Source: https://www.nature.com/articles/nphys3879?error=cookies_not_supported&code=48f2a4c8-bf23-4c74-9afd-abc8b0abf322
Timestamp: 2019-04-21 21:25:01+00:00

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Violent releases of space plasma energy from the Earth’s magnetotail during substorms produce strong electric currents and bright aurora. But what modulates these currents and aurora and controls dissipation of the energy released in the ionosphere? Using data from the THEMIS fleet of satellites and ground-based imagers and magnetometers, we show that plasma energy dissipation is controlled by field-aligned currents (FACs) produced and modulated during magnetotail topology change and oscillatory braking of fast plasma jets at 10–14 Earth radii in the nightside magnetosphere. FACs appear in regions where plasma sheet pressure and flux tube volume gradients are non-collinear. Faster tailward expansion of magnetotail dipolarization and subsequent slower inner plasma sheet restretching during substorm expansion and recovery phases cause faster poleward then slower equatorward movement of the substorm aurora. Anharmonic radial plasma oscillations build up displaced current filaments and are responsible for discrete longitudinal auroral arcs that move equatorward at a velocity of about 1 km s−1. This observed auroral activity appears sufficient to dissipate the released energy.
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We acknowledge NASA contract NAS5-02099 for use of data from the THEMIS Mission and, specifically, for the use of FGM data supported through the German Ministry for Economy and Technology and the German Center for Aviation and Space (DLR) under contract 50 OC 0302. For the GBO/ASIs, we acknowledge S. Mende and E. Donovan, NASA contract NAS5-02099 and the CSA for logistical support in fielding and data retrieval from the GBO stations. The authors gratefully acknowledge AUTUMN, CANMOS, CARISMA, DTU, GIMA, MACCS, McMAC, STEP, THEMIS and USGS for the use of ground-based magnetic field data over Greenland and North America. The work of M.V.K. was supported by RFBR grant 16-05-00470. The work of E.V.P. and R.N. was partly supported by the Austrian Science Fund (FWF) I2016-N20 and by the Seventh Framework European Commission Programme (FP7, project 269198 Geoplasmas). The authors thank O. Amm for helping with ionospheric currents calculations, J. Hohl for helping with editing, and K.-H. Glaßmeier, O. Panova, A. A. Petrukovich, V. A. Sergeev and F. R. Toffoletto for insightful discussions.
E.V.P. developed the research and did the main part of the data analysis; R.A.W. applied analytical thin filament calculations; W.B. and R.A.W. provided theoretical insight into interpretation of the observational data; R.N. and V.A. contributed to the data interpretation and manuscript preparation; J.M.W. applied the spherical elementary currents (SECSs) method to the ground magnetometer data; M.V.K. applied the AM-03 model to THEMIS data and traced THEMIS probes’ ionospheric footprints; E.V.P. wrote the manuscript, with revisions provided by V.A., W.B., R.N. and R.A.W.; all authors contributed to the discussion of the results and manuscript.
Correspondence to E. V. Panov.

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