[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-15] Duskward displacement of plasmoids and reconnection in the near-Earth magnetotail

*Akimasa Ieda¹, Yukinaga Miyashita^2,3 (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Korea Astronomy and Space Science Institute, 3.Korea National University of Science and Technology)

Keywords:substorm, magnetotail, magnetic reconnection, Mercury

Magnetic reconnection in the near-Earth magnetotail is responsible for explosive release of energy during auroral breakups. This near-tail reconnection was previously assumed to occur around the midnight meridian, where earthward flows were observed. Based on observations of tailward-moving plasmoids, the Geotail spacecraft mission discovered that the reconnection location was displaced toward dusk. This dusk preference is presumably caused by the Hall electric field, as was suggested later in simulations. However, recent spacecraft observations have suggested that the reconnection was displaced toward dawn, not dusk, in Mercury’s magnetotail. The cause of the difference between Earth and Mercury remains unclear.

This study reinterprets and integrates previous statistical results on the dawn–dusk location of fast plasma flows in the near-Earth magnetotail to address the controversy surrounding the dawn–dusk displacement of reconnection location. Thereby, we confirmed that dusk preference is generally evident for tailward-moving structures but found that location preference is variable among studies for earthward-moving structures. These results indicate that the statistical results of earthward flows are sensitive to event selection criteria. We conclude that the dawn–dusk location of earthward flow is statistically unclear at the time of substorm onset. Similarly, in the magnetotail of other planets the dawn-dusk location of planetward flow may be sensitive to event selection criteria. Hence, tailward-moving plasmoids and reconnection may be predominantly located on the duskside in Mercury. This hypothesis will be tested using observations of tailward-moving plasmoids by the BepiColombo Mio satellite, which will begin orbiting Mercury in the year 2025.