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Register a new userComparative Analysis of Dayside Reconnection Models in Global Magnetosphere Simulations
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We test and compare a number of existing models predicting the location of magnetic reconnection at Earths dayside magnetopause for various solar wind conditions. We employ robust image processing techniques to determine the locations where each model predicts reconnection to occur. The predictions are then compared to the magnetic separators, the magnetic field lines separating different magnetic topologies. The predictions are tested in distinct high-resolution simulations with interplanetary magnetic field (IMF) clock angles ranging from 30 to 165 degrees in global magnetohydrodynamic simulations using the three-dimensional Block-Adaptive Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the described techniques can be generally applied to any self-consistent magnetosphere code. Additional simulations are carried out to test location model dependence on IMF strength and dipole tilt. We find that most of the models match large portions of the magnetic separators when the IMF has a southward component, with the models saying reconnection occurs where the local reconnection rate and reconnection outflow speed are maximized performing best. When the IMF has a northward component, none of the models tested faithfully map the entire magnetic separator, but the maximum magnetic shear model is the best at mapping the separator in the cusp region where reconnection has been observed. Predictions for some models with northward IMF orientations improve after accounting for plasma flow shear parallel to the reconnecting components of the magnetic fields. Implications for observations are discussed.
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This review summarizes the research of Mercurys magnetosphere in the Post-MESSENGER era and compares its dynamics to those in other planetary magnetospheres, especially to those in Earths magnetosphere. This review starts by introducing the planet Mercury, including its interplanetary environment, magnetosphere, exosphere, and conducting core. The frequent and intense magnetic reconnection on the dayside magnetopause, which is represented by the flux transfer event shower, is reviewed on how they depend on magnetosheath plasma beta and magnetic shear angle across the magnetopause, following by how they contribute to the flux circulation and magnetosphere-surface-exosphere coupling. In the next, the progress of Mercurys magnetosphere under extreme solar events, including the core induction and the reconnection erosion on the dayside magnetosphere, the responses of the nightside magnetosphere, are reviewed. Then, the dawn-dusk properties of the plasma sheet, including the features of the ions, the structure of the current sheet, and the dynamics of magnetic reconnection, are summarized. The last topic reviews the particle energization in Mercurys magnetosphere, which includes the energization of the Kelvin-Helmholtz waves on the magnetopause boundaries, reconnection-generated magnetic structures, and the cross-tail electric field. In each chapter, the last section discusses the open questions related with each topic, which can be considered by the simulations and the future spacecraft mission. We close by summarizing the future BepiColombo opportunities, which is a joint mission between ESA and JAXA, and is en route to Mercury.
Reconnection outflows are regions of intense recent scrutiny, from in situ observations and from simulations. These regions are host to a variety of instabilities and intense energy exchanges, often even superior to the main reconnection site. We report here a number of results drawn from investigation of simulations. First, the outflows are observed to become unstable to drift instabilities. Second, these instabilities lead to the formation of secondary reconnection sites. Third, the secondary processes are responsible for large energy exchanges and particle energization. Finally, the particle distribution function are modified to become non-Maxwellian and include multiple interpenetrating populations.
Reconnection outflows are highly energetic directed flows that interact with the ambient plasma or with flows from other reconnection regions. Under these conditions the flow becomes highly unstable and chaotic, as any flow jets interacting with a medium. We report here massively parallel simulations of the two cases of interaction between outflow jets and between a single outflow with an ambient plasma. We find in both case the development of a chaotic magnetic field, subject to secondary reconnection events that further complicate the topology of the field lines. The focus of the present analysis is on the energy balance. We compute each energy channel (electromagnetic, bulk, thermal, for each species) and find where the most energy is exchanged and in what form. The main finding is that the largest energy exchange is not at the reconnection site proper but in the regions where the outflowing jets are destabilized.
Data from the NASA Magnetospheric Multiscale (MMS) mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earths magnetosphere and the solar wind (the magnetopause). High-resolution measurements of plasmas, electric and magnetic fields, and waves are used to identify highly localized (~15 electron Debye lengths) standing wave structures with large electric-field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory dissipation, which appears as alternatingly positive and negative values of J dot E (dissipation). For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the EDR. For larger guide fields the structures also occur near the reconnection x-line. This difference is explained in terms of channels for the out-of-plane current (agyrotropic electrons at the stagnation point and guide-field-aligned electrons at the x-line).
For the first time, we explore the tightly coupled interior-magnetosphere system of Mercury by employing a three-dimensional ten-moment multifluid model. This novel fluid model incorporates the non-ideal effects including the Hall effect, inertia, and tensorial pressures that are critical for collisionless magnetic reconnection; therefore, it is particularly well suited for investigating $collisionless$ magnetic reconnection in Mercurys magnetotail and at the planets magnetopause. The model is able to reproduce the observed magnetic field vectors, field-aligned currents, and cross-tail current sheet asymmetry (beyond the MHD approach) and the simulation results are in good agreement with spacecraft observations. We also study the magnetospheric response of Mercury to a hypothetical extreme event with an enhanced solar wind dynamic pressure, which demonstrates the significance of induction effects resulting from the electromagnetically-coupled interior. More interestingly, plasmoids (or flux ropes) are formed in Mercurys magnetotail during the event, indicating the highly dynamic nature of Mercurys magnetosphere.
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