J. P. McFadden

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

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Publications (353)679.34 Total impact

  • 06/2015; DOI:10.1002/2015JA021211
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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.
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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.
  • R. Livi, J. McFadden
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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: We present first results from the MAVEN Solar Energetic Particle (SEP) Experiment and its relevance to understanding the loss of the martian atmosphere.
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    ABSTRACT: Highlights from the LPW instrument: electron temperature profiles; nightside ionosphere structures; wave-particle interactions; and the dust.
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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
  • AAS/Division for Planetary Sciences Meeting Abstracts; 11/2014
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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; 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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    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.
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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 · 1.68 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 · 5.87 Impact Factor
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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 · 4.46 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
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    ABSTRACT: We report observations by the dual-probe ARTEMIS mission of Moon-related electron and ion signatures obtained above the dayside lunar surface in the terrestrial magnetotail lobes. While the Moon is often thought of as a passive absorber, recent observations from Kaguya, Chandrayaan, Chang'E, and ARTEMIS indicate that plasma of lunar origin can have significant effects on the near-lunar environment. We now present new observations from ARTEMIS showing that lunar plasma can play a dominant role in the low-density environment of the terrestrial magnetotail. Two-point observations reveal that the density of plasma of lunar origin is higher than that of the ambient lobe plasma even several hundreds of kilometers above the Moon's dayside. Meanwhile, the distributions of incoming electrons exhibit modifications correlated with Moon-related populations, suggesting direct or indirect interactions of the lobe electrons with plasma of lunar origin. We also observe high-energy photoelectron emission from the dayside lunar surface, supporting the existence of large positive potentials on the lunar surface. Pickup ions with nonzero parallel-velocity components provide further evidence for positive surface potentials of tens of volts or more. ARTEMIS data reveal not only the existence of the positive surface potentials much larger than those predicted from a current-balance model based on Maxwellian plasmas, but also their significant implications for the dynamics of both the dominant Moon-originating ions and the tenuous ambient plasma populations in the tail lobe.
    Journal of Geophysical Research: Space Physics 06/2013; 118(6):n/a-n/a. DOI:10.1002/jgra.50296 · 3.44 Impact Factor

Publication Stats

7k Citations
679.34 Total Impact Points

Institutions

  • 1–2015
    • University of California, Berkeley
      • • Space Sciences Laboratory
      • • Department of Electrical Engineering and Computer Sciences
      Berkeley, California, United States
  • 1996–2012
    • SSL
      Palo Alto, California, United States
  • 2008
    • Lawrence Berkeley National Laboratory
      Berkeley, 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