Statistical Properties of Meso-scale Plasma Flows in the Nightside High-latitude Ionosphere

The field of space weather has made great strides in understanding and simulating large-scale, global responses of the Earth's upper atmosphere to various inputs from the Sun; however, the meso-scale phenomena (~30-500 km wide) that are much more dynamic and powerful in the coupled system have thus far remained uncharacterized. We therefore present key parameters of meso-scale ionospheric plasma flows in order to evaluate their relationship within the coupled system and to inform global models. We characterize meso-scale plasma flow properties in the nightside polar cap and auroral oval using 9 years of SuperDARN line-of-sight velocity data from the stations at Rankin Inlet and Saskatoon. We quantify their width, velocity, occurrence rates, duration, and orientation, and how these characteristics depend on latitude, MLT, season, substorm activity (AL), solar cycle (F10.7), and interplanetary magnetic field (IMF) clock angle. Measuring the ionospheric footpoint of magnetospheric fast flows, our analysis technique from the ground also provides a 2D picture of flows and their characteristics that spacecraft alone cannot provide. Results include: A characteristic equatorward flow width of ~180 km in the polar cap and ~140-150 km in the auroral oval. Flow velocities vary under the different conditions we studied. Equatorward polar cap flows and poleward flows everywhere have a post-midnight preference, suggesting a connection to polar cap arcs. Equatorward auroral oval flows have a pre-midnight preference, suggesting a connection to substorm-related phenomena. The location and orientation of meso-scale flows dependent on IMF clock angle suggests that meso-scale flows follow the large-scale background convection.