Substorm‐Associated Ionospheric Flow Fluctuations During the 27 March 2017 Magnetic Storm: SuperDARN‐Arase Conjunction

• Published in: Geophysical research letters Vol. 45; no. 18; pp. 9441 - 9449
• Main Authors: Hori, T., Nishitani, N., Shepherd, S. G., Ruohoniemi, J. M., Connors, M., Teramoto, M., Nakano, S., Seki, K., Takahashi, N., Kasahara, S., Yokota, S., Mitani, T., Takashima, T., Higashio, N., Matsuoka, A., Asamura, K., Kazama, Y., Wang, S.‐Y., Tam, S. W. Y., Chang, T.‐F., Wang, B.‐J., Miyoshi, Y., Shinohara, I.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.09.2018
• Subjects: Bifurcations; Conjugates; Drift; Earth; Electric field; Electric fields; Electrons; ERG; Flow; Fluctuations; Ionosphere; Ionospheric plasma; Ionospheric plasma flow; Ionospheric propagation; Jupiter; Latitude; Magnetic storms; Magnetism; Magnetosphere; Magnetospheres; Magnetospheric substorms; Measuring instruments; M‐I coupling; Pressure; Pressure gradients; Radar; Radar networks; ring current electron; Ring currents; Satellite observation; Satellites; Storms; substorm injection; SuperDARN; ULF wave
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL079777

Super Dual Auroral Radar Network (SuperDARN) observations show that ionospheric flow fluctuations of millihertz or lower‐frequency range with horizontal velocities of a few hundred meters per second appeared in the subauroral to midlatitude region during a magnetic storm on 27 March 2017. A set of the radars have provided the first ever observations that the fluctuations propagate azimuthally both westward and eastward simultaneously, showing bifurcated phase propagation associated with substorm expansion. Concurrent observations near the conjugate site in the inner magnetosphere made by the Arase satellite provide evidence that multiple drifting clouds of electrons in the near‐Earth equatorial plane were associated with the electric field fluctuations propagating eastward in the ionosphere. We interpret this event in terms of mesoscale pressure gradients carried by drifting ring current electrons that distort field lines one after another as they drift through the inner magnetosphere, causing eastward propagating ionospheric electric field fluctuations. Plain Language Summary Midlatitude ionospheric radars called SuperDARN observed azimuthally propagating fluctuations of ionospheric plasma flow in association with substorm expansion during a magnetic storm on 27 March 2017. The radar observations have shown for the first time that the flow fluctuations bifurcate toward eastward and westward simultaneously. The Arase satellite in the near‐conjugate site of the eastward propagating ionospheric flow fluctuations in the inner magnetosphere saw repeated flux enhancement of energetic electrons. The good satellite‐radar conjunction gives observational evidence that the eastward propagating ionospheric flow fluctuations are driven by eastward drifting pressure bumps of electrons injected into the inner magnetosphere upon substorm expansion. Key Points This study shows the first ever comprehensive observation of azimuthal bifurcation of substorm‐associated ionospheric flow fluctuations The eastward propagating portion of the flow fluctuations can be mapped to electron pressure enhancements in the inner magnetosphere We propose that multiple pressure bumps of drifting energetic electrons directly cause the observed ionospheric flow fluctuations