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Found 6 entries in the Bibliography.

Showing entries from 1 through 6


Global Propagation of Magnetospheric Pc5 ULF Waves Driven by Foreshock Transients

Pc5 (2–7 mHz) ultralow frequency (ULF) waves play a significant role in resonating with particles and transferring energy in the coupled magnetospheric and ionospheric system. Recent studies found that Pc5 ULF waves can be triggered by foreshock transients which can perturb the magnetopause through dynamic pressure variation. However, whether foreshock transient-driven Pc5 ULF waves are geoeffective and can propagate globally is still poorly understood. In this study, we take advantage of the conjunction between in situ (by the THEMIS probes, Geotail satellite, GOES satellites, and Van Allen probes) and ground-based (by the all-sky imager at South Pole and ground-based magnetometers) observations to simultaneously analyze the waves from the foreshock region to the dayside and nightside magnetosphere. Both of our two events show that the Pc5 ULF waves are generated by foreshock transients in the dayside magnetosphere. The in situ observations by THEMIS A and D and the 2-D auroral signatures show that the compressional mode waves are likely broadband and coupled to the FLRs with different frequencies and different azimuthal phase speeds. This is the first report that foreshock transients can drive both low- and high-m FLRs, with the azimuthal wave numbers varying from ~5 to ~23. Moreover, the Pc5 ULF waves propagated antisunward to midnight, this can potentially modulate magnetospheric and ionospheric dynamics globally.

Wang, Boyi; Liu, Terry; Nishimura, Yukitoshi; Zhang, Hui; Hartinger, Michael; Shi, Xueling; Ma, Qianli; Angelopoulos, Vassilis; Frey, Harald;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2020

YEAR: 2020     DOI:

ULF wave; Field line resonance; wave number; global; THEMIS; aurora; Van Allen Probes


Identifying STEVE\textquoterights Magnetospheric Driver Using Conjugate Observations in the Magnetosphere and on the Ground

The magnetospheric driver of strong thermal emission velocity enhancement (STEVE) is investigated using conjugate observations when Van Allen Probes\textquoteright footprint directly crossed both STEVE and stable red aurora (SAR) arc. In the ionosphere, STEVE is associated with subauroral ion drift features, including electron temperature peak, density gradient, and westward ion flow. The SAR arc at lower latitudes corresponds to regions inside the plasmapause with isotropic plasma heating, which causes redline-only SAR emission via heat conduction. STEVE corresponds to the sharp plasmapause boundary containing quasi-static subauroral ion drift electric field and parallel-accelerated electrons by kinetic Alfv\ en waves. These parallel electrons could precipitate and be accelerated via auroral acceleration processes powered by Alfv\ en waves propagating along the magnetic field with the plasmapause as a waveguide. The electron precipitation, superimposed on the heat conduction, could explain multiwavelength continuous STEVE emission. The green picket-fence emissions are likely optical manifestations of electron precipitation associated with wave structures traveling along the plasmapause.

Chu, Xiangning; Malaspina, David; Gallardo-Lacourt, Bea; Liang, Jun; Andersson, Laila; Ma, Qianli; Artemyev, Anton; Liu, Jiang; Ergun, Robert; Thaller, Scott; Akbari, Hassanali; Zhao, Hong; Larsen, Brian; Reeves, Geoffrey; Wygant, John; Breneman, Aaron; Tian, Sheng; Connors, Martin; Donovan, Eric; Archer, William; MacDonald, Elizabeth;

Published by: Geophysical Research Letters      Published on: 11/2019

YEAR: 2019     DOI: 10.1029/2019GL082789

aurora; kinetic Alfven wave; Plasmapause; STEVE; subauroral ion drift; table red auroral arc; Van Allen Probes


Nonlinear coupling between whistler-mode chorus and electron cyclotron harmonic waves in the magnetosphere

Electromagnetic whistler-mode chorus and electrostatic electron cyclotron harmonic (ECH) waves can contribute significantly to auroral electron precipitation and radiation belt electron acceleration. In the past, linear and nonlinear wave-particle interactions have been proposed to explain the occurrences of these magnetospheric waves. By analyzing Van Allen Probes data, we present here the first evidence for nonlinear coupling between chorus and ECH waves. The sum-frequency and difference-frequency interactions produced the ECH sidebands with discrete frequency sweeping structures exactly corresponding to the chorus rising tones. The newly-generated weak sidebands did not satisfy the original electrostatic wave dispersion relation. After the generation of chorus and normal ECH waves by hot electron instabilities, the nonlinear wave-wave interactions could additionally redistribute energy among the resonant waves, potentially affecting to some extent the magnetospheric electron dynamics.

Gao, Zhonglei; Su, Zhenpeng; Xiao, Fuliang; Summers, Danny; Liu, Nigang; Zheng, Huinan; Wang, Yuming; Wei, Fengsi; Wang, Shui;

Published by: Geophysical Research Letters      Published on: 11/2018

YEAR: 2018     DOI: 10.1029/2018GL080635

aurora; Chorus wave; electron cyclotron harmonic wave; nonlinear wave-wave interaction; Radiation belt; Van Allen Probes


Correlated Pc4-5 ULF waves, whistler-mode chorus and pulsating aurora observed by the Van Allen Probes and ground-based systems

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10\textquoterights keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10\textquoterights keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS. In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4-5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth\textquoterights atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. Such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades, and may be a result of nonlinear chorus wave interactions in the equatorial region.

Jaynes, A.; Lessard, M.; Takahashi, K.; Ali, A.; Malaspina, D.; Michell, R.; Spanswick, E.; Baker, D.; Blake, J.; Cully, C.; Donovan, E.; Kletzing, C.; Reeves, G.; Samara, M.; Spence, H.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2015

YEAR: 2015     DOI: 10.1002/2015JA021380

aurora; precipitation; pulsating aurora; substorms; ULF waves; Van Allen Probes; VLF waves

Azimuthal flow bursts in the Inner Plasma Sheet and Possible Connection with SAPS and Plasma Sheet Earthward Flow Bursts

We have combined radar observations and auroral images obtained during the PFISR Ion Neutral Observations in the Thermosphere campaign to show the common occurrence of westward moving, localized auroral brightenings near the auroral equatorward boundary and to show their association with azimuthally moving flow bursts near or within the SAPS region. These results indicate that the SAPS region, rather than consisting of relatively stable proton precipitation and westward flows, can have rapidly varying flows, with speeds varying from ~100 m/s to ~1 km/s in just a few minutes. The auroral brightenings are associated with bursts of weak electron precipitation that move westward with the westward flow bursts and extend into the SAPS region. Additionally, our observations show evidence that the azimuthally moving flow bursts often connect to earthward (equatorward in the ionosphere) plasma sheet flow bursts. This indicates that rather than stopping or bouncing, some flow bursts turn azimuthally after reaching the inner plasma sheet and lead to the bursts of strong azimuthal flow. Evidence is also seen for a general guiding of the flow bursts by the large-scale convection pattern, flow bursts within the duskside convection being azimuthally turned to the west and those within the dawn cell being turned toward the east. The possibility that the SAPS-region flow structures considered here may be connected to localized flow enhancements from the polar cap that cross the nightside auroral poleward boundary and lead to flow bursts within the plasma sheet warrants further consideration.

Lyons, L.; Nishimura, Y.; Gallardo-Lacourt, B.; Nicolls, M.; Chen, S.; Hampton, D.; Bristow, W.; Ruohoniemi, J.; Nishitani, N.; Donovan, E.; Angelopoulos, V.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2015

YEAR: 2015     DOI: 10.1002/2015JA021023

aurora; convection; Flow bursts; plasma sheet; SAPS; streamers


Dynamics of the Earth\textquoterights Radiation Belts and Inner Magnetosphere

Trapped by Earth\textquoterights magnetic field far above the planet\textquoterights surface, the energetic particles that fill the radiation belts are a sign of the Sun\textquoterights influence and a threat to our technological future. In the AGU monograph Dynamics of the Earth\textquoterights Radiation Belts and Inner Magnetosphere, editors Danny Summers, Ian R. Mann, Daniel N. Baker, and Michael Schulz explore the inner workings of the magnetosphere. The book reviews current knowledge of the magnetosphere and recent research results and sets the stage for the work currently being done by NASA\textquoterights Van Allen Probes (formerly known as the Radiation Belt Storm Probes). In this interview, Eos talks to Summers about magnetospheric research, whistler mode waves, solar storms, and the effects of the radiation belts on Earth.

Schultz, Colin;

Published by: Eos, Transactions American Geophysical Union      Published on: 12/2013

YEAR: 2013     DOI: 10.1002/eost.v94.5210.1002/2013EO520007

aurora; Magnetosphere; Radiation belts; Van Allen Probes