First observation of the anomalous electric field in the topside ionosphere by ionospheric modification over EISCAT

Abstract

We have developed an active ground-based technique to estimate the steady state field-aligned anomalous electric field (E∗) in the topside ionosphere, up to ~600 km, using the European Incoherent Scatter (EISCAT) ionospheric modification facility and UHF incoherent scatter radar. When pumping the ionosphere with high-power high-frequency radio waves, the F region electron temperature is significantly raised, increasing the plasma pressure gradient in the topside ionosphere, resulting in ion upflow along the magnetic field line. We estimate E∗ using a modified ion momentum equation and the Mass Spectrometer Incoherent Scatter model. From an experiment on 23 October 2013, E∗ points downward with an average amplitude of ~1.6 μV/m, becoming weaker at higher altitudes. The mechanism for anomalous resistivity is thought to be low-frequency ion acoustic waves generated by the pump-induced flux of suprathermal electrons. These high-energy electrons are produced near the pump wave reflection altitude by plasma resonance and also result in observed artificially induced optical emissions. Key Points New ground-based techniquePump-induced suprathermal electrons cause anomalous resistivityAnomalous electric field hinders ion outflow