Browsing by Author "Nakamura, R."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Anharmonic oscillatory flow braking in the Earth's magnetotail
    (Wiley, 2015) Panov, E.V.; Wolf, R.A.; Kubyshkina, M.V.; Nakamura, R.; Baumjohann, W.
    Plasma sheet bursty bulk flows often oscillate around their equilibrium position at about 10 REdowntail. The radial magnetic field, pressure, and flux tube volume profiles usually behave differently earthward and tailward of this position. Using data from five Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes, we reconstruct these profiles with the help of an empirical model and apply thin filament theory to show that the oscillatory flow braking can occur in an asymmetric potential. Thus, the thin filament oscillations appear to be anharmonic, with a power spectrum exhibiting peaks at both the fundamental frequency and the first harmonic. Such anharmonic oscillatory braking can explain the presence of the first harmonic in Pi2 pulsations (frequency doubling), which are simultaneously observed by magnetometers on the ground near the conjugate THEMIS footprints.
  • Thumbnail Image
    Item
    Cross-Scale Processes of Magnetic Reconnection
    (Springer Nature, 2023) Hwang, K.-J.; Nakamura, R.; Eastwood, J. P.; Fuselier, S. A.; Hasegawa, H.; Nakamura, T.; Lavraud, B.; Dokgo, K.; Turner, D. L.; Ergun, R. E.; Reiff, P. H.
    Various physical processes in association with magnetic reconnection occur over multiple scales from the microscopic to macroscopic scale lengths. This paper reviews multi-scale and cross-scale aspects of magnetic reconnection revealed in the near-Earth space beyond the general global-scale features and magnetospheric circulation organized by the Dungey Cycle. Significant and novel advancements recently reported, in particular, since the launch of the Magnetospheric Multi-scale mission (MMS), are highlighted being categorized into different locations with different magnetic topologies. These potentially paradigm-shifting findings include shock and foreshock transient driven reconnection, magnetosheath turbulent reconnection, flow shear driven reconnection, multiple X-line structures generated in the dayside/flankside/nightside magnetospheric current sheets, development and evolution of reconnection-driven structures such as flux transfer events, flux ropes, and dipolarization fronts, and their interactions with ambient plasmas. The paper emphasizes key aspects of kinetic processes leading to multi-scale structures and bringing large-scale impacts of magnetic reconnection as discovered in the geospace environment. These key features can be relevant and applicable to understanding other heliospheric and astrophysical systems.
  • Thumbnail Image
    Item
    Global-Scale Processes and Effects of Magnetic Reconnection on the Geospace Environment
    (Springer Nature, 2024) Fuselier, S. A.; Petrinec, S. M.; Reiff, P. H.; Birn, J.; Baker, D. N.; Cohen, I. J.; Nakamura, R.; Sitnov, M. I.; Stephens, G. K.; Hwang, J.; Lavraud, B.; Moore, T. E.; Trattner, K. J.; Giles, B. L.; Gershman, D. J.; Toledo-Redondo, S.; Eastwood, J. P.
    Recent multi-point measurements, in particular from the Magnetospheric Multiscale (MMS) spacecraft, have advanced the understanding of micro-scale aspects of magnetic reconnection. In addition, the MMS mission, as part of the Heliospheric System Observatory, combined with recent advances in global magnetospheric modeling, have furthered the understanding of meso- and global-scale structure and consequences of reconnection. Magnetic reconnection at the dayside magnetopause and in the magnetotail are the drivers of the global Dungey cycle, a classical picture of global magnetospheric circulation. Some recent advances in the global structure and consequences of reconnection that are addressed here include a detailed understanding of the location and steadiness of reconnection at the dayside magnetopause, the importance of multiple plasma sources in the global circulation, and reconnection consequences in the magnetotail. These advances notwithstanding, there are important questions about global reconnection that remain. These questions focus on how multiple reconnection and reconnection variability fit into and complicate the Dungey Cycle picture of global magnetospheric circulation.
  • Thumbnail Image
    Item
    Multispacecraft observations and modeling of the 22/23 June 2015 geomagnetic storm
    (Wiley, 2016) Reiff, P.H.; Daou, A.G.; Sazykin, S.Y.; Nakamura, R.; Hairston, M.R.; Coffey, V.; Chandler, M.O.; Anderson, B.J.; Russell, C.T.; Welling, D.; Fuselier, S.A.; Genestreti, K.J.
    The magnetic storm of 22–23 June 2015 was one of the largest in the current solar cycle. We present in situ observations from the Magnetospheric Multiscale Mission (MMS) and the Van Allen Probes (VAP) in the magnetotail, field-aligned currents from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response), and ionospheric flow data from Defense Meteorological Satellite Program (DMSP). Our real-time space weather alert system sent out a “red alert,” correctly predicting Kp indices greater than 8. We show strong outflow of ionospheric oxygen, dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS Fast Plasma Instrument suite. At ionospheric altitudes, the AMPERE data show highly variable currents exceeding 20 MA. We present numerical simulations with the Block Adaptive Tree-Solarwind - Roe - Upwind Scheme (BATS-R-US) global magnetohydrodynamic model linked with the Rice Convection Model. The model predicted the magnitude of the dipolarizations, and varying polar cap convection patterns, which were confirmed by DMSP measurements.