Effect of interplanetary shocks on geomagnetic pulsations in the Pc4 and Pc5 range

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dc.contributor Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta fi
dc.contributor University of Helsinki, Faculty of Science en
dc.contributor Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten sv
dc.contributor.author Lehtinen, Simo
dc.date.issued 2021
dc.identifier.uri URN:NBN:fi:hulib-202106082540
dc.identifier.uri http://hdl.handle.net/10138/330721
dc.description.abstract The solar corona constantly emits a flow of charged particles, called the solar wind, into interplanetary space. This flow is diverted around the Earth by the magnetic pressure of the Earth’s own geomagnetic field, shielding the Earth from the effect of this particle radiation. On occasion the Sun ejects a large amount of plasma outwards from the corona in an event called a Coronal Mass Ejection (CME). Such events can drive discontinuities in the solar wind plasma, called interplanetary shocks. Shocks can affect the Earth’s magnetosphere, compressing it inwards and generating electromagnetic waves inside it. In this thesis we will cover a study of the ultra-low frequency (ULF) wave response in the magnetosphere to CME-driven shocks. Geomagnetic pulsations are ultra-low frequency plasma waves in the magnetosphere, observable from ground-based magnetometers. The compression of the magnetosphere by interplanetary shocks generates geomagnetic pulsations in the Pc4 and Pc5 frequency ranges (2 - 22 mHz). These waves play an important role in magnetospheric dynamics and the acceleration and depletion of high energy electrons in the radiation belts. We consider 39 interplanetary shock events driven by CMEs, and analyse ground-based magnetometer data from stations located near local noon at the time of the shock arrival. Solar wind measurements are used to categorise interplanetary shocks based on their Mach number and the dynamic pressure differential as main indicators of shock strength. The importance of these parameters in determining the strength of the wave response in the geomagnetic field is then studied using wavelet analysis and superposed epoch analysis. Stronger shocks are found to result in larger increases in wave activity, especially in the Pc4 range. Ground stations at higher latitudes observe higher wavepower, but there is an interesting anomaly in the Pc4 range at stations magnetically connected to regions near the plasmapause, which show an enhanced wavepower response. We quantify the decay time of the wave activity and find that it is around 20 hours for Pc5 waves and 7 hours for Pc4 waves. en
dc.language.iso eng
dc.publisher Helsingin yliopisto fi
dc.publisher University of Helsinki en
dc.publisher Helsingfors universitet sv
dc.subject Geomagnetic pulsations
dc.subject Interplanetary shocks
dc.subject Ultra-low frequency waves
dc.subject Pc5 waves
dc.subject Pc4 waves
dc.title Effect of interplanetary shocks on geomagnetic pulsations in the Pc4 and Pc5 range en
dc.type.ontasot pro gradu -tutkielmat fi
dc.type.ontasot master's thesis en
dc.type.ontasot pro gradu-avhandlingar sv
dct.identifier.urn URN:NBN:fi:hulib-202106082540
dc.subject.specialization Astrofysikaaliset tieteet fi
dc.subject.specialization Astrophysical Sciences en
dc.subject.specialization De astrofysikaliska vetenskaperna sv
dc.subject.degreeprogram Alkeishiukkasfysiikan ja astrofysikaalisten tieteiden maisteriohjelma fi
dc.subject.degreeprogram Master's Programme in Particle physics and Astrophysical Sciences en
dc.subject.degreeprogram Magisterprogrammet i elementarpartikelfysik och astrofysikaliska vetenskaper sv

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