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

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Titel: Effect of interplanetary shocks on geomagnetic pulsations in the Pc4 and Pc5 range
Författare: Lehtinen, Simo
Medarbetare: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta
University of Helsinki, Faculty of Science
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten
Utgivare: Helsingin yliopisto
Datum: 2021
Språk: eng
Permanenta länken (URI): http://urn.fi/URN:NBN:fi:hulib-202106082540
Nivå: pro gradu-avhandlingar
Utbildningsprogram: Alkeishiukkasfysiikan ja astrofysikaalisten tieteiden maisteriohjelma
Master's Programme in Particle physics and Astrophysical Sciences
Magisterprogrammet i elementarpartikelfysik och astrofysikaliska vetenskaper
Studieinriktning: Astrofysikaaliset tieteet
Astrophysical Sciences
De astrofysikaliska vetenskaperna
Abstrakt: 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.
Subject: Geomagnetic pulsations
Interplanetary shocks
Ultra-low frequency waves
Pc5 waves
Pc4 waves

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