Modeling the equatorial electrojet

The equivalent circuit method has been modified to give greater accuracy and greater detail near the equator in order to model the equatorial electrojet. Electron collision frequencies used in the conductivity model are consistent with laboratory measurements. Variations with longitude are allowed, and the electrojet in the model is driven by suitable emf's generated by a global thermotidal wind system. The height of maximum current density in the Indian electrojet provided by the model at 104 km is consistent with some observations. The model gives the same height in Peru when an electron density profile typical of that region is used. The form of the electron density profile is shown to have a considerable affect on the current profile. The calculated variation with latitude of height-integrated current density gives good agreement. The two-layer equivalent circuit model is more successful than the single-layer model in modeling the latitude profile of the jet, but the observed depression in ΔH near 4° dip latitude requires much larger changes in currents with latitude than either model can provide. The theory that currents are limited by the two-stream instability does not agree with measured altitude profiles of the jet. Before latitude variations of ΔH and ΔZ on the ground can satisfactorily be explained, greater understanding of the contribution of conductivity anomalies to internal components will be required, but with suitable assumptions, a good fit with observed results is obtained. The effects produced by a simple local F region wind system are also investigated. A discrepancy with the observed relationship between integrated current densities and ΔH still awaits explanation.

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