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  • 1
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    Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks (2019)
    In:  Other Sources
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    Publication Date: 2019-05-22
    Description: We present recent high time resolution observations from an oblique (43 deg) shock crossing from the Magnetospheric Multiscale mission. Short-duration bursts between 10 and 100 ms of ion acoustic waves are observed in this event alongside a persistent reflected ion population. High time resolution (150 ms) particle measurements show strongly varying ion distributions between successive measurements, implying that they are bursty and impulsive by nature. Such signatures are consistent with ion bursts that are impulsively reflected at various points within the shock. We find that, after instability analysis using a Fried-Conte dispersion solver, the insertion of dispersive ion bursts into an already stable ion distribution can lead to wave growth in the ion acoustic mode for short durations of time. We find that impulsively reflected ions are a plausible mechanism for ion acoustic wave growth in the terrestrial bow shock and, furthermore, suggest that wave growth can lead to a small but measurable momentum exchange between the solar wind ions and the reflected population.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN68433 , Journal of Geophysical Research: Space Physics (e-ISSN 2169-9402); 124; 3; 1855-1865
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  • 2
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    THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) 〉 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN10607 , Geophysical Research Letters (ISSN 1944-8007); 40; 12; 2884–2890,
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  • 3
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    Characteristics of Electron Distributions Observed During Large Amplitude Whistler Wave Events in the Magnetosphere (2010)
    In:  CASI
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    Publication Date: 2019-07-19
    Description: We present a statistical study of the characteristics of electron distributions associated with large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data as an addition of the study by Kellogg et al., [2010b]. We identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics dependent upon the observed electron distributions. The majority of the waveforms observed in our study have f/fce 〈 or = 0.5 and are observed primarily in the radiation belts outside the plasmapause simultaneously with anisotropic electron distributions. We also present an example waveform capture of the largest magnetic field amplitude (〉 or = 8 nT pk-pk) whistler wave measured in the radiation belts. The majority of the largest amplitude whistlers occur during magnetically active periods (AE 〉 200 nT).
    Keywords: Geophysics
    Type: 2010 AGU (American Geophysical Union) Fall Meeting; Dec 13, 2010 - Dec 17, 2010; San Francisco, CA; United States
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  • 4
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    Atypical Particle Heating at a Supercritical Interplanetary Shock (2010)
    In:  CASI
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    Publication Date: 2019-07-19
    Description: We present the first observations at an interplanetary shock of large amplitude (〉 100 mV/m pk-pk) solitary waves and large amplitude (approx.30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.
    Keywords: Solar Physics
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  • 5
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    The Statistical Properties of Solar Wind Temperature Parameters Near 1 Au (2018)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present a long-duration (approx. 10 yr) statistical analysis of the temperatures, plasma betas, and temperature ratios for the electron, proton, and alpha-particle populations observed by the Wind spacecraft near 1 au. The mean(median) scalar temperatures are T(sub e)(sub tot) = 12.2(11.9) eV, T(sub p)(sub tot) = 12.7(8.6) eV, and T(sub a)(sub tot) = 23.9(10.8) eV. The mean(median) total plasma betas are Beta(sub e)(sub tot) = 2.31(1.09), Beta(sub p)(sub tot) = 1.79(1.05), and Beta(sub a)(sub tot) = 0.17(0.05). The mean(median) temperature ratios are (T(sub e)/T(sub p))(sub tot) = 1.64(1.27), (T(sub e)/T(sub a))(sub tot) = 1.24(0.82), and (T(sub a)/T(sub p))(sub tot) = 2.50(1.94). We also examined these parameters during time intervals that exclude interplanetary (IP) shocks, times within the magnetic obstacles (MOs) of interplanetary coronal mass ejections (ICMEs), and times that exclude MOs. The only times that show significant alterations to any of the parameters examined are those during MOs. In fact, the only parameter that does not show a significant change during MOs is the electron temperature. Although each parameter shows a broad range of values, the vast majority are near the median. We also compute particleparticle collision rates and compare to effective waveparticle collision rates. We find that, for reasonable assumptions of wave amplitude and occurrence rates, the effect of waveparticle interactions on the plasma is equal to or greater than the effect of Coulomb collisions. Thus, waveparticle interactions should not be neglected when modeling the solar wind.
    Keywords: Plasma Physics
    Type: GSFC-E-DAA-TN57364 , The Astrophysical Journal Supplement Series (ISSN 0067-0049) (e-ISSN 1538-4365); 236; 41; No. 2
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  • 6
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    MMS Observations of Electrostatic Waves in an Oblique Shock Crossing (2018)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: High-resolution particle and wave measurements taken during an oblique bow shock crossing by the Magnetospheric Multiscale (MMS) mission are analyzed. Two regions of differing magnetic behavior are identified within the shock, one with active magnetic fluctuations and one with laminar interplanetary magnetic field topology. A prominent reflected ion population is observed in both regions. The active magnetic region is characterized by large-amplitude (〉100 mV/m) electrostatic solitary waves, electron Bernstein waves, and ion acoustic waves, along with intermittent current activity and localized electron heating. In the region of laminar magnetic field, ion acoustic waves are prominently observed. Solar wind ion deceleration is observed in both regions of active and laminar magnetic field. All observations suggest that solar wind deceleration can occur as a result of multiple independent processes, in this case current and ion-ion instabilities.
    Keywords: Solar Physics
    Type: GSFC-E-DAA-TN65409 , Journal of Geophysical Research: Space Physics (e-ISSN 2169-9402); 123; 11; 9430-9442
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  • 7
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    Kinetic Properties of an Interplanetary Shock Propagating Inside a Coronal Mass Ejection (2018)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We investigate the kinetic properties of a typical fast-mode shock inside an interplanetary coronal mass ejection (ICME) observed on 1998 August 6 at 1 au, including particle distributions and wave analysis with the in situ measurements from Wind. Key results are obtained concerning the shock and the shock-ICME interaction at kinetic scales: (1) gyrating ions, which may provide energy dissipation at the shock in addition to wave-particle interactions, are observed around the shock ramp; (2) despite the enhanced proton temperature anisotropy of the shocked plasma, the low plasma beta inside the ICME constrains the shocked plasma under the thresholds of the ion cyclotron and mirror-mode instabilities; (3) whistler heat flux instabilities, which can pitch-angle scatter halo electrons through a cyclotron resonance, are observed around the shock, and can explain the disappearance of bi-directional electrons (BDEs) inside the ICME together with normal betatron acceleration; (4) whistler waves near the shock are likely associated with the whistler heat flux instabilities excited at the shock ramp, which is consistent with the result that the waves may originate from the shock ramp; (5) the whistlers share a similar characteristic with the shocklet whistlers observed by Wilson et al., providing possible evidence that the shock is decaying because of the strong magnetic field inside the ICME.
    Keywords: Plasma Physics
    Type: GSFC-E-DAA-TN57040 , The Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 859; L4; No. 1
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  • 8
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    A Database of Interplanetary and Interstellar Dust Detected by the Wind Spacecraft (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: It was recently discovered that the WAVES instrument on the Wind spacecraft has been detecting, in situ, interplanetary and interstellar dust of approximately 1 micron radius for the past 22 years. These data have the potential to enable advances in the study of cosmic dust and dust-plasma coupling within the heliosphere due to several unique properties: the Wind dust database spans two full solar cycles; it contains over 107,000 dust detections; it contains information about dust grain direction of motion; it contains data exclusively from the space environment within 350 Earth radii of Earth; and it overlaps by 12 years with the Ulysses dust database. Further, changes to the WAVES antenna response and the plasma environment traversed by Wind over the lifetime of the Wind mission create an opportunity for these data to inform investigations of the physics governing the coupling of dust impacts on spacecraft surfaces to electric field antennas. A Wind dust database has been created to make the Wind dust data easily accessible to the heliophysics community and other researchers. This work describes the motivation, methodology, contents, and accessibility of the Wind dust database.
    Keywords: Space Sciences (General)
    Type: GSFC-E-DAA-TN37663 , Journal of Geophysical Research: Space Physics; 121; 10; 9369–9377
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  • 9
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    On the Connection Between Microbursts and Nonlinear Electronic Structures in Planetary Radiation Belts (2016)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Using a dynamical-system approach, we have investigated the efficiency of large-amplitude whistler waves for causing microburst precipitation in planetary radiation belts by modeling the microburst energy and particle fluxes produced as a result of nonlinear wave-particle interactions. We show that wave parameters, consistent with large amplitude oblique whistlers, can commonly generate microbursts of electrons with hundreds of keV-energies as a result of Landau trapping. Relativistic microbursts (greater than 1 MeV) can also be generated by a similar mechanism, but require waves with large propagation angles Theta (sub k)B greater than 50 degrees and phase-speeds v(sub phi) greater than or equal to c/9. Using our result for precipitating density and energy fluxes, we argue that holes in the distribution function of electrons near the magnetic mirror point can result in the generation of double layers and electron solitary holes consistent in scales (of the order of Debye lengths) to nonlinear structures observed in the radiation belts by the Van Allen Probes. Our results indicate a relationship between nonlinear electrostatic and electromagnetic structures in the dynamics of planetary radiation belts and their role in the cyclical production of energetic electrons (E greater than or equal to 100 keV) on kinetic timescales, which is much faster than previously inferred.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN30953 , The Astrophysical Journal (e-ISSN 2041-8213); 816; 2; 51
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  • 10
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    A Vortical Dawn Flank Boundary Layer for Near-Radial IMF: Wind Observations on 24 October 2001 (2014)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: We present an example of a boundary layer tailward of the dawn terminator which is entirely populated by rolled-up flow vortices. Observations were made by Wind on 24 October 2001 as the spacecraft moved across the region at the X plane approximately equal to 13 Earth radii. Interplanetary conditions were steady with a near-radial interplanetary magnetic field (IMF). Approximately 15 vortices were observed over the 1.5 hours duration of Wind's crossing, each lasting approximately 5 min. The rolling up is inferred from the presence of a hot tenuous plasma being accelerated to speeds higher than in the adjoining magnetosheath, a circumstance which has been shown to be a reliable signature of this in single-spacecraft observations. A blob of cold dense plasma was entrained in each vortex, at whose leading edge abrupt polarity changes of field and velocity components at current sheets were regularly observed. In the frame of the average boundary layer velocity, the dense blobs were moving predominantly sunward and their scale size along the X plane was approximately 7.4 Earth radii. Inquiring into the generation mechanism of the vortices, we analyze the stability of the boundary layer to sheared flows using compressible magnetohydrodynamic Kelvin-Helmholtz theory with continuous profiles for the physical quantities. We input parameters from (i) the exact theory of magnetosheath flow under aligned solar wind field and flow vectors near the terminator and (ii) the Wind data. It is shown that the configuration is indeed Kelvin-Helmholtz (KH) unstable. This is the first reported example of KH-unstable waves at the magnetopause under a radial IMF.
    Keywords: Plasma Physics; Solar Physics; Geophysics
    Type: GSFC-E-DAA-TN22214 , Journal of Geophysical Research: Space Physics ; 119; 6; 4572-4590
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