In situ observations by the Swarm satellites are revealing intriguing ionospheric plasma density structures and electromagnetic properties. These occur for equatorial plasma depletions (EPDs) that evolve after sunset at ionospheric F region altitudes (200 to 1500 km). In the first phase of our project, we discovered EPDs features that have not been predicted by physical modeling so far. We could observe that plasma depletion related field-aligned currents flow from one magnetic hemisphere to the other rather than symmetrically away from and towards the equator, as was expected from theory. We also reported the first observational evidence of the EPDs-related electromagnetic energy. In the same fashion, the Poynting vector described an unexpected interhemispheric flux. Moreover, the direction of both the Poynting flux and field-aligned currents showed a significant seasonal and longitudinal dependence, which we relate to the seasonal effects of ionospheric conductivity. 

In the second phase of our project, we want to improve our understanding of the underlying physics by (1) analyzing an extended data set allowing for a better seasonal and local time coverage and (2) adding simulations by physics-based models. Additionally, we plan to use conjunctions of  Swarm with a newly installed radar mode (medium incoherent scatter radar (ISR) long runs) at the equatorial Jicamarca observatory to correlate EPDs-related plasma drifts. ISR-runs will provide larger-scale pictures of the EPD dynamics supporting the Swarm in situ measurements' interpretation. This project also investigates EPD features related to outages of GPS navigation signals onboard the Swarm satellites. To this end, we will perform a frequency domain analysis of 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 before mentioned questions with multiple parameter data sets, we expect new, fundamental insights into the electromagnetic mechanisms of the upper atmosphere and significant advances in our ability to describe and forecast EPDs and, finally, to mitigate their impact on radio wave-based technological infrastructure like GPS. Knowledge of EPDs is also relevant for precise core and lithospheric magnetic field modeling since EPD-related electric currents produce systematic biases.