After local sunset, the low latitude F region ionosphere becomes highly unstable due to a sudden decrease in plasma density at lower altitudes (E region). The northward directed Earth’s magnetic field and eastward directed electric field push the regions of depleted plasma from the bottom side F region to heights of up to about 2000km. Currently, the global seasonal-longitudinal distribution of Equatorial Plasma Depletions (EPD) is well known (e.g., Stolle et al, 2008), but the day-to-day variability of their occurrence is still subject to research. EPD’s are a major cause of disturbances of radio waves used by communication and navigation systems, such as GPS (e.g., Xiong et al., 2016).
This project aims at improving our knowledge of the spatiotemporal variations of the electromagnetic signatures of EPD. Therefore, we use in-situ high-resolution measurements of the Swarm mission. We have applied its geomagnetic observations to infer the direction of the EPD-related field-aligned currents (FAC). By using electric field data we were able to determine the preferable direction of the EPD-related Poynting flux (Rodriguez-Zuluaga et al., 2017). Differently than predicted by theoretical approaches, both FAC and Poynting flux were observed to be interhemispheric and the flow directions show a well-defined seasonal and longitudinal dependence. We have also compared Swarm observations with results from physics-based models (Yokoyama and Stolle, 2017), and could well reproduce the amplitudes of associated electric currents.
We further want to improve our understanding of the EPD’s underlying physics by analysing extended Swarm data sets allowing for a better seasonal and local time coverage, adding dedicated simulations by physics-based models, and low latitude radar observations, e.g., from Jicamarca observatory. We will further analyse high-cadence electron density and magnetic field records by Swarm and relate it to GPS observations to identify the scattering conditions that cause scintillations. Thus, we make full use of the multi-instrument capabilities of the Swarm mission.
By addressing the aforementioned questions with multiple parameter data sets, we expect new, fundamental insights into the electromagnetic mechanisms of the upper atmosphere as well as significant advances in our ability to describe and forecast EPDs and, finally, to mitigate their impact on radio wave based technological infrastructure like GPS.
DFG, Priority Programme 1788 “DynamicEarth”.