Browsing by Author "Kilpua, E. K.J."

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Cone angle control of the interaction of magnetic clouds with the Earth's bow shock
(2016) Turc, L.; Escoubet, C. P.; Fontaine, D.; Kilpua, E. K.J.; Enestam, S.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We study the interaction of magnetic clouds (MCs) with the near-Earth environment. Recent works suggest that the bow shock crossing may modify significantly the magnetic structure of an MC, and thus its ability to drive geomagnetic storms. This change is largely controlled by the bow shock configuration, which depends on the upstream interplanetary magnetic field (IMF) orientation. From the distribution of the magnetic field orientation in 152 Earth-impacting MCs, we determine for the first time the typical shock configuration during MC events. We find that 56% (6.3%) of the time, the subsolar bow shock configuration is exclusively quasi-perpendicular (quasi-parallel). The rest of the time, both configurations coexist. Furthermore, using a subset of 63 MCs observed simultaneously in the solar wind and in the dayside magnetosheath, we determine the magnitude of the magnetic field alteration, how it depends on the shock configuration, and how it relates to the IMF cone angle.
FORESAIL-1 CubeSat Mission to Measure Radiation Belt Losses and Demonstrate Deorbiting
(2019-07) Palmroth, M.; Praks, J.; Vainio, R.; Janhunen, P.; Kilpua, E. K.J.; Afanasiev, A.; Ala-Lahti, M.; Alho, A.; Asikainen, T.; Asvestari, E.; Battarbee, M.; Binios, A.; Bosser, A.; Brito, T.; Dubart, M.; Envall, J.; Ganse, U.; Ganushkina, N. Yu; George, H.; Gieseler, J.; Good, S.; Grandin, M.; Haslam, S.; Hedman, H. P.; Hietala, H.; Jovanovic, N.; Kakakhel, S.; Kalliokoski, M.; Kettunen, V. V.; Koskela, T.; Lumme, E.; Meskanen, M.; Morosan, D.; Mughal, M. Rizwan; Niemelä, P.; Nyman, S.; Oleynik, P.; Osmane, A.; Palmerio, E.; Peltonen, J.; Pfau-Kempf, Y.; Plosila, J.; Polkko, J.; Poluianov, S.; Pomoell, J.; Price, D.; Punkkinen, A.; Punkkinen, R.; Riwanto, B.; Salomaa, L.; Slavinskis, A.; Säntti, T.; Tammi, J.; Tenhunen, H.; Toivanen, Petri; Tuominen, J.; Turc, L.; Valtonen, E.; Virtanen, Pasi; Westerlund, T.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Today, the near-Earth space is facing a paradigm change as the number of new spacecraft is literally skyrocketing. Increasing numbers of small satellites threaten the sustainable use of space, as without removal, space debris will eventually make certain critical orbits unusable. A central factor affecting small spacecraft health and leading to debris is the radiation environment, which is unpredictable due to an incomplete understanding of the near-Earth radiation environment itself and its variability driven by the solar wind and outer magnetosphere. This paper presents the FORESAIL-1 nanosatellite mission, having two scientific and one technological objectives. The first scientific objective is to measure the energy and flux of energetic particle loss to the atmosphere with a representative energy and pitch angle resolution over a wide range of magnetic local times. To pave the way to novel model-in situ data comparisons, we also show preliminary results on precipitating electron fluxes obtained with the new global hybrid-Vlasov simulation Vlasiator. The second scientific objective of the FORESAIL-1 mission is to measure energetic neutral atoms of solar origin. The solar energetic neutral atom flux has the potential to contribute importantly to the knowledge of solar eruption energy budget estimations. The technological objective is to demonstrate a satellite deorbiting technology, and for the first time, make an orbit maneuver with a propellantless nanosatellite. FORESAIL-1 will demonstrate the potential for nanosatellites to make important scientific contributions as well as promote the sustainable utilization of space by using a cost-efficient deorbiting technology.
Outer Van Allen Radiation Belt Response to Interacting Interplanetary Coronal Mass Ejections
(2019-03-01) Kilpua, E. K.J.; Turner, D. L.; Jaynes, A. N.; Hietala, H.; Koskinen, H. E.J.; Osmane, A.; Palmroth, M.; Pulkkinen, T. I.; Vainio, R.; Baker, D.; Claudepierre, S. G.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We study the response of the outer Van Allen radiation belt during an intense magnetic storm on 15–22 February 2014. Four interplanetary coronal mass ejections (ICMEs) arrived at Earth, of which the three last ones were interacting. Using data from the Van Allen Probes, we report the first detailed investigation of electron fluxes from source (tens of kiloelectron volts) to core (megaelectron volts) energies and possible loss and acceleration mechanisms as a response to substructures (shock, sheath and ejecta, and regions of shock-compressed ejecta) in multiple interacting ICMEs. After an initial enhancement induced by a shock compression of the magnetosphere, core fluxes strongly depleted and stayed low for 4 days. This sustained depletion can be related to a sequence of ICME substructures and their conditions that influenced the Earth's magnetosphere. In particular, the main depletions occurred during a high-dynamic pressure sheath and shock-compressed southward ejecta fields. These structures compressed/eroded the magnetopause close to geostationary orbit and induced intense and diverse wave activity in the inner magnetosphere (ULF Pc5, electromagnetic ion cyclotron, and hiss) facilitating both effective magnetopause shadowing and precipitation losses. Seed and source electrons in turn experienced stronger variations throughout the studied interval. The core fluxes recovered during the last ICME that made a glancing blow to Earth. This period was characterized by a concurrent lack of losses and sustained acceleration by chorus and Pc5 waves. Our study highlights that the seemingly complex behavior of the outer belt during interacting ICMEs can be understood by the knowledge of electron dynamics during different substructures.