Ion‐scale flux rope observed inside a hot flow anomaly

We report an earthward moving ion-scale flux rope embedded within the trailing edge of a hot flow anomaly (HFA) observed by the Magnetospheric Multiscale satellite constellation on 17 December 2016 upstream of Earth's quasi-parallel bow shock. The driver of the HFA, a tangential discontinuity, was observed by the Wind spacecraft without flux rope signatures around it in the solar wind. This suggests that the earthward moving flux rope was generated inside the HFA. This ion-scale flux rope is not a force free structure and expands due to a strong magnetic pressure gradient force. Solar wind ions are decelerated inside the flux rope by the static electric field likely caused by the charge separation of solar wind particles. Our observations imply that magnetic reconnection may have occurred inside the HFA. Reconnection and flux ropes may play a role in particle acceleration/heating inside foreshock transients.