| Summary: | The Earth is in a constant interaction with the solar wind. This interaction varies over different time scales, depending on the conditions of the Sun and the near-Earth space. The solar wind energy convection and dissipation in the Earth’s magnetosphere and ionosphere give rise to disturbances in the geomagnetic field, collectively called geomagnetic activity. Auroral substorm, a common phenomenon in the northern and southern auroral region, is one of the main forms of geomagnetic activity. Understanding the substorm variability over time and at different locations improves the capability to predict the activity and prepare for it. This master's thesis examined the long-term and seasonal substorm variation and latitudinal distribution in the northern auroral region, with the focus on the ionospheric energy dissipation. Substorms were identified with an automated search algorithm from ground-based magnetometer measurements in Fennoscandia and Svalbard. The latitudinal analysis covered years 1993-2018, and the centennial activity at Sodankylä was examined during 1914-2015. The interannual and annual substorm trends were found to vary over the latitude range, with the largest overall energy dissipation observed at the Sørøya station (70.5N) and the most frequent substorm activity at the Bear Island station (74.5N). The longest substorms, on average, were observed at Kevo (69.7N) and the strongest at Sodankylä (67.4N) and Muonio (68.0N). In the centennial analysis of the Sodankylä observations, substorms were found to occur most frequently during the declining phase of the solar cycles. It was concluded that the observation latitude may make a significant difference in ground-based substorm research, and thus sufficient latitudinal coverage should be considered. Maapallo on jatkuvassa vuorovaikutuksessa aurinkotuulen kanssa. Tämä vuorovaikutus vaihtelee eri aikaskaaloilla riippuen Auringon ja Maan lähiavaruuden olosuhteista. Aurinkotuulen syöttämän energian kierto ja dissipaatio Maan magnetosfäärissä ja ...
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