Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms
Russell, C. T.; Lavraud, B.; Anderson, B. J.; Nakamura, R.; Sergeev, V. A.; Baumjohann, W.; Baker, D. N.; Fuselier, S. A.; Torbert, R. B.; Mauk, B. H.; Magnes, W.; Plaschke, F.; Khotyaintsev, Y. V.; Strangeway, R. J.; Burch, J. L.; Fischer, D.; Moore, T. E.; Varsani, A.; Giles, B. L.; Nakamura, T. K. M.; Singer, H. J.; Lindqvist, P. -A.; Jaynes, A. N.; Slavin, J. A.; Marklund, G. T.; Dorelli, J. C.; Saito, Y.; Gershman, D. J.; Schmid, D.; Argall, M. R.; Ergun, R. E.; Chutter, M.; Bromund, K. R.; Le, G.; Pollock, C. J.; Avanov, L. A.; Cohen, I. J.; Coffey, V.; Leinweber, H. K.; Kepko, E. L.; Paterson, W.; Genestreti, K.
Austria, Russia, United States, Sweden, France, Japan
Abstract
We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.