Inverse energy dispersion of energetic ions observed in the magnetosheath. Issue 14 (22nd July 2016)

• Record Type: Journal Article
• Authors: Lee, S. H.; Sibeck, D. G.; Hwang, K.‐J.; Wang, Y.; Silveira, M. V. D.; Fok, M.‐C.; Mauk, B. H.; Cohen, I. J.; Ruohoniemi, J. M.; Kitamura, N.; Burch, J. L.; Giles, B. L.; Torbert, R. B.; Russell, C. T.; Lester, M.
• Is Part Of: Geophysical research letters. Volume 43:Issue 14(2016)
• Page Start: 7338
• Page End: 7347
• Publication Date: 2016-07-22
• Subjects: particle escape -- energetic ions -- magnetosheath -- magnetic reconnection -- solar wind‐magnetosphere interaction; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL069840
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We present a case study of energetic ions observed by the Energetic Particle Detector (EPD) on the Magnetospheric Multiscale spacecraft in the magnetosheath just outside the subsolar magnetopause that occurred at 1000 UT on 8 December 2015. As the magnetopause receded inward, the EPD observed a burst of energetic (∼50–1000 keV) proton, helium, and oxygen ions that exhibited an inverse dispersion, with the lowest energy ions appearing first. The prolonged interval of fast antisunward flow observed in the magnetosheath and transient increases in the H components of global ground magnetograms demonstrate that the burst appeared at a time when the magnetosphere was rapidly compressed. We attribute the inverse energy dispersion to the leakage along reconnected magnetic field lines of betatron‐accelerated energetic ions in the magnetosheath, and a burst of reconnection has an extent of about 1.5 R E using combined Super Dual Auroral Radar Network radar and EPD observations. Key Points: A burst of energetic proton, helium, and oxygen ions that exhibited an inverse dispersion was observed by MMS in the magnetosheath The observed inverse energy dispersion signatures can be caused by betatron acceleration that energizes the energetic magnetospheric ions The energetic ions can escape through reconnection that can be triggered by a transient solar wind dynamic pressure pulse