Energetic electron dynamics in the outer Van Allen radiation belt during sheath regions driven by interplanetary coronal mass ejections

Phenomena originating in the Sun are the main drivers of activity in the near-Earth space environment. Plasma and magnetic fields constantly flow out of the solar atmosphere, including eruptions of large magnetized plasma clouds. These clouds propagate away from the Sun to large distances, and when detected directly, they are called interplanetary coronal mass ejections (ICMEs). When ICMEs impact the Earth, they compress the magnetosphere and fill it with different plasma waves, which further affect the charged particles trapped in the geomagnetic field. These energetic particles in the Earth’s radiation belts are important to understand because they pose a significant threat for satellites. However, which physical processes – such as acceleration, scattering loss or radial diffusion – dominate the radiation belt response to a given solar wind driver structure cannot yet be predicted accurately. The dynamics remain elusive especially on short timescales of less than an hour due to the demanding level of the required data density. This thesis performs the first comprehensive and detailed statistical study on how turbulent sheath regions ahead of ICMEs affect plasma waves in the inner magnetosphere and outer radiation belt electrons. With high quality multi-point satellite measurements, the outer belt response to sheaths as a function of electron energy and radial location has been revealed. The studied sheath events were also divided based on their capability to drive geomagnetic activity, and computational tools were employed to separate adiabatic and nonadiabatic effects. Statistical analysis presented in this thesis shows that wave activity is elevated during sheaths which provides favorable conditions for wave-particle interactions. The high dynamic pressure of the sheaths also pushes the magnetopause inward facilitating significant electron losses. Flux measurements from both the Van Allen Probes and the Global Positioning System (GPS) satellite missions evidence that sheaths tend to enhance the fluxes of low energy (10s to 100s keV) electrons but deplete the high energy (> MeV) electrons. The larger number of satellites in the GPS constellation was crucial in confirming that the obtained results were due to the sheath and not influenced significantly by the following ejecta. Additionally, computation of phase space density showed that all sheaths can cause permanent loss, either by loss at the magnetopause or scattering to the atmosphere, but energization of electrons requires a sheath than can also drive storm conditions in the magnetosphere. This thesis shows that by utilizing multi-point and multi-satellite observations, assessing the overall geospace conditions from waves, geomagnetic activity and radiation belt electron variability, the impact of sheath regions could be determined. This thesis also demonstrates that sheaths which do not generate geomagnetic storms are able to drive significant changes in the outer belt electron populations, which should be noted in the event selection that often focuses on storm periods. Furthermore, the work presented in this thesis highlights the high data density of GPS satellites, which enables studying electron dynamics on timescales of a few tens of minutes, and its good synergy with Van Allen Probes measurements.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2022

Author dc:creator

• Kalliokoski, Milla

• avaruusfysiikka

Statement dc:rights

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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/347468

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F347468