Ionospheric dynamo in the equatorial region

Abstract

Thermospheric winds play a crucial role in the ionospheric electrodynamics via the ion-neutral interaction. While the thermospheric winds in the F-region are driven by absorption of energy in the thermosphere itself, the winds in the E-region are originated from the tidal modes propagating into the thermosphere from the lower atmosphere. The neutral winds in the altitude regions of 90~150 km move the ions and electrons in different directions through the geomagnetic field lines, producing an electromotive force. This force creates current divergence and sets up polarization electric fields to make divergent-free current everywhere. The electric field has strong implications in the ionosphere-thermosphere system, particularly in the equatorial region. For example, the E-region dynamo is responsible for the well-known equatorial anomaly and electrojet. In this presentation, fundamentals of ionospheric dynamo will be briefly reviewed with a recent example, showing strong influences of the lower atmosphere onto the ionosphere. In particular, physical mechanism of the E-region dynamo responsible for the equatorial anomaly will be described in detail with a question: which component of the neutral winds drive the dynamo, zonal or meridional?