Magnetosphere-Ionosphere Coupling and Magnetospheric Multiscale Observations of Field-Aligned Currents Near the Dayside Magnetopause

Strangeway, Robert

Magnetosphere-Ionosphere Coupling and Magnetospheric Multiscale Observations of Field-Aligned Currents Near the Dayside Magnetopause

Friday, 14 July 2017: 11:10

Furong Room (Cynn Hotel)

Robert J Strangeway¹, Christopher T Russell², Cong Zhao¹, Werner Magnes³, Kenneth R Bromund⁴, Ferdinand Plaschke³, David Fischer³, Brian J Anderson⁵, James M Weygand¹, Guan Le⁴, Larry Kepko⁴, Mark Chutter⁶, James A Slavin⁷, Rumi Nakamura³, Wolfgang Baumjohann³, William R Paterson⁴, Barbara L Giles⁴, Daniel J Gershman⁸, Roy B Torbert⁶ and James L Burch⁹, (1)University of California Los Angeles, IGPP/EPSS, Los Angeles, CA, United States, (2)University of California Los Angeles, Earth, Planetary, and Space Sciences, Los Angeles, CA, United States, (3)Space Research Institute (IWF)/Austrian Academy of Sciences, Graz, Austria, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)Johns Hopkins University, Baltimore, MD, United States, (6)University of New Hampshire, Durham, NH, United States, (7)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (8)University of Maryland College Park, College Park, MD, United States, (9)Southwest Research Institute, San Antonio, TX, United States

Abstract:

The four-spacecraft Magnetotail Multiscale mission has acquired very high quality particles and fields data at the dayside magnetopause. These data allow us to compare field-aligned currents as calculated from the curl of the magnetic field with the currents as deduced by electron and ion measurements provided by the Fast Plasma Investigation (FPI). We find, not surprisingly, given the electron mobility, that the field-aligned current derived from the magnetic field is consistent with that obtained from the measured electron flux. In general the field-aligned current can be several hundreds of nA/m². These current densities are much larger than those typically observed at the ionosphere, after taking into account the factor of ~1000 reduction in flux-tube area when mapped to the ionosphere. This strongly suggests that most of these currents must be closed locally, via perpendicular currents. As the spacecraft move deeper into the magnetosphere the current density tends to be reduced, and can show an oscillatory signature. The dominant current does appear to be consistent with Region-1 polarity. It is not clear if the oscillations are temporal or spatial, but if the latter this may be consistent with an Alfvén wing, where the currents are reflected at a conductivity or refractive index gradient, but are also advected deeper into the magnetosphere because of the underlying plasma flow. Given the finite transit time of the waves and the particles carrying the current, understanding the mapping of the currents to the ionosphere requires models that take these finite transit-time effects into account. It is also apparent that such models should include processes that allow for more local closure of the currents.