Statistical Properties of Mesoscale Plasma Flows in the Nightside High‐Latitude Ionosphere. Issue 8 (15th August 2018)

• Record Type: Journal Article
• Authors: Gabrielse, Christine; Nishimura, Yukitoshi; Lyons, Larry; Gallardo‐Lacourt, Beatriz; Deng, Yue; Donovan, Eric
• Is Part Of: Journal of geophysical research. Volume 123:Issue 8(2018)
• Page Start: 6798
• Page End: 6820
• Publication Date: 2018-08-15
• Subjects: mesoscale -- MI coupling -- plasma flows -- SuperDARN -- convection -- ionosphere; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA025440
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: 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 mesoscale phenomena (~30–500 km wide) that are much more dynamic and powerful in the coupled system have remained uncharacterized. We therefore present key parameters of mesoscale ionospheric plasma flows in order to evaluate their relationship within the coupled system and to inform global models. We characterize mesoscale plasma flow properties in the nightside polar cap and auroral oval using nine years of Super Dual Auroral Radar Network (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, magnetic local time (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 2‐D 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 postmidnight preference, suggesting a connection to polar cap arcs. Equatorward auroral oval flows have a premidnight preference, suggesting a connection to substorm‐related phenomena. The location and orientation of mesoscale flows dependent on IMF clock angle suggests that mesoscale flows follow the large‐scale background convection. Plain Language Summary: Space weather models do well at predicting global, large‐scale phenomena in Earth's upper atmosphere based on what the solar wind is doing. However, these models miss the smaller‐scale phenomena that are very dynamic and important to the system. They get washed out by the Earth's global reaction to the Sun. It is therefore necessary to study these smaller phenomena to know how big they are, how long they last, where they occur, and under what conditions they occur. We answer these questions by using radar stations on Earth's surface to measure fast flows of charged particles in Earth's upper atmosphere. We find that flow width does not change with the changing solar wind or changing space weather—they are usually ~180 km wide in the polar cap and ~140–150 km wide in the latitudes where the aurora occur. Flow speeds do depend on space weather, though. Faster flows occur in the auroral region during big space weather events. Fast flows occur in the polar cap when the Sun is more active. These flows are oriented in the direction of the global flows that always exist in the upper atmosphere. In our paper we also relate them to other space weather phenomena. Key Points: Nine years of SuperDARN data were used to build an empirical model of mesoscale ionospheric plasma flows and their characteristics Polar cap flows have postmidnight preference like polar cap arcs. Auroral oval flows have premidnight preference like substorm phenomena Flow orientation dependence on IMF B Y suggests that mesoscale flows have a tendency to be aligned with large‐scale background convection