From strong to superstorms: regional effects and spatial geomagnetic gradients driven by extreme space weather
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Auditorium TA105 (Linnanmaa), University of Oulu
Topic of the dissertation
From strong to superstorms: regional effects and spatial geomagnetic gradients driven by extreme space weather
Doctoral candidate
Master of Science (Technology) Otto Kärhä
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Sodankylä Geophysical Observatory
Subject of study
Physics
Opponent
Extra-Ordinary Professor Pieter Kotzé, North-West University
Custos
Professor Eija Tanskanen, University of Oulu
Large regional differences in the effects of magnetic storms
Coronal mass ejections and variations in the solar wind originating from the Sun can cause large-scale disturbances in Earth’s magnetic field, known as magnetic storms. These storms are one of the most intense manifestations of space weather, and they can disrupt power transmission and communication systems that are essential to modern society.
The effects of geomagnetic storms are studied by measuring variations in the geomagnetic field with magnetometers. Magnetometer stations have been installed especially within the auroral zone, where the strongest magnetic disturbances typically occur, unless the auroral oval has expanded toward the equator. Numerous stations together form measurement networks that make it possible to observe magnetic disturbances occurring even within very limited regions, as well as to collect information on how the strongest disturbances are distributed across different latitudes, for example when the auroral oval expands. Such information on regional disturbances is particularly important when assessing the risks that space weather poses to various systems.
This thesis studied how large the momentary differences in storm-time magnetic field variations can become between magnetometer stations, and thereby assessed the regional variability of the disturbances. The results show that during a storm observed in Fennoscandia in October 1977, the disturbance in the northward component of the magnetic field differed by more than 500 nanoteslas over a distance of about 170 kilometers, which is already a large difference over such a short distance. During the much stronger Halloween superstorm of October 2003, the corresponding difference between the magnetometer stations reached about 1,200 nanoteslas over a distance of 160 kilometers.
The largest differences in disturbance intensity were observed on the nightside of Earth during the most intense phases of the storms. The study utilized modern digital measurements and historical data recorded on 35 mm film in the 1970s. As part of this thesis, a digitization method was developed that enables the magnetic component traces recorded on film to be converted into digital data for use in this and future research.
The effects of geomagnetic storms are studied by measuring variations in the geomagnetic field with magnetometers. Magnetometer stations have been installed especially within the auroral zone, where the strongest magnetic disturbances typically occur, unless the auroral oval has expanded toward the equator. Numerous stations together form measurement networks that make it possible to observe magnetic disturbances occurring even within very limited regions, as well as to collect information on how the strongest disturbances are distributed across different latitudes, for example when the auroral oval expands. Such information on regional disturbances is particularly important when assessing the risks that space weather poses to various systems.
This thesis studied how large the momentary differences in storm-time magnetic field variations can become between magnetometer stations, and thereby assessed the regional variability of the disturbances. The results show that during a storm observed in Fennoscandia in October 1977, the disturbance in the northward component of the magnetic field differed by more than 500 nanoteslas over a distance of about 170 kilometers, which is already a large difference over such a short distance. During the much stronger Halloween superstorm of October 2003, the corresponding difference between the magnetometer stations reached about 1,200 nanoteslas over a distance of 160 kilometers.
The largest differences in disturbance intensity were observed on the nightside of Earth during the most intense phases of the storms. The study utilized modern digital measurements and historical data recorded on 35 mm film in the 1970s. As part of this thesis, a digitization method was developed that enables the magnetic component traces recorded on film to be converted into digital data for use in this and future research.
Created 13.11.2025 | Updated 14.11.2025