Browsing by Author "Jarvinen, Riku"

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  • Auroral Imaging With Combined Suomi 100 Nanosatellite and Ground-Based Observations: A Case Study
    (2023-05) Kallio, Esa; Harri, Ari Matti; Knuuttila, Olli; Jarvinen, Riku; Kauristie, Kirsti; Kestilä, Antti; Kivekäs, Jarmo; Koskimaa, Petri; Lukkari, Juha Matti; Partamies, Noora; Rynö, Jouni; Syrjäsuo, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on 3 December 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a CubeSat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modeling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modeling demonstrate how even a small 1-Unit (size: 10 × 10 × 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.
  • BepiColombo Science Investigations During Cruise and Flybys at the Earth, Venus and Mercury
    (2021-02-11) Mangano, Valeria; Dósa, Melinda; Fränz, Markus; Milillo, Anna; Oliveira, Joana S.; Lee, Yeon Joo; McKenna-Lawlor, Susan; Grassi, Davide; Heyner, Daniel; Kozyrev, Alexander S.; Peron, Roberto; Helbert, Jörn; Besse, Sebastien; de la Fuente, Sara; Montagnon, Elsa; Zender, Joe; Volwerk, Martin; Chaufray, Jean Yves; Slavin, James A.; Krüger, Harald; Maturilli, Alessandro; Cornet, Thomas; Iwai, Kazumasa; Miyoshi, Yoshizumi; Lucente, Marco; Massetti, Stefano; Schmidt, Carl A.; Dong, Chuanfei; Quarati, Francesco; Hirai, Takayuki; Varsani, Ali; Belyaev, Denis; Zhong, Jun; Kilpua, Emilia K.J.; Jackson, Bernard V.; Odstrcil, Dusan; Plaschke, Ferdinand; Vainio, Rami; Jarvinen, Riku; Ivanovski, Stavro Lambrov; Madár, Ákos; Erdős, Géza; Plainaki, Christina; Alberti, Tommaso; Aizawa, Sae; Benkhoff, Johannes; Murakami, Go; Quemerais, Eric; Hiesinger, Harald; Mitrofanov, Igor G.; Iess, Luciano; Santoli, Francesco; Orsini, Stefano; Lichtenegger, Herbert; Laky, Gunther; Barabash, Stas; Moissl, Richard; Huovelin, Juhani; Kasaba, Yasumasa; Saito, Yoshifumi; Kobayashi, Masanori; Baumjohann, Wolfgang
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The dual spacecraft mission BepiColombo is the first joint mission between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet Mercury. BepiColombo was launched from Kourou (French Guiana) on October 20th, 2018, in its packed configuration including two spacecraft, a transfer module, and a sunshield. BepiColombo cruise trajectory is a long journey into the inner heliosphere, and it includes one flyby of the Earth (in April 2020), two of Venus (in October 2020 and August 2021), and six of Mercury (starting from 2021), before orbit insertion in December 2025. A big part of the mission instruments will be fully operational during the mission cruise phase, allowing unprecedented investigation of the different environments that will encounter during the 7-years long cruise. The present paper reviews all the planetary flybys and some interesting cruise configurations. Additional scientific research that will emerge in the coming years is also discussed, including the instruments that can contribute.
  • Cavitons and spontaneous hot flow anomalies in a hybrid-Vlasov global magnetospheric simulation
    (2018-08-08) Blanco-Cano, Xochitl; Battarbee, Markus; Turc, Lucile; Dimmock, Andrew P.; Kilpua, Emilia K.J.; Hoilijoki, Sanni; Ganse, Urs; Sibeck, David G.; Cassak, Paul A.; Fear, Robert C.; Jarvinen, Riku; Juusola, Liisa; Pfau-Kempf, Yann; Vainio, Rami; Palmroth, Minna
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this paper we present the first identification of foreshock cavitons and the formation of spontaneous hot flow anomalies (SHFAs) with the Vlasiator global magnetospheric hybrid-Vlasov simulation code. In agreement with previous studies we show that cavitons evolve into SHFAs. In the presented run, this occurs very near the bow shock. We report on SHFAs surviving the shock crossing into the downstream region and show that the interaction of SHFAs with the bow shock can lead to the formation of a magnetosheath cavity, previously identified in observations and simulations. We report on the first identification of long-term local weakening and erosion of the bow shock, associated with a region of increased foreshock SHFA and caviton formation, and repeated shock crossings by them. We show that SHFAs are linked to an increase in suprathermal particle pitch-angle spreads. The realistic length scales in our simulation allow us to present a statistical study of global caviton and SHFA size distributions, and their comparable size distributions support the theory that SHFAs are formed from cavitons. Virtual spacecraft observations are shown to be in good agreement with observational studies.
  • Comparison of Global Martian Plasma Models in the Context of MAVEN Observations
    (2018) Egan, Hilary; Ma, Yingjuan; Dong, Chuanfei; Modolo, Ronan; Jarvinen, Riku; Bougher, Stephen; Halekas, Jasper; Brain, David; Mcfadden, James; Connerney, John; Mitchell, David; Jakosky, Bruce
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single-fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low-altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment.
  • Energization of planetary pickup ions in the solar system
    (2014) Jarvinen, Riku; Kallio, Esa
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Fast plasma sheet flows and X line motion in the Earth's magnetotail: Results from a global hybrid-Vlasov simulation
    (2018-09-10) Juusola, Liisa; Hoilijoki, Sanni; Pfau-Kempf, Yann; Ganse, Urs; Jarvinen, Riku; Battarbee, Markus; Kilpua, Emilia; Turc, Lucile; Palmroth, Minna
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Fast plasma flows produced as outflow jets from reconnection sites or X lines are a key feature of the dynamics in the Earth's magnetosphere. We have used a polar plane simulation of the hybrid-Vlasov model Vlasiator, driven by steady southward interplanetary magnetic field and fast solar wind, to study fast plasma sheet ion flows and related magnetic field structures in the Earth's magnetotail. In the simulation, lobe reconnection starts to produce fast flows after the increasing pressure in the lobes has caused the plasma sheet to thin sufficiently. The characteristics of the earthward and tailward fast flows and embedded magnetic field structures produced by multi-point tail reconnection are in general agreement with spacecraft measurements reported in the literature. The structuring of the flows is caused by internal processes: interactions between major X points determine the earthward or tailward direction of the flow, while interactions between minor X points, associated with leading edges of magnetic islands carried by the flow, induce local minima and maxima in the flow speed. Earthward moving flows are stopped and diverted duskward in an oscillatory (bouncing) manner at the transition region between tail-like and dipolar magnetic fields. Increasing and decreasing dynamic pressure of the flows causes the transition region to shift earthward and tailward, respectively. The leading edge of the train of earthward flow bursts is associated with an earthward propagating dipolarization front, while the leading edge of the train of tailward flow bursts is associated with a tailward propagating plasmoid. The impact of the dipolarization front with the dipole field causes magnetic field variations in the Pi2 range. Major X points can move either earthward or tailward, although tailward motion is more common. They are generally not advected by the ambient flow. Instead, their velocity is better described by local parameters, such that an X point moves in the direction of increasing reconnection electric field strength. Our results indicate that ion kinetics might be sufficient to describe the behavior of plasma sheet bulk ion flows produced by tail reconnection in global near-Earth simulations.
  • Forcing continuous reconnection in hybrid simulations
    (2014) Laitinen, Tiera; Jarvinen, Riku; Kallio, Esa; Janhunen, Pekka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Hybrid Simulations of the Martian Magnetotail Twist
    (2024-11-01) Zhou, Jingyi; Liu, Kaijun; Jarvinen, Riku; Kallio, Esa; Cheng, Kun; Zhang, Shuai; Liu, Qi; Liu, Yuqi; Wang, Yan; Wang, Ruohan; Wang, Xinye; Shang, Xuanyu; Xu, Zhongyuan; Yuan, Yi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Three-dimensional global hybrid simulations are performed to explore how the interplanetary magnetic field (IMF), the Martian crustal fields, and planetary pickup ions affect the twisting of the Martian magnetotail. The results agree with previous studies that the crustal magnetic fields cause the Martian magnetotail to twist counterclockwise or clockwise depending on the sign of the IMF Y-component in the Mars solar orbital coordinates. However, the twist is more pronounced when the crustal fields are on the nightside, contradicting the early explanation that the crustal fields affect the twist through dayside magnetic reconnection between the crustal fields and the draped IMF. Additionally, planetary pickup ions also contribute to the twist because their mass loading slows down the plasma flow and leads to the bending of the magnetic field lines in the magnetotail. It is demonstrated that the twist inside Mars' shadow in the near magnetotail region (at X = -1.5 RM, where RM is Mars' radius) is mainly attributable to the crustal fields, while the influence of planetary pickup ions starts to dominate outside Mars' shadow and in regions further away from Mars.
  • Solar Orbiter Data-Model Comparison in Venus' Induced Magnetotail
    (2023-02) Stergiopoulou, Katerina; Jarvinen, Riku; Andrews, David J.; Edberg, Niklas J.T.; Dimmock, Andrew P.; Kallio, Esa; Persson, Moa; Khotyaintsev, Yuri V.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We investigate the structure of the Venusian magnetotail utilizing magnetic field and electron density measurements that cover a wide range of distances from the planet, from the first two Solar Orbiter Venus flybys. We examine the magnetic field components along the spacecraft trajectory up to 80 Venus radii down the tail. Even though the magnetic field behavior differs considerably between the two cases, we see extended electron density enhancements covering distances greater than ∼20 RV in both flybys. We compare the magnetic field measurements with a global hybrid model of the induced magnetosphere and magnetotail of Venus, to examine to what degree the observations can be understood with the simulation. The model upstream conditions are stationary and the solution encloses a large volume of 83 RV × 60 RV × 60 RV in which we look for spatial magnetic field and plasma variations. We rotate the simulation solution to describe different stationary upstream IMF clock angle cases with a 10° step and find the clock angle for which the agreement between observations and model is maximized along Solar Orbiter's trajectory in 1-min steps. We find that in both flybys there is better agreement with the observations when we rotate the model for some intervals, while there are parts that cannot be well reproduced by the model irrespective of how we vary the IMF clock angle, suggesting the presence of non-stationary features in the Venus-solar wind interaction not accounted for in the hybrid model.