The Relationship Between the Ionospheric Current System and Magnetic Field Perturbations on Ground and in Space
Monday, 23 May 2016
Karl Laundal1, Christopher C Finlay2, Nils Olsen3, Stein Haaland4, Nikolai Ostgaard1, Jone Peter Reistad1, Paul Tenfjord1, Kristian Snekvik1 and Jesper W Gjerloev5, (1)University of Bergen, Birkeland Centre for Space Science, Bergen, Norway, (2)DTU National Space Institute, København Ø, Denmark, (3)Technical University of Denmark, Kgs. Lyngby, Denmark, (4)University of Bergen, Bergen, Norway, (5)Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States
Abstract:
We investigate how the global ionospheric current system and associated magnetic field perturbations depend on sunlight. We use magnetic field measurements from ground and from low Earth orbiting satellites CHAMP and Swarm to calculate global maps of the ionospheric current system at polar latitudes. Ground magnetometers can be used to calculate the horizontal equivalent current at high latitudes. Measurements from low Earth orbit can provide both the horizontal equivalent (divergence-free) current and the field-aligned (Birkeland) currents. Statistical maps of the global current systems show that the relationship between the equivalent horizontal current, the actual horizontal current, and the Birkeland current is different in darkness and sunlight. In the polar cap, the equivalent current tends to be anti-parallel to the horizontal curl-free currents in darkness but not in sunlight. In sunlight, the equivalent current is typically anti-parallel to the convection, indicating that the Hall current system dominates. Thus on average the ground magnetic field in the polar cap is dominated by different current systems in sunlight and in darkness. Consequently large inter-hemispheric differences in high-latitude magnetic field perturbations can be expected, particularly during solstices.
