Currents in the Ionosphere: Examining Sources and their Coupling with the Thermosphere

The availability of geomagnetic field perturbations by satellites have provided unprecedented details on the structure and variability of ionospheric currents. These observations rely on careful corrections applied to magnetic field data collected by Low Earth Orbit (LEO) satellites. The magnetic field measured by the LEO satellite consists of contributions from sources both internal (core, crustal) and external (ionospheric and magnetospheric currents) to Earth, including the induced component of the external current.

In general, when developing internal geomagnetic field models, which capture horizontal scales up to ~1000 km (e.g. CHAOS-7 model), data are carefully selected to reduce the effects of the external currents by focusing on geomagnetic quiet periods. The sources of ionospheric currents are wind, electric field, gravity and plasma pressure-gradients. Among these, wind and electric fields contribute significantly to the well-known current systems such as the Equatorial Electrojet (EEJ) and Sq currents, which flow in the ionospheric E region. However, at the altitudes where LEO satellites orbit, magnetic field contributions from pressure gradients and gravity-driven currents become apparent since the satellites are orbiting at the source of these currents in the F region ionosphere.

Hence, while estimating the Equatorial Electrojet currents or for developing internal field models, there is a need to estimate the currents and magnetic perturbations due to gravity and pressure-gradients.  In the past, only the diamagnetic effects due to pressure-gradients were applied to the residual ionospheric fields ignoring the magnetic effects due to gravity-driven currents. Since LEO satellites are orbiting in the source region of these currents, the accuracy of correcting for only one of these currents is examined using satellite data and model simulations.

Moreover, our work focuses on the effect of lower thermospheric horizontal winds on the local currents in the E region. We demonstrate observationally that the magnitude of the EEJ sideband current is proportional to the strength of westward turning winds with altitude in the Pedersen conductivity dominated region. These findings advance our understanding of ionospheric dynamics and their coupling with the thermosphere.