Impact of Near-Earth Plasma Sheet Dynamics on the Ring Current Composition

Lynn M Kistler1, Christopher Mouikis1, Andrew Menz2, Harlan E Spence3, Donald G Mitchell4, Matina Gkioulidou5, Louis J Lanzerotti6, Ruth M Skoug7, Brian Larsen8, Seth G Claudepierre9, J. F. Fennell10 and J Bernard Blake9, (1)University of New Hampshire, Durham, United States, (2)University of New Hampshire, Durham, NH, United States, (3)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (4)JHU/APL, Laurel, MD, United States, (5)JHU/APL, Laurel, United States, (6)New Jersey Institute of Technology, Center for Solar-Terrestrial Research, Newark, NJ, United States, (7)Los Alamos National Laboratory, Los Alamos, NM, United States, (8)Los Alamos Natl Lab, Los Alamos, NM, United States, (9)The Aerospace Corp, Los Angeles, CA, United States, (10)The Aerospace Corporation, Space Sciences Department, EI Segundo, CA, United States
Abstract:
How the dynamics in the near-earth plasma sheet affects the heavy ion content, and therefore the ion pressure, of the ring current in Earth's magnetosphere is an outstanding question. Substorms accelerate plasma in the near-earth region and drive outflow from the aurora, and both these processes can preferentially enhance the population of heavy ions in this region. These heavy ions are then driven into the inner magnetosphere during storms. Thus understanding how the composition of the ring current changes requires simultaneous observations in the near-earth plasma sheet and in the inner magnetosphere. We use data from the CODIF instrument on Cluster and HOPE, RBSPICE, and MagEIS instruments on the Van Allen Probes to study the acceleration and transport of ions from the plasma sheet into the ring current. During the main phase of a geomagnetic storm on Aug 4-6, 2013, the Cluster spacecraft were moving inbound in the midnight central plasma sheet, while the apogees of the two Van Allen Probes were located on the duskside. The Cluster spacecraft measure the composition and spectral changes in the plasma sheet, while the Van Allen Probes measure the ions that reach the inner magnetosphere. A strong increase in 1-40 keV O+ was observed at the Cluster location during the storm main phase, and the Van Allen Probes observed both H+ and O+ being driven deep into the inner magnetosphere. By comparing the variations in phase space density (PSD) vs. magnetic moment at the Cluster and the Van Allen Probes locations, we examine how the composition changes non-adiabatically in the near-earth plasma sheet, and how those changes are propagated into the inner magnetosphere, populating the hto ion ring current.
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