Spatiotemporal variations of electromagnetic charachteristics of equatorial plasma depletions

• Applicant: Professorin Dr. Claudia Stolle
• Subject Area: Geophysics ; Atmospheric Science
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273589349

New 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 features of the plasma depletions from Swarm satellite observations that have not been predicted by physical modelling so far. We could observe that plasma depletion related field-aligned currents are mainly flowing interhemispherically (from one 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 Poynting flux of plasma-depletions. Again, surprisingly, the Poynting flux is found to be mainly interhemispheric. Furthermore, the interhemispheric Poynting flux and field-aligned current directions shows 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) analysing an extended data set allowing for a better seasonal and local time coverage and (2) adding simulations by physics-based models. Additionally, we will use a newly installed radar mode (medium incoherent scatter radar (ISR) long runs) at the equatorial Jicamarca observatory to correlate plasma drifts before and during sunset hours with Swarm observations of plasma depletions during different seasons. ISR runs will provide larger-scale pictures of the EPD dynamics supporting the interpretation of the Swarm in situ measurements. Another aim of this project is the investigation of EPD features related to outages of GPS navigation signals on board 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 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. Knowledge on EPDs is also relevant for precise core and lithospheric magnetic field modelling since EPD-related electric currents produce systematic biases.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1788: Study of Earth system dynamics with a constellation of potential field missions
• Co-Investigator: Professor Jorge Chau, Ph.D.