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Found 4 entries in the Bibliography.

Showing entries from 1 through 4


Determining the mode, frequency, and azimuthal wave number of ULF waves during a HSS and moderate geomagnetic storm

Ultra-low frequency (ULF) waves play a fundamental role in the dynamics of the inner-magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale (MMS) mission, we characterize the evolution of ULF waves during a high-speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations (AFINO) code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the MMS spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSSs compresses the day side magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the Kelvin-Helmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner-magnetospheric and radiation belt dynamics.

Murphy, Kyle; Inglis, Andrew; Sibeck, David; Rae, Jonathan; Watt, Clare; Silveira, Marcos; Plaschke, Ferdinand; Claudepierre, Seth; Nakamura, Rumi;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2018

YEAR: 2018     DOI: 10.1029/2017JA024877

azimuthal wave number; Geomagnetic storms; mode structure; Radiation belts; ULF waves; Van Allen Probes


Lower-hybrid drift waves and electromagnetic electron space-phase holes associated with dipolarization fronts and field-aligned currents observed by the Magnetospheric Multiscale mission during a substorm

We analyse two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on August 10, 2016. The first event corresponds to a fast dawnward flow with an anti-parallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower-hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing, and with a smaller lower-hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet, we cannot rule out the possibility that the drift waves are produced by the anti-parallel current associated with the fast flows, leaving the source for the electron holes unexplained.

Contel, O.; Nakamura, R.; Breuillard, H.; Argall, M.; Graham, D.; Fischer, D.; o, A.; Berthomier, M.; Pottelette, R.; Mirioni, L.; Chust, T.; Wilder, F.; Gershman, D.; Varsani, A.; Lindqvist, P.-A.; Khotyaintsev, Yu.; Norgren, C.; Ergun, R.; Goodrich, K.; Burch, J.; Torbert, R.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Russell, C.; Magnes, W.; Strangeway, R.; Bromund, K.; Wei, H; Plaschke, F.; Anderson, B.; Le, G.; Moore, T.; Giles, B.; Paterson, W.; Pollock, C.; Dorelli, J.; Avanov, L.; Saito, Y.; Lavraud, B.; Fuselier, S.; Mauk, B.; Cohen, I.; Turner, D.; Fennell, J.; Leonard, T.; Jaynes, A.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2017

YEAR: 2017     DOI: 10.1002/2017JA024550

dipolarization front; electron hole; fast flow:Van allen Probes; Field-Aligned Current; lower-hybrid drift wave; substorm

Global observations of magnetospheric high- m poloidal waves during the 22 June 2015 magnetic storm

We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step-like frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 RE, suggesting that there exist a discrete number of drift-bounce resonance regions across L shells during storm times.

Le, G.; Chi, P.; Strangeway, R.; Russell, C.; Slavin, J.; Takahashi, K.; Singer, H.; Anderson, B.; Bromund, K.; Fischer, D.; Kepko, E.; Magnes, W.; Nakamura, R.; Plaschke, F.; Torbert, R.;

Published by: Geophysical Research Letters      Published on: 04/2017

YEAR: 2017     DOI: 10.1002/2017GL073048

field line resonances; high-m poloidal waves; magnetic storm; magnetospheric multiscale mission; ULF waves; Van Allen Probes


What frequencies of standing surface waves can the subsolar magnetopause support?

It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so-called Kruskal-Schwartzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not know. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle\textquoterights worth of solar wind data, we perform time-of-flight calculations yielding a database of KS mode frequencies. Under non-storm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be inline image mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order \textpm0.3 mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of KS modes is shown to be controlled by the dipole tilt angle.

Archer, M.; Plaschke, F.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2015

YEAR: 2015     DOI: 10.1002/2014JA020545

magnetopause; magnetosheath; Magnetosphere; Ulf; waves