A calculation of ionospheric currents due to semidiurnal antisymmetric tides

Abstract

The fully developed equivalent circuit method is used to calculate the ionospheric electric current flow due to the (2,3) and (2,5) tidal modes. The (2,5) mode currents are of negligibly small amplitude. The (2,3) current pattern has meridional currents in the same direction at a given local time in both north and south hemispheres. There is also sometimes a minimum in the zonal current around 10° dip latitude and the equatorial electrojet pattern may be different in different longitude zones. These features may be possible explanations of (1) the meridional current pattern observed at Saint‐Santin, (2) current flows on abnormal quiet days (AQDs), (3) the reverse equatorial electrojet, (4) the seasonal phase anomaly in the lunar geomagnetic tide, and (5) the “invasion” of one hemisphere's current pattern by that from the opposite hemisphere. The recent detection of antisymmetric semidiurnal winds just below the dynamo region further demonstrates the importance of these modes.