A recent study shows that ionospheric plasma can have very high velocities within a narrow channel in the high-latitude ionosphere. Typical plasma flow velocities are 200 – 1000 m/s in the ionospheric F-region at about 300 km altitude. However, in this specific event plasma flow velocities reached 3300 m/s. These flows occurred in a region located to the north of east-west aligned auroral arcs during a magnetospheric substorm and were measured by the EFI instrument onboard ESA’s Swarm satellite. Since the satellite passes over Northern Scandinavia in a few minutes, it can provide a snapshot of the electric fields and currents along its orbit from south to north. The EISCAT UHF and VHF radars at Tromsø, Northern Norway, were measuring during this event by using the Finnish Special Programme time. They also measured these very strong plasma flows, with were associated with an electric field of 150 mV/m and a region of no particle precipitation and hence very low electrical conductivities. Since this event occurred shortly after the onset of a magnetospheric substorm, it was suggested that the ionospheric flows were produced by magnetic reconnection process taking place in the magnetospheric tail region and creating the so called merging line in the nightside ionosphere. While magnetospheric reconnection is a common process, these kind of fast flows spanning 1.5 deg wide region in latitude and accommodating a large potential difference have been very seldom observed. Further research is needed to study how common they are and whether they are always associated with substorm expansion phases.
Reference: Aikio, A. T., Vanhamäki, H.,Workayehu, A. B., Virtanen, I. I., Kauristie, K., Juusola, L., S. Buchert, and D. Knudsen (2018). Swarm satellite and EISCAT radar observations of a plasma flow channel in the auroral oval near magnetic midnight. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1029/2018JA025409
Schematic figure: A map showing plasma flow lines as solid curves. Over Northern Scandinavia the flow lines are concentrated within a narrow flow channel with high velocities. South of the flow channel, a westward directed electrojet current (WEJ), typical of substorm expansion phase, is flowing. Within the WEJ region, at least five auroral arcs were identified.
Last updated: 19.5.2020