Browsing by Subject "Space physics"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Suni, Jonas (Helsingin yliopisto, 2021)
    Magnetosheath jets are a class of structures in the Earth's magnetosheath usually defined by an enhancement of the dynamic pressure of the plasma. Magnetosheath jets have been observed by several different spacecraft over the past few decades, but their origin and formation mechanism have remained unclear. The aim of this thesis is to use data from a global simulation to investigate the origin of magnetosheath jets. We defined two different kinds of structures, magnetosheath jets and foreshock compressive structures (FCS), and collected a database of individual jets and FCSs from 4 Vlasiator global hybrid-Vlasov simulation runs, all of which simulate only the ecliptic plane. We then conducted a statistical analysis of the properties of jets and FCSs, and their occurrence rates as a function of the definition of the FCS criterion. Jets were separated into two categories: jets that form in contact with FCSs (FCS-jets), and those that do not (non-FCS-jets). We found that up to 75% of magnetosheath jets form in association with an FCS impacting the Earth's bow shock. We also found that FCS-jets penetrate deeper into the magnetosheath than non-FCS-jets. Finally, we found no conclusive explanation for the formation of non-FCS-jets. The properties of both jets and FCSs agree qualitatively and to some extent quantitatively with spacecraft observations and other simulations in the literature. The formation of jets from FCSs impacting the bow shock is similar to the proposed theory that jets are linked to Short Large-Amplitude Magnetic Structures (SLAMS). In the future, we will study magnetosheath jets and FCSs in polar plane simulation runs as well, and ultimately in full 3D simulation runs. If made possible by new simulations, the effects of electron kinetic effects on jets and FCSs will also be studied. Comparison studies with spacecraft observations of jet formation from FCSs will also be conducted, if and when such observations are found and become available.
  • Palmroth, M.; Tapio, J.; Soucek, A.; Perrels, A.; Jah, M.; Lönnqvist, M.; Nikulainen, M.; Piaulokaite, V.; Seppälä, T.; Virtanen, J. (2021)
    During the last few years, the amount of space debris has been frequently mentioned as a potential risk to current and future space operations. The purpose of this article was to describe the discussions held at the First Sustainable Space Economy Workshop held in Finland 2019. The workshop gathered together experts with economic, legal, regulatory, technological, and environmental backgrounds, with an aim of discussing the sustainable use of space from all these perspectives. As an outcome of these discussions, we find that two concepts, satellite sustainability footprint and orbital capacity, should be introduced at an international level. The satellite sustainability footprint measures how likely the satellite stays healthy and operating, without causing risks to self or others. The orbit capacity is essentially an integral of the footprint over an orbit, and it determines how many satellites of different footprints could be launched to the same orbit. In addition, in this article, we discuss how to realize such concepts within the current normative framework. The authors suggest both top-down and bottom-up approaches, necessitating negotiations within an intergovernmental framework and with the relevant space actors. The most important finding of the workshop and this article, however, is that different space-related fields and experts having diverse backgrounds should continuously discuss in a constructive and informal manner to realize the sustainable utilization of space in practice. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).