Rarefaction and compressional standing slow mode structures in Mercury's magnetosheath: 3D MHD simulations

Pantellini, Filippo; Griton, Léa; Varela, J.

doi:10.1016/j.pss.2015.04.007

Cited by 10 publications

(12 citation statements)

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“…However, when considering planetary heavy ions with their gyroradii comparable to Mercury's radius, individual ion motion needs to be taken into account. Both hybrid (Fatemi et al., 2018; Herčík et al., 2013; Müller et al., 2012; Parunakian et al., 2017; Richer et al., 2012; Trávníček et al., 2010) and magnetohydrodynamics (MHD) models (Jia et al., 2015, 2019; Pantellini et al., 2015; Varela et al., 2016; Yagi et al., 2010) have been applied to describe solar wind dynamics near Mercury. As we analyze the feedback of exospheric sodium ions onto Mercury's magnetosphere, which have a pickup gyroradius of about 2.4 R M , the application of a hybrid model is indeed mandatory.…”

Section: Hybrid Model Aikefmentioning

confidence: 99%

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

et al. 2020

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Mercury is embedded in a tenuous and highly anisotropic sodium exosphere, generated mainly by plasma‐surface interactions. The absolute values of the sodium ion density are still under debate. Observations by MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) instrument suggest the density of exospheric ions to be several orders of magnitude lower than the upstream solar wind density, indicating that the sodium exosphere has no substantial influence on the magnetospheric current systems. However, MESSENGER magnetic field observations of field line resonances revealed sodium ion densities comparable to the upstream solar wind density. To investigate how a dense exosphere would affect the current systems within Mercury's magnetosphere, we apply an established hybrid (kinetic ions, fluid electrons) model and conduct multiple model runs with gradually increasing exospheric density, ranging from no sodium ions at all to comet‐like configurations. We demonstrate how a sufficiently dense exosphere leads to self‐shielding of the sodium ion population from the ambient electric field and a significant inflation and symmetrization of Mercury's magnetosphere, which is decreasingly affected by the dipole offset. Once the sodium ion density is sufficiently high, Region 2 field‐aligned currents emerge close to the planet. The modeled Region 2 currents are located below the orbit of MESSENGER, thereby providing a possible explanation for the absence of these currents in observations. The sodium exosphere also closes a significant fraction of the Region 1 currents through Pedersen and Hall currents before the “guiding” magnetic field lines even reach the planetary surface. The modeled sodium ion and solar wind densities agree well with observations.

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Section: Hybrid Model Aikefmentioning

confidence: 99%

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

et al. 2020

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“…This is not surprising, as the parameter a is substantially larger than unity, in which case equation 18, which has been used to compute θ app , provides an excellent approximation. As suggested by Pantellini et al (2015), standing slow mode fronts possibly form downstream of planetary bow shocks (the magnetosheath) where the plasma flow velocity vector and the magnetic field vector are nearly parallel to each other (i.e. ∆ f 1).…”

Section: Sample Application For the Slow Modementioning

confidence: 99%

“…The interaction of the solar wind with any of the magnetized planets of the solar system produces such fronts in the form of a bow shock. Figure 12 shows a plane cut through a three-dimensional simulation of Mercury's magnetosphere (parameters are those of Pantellini et al (2015)) with the solar wind flow streaming from left to right. Simulation parameters are such that the solar wind flow, the solar wind magnetic field, and the planet's magnetic axis are in the plane shown in Figure 12.…”

Section: Sample Application For the Fast Modementioning

confidence: 99%

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Identification of standing fronts in steady state fluid flows: exact and approximate solutions for propagating MHD modes

Pantellini

Griton

2016

Astrophys Space Sci

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International audienceThe spatial structure of a steady state plasma flow is shaped by the standing modes with local phase velocity exactly opposite to the flow velocity. The general procedure of finding the wave vectors of all possible standing MHD modes in any given point of a stationary flow requires numerically solving an algebraic equation. We present the graphical procedure (already mentioned by some authors in the 1960's) along with the exact solution for the Alfvén mode and approximate analytic solutions for both fast and slow modes. The technique can be used to identify MHD modes in space and laboratory plasmas as well as in numerical simulations

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“…Among these structures this study is focus in the slow modes. The slow modes are standing structures in the magnetosheath, extensively analyzed in the Earth magnetosphere [9,10,11] and recently in the Hermean magnetosphere [12]. Numerical analysis of slow modes in Mercury predict the existence of slow modes fronts and eventually slow mode shocks just upstream of the magnetopause, particularly strong in the regions with large magnetic shear near the reconnection points.…”

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confidence: 99%