Delayed Arrival of Energetic Solar Particles at MMS on 16 July 2017

Abstract

A shock in the solar wind was observed shortly after 05:00 by heliospheric spacecraft stationed at L1. Behind the shock, protons and electrons in the tens to hundreds of keV energy range were found to be enhanced several-fold. The shock reached the Earth precisely at 06:00 and was detected by particle sensors aboard GOES and ARTEMIS, and by ground-based magnetometers. In addition, the arrival of the shock was seen promptly by the magnetometer investigation aboard MMS, which at the time was located 16 R E down the geomagnetic tail. However, the arrival of the energetic particles at MMS was delayed for ~23 min, and first arrived moving earthward up the geomagnetic tail. Timing considerations between the solar wind speed and the energetic particles indicated that the solar particles first gained access to field lines connected to MMS around 115 R E downstream. Once the shock and its entrained solar particles passed the access region, the solar particles were no longer seen.