Flux transfer events (FTEs) are transient magnetic flux ropes at Earth’s dayside magnetopause formed due to magnetic reconnection. As they move across the magnetopause surface, they can generate disturbances in the ultra-low frequency (ULF) range, which then propagate into the magnetosphere. This study provides evidence of ULF waves in the Pc2 wave frequency range caused by FTEs during dayside reconnection using a global 3D hybrid-Vlasov simulation (Vlasiator). These waves resulted from FTE formation and propagation at the magnetopause are particularly associated with large, rapidly moving FTEs. The wave power is stronger in the morning than afternoon, showing local time asymmetry. In the pre and postnoon equatorial regions, significant poloidal and toroidal components are present alongside the compressional component. The noon sector, with fewer FTEs, has lower wave power and limited magnetospheric propagation.

Turbulent and compressed sheath regions preceding interplanetary coronal mass ejections (ICMEs) strongly impact electron dynamics in the outer radiation belt. Changes in electron flux can occur on timescales of tens of minutes, which is difficult to capture by a two-satellite mission such as the Van Allen Probes (RBSP). The recently released Global Positioning System (GPS) data set has higher data density owing to the large number of satellites in the constellation equipped with energetic particle detectors. Investigating electron fluxes in a wide range of energies and sheaths observed from 2012 to 2018, we show that the flux response to sheaths on a timescale of 6 hours, previously reported from RBSP data, is reproduced by GPS measurements. Furthermore, GPS data enables derivation of the response on a shorter timescale of 30 minutes, which further confirms that the energy and L-shell dependent changes in electron flux are due to the impact of the sheath. Sheath-driven loss is underestimated over longer timescales as the electrons recover during the ejecta. We additionally show the response of electron phase space density (PSD), which is a key quantity in identifying true loss from the system and electron energization through wave-particle interactions. The PSD response is calculated from both RBSP and GPS data for the 6-hour timescale, as well as from GPS data for the 30-minute timescale. The response is divided based on the geoeffectiveness of the sheaths revealing that electrons are effectively accelerated only during geoeffective sheaths, while loss is commonly caused by all sheaths.

Coronal mass ejection driven sheath regions are one of the key drivers of drastic outer radiation belt responses. The response can however be significantly different based on the sheath properties and associated inner magnetospheric wave activity. We performed here two case studies on the effects of sheaths on outer belt electrons of various energies using data from the Van Allen Probes. One sheath caused a major geomagnetic disturbance and the other one had only a minor impact. We especially investigated phase space density of high-energy electrons to determine the dominant energization and loss processes taking place during the events. Both sheaths produced substantial variation in the electron fluxes from tens of kiloelectronvolts up to ultrarelativistic energies. The responses were however almost the opposite: the geoeffective sheath led to enhancement, while the nongeoeffective one caused a depletion throughout most of the outer belt. The case studies highlight that both inward and outward radial transport driven by ultra-low frequency waves, combined with compression of the magnetopause, played an important role in governing electron dynamics during these sheaths. Chorus waves also likely caused a local peak in phase space density, leading to the energization of the ultrarelativistic population during the geoeffective event. The occurrence of chorus waves was based on measurements of precipitating and trapped fluxes by low-altitude Polar Operational Environmental Satellites. The distinct responses and different mechanisms in action during these events are related to differing levels of substorm activity and timing of the peaked solar wind dynamic pressure in the sheaths.