THEMIS statistical study of double population ion and electron boundary layers: implications for MMS
Thursday, 17 December 2015: 12:08
2018 (Moscone West)
While double ion populations, with the cold population originating from the solar wind and the hotter one from the magnetosphere, are frequently observed in Earth’s low-latitude boundary layers, similar double electron populations are seldom recorded. We performed a large-scale statistical study on 7 years of THEMIS particle data when these are suitably located close to the magnetopause. Our findings show that combined double populations in both ions and electrons appear much less frequently than double ion populations alone. The analysis of IMF data suggests that such boundary layers form preferentially under northward IMF but with a significant By component. We interpret this trend as a result of reconnection of the same magnetosheath field line in both hemispheres, but with at least one end reconnecting in its hemisphere at a rather low latitude with a closed magnetospheric field line which already contains a hot electron source. We explain how a full understanding of the dayside magnetopause topology under northward IMF will require much higher resolution observations at the subsolar magnetopause by MMS.