appear to be suppressed in the forenoon sector. Since even a small displacement or meandering of the main eastward electroject flow can produce changes in declination, various scenarios for the current flow are also considered, and temporal and latitudinal dependence of the <i>D</i> variation evaluated in a bid to identify the source of this forenoon-afternoon asymmetry. It has been shown that, in principle, the field due to deviation of the flow from pure eastward direction can be responsible for, at least, a part of the observed asymmetry. There may also be contributions from the channeling of the induced currents round the southern peninsula in the lower crust and upper mantle.