Preprints
https://doi.org/10.5194/angeo-2021-35
https://doi.org/10.5194/angeo-2021-35

  28 Jun 2021

28 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal ANGEO.

Magnetotail Reconnection Asymmetries in a Small, Earth-Like Magnetosphere

Christopher Bard and John Dorelli Christopher Bard and John Dorelli
  • Geospace Physics Lab, NASA Goddard Space Flight Center

Abstract. We use a newly developed global Hall MHD code to investigate how reconnection drives magnetotail asymmetries in small magnetospheres. Here, we consider a scaled-down, Earth-like magnetosphere where the ion inertial length (δi) is artificially inflated to one planetary radius (the real Earth's δi ≈ 1/15–1/20 RE in the magnetotail). This results in a magnetotail width on the order of 30 δi, slightly smaller than Mercury's tail and much smaller than Earth's. At this small size, we find that the Hall effect has significant impact on the global flow pattern, changing from a symmetric, Dungey-like convection under resistive MHD to an asymmetric pattern similar to that found in previous Hall MHD simulations of Ganymede's subsonic magnetosphere as well as other simulations of Mercury's using multi-fluid or embedded kinetic physics. We demonstrate that the Hall effect is sufficient to induce a dawnward asymmetry in observed dipolarization front locations and find quasi-periodic global scale dipolarizations under steady, southward solar wind conditions. On average, we find a thinner current sheet dawnward; however, the measured thickness oscillates with the dipolarization cycle. During the flux-pileup stage, the dawnward current sheet can be thicker than the duskward sheet. This could be an explanation for recent observations that suggest Mercury's current sheet is actually thicker on the duskside: a sampling bias due to a longer-lasting "thick" state in the sheet.

Christopher Bard and John Dorelli

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on angeo-2021-35', Gabor Toth, 27 Jul 2021
    • AC1: 'Reply on RC1', Chris Bard, 01 Oct 2021
  • RC2: 'Comment on angeo-2021-35', Anonymous Referee #2, 11 Aug 2021
    • AC2: 'Reply on RC2', Chris Bard, 01 Oct 2021

Christopher Bard and John Dorelli

Christopher Bard and John Dorelli

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Short summary
We use a computer code to study how a particular plasma effect, the Hall effect, changes how plasma behaves and interacts with magnetic fields behind planets in the magnetotail. We find that when the scale of the Hall effect is big enough compared to the scale of the magnetotail, plasma behavior is no longer symmetric. Measurements of magnetic activity and structure vary in time and differ between opposite sides of the tail. This fits well with findings from spacecraft data and other models.