Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

Fatemi, Shahab; Holmström, Mats; Futaana, Yoshifumi; Lue, Charles; Collier, M. R.; Barabash, S.; Stenberg, G.

doi:10.1002/2014ja019900

Cited by 41 publications

(49 citation statements)

References 52 publications

(103 reference statements)

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“…Thus, ARTEMIS observations suggest an interaction driven by the reflected protons from crustal magnetic fields rather than by the magnetic fields themselves, consistent with Fatemi et al [2014].…”

Section: 1002/2014gl061973supporting

confidence: 77%

“…We note that simulation results [Fatemi et al, 2014] show the greatest solar wind flow deflection and enhancement in density and magnetic field in the hemisphere where the convection electric field points into the surface. In support of this, we have found that most events with shock-like features seen by ARTEMIS occur for a similar geometry (not shown).…”

Section: 1002/2014gl061973mentioning

confidence: 73%

“…Simulations indicate that these electric fields may form at quite low altitudes [Deca et al, 2014] and that the reflected protons can subsequently interact with the solar wind to drive a compressive interaction with similar properties to that observed by Fatemi et al [2014].…”

Section: Geophysical Research Letters Research Lettermentioning

confidence: 79%

“…However, the question of "shock" or "compression" remains unanswered, although Fatemi et al's [2014] results display features consistent with a shock, including compression, heating, and flow deflection. If shocks do exist at the Moon, they may be small, marginal, and/or infrequent, since numerous missions have not found clear evidence for the presence of a shock.…”

Section: Geophysical Research Letters Research Lettermentioning

confidence: 99%

“…Second, rather than remaining constant on the downstreamside of the discontinuity, the perturbed parameters quickly return to values close to their upstream values. This may result from the spacecraft entering the wake shortly after passing through the discontinuity and/or from the fact that the interaction must have a rather small lateral scale size and so will decay in amplitude rapidly with downstream distance, as shown by Fatemi et al [2014].…”

Section: 1002/2014gl061973mentioning

confidence: 99%

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Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Halekas

Poppe

McFadden

et al. 2014

Geophysical Research Letters

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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 supermagnetosonic to submagnetosonic 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 gyroradius and inertial length.

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Section: 1002/2014gl061973supporting

confidence: 77%

Section: 1002/2014gl061973mentioning

confidence: 73%

Section: Geophysical Research Letters Research Lettermentioning

confidence: 79%

Section: Geophysical Research Letters Research Lettermentioning

confidence: 99%

Section: 1002/2014gl061973mentioning

confidence: 99%

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Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Halekas

Poppe

McFadden

et al. 2014

Geophysical Research Letters

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Extended lunar precursor regions: Electron‐wave interaction

et al. 2014

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We present Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (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 1 lunar radius. The electron anisotropy and whistler intensity exhibit clear anticorrelation 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.

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Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

et al. 2015

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We present the results of the first local hybrid simulations (particle ions and fluid electrons) for the solar wind plasma interaction with realistic lunar crustal fields. We use a three‐dimensional hybrid model of plasma and an empirical model of the Gerasimovich magnetic anomaly based on Lunar Prospector observations. We examine the effects of low and high solar wind dynamic pressures on this interaction when the Gerasimovich magnetic anomaly is located at nearly 20∘ solar zenith angle. We find that for low solar wind dynamic pressure, the crustal fields mostly deflect the solar wind plasma, form a plasma void at very close distances to the Moon (below 20 km above the surface), and reflect nearly 5% of the solar wind in charged form. In contrast, during high solar wind dynamic pressure, the crustal fields are more compressed, the solar wind is less deflected, and the lunar surface is less shielded from impinging solar wind flux, but the solar wind ion reflection is more locally intensified (up to 25%) compared to low dynamic pressures. The difference is associated with an electrostatic potential that forms over the Gerasimovich magnetic anomaly as well as the effects of solar wind plasma on the crustal fields during low and high dynamic pressures. Finally, we show that an antimoonward Hall electric field is the dominant electric field for ∼3 km altitude and higher, and an ambipolar electric field has a noticeable contribution to the electric field at close distances (<3 km) to the Moon.

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Effects of protons reflected by lunar crustal magnetic fields on the global lunar plasma environment

Cited by 41 publications

References 52 publications

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Extended lunar precursor regions: Electron‐wave interaction

Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

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