Dissertation Defence (physics): Nasrin Talebpour Sheshvan 7.8.
Time
7.8.2024 at 12.00 - 16.00
MSc Nasrin Talebpour Shesvan defends the?dissertation in physics titled ELECTRON ACCELERATION IN INTERPLANETARY SPACE: RADIO SIGNATURES AND IN-SITU OBSERVATIONS.
Opponent: Professor Lidia van Driel-Gesztelyi, University College London, United Kingdom
Custos: Rami Vainio, Professor, University of Turku
The audience can participate in the defence also through remote access.
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Coronal Mass Ejections (CMEs) are large-scale releases of hot plasma, to which the magnetic field is frozen-in. If the CMEs are faster than the local magnetosonic velocity in the solar wind, they create shock waves as they travel through the corona and Interplanetary (IP) space. Shock waves driven by CMEs can accelerate Solar Energetic Particles (SEPs). Both phenomena involve the acceleration of electrons, which can be observed as electromagnetic radiation and plasma radiation.
This doctoral thesis presents analyses of the presence and propagation of accelerated electrons in the IP medium. By utilizing the observations of multiple science satellites, such as STEREO-A, STEREO-B, and Wind, we get a comprehensive picture of the accelerated particles and solar radio bursts, at various wavelengths. We can use this information to determine the origin of the eruptions, their directivity, and connections to other solar events. In particular, the role of shock waves in the acceleration of relativistic electrons is the subject of this research. Earlier studies have already confirmed the role of shock waves in the acceleration of electrons to keV energies using radio bursts, but for the higher energies, the research is still in progress.
As a result of observations by many space instruments we now have a 3D view of the Sun, particularly in the analysis of type IV radio bursts in multi-spacecraft radio dynamic spectra. The directivity of radio bursts, i.e., being seen only toward a certain direction, can be explained either by absorption in the surrounding medium or by obstruction of dense plasma region, even by the solar disk itself. The presence of dense plasma regions like solar streamers, in directions no radiation is visible, strengthens this conclusion. Type II radio bursts can be associated with the interaction of streamers and shock waves. Our analysis of three separate type IV radio bursts revealed that their radiation was not visible toward directions type II radio bursts were observed. The eruptions were generated by the same active region on three different days, and the location of the eruption region on the Sun changed from the disk center to the solar limb. The directivity of the type IV rad
io bursts could therefore be explained as absorption in the type II burst regions, as the shock fronts contain higher-density plasma.
Opponent: Professor Lidia van Driel-Gesztelyi, University College London, United Kingdom
Custos: Rami Vainio, Professor, University of Turku
The audience can participate in the defence also through remote access.
***
Coronal Mass Ejections (CMEs) are large-scale releases of hot plasma, to which the magnetic field is frozen-in. If the CMEs are faster than the local magnetosonic velocity in the solar wind, they create shock waves as they travel through the corona and Interplanetary (IP) space. Shock waves driven by CMEs can accelerate Solar Energetic Particles (SEPs). Both phenomena involve the acceleration of electrons, which can be observed as electromagnetic radiation and plasma radiation.
This doctoral thesis presents analyses of the presence and propagation of accelerated electrons in the IP medium. By utilizing the observations of multiple science satellites, such as STEREO-A, STEREO-B, and Wind, we get a comprehensive picture of the accelerated particles and solar radio bursts, at various wavelengths. We can use this information to determine the origin of the eruptions, their directivity, and connections to other solar events. In particular, the role of shock waves in the acceleration of relativistic electrons is the subject of this research. Earlier studies have already confirmed the role of shock waves in the acceleration of electrons to keV energies using radio bursts, but for the higher energies, the research is still in progress.
As a result of observations by many space instruments we now have a 3D view of the Sun, particularly in the analysis of type IV radio bursts in multi-spacecraft radio dynamic spectra. The directivity of radio bursts, i.e., being seen only toward a certain direction, can be explained either by absorption in the surrounding medium or by obstruction of dense plasma region, even by the solar disk itself. The presence of dense plasma regions like solar streamers, in directions no radiation is visible, strengthens this conclusion. Type II radio bursts can be associated with the interaction of streamers and shock waves. Our analysis of three separate type IV radio bursts revealed that their radiation was not visible toward directions type II radio bursts were observed. The eruptions were generated by the same active region on three different days, and the location of the eruption region on the Sun changed from the disk center to the solar limb. The directivity of the type IV rad
io bursts could therefore be explained as absorption in the type II burst regions, as the shock fronts contain higher-density plasma.
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