J. P. McFadden

University of California, Berkeley, Berkeley, California, United States

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Publications (355)670.35 Total impact

  • H. Hietala · J. F. Drake · T. D. Phan · J. P. Eastwood · J. P. McFadden
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    ABSTRACT: A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual-spacecraft observations of a long-duration magnetotail exhaust generated by anti-parallel reconnection in conjunction with Particle-In-Cell simulations, showing spatial variations in the anisotropy across the outflow far (> 100di) downstream of the X-line. A consistent pattern is found in both the spacecraft data and the simulations: Whilst the total temperature across the exhaust is rather constant, near the boundaries Ti,|| dominates. The plasma is well-above the firehose threshold within patchy spatial regions at |BX| ∈ [0.1, 0.5]B0, suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the mid-plane (|BX|0.1 B0), Ti,⊥ > Ti,|| and ions undergo Speiser-like motion despite the large distance from the X-line.
    08/2015; DOI:10.1002/2015GL065168
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    ABSTRACT: The accepted version of the above article was posted prematurely on July 2, 2015. The final version of record will be made fully available at a later date along with a special collection of related papers.
    07/2015; DOI:10.1002/2015GL064781
  • Y. Harada · J. S. Halekas · A. R. Poppe · Y. Tsugawa · S. Kurita · J. P. McFadden
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    ABSTRACT: Although the zeroth-order picture of the Moon-solar wind interaction involves no upstream perturbation, the presence of the Moon does affect the upstream plasma in a variety of ways. In this paper, a large volume of data obtained by the dual-probe Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission are used to characterize the large-scale morphology of the “foremoon,” which is defined as the region upstream of the Moon and its wake that contains Moon-related particles and waves. Solar wind ions reflected from the unshielded surface and by crustal magnetic fields, together with heavy ions of lunar surface/exospheric origin, are picked up by the solar wind magnetic and electric fields. Partially coinciding with populations of these Moon-related ions, ∼0.01 Hz and ∼1 Hz magnetic field fluctuations are observed. The morphology of the Moon-related ion and wave distributions is well organized by the upstream magnetic field direction. In addition, the low-frequency wave distributions depend on the upstream Alfvén Mach numbers, suggesting that propagation effects also play a role in determining the wave foremoon morphology. Occurrence of modified electron velocity distributions and higher-frequency, electromagnetic, and electrostatic waves is primarily controlled by magnetic connection to the Moon and its wake. These statistical results observationally demonstrate the large-scale properties of the foremoon and upstream-parameter control thereof.
    06/2015; 120(6). DOI:10.1002/2015JA021211
  • N. Kitamura · K. Seki · Y. Nishimura · J. P. McFadden
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    ABSTRACT: A statistical analysis using a long-term (over one solar cycle) photoelectron dataset obtained by the Fast Auroral SnapshoT (FAST) satellite demonstrates that photoelectron outflows has little impact on the polar wind ion flux. This result implies that it is the source region of H+ ions in the topside ionosphere and not the photoelectron flux that controls the terrestrial polar wind flux. The polar wind ion flux, estimated from electron outflow does not change with increasing net photoelectron production due to increasing solar activity. The magnitude of a self-created field-aligned potential drop is likely determined so as to equilibrate electron fluxes with ion fluxes regulated by a net production rate of H+ ions. The result suggests that the polar wind H+ ion flux from magnetized terrestrial planets, including Earth-like exoplanets, can be estimated once the composition and temperature of its atmosphere, which determine the net ion production rate, are known.
    03/2015; 42(9). DOI:10.1002/2015GL063452
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    ABSTRACT: We present the first observations of the structure and dynamics of the martian magnetosphere from MAVEN.
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    ABSTRACT: Highlights from the LPW instrument: electron temperature profiles; nightside ionosphere structures; wave-particle interactions; and the dust.
  • J. S. Halekas · J. P. McFadden · J. G. Luhmann · R. J. Lillis
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    ABSTRACT: We present MAVEN observations of a newly discovered population of solar wind protons that penetrate to low altitude by interacting with Mars' atmosphere.
  • A. R. Poppe · S. M. Curry · S. Fatemi · J. P. McFadden · G. T. Delory
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    ABSTRACT: We present a model of the neutral and ionized components of the Phobos and Deimos neutral gas tori. We discuss the possibility of detection by MAVEN.
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    ABSTRACT: The accepted version of the above article was posted prematurely on September 11, 2015. The final version of record will be made fully available at later date along with a special collection of related papers.
    01/2015; DOI:10.1002/2015GL065346
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    ABSTRACT: ARTEMIS observes structures near the Moon that display many properties commonly associated with collisionless shocks, including a discontinuity with downstream compression of magnetic field and density, heating and wave activity, and velocity deflections away from the Moon. The two-probe ARTEMIS measurements show that these features do not exist in the pristine solar wind, and thus must result from lunar influences. Discontinuity analyses indicate mass flux and heating across the boundary, with the normal velocity dropping from super-magnetosonic to sub-magnetosonic across the discontinuity. The shock location with respect to crustal magnetic fields suggests a causal relationship, implying that solar wind protons reflected from crustal fields may produce the observed structures. These observations may indicate some of the smallest shocks in the solar system (in terms of plasma scales), driven by solar wind interaction with magnetic fields on the order of the ion gyro-radius and inertial length.
    11/2014; 41(21). DOI:10.1002/2014GL061973
  • Y. Harada · J. S. Halekas · A. R. Poppe · S. Kurita · J. P. McFadden
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    ABSTRACT: We present ARTEMIS observations of electron-wave interactions which extend to quite large distances upstream from the Moon. We first study electron velocity distributions and wave spectra on an event basis. In both the solar wind and terrestrial plasma sheet, we observe strong whistler wave activity on the magnetic field lines connected to the dayside lunar surface. These whistlers are most likely driven by the anisotropy of upward electrons caused by surface absorption. The whistler growth rates computed from the measured electron distributions successfully reproduced the spectral characteristics of the observed ~100 Hz narrowband oscillations and those reaching lower frequencies. Meanwhile, the incoming solar wind strahl beam is occasionally isotropized near the Moon and broadband electrostatic waves are observed simultaneously, suggesting streaming instabilities between the incoming and outgoing beams. Based on the case study, we statistically survey the spatial variations of the characteristic quantities of the upstream electron-wave interactions. Both the electron anisotropy and electromagnetic wave intensity decay with increasing field-line distances but remain higher than the ambient level at 6 lunar radii (~10,000 km) or more. The strahl electron isotropization and electrostatic waves are found mainly at lower altitudes below one lunar radius. The electron anisotropy and whistler intensity exhibit clear anti-correlation with crustal magnetic fields, indicating that the magnetic anomalies suppress the whistler wave growth. The ARTEMIS observations convincingly illustrate that the lunar influence on electrons reaches out to 6 lunar radii or more upstream from the Moon.
    Journal of Geophysical Research: Space Physics 11/2014; 119(11). DOI:10.1002/2014JA020618 · 3.44 Impact Factor
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    ABSTRACT: We have performed a detailed analysis of plasma and wave observations in a magnetic flux rope encountered by THEMIS-D at the subsolar magnetopause. The extent of the flux rope was ~ 270 ion skin depths in the outflow direction and it was flanked by two active X-lines producing colliding plasma jets in the flux rope core where ion heating and supra-thermal electrons were observed. The colliding jet region was highly dynamic and characterized by enhanced wave power in a broad frequency range. High frequency waves, including ion acoustic like waves, electron holes, and whistler mode waves were observed in a limited spatial region near the flux rope center and did not appear to be associated with the observed large-scale heating and energization. Low frequency kinetic Alfvén waves (KAWs), on the other hand, were enhanced in the entire flux rope core, suggesting a possible link with the observed ion heating.
    Journal of Geophysical Research: Space Physics 08/2014; 119(8). DOI:10.1002/2014JA020124 · 3.44 Impact Factor
  • J. S. Halekas · A. R. Poppe · J. P. McFadden
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    ABSTRACT: The lunar plasma wake refills from all directions, with processes operating both parallel and perpendicular to the magnetic field. The resulting wake structure depends sensitively on the properties of the flowing plasma, including the form of the ion and electron velocity distributions. In this manuscript, we discuss theoretical approximations for the refilling of the lunar wake along the magnetic field. While an often-used treatment for the parallel refilling assumes cold ions, one can derive solutions for arbitrary ion velocity distributions. Similarly, though the most tractable theory utilizes Maxwellian electrons, one can derive solutions for other types of distributions. We discuss the theoretical framework for various one-dimensional solutions, spanning the full range from cold ion theories to gas-dynamic solutions, and utilizing both Maxwellian and kappa electron distributions. We compare these solutions to ARTEMIS observations of the lunar wake, for time periods with appropriate plasma parameters. We also present cases that reveal the inherent limitations of one-dimensional approximations, including those related to electron anisotropies and those related to perpendicular processes associated with both fluid flow and ion gyro-motion.
    Journal of Geophysical Research: Space Physics 07/2014; 119(7). DOI:10.1002/2014JA020083 · 3.44 Impact Factor
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    G. Q. Yan · F. S. Mozer · C. Shen · T. Chen · G. K. Parks · C. L. Cai · J. P. McFadden
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    ABSTRACT: THEMIS observed several magnetopause crossings periodically at the duskside of magnetopause under southward IMF, with significant sunward returning flows inside the magnetopause. The vortex features of the flows and the periodic enhancements in the calculated vorticity normal to the spacecraft plane could be found in the observation. The distortion of the magnetopause, the periodic features of vortex flows, the tailward propagation, and the evaluation of Kelvin-Helmholtz instability (KHI) condition support the evidence of the Kelvin-Helmholtz vortices produced by the velocity shear at the duskside of magnetopause. Based on three-point simultaneous observations of the flow, the vorticity was calculated to be about 0.15 s-1, similar to previous results. The tailward propagation of the vortices along the flank magnetopause was estimated about 292 km/s. The circular induced electric field of several mV/m was deduced perpendicular to the magnetic field when the magnetic field compression occurred at the edge of the vortices.
    07/2014; 41(13). DOI:10.1002/2014GL060589
  • J. S. Halekas · A. R. Poppe · J. P. McFadden
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    ABSTRACT: ARTEMIS measures the ionized constituents of the exosphere, providing a long-term exospheric dataset covering ~2.5 years, including the LADEE mission.
  • S. Machida · Y. Miyashita · A. Ieda · M. Nosé · V. Angelopoulos · J. P. McFadden
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    ABSTRACT: To investigate the physical mechanism responsible for substorm triggering, we performed a superposed-epoch analysis using plasma and magnetic-field data from THEMIS probes. Substorm onset timing was determined based on auroral breakups detected by all-sky imagers at the THEMIS ground-based observatories. We found earthward flows associated with north-south auroral streamers during the substorm growth phase. At around X = -12 Earth radii (RE), the northward magnetic field and its elevation angle decreased markedly approximately 4 min before substorm onset. Moreover, a northward magnetic-field increase associated with pre-onset earthward flows was found at around X = -17 RE. This variation indicates that local dipolarization occurs. Interestingly, in the region earthwards of X = -18 RE, earthward flows in the central plasma sheet (CPS) reduced significantly approximately 3 min before substorm onset, which was followed by a weakening of dawn-/duskward plasma-sheet boundary-layer flows (subject to a 1 min time lag). Subsequently, approximately 1 min before substorm onset, earthward flows in the CPS were enhanced again and at the onset, tailward flows started at around X = -20 RE. Following substorm onset, an increase in the northward magnetic field caused by dipolarization was found in the near-Earth region. Synthesizing these results, we confirm our previous results based on GEOTAIL data, which implied that significant variations start earlier than both current disruption and magnetic reconnection, at approximately 4 min before substorm onset roughly halfway between the two regions of interest; i.e. in the catapult current sheet.
    Annales Geophysicae 01/2014; 32(2). DOI:10.5194/angeo-32-99-2014 · 1.71 Impact Factor
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    ABSTRACT: The Solar Wind Ion Analyzer (SWIA) on the MAVEN mission will measure the solar wind ion flows around Mars, both in the upstream solar wind and in the magneto-sheath and tail regions inside the bow shock. The solar wind flux provides one of the key energy inputs that can drive atmospheric escape from the Martian system, as well as in part controlling the structure of the magnetosphere through which non-thermal ion escape must take place. SWIA measurements contribute to the top level MAVEN goals of characterizing the upper atmosphere and the processes that operate there, and parameterizing the escape of atmospheric gases to extrapolate the total loss to space throughout Mars' history. To accomplish these goals, SWIA utilizes a toroidal energy analyzer with electrostatic deflectors to provide a broad 360∘×90∘ field of view on a 3-axis spacecraft, with a mechanical attenuator to enable a very high dynamic range. SWIA provides high cadence measurements of ion velocity distributions with high energy resolution (14.5 %) and angular resolution (3.75∘×4.5∘ in the sunward direction, 22.5∘×22.5∘ elsewhere), and a broad energy range of 5 eV to 25 keV. Onboard computation of bulk moments and energy spectra enable measurements of the basic properties of the solar wind at 0.25 Hz.
    Space Science Reviews 11/2013; DOI:10.1007/s11214-013-0029-z · 6.28 Impact Factor
  • J. S. Halekas · A. R. Poppe · J. P. McFadden · K.-H. Glassmeier
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    ABSTRACT: For the unique case of magnetic field parallel to the solar wind flow, a column of reflected protons can accumulate upstream from the Moon. We investigate observations from the ARTEMIS probes for an extended period with this geometry. During this time, P2 observes strong wave turbulence in two frequency bands above and below the ion cyclotron frequency near the Moon, not seen by P1 farther from the Moon. The lower frequency oscillations prove consistent with kinetic magnetosonic waves resonantly generated by reflected protons, and test particle calculations confirm that a significant column of reflected protons lies upstream when the waves occur. The reflected protons perturb a large volume of plasma around the Moon, extending upstream as well as into the wake. The waves observed near the Moon during this time period have many similarities to those found in the terrestrial foreshock and at comets, suggesting the potential for comparative studies.
    Geophysical Research Letters 09/2013; 40(17):4544-4548. DOI:10.1002/grl.50892 · 4.20 Impact Factor
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    ABSTRACT: We report on the time evolution of energetic neutral atom (ENA) emissions measured by the Interstellar Boundary Explorer (IBEX) during instances of compressed and expanded dayside magnetosheath. The ENA observations, taken during the passage of a corotating interaction region on 27 and 28 November 2010, are compared with in situ observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft. IBEX's field of view (6.5° full width at half maximum) covered a wide region of the dayside magnetosheath for several days, providing continuous information from that region. The high sensitivity and high‐energy resolution of IBEX instruments enabled unprecedented remote‐sensing diagnostics of dayside magnetosheath ENA spectra at energies between ~0.1 and ~6 keV, which can be directly compared with various upstream parameters. The inferred plasma spectra from ENA observations showed characteristic suprathermal tails described by kappa distributions that correlate well with the solar wind cone angle and are in agreement with in situ observations, suggesting that the shock angle contributed to magnetosheath particle heating. Simultaneous in situ ion measurements in the dayside magnetosheath provided by THEMIS agree reasonably well with IBEX‐inferred spectra, demonstrating synergy between remote IBEX ENA observations (global) and in situ measurements (local) for studying localized magnetospheric processes.
    06/2013; 118(6). DOI:10.1002/jgra.50353

Publication Stats

8k Citations
670.35 Total Impact Points


  • 1–2015
    • University of California, Berkeley
      • • Space Sciences Laboratory
      • • Department of Electrical Engineering and Computer Sciences
      Berkeley, California, United States
  • 2008
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
  • 1996
    • SSL
      Palo Alto, California, United States
  • 1991
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 2
    • University of California, Los Angeles
      • Department of Atmospheric and Oceanic Sciences (AOS)
      Los Angeles, CA, United States