Upstream Ultra‐Low Frequency Waves Observed by MESSENGER's Magnetometer: Implications for Particle Acceleration at Mercury's Bow Shock

Romanelli, Norberto; DiBraccio, G. A.; Gershman, D. J.; Le, G.; Mazelle, Christian; Meziane, K.; Boardsen, S. A.; Slavin, J. A.; Raines, J. M.; Glass, A. N.; Espley, J. R.

doi:10.1029/2020gl087350

Cited by 13 publications

(28 citation statements)

References 42 publications

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“…Possibly, refraction can lead to the observed oblique propagation (Eastwood et al, 2004). Waves with similar properties also occur in the foreshocks of Mercury, Venus, and Mars (Dubinin & Fraenz, 2016;Guan Le et al, 2013;Romanelli et al, 2020;Ruhunusiri et al, 2016;Russell, 1994).…”

Section: Introductionmentioning

confidence: 99%

Properties of Plasma Waves Observed Upstream From Mars

et al. 2020

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We describe a new method to analyze the properties of plasma waves and apply it to observations made upstream from Mars by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The slow measurement cadence of most charged particle instrumentation has limited the application of analysis techniques based on correlations between particle and magnetic field measurements. We show that we can extend the frequency range of applicability for these techniques, for a subset of waves that remain nearly coherent over multiple wave periods, by subsampling velocity distribution function measurements and binning them by the wave phase. This technique enables the computation of correlations and transport ratios for plasma waves previously inaccessible to this technique at Mars. By computing the cross helicity, we find that most identified waves propagate upstream in the plasma frame. This supports the conclusions of previous studies but enables a clearer determination of the intrinsic wave mode and characteristics. The intrinsic properties of observed waves with frequencies close to the proton cyclotron frequency have little spatial variability but do have large temporal variations, likely due to seasonal changes in the hydrogen exosphere. In contrast, the predominant characteristics of waves at higher frequencies have less temporal variability but more spatial variability. We find several indications of the presence of multiple wave modes in the lower frequency wave observations, with unusual wave properties observed for propagation parallel to the magnetic field and for background magnetic fields nearly perpendicular to the solar wind flow. Plain Language Summary The interaction between the solar wind and planetary environments leads to the growth of a variety of plasma waves. These waves serve as a sensitive tracer of the physical interactions between the solar wind and local charged particle populations. Plasma waves reveal the conversion of energy between kinetic and electromagnetic forms, as well as mediating the exchange of energy between different particle populations. However, identifying the intrinsic characteristics of low-frequency plasma waves often proves quite challenging, because the solar wind sweeps them downstream, altering their properties as measured by an orbiting spacecraft. By combining magnetic field and charged particle data, one can remove some of the resulting ambiguities. However, the low cadence of many charged particle observations limits the applicability of such analyses. In this work, we describe a new technique to eke higher time resolution out of the charged particle measurements and apply it to observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, opening a new window on the properties of plasma waves at Mars.

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Section: Introductionmentioning

confidence: 99%

Properties of Plasma Waves Observed Upstream From Mars

et al. 2020

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“…Mercury constitutes an ideal natural laboratory to test this theory and previous reports, as the solar wind around Mercury is characterized by relatively low SW Alfvénic Mach number (~3-6) and beta that vary with the planet's heliocentric distance [e.g., [26][27][28][29] ]. However, the SW Alfvénic Mach number at Mercury's heliocentric distance range is expected to be above the critical value (~2-3), thus particle reflection at the bow shock is not negligible 16,23,30 . Mercury's plasma environment properties are unique in the solar system, as the solar wind Alfvén Mach number is small but sufficient for the development of a foreshock.…”

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Occurrence rate of ultra-low frequency waves in the foreshock of Mercury increases with heliocentric distance

Romanelli

DiBraccio

2021

Nat Commun

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Studies of Mercury’s foreshock have analyzed in detail the properties of ultra-low frequency waves. However, an open question remains in regards to understanding favorable conditions for these planetary foreshocks waves. Here, we report that 0.05–0.41 Hz quasi-monochromatic waves are mostly present under quasi-radial and relatively low intensity Interplanetary Magnetic Field, based on 17 Mercury years of MESSENGER Magnetometer data. These conditions are consistent with larger foreshock size and reflection of solar wind protons, their most likely source. Consequently, we find that the wave occurrence rate increases with Mercury’s heliocentric distance. Detection of these waves throughout Mercury’s highly eccentric orbit suggests the conditions for backstreaming protons are potentially present for all of Mercury’s heliocentric distances, despite the relatively low solar wind Alfvén Mach number regime. These results are relevant for planetary magnetospheres throughout the solar system, and the magnetospheres of exoplanets, and provide knowledge of particle acceleration mechanisms occurring inside foreshocks.

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“…Earlier and analytical models have shown that the hemisphere magnetically connected to is also the region of intense precipitation of solar wind particles to Mercury's surface (see e.g., Kallio & Janhunen, 2003;Massetti et al, 2003). Moreover, the IMF connected on the surface on the dawn side passed through the quasi-parallel bow shock (e.g., Figures and 3), where ULF waves have been observed (see e.g., Romanelli et al, 2020) and identified from hybrid simulations (Jarvinen et al, 2020b).…”

Section: Discussionmentioning

confidence: 95%

Ultra‐Low Frequency Waves in the Hermean Magnetosphere: On the Role of the Morphology of the Magnetic Field and the Foreshock

Kallio

Järvinen

Massetti

et al. 2022

Geophysical Research Letters

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Characterization of the properties of the Ultra-low frequency (ULF) waves in planetary magnetospheres provides a way to investigate magnetospheric dynamics and the properties of the magnetosphere, such as the density of magnetospheric plasma. The dynamics of Mercury's magnetosphere are anticipated to have unique properties as it has an intrinsic magnetic field that is weak compared to that of the Earth, but strong compared to the other terrestrial planets and the interplanetary magnetic field (IMF).A unique magnetic feature at Mercury is that the relatively low conductivity of the crust and mantle results in a rapid (timescale of minutes) transmission of magnetic field perturbations from the high-altitude solar wind interaction and magnetosphere down to the outermost layers of the iron core. These perturbations include large-scale compressions and rarefactions (

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Upstream Ultra‐Low Frequency Waves Observed by MESSENGER's Magnetometer: Implications for Particle Acceleration at Mercury's Bow Shock

Cited by 13 publications

References 42 publications

Properties of Plasma Waves Observed Upstream From Mars

Properties of Plasma Waves Observed Upstream From Mars

Occurrence rate of ultra-low frequency waves in the foreshock of Mercury increases with heliocentric distance

Ultra‐Low Frequency Waves in the Hermean Magnetosphere: On the Role of the Morphology of the Magnetic Field and the Foreshock

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