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Magnetotail Reconnection Asymmetries in a Small, Earth-Like Magnetosphere
  • Christopher Bard,
  • John C. Dorelli
Christopher Bard
NASA Goddard Space Flight Center

Corresponding Author:[email protected]

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John C. Dorelli
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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 we have artificially inflated the ion inertial length ($\delta_i$) to one Earth radius (the real Earth’s $\delta_i\approx 1/15-1/20 R_E \approx 300-400\unit{km}$ in the magnetotail). This results in a magnetotail width on the order of $30 \delta_i$, 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.