Energetic ions near the dayside magnetopause reconnection site: Implications for energization sources

During a magnetopause crossing by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, signatures of magnetic reconnection and of accelerated flows were observed. The maximum magnetic shear model of the reconnection X-line suggests that the spacecraft passed very close to the reconnection line. At the inner edge of the low latitude boundary layer (LLBL), accelerated ions are observed, which are magnetically connected to the quasi-parallel bow shock and travel towards the northern cusp region. However, a short time later the THEMIS satellite crossed the reconnection line, onto field lines, which map out to the quasi-perpendicular bow shock (or, the weak quasi-parallel bow shock very far downstream). At these times there is no significant difference in the energetic ion flux component observed coming from the shock versus from the cusp. These signatures suggest that, at least in some cases, energetic particles observed in the cusp regions originate at the quasi-parallel bow shock.

► Energetic ions observed close the magnetopause reconnection X-line.
► Enhanced flux of field-aligned ions when B-field connected to quasi-parallel shock.
► No enhanced flux observed when B-field disconnected from quasi-parallel bow shock.
► Appearance of field-aligned energetic ions suggests the bow shock as likely source.