Effects of geomagnetic storms on ionospheric electron density
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Lecture Hall F101, Aapistie 7, Kontinkangas Campus
Topic of the dissertation
Effects of geomagnetic storms on ionospheric electron density
Doctoral candidate
Master of Science (Physics) Gopika Prasannakumara Pillai Geethakumari
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Space Physics and Astronomy Research Unit
Subject of study
Physics
Opponent
Professor Shasha Zou, University of Michigan, USA
Custos
Professor Anita Aikio, University of Oulu
Effects of geomagnetic storms on ionospheric electron density
Geomagnetic storms are large-scale disturbances in the Earth’s magnetic field caused by the interaction between the solar wind and the Earth’s magnetosphere. The intensity, duration, and characteristics of these storms depend strongly on solar wind drivers. The two primary drivers are interplanetary coronal mass ejections (ICMEs) and high-speed solar wind streams (HSSs) and associated stream interaction regions (SIRs). Geomagnetic storms strongly affect the ionosphere, the ionized region of the Earth’s upper atmosphere. They can disrupt radio wave propagation, thereby impacting communication, navigation, and satellite-based technologies. Storm-time increases and decreases in electron density relative to quiet-time conditions are called positive and negative ionospheric storms, respectively.
This thesis investigates ionospheric electron density variations during two less explored geomagnetic storm types: a moderate HSS-driven storm and an ICME-driven superstorm, the strongest storm since 2003. The study uses global navigation satellite system (GNSS) total electron content (TEC) measurements, complemented by incoherent scatter radar and other ground-based and satellite observations. The thesis shows that the moderate HSS-driven storm caused significant TEC decreases from mid-latitudes to polar regions in the day and dusk local times. The TEC decreases were driven by upwelling of the neutral atmosphere due to Joule heating by ionospheric electrical currents. The thesis demonstrates, for the first time, that the initial positive ionospheric storm at mid-latitudes was caused by southward propagating large-scale traveling ionospheric disturbance waves launched by northern high-latitude Joule heating. During the May 2024 superstorm, exceptionally large amount of solar wind energy was deposited at high latitudes. This triggered severe disturbances in the upper atmosphere and ionosphere, ultimately leading to almost total disappearance of the polar ionosphere for 1.5 days.
This thesis investigates ionospheric electron density variations during two less explored geomagnetic storm types: a moderate HSS-driven storm and an ICME-driven superstorm, the strongest storm since 2003. The study uses global navigation satellite system (GNSS) total electron content (TEC) measurements, complemented by incoherent scatter radar and other ground-based and satellite observations. The thesis shows that the moderate HSS-driven storm caused significant TEC decreases from mid-latitudes to polar regions in the day and dusk local times. The TEC decreases were driven by upwelling of the neutral atmosphere due to Joule heating by ionospheric electrical currents. The thesis demonstrates, for the first time, that the initial positive ionospheric storm at mid-latitudes was caused by southward propagating large-scale traveling ionospheric disturbance waves launched by northern high-latitude Joule heating. During the May 2024 superstorm, exceptionally large amount of solar wind energy was deposited at high latitudes. This triggered severe disturbances in the upper atmosphere and ionosphere, ultimately leading to almost total disappearance of the polar ionosphere for 1.5 days.
Created 20.5.2026 | Updated 25.5.2026