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Ion beam instabilities in the ion foreshock are an important source of ULF wave activity in near-Earth space. Foreshock 30-second waves are thought to be the main driver of Pc3 waves (10-45 s) observed routinely in the dayside magnetosphere. A handful of case studies with suitable spacecraft conjunctions have allowed simultaneous investigations of the wave properties in different geophysical regions, but the global picture of the wave transmission from the foreshock into the magnetosphere is still not known. In this study, we analyse global 2D simulations performed with the hybrid-Vlasov model Vlasiator to investigate Pc3 wave activity in near-Earth space. The simulations enable us to study the waves in their global context, and compare their properties in the foreshock, magnetosheath and dayside magnetosphere, for different sets of upstream solar wind conditions. Inside the magnetosphere, we focus on compressional Pc3 waves, because the 2D geometry of our simulation prevents the development of field-line resonances. We find that the Pc3 wave power is significantly enhanced in all three geophysical regions for higher solar wind Alfvén Mach number. Other parameters that are found to influence the foreshock wave power are the solar wind density and the IMF cone angle. Inside the magnetosphere, the wave power distribution depends strongly on the IMF orientation, which controls the foreshock position upstream of the bow shock. The wave power is largest when the angle between the IMF and the Sun-Earth line is smallest, suggesting that wave generation and transmission are most efficient in these conditions., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Earth is surrounded by doughnut-shaped regions of charged particles trapped in the geomagnetic field, called the radiation belts. These belts are highly dynamic and can have major space weather effects. The electrons that form the outer radiation belt have a huge range of energies, with some of them approaching the speed of light. A large number of satellites orbit through the radiation belts and these high-energy electrons can damage their sensitive electronics. It is therefore essential to thoroughly understand the particle dynamics within the radiation belts to protect the satellites. The dynamics of radiation belt electrons can be broadly divided into three categories: acceleration, transport, and loss. Acceleration of particles to higher energies can occur due to local interactions with plasma waves, or by being transported radially inwards in a non-adiabatic process called radial diffusion. Loss of particles from the radiation belts can occur when the particles travel along the Earth’s magnetic field lines and enter the atmosphere, in a process called precipitation. Loss can also occur when the particles cross the outer boundary of the Earth’s magnetosphere and are swept away by the solar wind. This is called magnetopause shadowing, and can be enhanced when particles are transported outward beyond the magnetopause. Radial diffusion therefore contributes both to the loss and acceleration of radiation belt particles. Acceleration, transport and loss of particles all often enhance when an interplanetary coronal mass ejection (ICME) - a large-scale heliospheric transient originating from solar eruptions - impacts the Earth, causing large disruptions to the radiation belt environment. This thesis uses spacecraft observations and simulations of near-Earth space to study the transport and loss of radiation belt electrons. Observational data of electron fluxes were obtained from Polar Orbiting Environmental Satellites (POES), Meteorological Operational (MetOp) satellites, the Van Allen Probes (RBSP) and the Global Positioning System (GPS). The Vlasiator model, a hybrid-Vlasov model of near-Earth space, and the Fokker-Planck DREAM3D simulation were used to obtain the inner magnetospheric wave activity and the phase space density (PSD) of radiation belt electrons respectively. Three first-author articles are included in this thesis, which have all been published in peer-reviewed journals. The first article uses POES / MetOp data to obtain the precipitating electron fluxes in the 30 - 300 keV energy range during the impact of two ICMEs that have rotating magnetic fields of opposite polarity. The timing, strength and location of the electron precipitation was closely tied to the magnetic field orientation, with the strongest precipitation occurring during the southward phase of the ICME These precipitating fluxes were studied in relation to the radiation belt electron fluxes observed by the RBSP during these two events. The greatest variations in electron fluxes at energies ranging from 33 keV to 3.4 MeV also occurred during the southward phase of the ICME. This shows that the substructure of ICMEs can be a major factor controlling the radiation belt response. The second article included in this thesis used the hybrid-Vlasov Vlasiator simulation to develop a methodology to evaluate radial diffusion, using a theoretical formalism that goes beyond quasilinear theory. The vast majority of radial diffusion formalisms are based on quasilinear theory, which assumes that any changes in the particle’s location are small and occur slowly. During ICME-driven storms however, it is possible that radial diffusion of particles occurs more quickly and to a greater degree than can be accurately studied under quasilinear theory. The methodology developed in the second article enables a more accurate evaluation of radial diffusion during these times, using electric and magnetic field data directly from a simulation. Evaluation of radial diffusion beyond quasilinear theory allows in turn a more precise understanding of the role that radial diffusion plays in the acceleration and loss of radiation belt particles. The final paper included in this thesis studied a dropout of relativistic electrons during the impact of the ICME. This paper specifically examined the loss to the magnetopause and the effect of different treatments of the Earth’s magnetic field on the calculated loss. The outward radial diffusion, which transported particles across the magnetopause, was treated according to two models. The first radial diffusion model assumed that the Earth’s magnetic field was a dipole, while the second radial diffusion model allowed a non-dipolar geomagnetic field that accounted for features such as dayside compression and nightside stretching of the Earth’s magnetic field. Up to 10\% more loss of a given electron population to the magnetopause occurred when radial diffusion was modelled with a non-dipolar geomagnetic field than with a dipole. This study shows that over-simplified treatment of the Earth’s magnetic field can significantly affect the modelled radial diffusion of electron populations, which can then have large impact on phenomena such as dropout events, highlighting the importance of accurate treatment of both the Earth’s magnetic field and radial diffusion. Säteilyvyöt ovat osa maapallon lähiavaruutta ja koostuvat maapallon magneettikentän vangitsemista varatuista hiukkasista. Säteilyvöiden hiukkasten energia vaihtelee suuresti hyvin hitaista hiukkaisista hiukkasiin, jotka liikkuvat lähes valonnopeudella. Suuri määrä jokapäiväiselle elämälle tarpeellisia satelliitteja, kuten GPS-satelliitit, kiertävät maapalloa säteilyvöiden alueella, jolloin on eittäin tärkeää suojata näitä satelliitteja vahingollisilta korkeaenergisiltä hiukkasilta. Tämän vuoksi meidän tulee ymmärtää säteilyvöiden hiukkasten käyttäytymistä. Säteilyvöiden olosuhteet riippuvat hiukkasiin kohdistuvien vuorovaikutusten summasta. Kulkeutuessaan lähemmäksi maapalloa hiukkaset kiihtyvät ja saavat energiaa. Jos taas hiukkaset kulkeutuvat ulospäin, ne voivat ylittää maapallon magneettikentän vaikutusalueen rajan, jolloin hiukkaset poistuvat säteilyvöistä. Hiukkasia häviää säteilyvöistä myös niiden iskeytyessä ilmakehään lähellä napa-alueita. Auringon pinnalla tapahtuu voimakkaita purkauksia, jotka syöksevät valtavia määriä magnetisoitunutta materiaa planeettainväliseen avaruuteen. Näiden koronan massapurkausten törmätessä maapalloon säteilyvöiden olosuhteissa tapahtuu huomattavia muutoksia. Hiukkasia voi kiihtyä hyvin korkeille energioille, häviöt voivat olla hyvin suuria ja nopea hiukkasten kulkeutuminen voi järjestää uudelleen säteilyvöiden hiukkasjakauman. Tällä auringonpurkausten aiheuttaman säteilyvöiden vasteen ymmärtämisellä on tärkeä osa satelliittien suojauksen kehittämisessä. Tässä väitöskirjassa tutkitaan elektronien kulkeutumista ja häviöitä säteilyvöissä, erityisesti koronan massapurkausten vaikutuksen aikana. Häviöt ilmakehään riippuvat erityisesti massapurkausten magneettikentän suunnasta. Laskennallisiin arvioihin häviöiden määrästä säteilyvöistä planeettainväliseen avaruuteen vaikuttaa merkittävästi maapallon magneettikentän mallintamistapa. Yksinkertainen dipolikenttä aliarvio häviöiden määrän. Lisäksi väitöskirjassa kehitetään menetelmä, joka mahdollistaa elektronien kulkeutumisen tutkimisen aiempaa tarkemmalla teoreettisella pohjalla. Tätä menetelmää sovelletaan tietokonemallinnukseen maapallon lähiavaruudesta.

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 the associated inner magnetospheric wave activity. We performed 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 had only a minor impact. We especially investigated the phase space density (PSD) of seed, core, and ultrarelativistic 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 the opposite: the geoeffective sheath mainly 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 played an important role in both electron energization and loss. Additionally, PSD radial profiles revealed a local peak that indicated significant acceleration to core energies by chorus waves during the geoeffective event. The distinct responses and different mechanisms in action during these events were related to the timing of the peaked solar wind dynamic pressure causing magnetopause compression, and the differing levels of substorm activity. The most remarkable changes in the radiation belt system occurred in key sheath sub-regions near the shock and the ejecta leading edge.