Browsing by Author "Järvinen, Riku"

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  • Cometary Ion Dynamics with Rosetta Ion Composition Analyzer
    (2019-10-21) Gupta, Shashikant
     Sähkötekniikan korkeakoulu | Master's thesis
    For centuries, comet sightings have fascinated us and we have strived to understand their nature. The knowledge of the behavior and composition of comets would help in understanding the formation of the Solar System, as they are believed to be the oldest objects in it. Cometary research, however, is in a developing stage because from an estimated trillion of comets, we have studied one through extended in-situ in-orbit measurements. Previous research has now established that comets become visible when they approach close to the Sun while their surface volatile material is sublimed by the solar radiation. The neutral atmosphere thus created is also ionized by the solar radiation, resulting in creation of positive cometary ions that are picked up and accelerated by the solar wind electric and magnetic fields. The fields influence the trajectories of these accelerated ions, causing variations in their flow angles as a function of their energy, a mechanism called energy - angle dispersion. Dispersion has only been studied for specific cases so far. In this work, the nature of the energy - angle dispersion is statistically examined using scientific data from the Rosetta mission, which orbited the Comet 67P/Churyumov-Gerasimenko from August 2014 to September 2016. One of the instruments onboard Rosetta, the Ion Composition Analyzer (ICA), measured the three-dimensional 360◦ × 90◦ energy and mass distribution of positive ions around the comet. In this work, the ICA data is used to identify dispersion events, their properties and trends using data analysis and image processing techniques at different temporal resolutions. The results are analyzed against the data from physical simulations, models and instruments onboard Rosetta. With the detailed statistical and quantitative analysis of the evolution of the energy - angle dispersion, it is found that the dispersion events are quite coherent over time scales of a few days and that the dispersion is very dynamic in nature. An understanding of this dispersion of accelerated cometary ions is key to understand the cometary ion dynamics.
  • Development of the Aalto Virtual Planetarium for space science and applications
    (2023-10-09) Helander, Henry
     Sähkötekniikan korkeakoulu | Master's thesis
    The thesis describes the development process of the Aalto Virtual Planetarium software. It introduces the topic by first discussing the basic space physic concepts related to space plasma environment. Four different types of interaction are discussed: Earth-like, Venus-like, comet-like and Moon-like interaction. After this, the concept of plasma modelling is explained. The three most common plasma models: the full kinetic, the magnetohydrodynamic and the hybrid model are each briefly described. Next, the hybrid model developed by the Finnish Meteorological Institute and the Aalto University is introduced along with the related equations. After these basic plasma modelling concepts, virtual reality and related simulation and coding tools are discussed. Following this, the Aalto Virtual Planetarium software is introduced as well as the basic astronomical principles used for calculating the orbital locations of the planets. After this, the new features added to the Aalto Virtual Planetarium are discussed in detail. They include the trajectories of BepiColombo and JUICE spacecraft, interplanetary magnetic field (IMF), the Moon of Earth, hand-menu additions, start-screen improvements, 3D models of spacecraft, background stars and the Galilean moons of the planet Jupiter: Io, Europa, Ganymede and Callisto. Implementation and testing of these newly added major and minor software features during the thesis are then described. This is followed by a discussion of the software versions for other platforms. Specific changes made to the Windows version of the Aalto Virtual Planetarium are listed, and the Linux and ThingLink software versions are also briefly introduced. Finally, suggestions are made regarding possible future improvements that could be made to the software tool. For example, additional platforms and new features are suggested.
  • High-energy particle enhancements in the solar wind upstream Mercury during the first BepiColombo flyby: SERENA/PICAM and MPO-MAG observations
    (2023-01-03) Alberti, Tommaso; Sun, W.; Varsani, Ali; Heyner, D.; Orsini, S; Milillo, Anna; Slavin, J.A.; Raines, J. M.; Aronica, Alessandro; Auster, H.-U.; Barabash, Stas; De Angelis, Enrico; Dandouras, Iannis; Järvinen, Riku; Jeszenszky, H.; Kallio, Esa; Kazakov, A.; Laky, G.; Livi, S. A.; Mangano, Valeria; Massetti, Stefano; Moroni, M; Mura, A.; Noschese, R.; Plainaki, Christina; Plaschke, F.; Richter, I.; Rispoli, R.; Sordini, R.; Wurz, Peter
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. The first BepiColombo Mercury flyby offered the unique opportunity to simultaneously characterize the plasma and the magnetic field properties of the solar wind in the vicinity of the innermost planet of the Solar System (0.4 AU). Aims. In this study, we use plasma observations by SERENA/PICAM and magnetic field measurements by MPO-MAG to characterize the source with intermittent features (with a timescale of a few minutes) at ion energies above 1 keV observed in the solar wind upstream of Mercury. Methods. The solar wind properties have been investigated by means of low-resolution magnetic field (1 s) and plasma (64 s) data. The minimum variance analysis and the Lundquist force-free model have been used. Results. The combined analyses demonstrate that the intermittent ion features observed by PICAM at energies above 1 keV can be associated with the passage of an interplanetary magnetic flux rope. We also validate our findings by means of Solar Orbiter observations at a larger distance (0.6 AU). Conclusions. The core of an interplanetary magnetic flux rope, hitting BepiColombo during its first Mercury flyby, produced high-energy (> -pagination1 keV) intermittent-like particle acceleration clearly distinct from the background solar wind, while at the edges of this interplanetary structure compressional low-energy fluctuations have also been observed.
  • Hybrid modeling of cometary plasma environments: II. Remote-sensing of a cometary bow shock
    (2019-10-01) Alho, Markku; Simon Wedlund, Cyril; Nilsson, Hans; Kallio, Esa; Järvinen, Riku; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Context. The ESA Rosetta probe has not seen direct evidence of a fully formed bow shock at comet 67P/Churyumov-Gerasimenko (67P). Ion spectrometer measurements of cometary pickup ions measured in the vicinity of the nucleus of 67P are available and may contain signatures of the large-scale plasma environment. Aims. The aim is to investigate the possibility of using pickup ion signatures to infer the existence or nonexistence of a bow shock-like structure and possibly other large-scale plasma environment features. Methods. A numerical plasma model in the hybrid plasma description was used to model the plasma environment of a comet. Simulated pickup ion spectra were generated for different interplanetary magnetic field conditions. The results were interpreted through test particle tracing in the hybrid simulation solutions. Results. Features of the observed pickup ion energy spectrum were reproduced, and the model was used to interpret the observation to be consistent with a shock-like structure. We identify (1) a spectral break related to the bow shock, (2) a mechanism for generating the spectral break, and (3) a dependency of the energy of the spectral break on the interplanetary magnetic field magnitude and bow shock standoff distance.
  • Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission
    (2022-12) Orsini, S; Milillo, Anna; Lichtenegger, Herbert I M; Varsani, Ali; Barabash, Stas; Livi, S.; De Angelis, Enrico; Alberti, Tommaso; Laky, G.; Nilsson, H.; Phillips, M; Aronica, Alessandro; Kallio, Esa; Wurz, Peter; Olivieri, Angelo; Plainaki, Christina; Slavin, James A.; Dandouras, Iannis; Raines, J. M.; Benkhoff, Johannes; Zender, J.; Berthelier, J. -J.; Dósa, Melinda; Ho, G.; Killen, R. M.; McKenna-Lawlor, S.; Torkar, K; Vaisberg, O.; Allegrini, Frederic A.; Daglis, I. A.; Dong, Chuanfei; Escoubet, C. P.; Fatemi, S.; Fränz, Markus; Ivanovski, S. L.; Krupp, N.; Lammer, H.; Leblanc, François; Mangano, Valeria; Mura, A.; Rispoli, R.; Sarantos, M.; Smith, H. T.; Wieser, Martin; Camozzi, F.; Di Lellis, A. M.; Fremuth, G.; Giner, F.; Gurnee, R.; Hayes, J.; Jeszenszky, H.; Trantham, Bradley; Balaz, Jan; Baumjohann, Wolfgang; Cantatore, M.; Delcourt, D.; Delva, M.; Desai, M.; Fischer, Henning; Galli, A.; Grande, Manuel; Holmström, Mats; Horvath, I.; Hsieh, Kechiang; Järvinen, Riku; Johnson, R. E.; Kazakov, A.; Kecskemety, K.; Krüger, H.; Kürbisch, C.; Leblanc, Frederic; Leichtfried, M.; Mangraviti, E; Massetti, Stefano; Moissenko, D.; Moroni, M; Noschese, R.; Nuccilli, F.; Paschalidis, N.; Ryno, J.; Seki, K.; Shestakov, A.; Shuvalov, S.; Sordini, R.; Stenbeck, F; Svensson, J.; Szalai, Sandor; Szego, K.; Toublanc, D.; Vertolli, N.; Wallner, R.; Vorburger, A
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.
  • Oxygen Ion Escape from Venus is Modulated by Ultra-Low-Frequency Waves
    (2020-06-16) Järvinen, Riku; Alho, Markku; Kallio, Esa; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the solar wind-driven, nonthermal escape of O+ ions from Venus in a global hybrid simulation. In the model, a well-developed ion foreshock forms ahead of the Venusian quasi-parallel bow shock under nominal upstream conditions. Large-scale magnetosonic ultra-low frequency (ULF) waves at 20- to 30-s period are excited and convect downstream along the foreshock with the solar wind. We show that the foreshock ULF waves transmit through the bow shock in the downstream region and interact with the planetary ion acceleration, causing 25% peak-to-peak fluctuations in the O+ escape rate. These results demonstrate the importance of upstream plasma waves on the energization and escape of heavy ions from the planetary atmospheres.
  • Particle-In-Cell Modeling of Martian Magnetic Cusps and Their Role in Enhancing Nightside Ionospheric Ion Escape
    (2021-01-16) Poppe, A.R.; Brain, D. A.; Dong, Yaxue; Xu, Shaosui; Järvinen, Riku
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Amongst various escape channels, ion outflow is a major contributor to atmospheric loss at Mars over geologic time. On Mars' nightside, observations have indicated that cusp regions within crustal magnetic fields are associated with phenomena such as accelerated particle populations, discrete auroral emissions, and ionospheric outflow; however, the kinetic physics occurring within crustal magnetic cusps is poorly understood. Here, we present 1.5-dimensional particle-in-cell simulations of magnetospheric-ionospheric interactions within martian crustal magnetic cusp regions of varying strength. Simulation results demonstrate the formation of quasi-static, field-aligned potentials pointing away from Mars that accelerate electrons into the martian atmosphere while accelerating ions away, thereby enhancing ionospheric escape. Escaping ionospheric flux scales with crustal field strength, with 160 nT crustal fields yielding >2× the ion escape flux than in the case with no crustal fields. We discuss these results and conclude that magnetic cusp regions may be significant sources of ion loss at Mars.
  • Planetary magnetic field control of ion escape from weakly magnetized planets
    (2019-09) Egan, Hilary; Järvinen, Riku; Ma, Y.; Brain, D. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars-sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet’s magnetic field enhances ion escape until the magnetic dipole’s standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the Southern hemisphere from ‘misaligned’ ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle, and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships.
  • Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF
    (2019-06) Hoilijoki, Sanni; Ganse, Urs; Sibeck, David G.; Cassak, Paul A.; Turc, Lucile; Battarbee, Markus; Fear, Robert C.; Blanco-Cano, Xochitl; Dimmock, Andrew; Kilpua, Emilia K.J.; Järvinen, Riku; Juusola, Liisa; Pfau-Kempf, Yann; Palmroth, Minna
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This paper describes properties and behavior of magnetic reconnection and flux transfer events (FTEs) on the dayside magnetopause using the global hybrid-Vlasov code Vlasiator. We investigate two simulation runs with and without a sunward (positive) B x component of the interplanetary magnetic field (IMF) when the IMF is southward. The runs are two-dimensional in real space in the noon-midnight meridional (polar) plane and three-dimensional in velocity space. Solar wind input parameters are identical in the two simulations with the exception that the IMF is purely southward in one but tilted 45° toward the Sun in the other. In the purely southward case (i.e., without B x) the magnitude of the magnetosheath magnetic field component tangential to the magnetopause is larger than in the run with a sunward tilt. This is because the shock normal is perpendicular to the IMF at the equatorial plane, whereas in the other run the shock configuration is oblique and a smaller fraction of the total IMF strength is compressed at the shock crossing. Hence, the measured average and maximum reconnection rate are larger in the purely southward run. The run with tilted IMF also exhibits a north-south asymmetry in the tangential magnetic field caused by the different angle between the IMF and the bow shock normal north and south of the equator. Greater north-south asymmetries are seen in the FTE occurrence rate, size, and velocity as well; FTEs moving toward the Southern Hemisphere are larger in size and observed less frequently than FTEs in the Northern Hemisphere.
  • Radar – CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility
    (2022-10) Kallio, Esa; Kero, Antti; Harri, Ari-Matti; Kestilä, Antti; Aikio, Anita; Fontell, Mathias; Järvinen, Riku; Kauristie, Kirsti; Knuuttila, Olli; Koskimaa, Petri; Loyala, Jauaries; Lukkari, Juha; Modabberian, Amin; Niittyniemi, Joonas; Rynö, Jouni; Vanhamäki, Heikki; Varberg, Erik
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of High Frequency (HF) electromagnetic waves. We have conducted a transionospheric HF-propagation research campaign with a nanosatellite on a low-Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the HEARER radio spectrometer onboard 1 Unit (size: 10 cm × 10 cm × 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite’s radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater’s antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O- and X-wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater’s electromagnetic wave energy. This paper is, to authors’ best knowledge, the first observation of this kind of "self-absorption" measured from the transionospheric signal path from a powerful radio source on the ground to the satellite-borne receiver.
  • Remote sensing of cometary bow shocks: Modelled asymmetric outgassing and pickup ion observations
    (2021-10) Alho, Markku; Järvinen, Riku; Simon Wedlund, Cyril; Nilsson, Hans; Kallio, Esa; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Despite the long escort by the ESA Rosetta mission, direct observations of a fully developed bow shock around 67P/Churyumov–Gerasimenko have not been reported. Expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the ESA Rosetta Plasma Consortium Ion Composition Analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. Using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67P, and varied interplanetary magnetic field (IMF) clock angles, we model the evolution of the large-scale plasma environment. We find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to 18000km approaching perihelion. We find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and IMF configuration. Asymmetric outgassing along with IMF clock angle is found to have a strong effect on the location of the spectral features, while the IMF clock angle causes no significant effect on the bow shock standoff distance. These dependences further complicate the interpretation of the ion observations made by Rosetta. Our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet’s activity is comparable to that of 67P, and the solar wind parameters are known.
  • Solar Intensity X-Ray and Particle Spectrometer SIXS: Instrument Design and First Results
    (2020-08-01) Huovelin, J.; Vainio, R.; Lehtolainen, A.; Kilpua, E.; Korpela, S.; Esko, Eero; Muinonen, K.; Bunce, E.; Martindale, A.; Grande, M.; Andersson, H.; Nenonen, S.; Lehti, Jussi; Schmidt, W.; Genzer, M.; Vihavainen, T.; Saari, J.; Peltonen, J.; Valtonen, E.; Talvioja, M.; Portin, P.; Narendranath, S.; Järvinen, Riku; Okada, T.; Milillo, A.; Laurenza, M.; Heino, E.; Oleynik, P.
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The Solar Intensity X-ray and particle Spectrometer (SIXS) on the BepiColombo Mercury Planetary Orbiter (“Bepi”) measures the direct solar X-rays, energetic protons, and electrons that bombard, and interact with, the Hermean surface. The interactions result in X-ray fluorescence and scattering, and particle induced X-ray emission (PIXE), i.e. “glow” of the surface in X-rays. Simultaneous monitoring of the incident and emitted radiation enables derivation of the abundances of some chemical elements and scattering properties of the outermost surface layer of the planet, and it may reveal other sources of X-ray emission, due to, for example, weak aurora-like phenomena in Mercury’s exosphere. Mapping of the Hermean X-ray emission is the main task of the MIXS instrument onboard BepiColombo. SIXS data will also be used for investigations of the solar X-ray corona and solar energetic particles (SEP), both in the cruise phase and the passes of the Earth, Venus and Mercury before the arrival at Mercury’s orbit, and the final science phase at Mercury’s orbit. These observations provide the first-ever opportunity for in-situ measurements of the propagation of SEPs, their interactions with the interplanetary magnetic field, and space weather phenomena in multiple locations throughout the inner solar system far away from the Earth, and more extensively at Mercury’s orbit. In this paper we describe the scientific objectives, design and calibrations, operational principles, and scientific performance of the final SIXS instrument launched to the mission to planet Mercury onboard BepiColombo. We also provide the first analysis results of science observations with SIXS, that were made during the Near-Earth Commissioning Phase and early cruise phase operations in 2018–19, including the background X-ray sky observations and “first light” observations of the Sun with the SIXS X-ray detection system (SIXS-X), and in-situ energetic electron and proton observations with the SIXS Particle detection system (SIXS-P).
  • Space Walk – Visiting the Solar System Through an Immersive Sonic Journey in VR
    (2021-11-11) Mancianti, Andrea; Schlecht, Sebastian; Välimäki, Vesa; Järvinen, Riku; Kallio, Esa
     A4 Artikkeli konferenssijulkaisussa
    SpaceWalk is a navigable virtual planetarium designed for the Oculus Quest VR headset. It provides an educational yet accurate representation of the Solar System, including visualizations of scientific data, such as magnetic field lines and atmospheric phenomena, and accompanying explanatory text. A navigational interface allows the visitor to travel between planets. As a complement to the visual content, an ad hoc modular soundtrack has been composed, meant to characterize sonically each celestial object and to offer an audio counterpart for each of their possible data visualization layers. Each sound layer could work both in isolation and together with all the other layers, still keeping coherence of the musical discourse. It is also meant to pay tribute to a vast network of literature from Sci-Fi filmand video game music, remaining appropriate within a rigorous scientific context. Finally, it integrates both stereophonic and immersive sound spatialization techniques. A fixed rendering through the interactive sound journey can be found online. The full VR experience is freely available on the Oculus AppLab and can be played on Oculus Quest 1 and 2 devices.
  • Stellar Influence on Heavy Ion Escape from Unmagnetized Exoplanets
    (2019-06) Egan, Hilary; Järvinen, Riku; Brain, David A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Planetary habitability is in part determined by the atmospheric evolution of a planet; one key component of such evolution is escape of heavy ions to space. Ion loss processes are sensitive to the plasma environment of the planet, dictated by the stellar wind and stellar radiation. These conditions are likely to vary from what we observe in our own solar system when considering a planet in the habitable zone around an M-dwarf. Here we use a hybrid global plasma model to perform a systematic study of the changing plasma environment and ion escape as a function of stellar input conditions, which are designed to mimic those of potentially habitable planets orbiting M-dwarfs. We begin with a nominal case of a solar wind experienced at Mars today, and incrementally modify the interplanetary magnetic field orientation and strength, dynamic pressure, and Extreme Ultraviolet input. We find that both ion loss morphology and overall rates vary significantly, and in cases where the stellar wind pressure was increased, the ion loss began to be diffusion or production limited with roughly half of all produced ions being lost. This limit implies that extreme care must be taken when extrapolating loss processes observed in the solar system to extreme environments.
  • Ultra-low Frequency Foreshock Waves and Ion Dynamics at Mars
    (2022-05) Järvinen, Riku; Kallio, Esa; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the solar wind interaction with Mars in a global three-dimensional hybrid model. A well-developed, vast ion foreshock forms under a strongly flow-aligned interplanetary magnetic field (IMF) configuration but otherwise nominal solar wind and solar minimum photon flux conditions. Large-scale ultra-low frequency (ULF) waves are excited in the foreshock by backstreaming ions. The foreshock ULF waves constitute two distinct regions in the analyzed solar wind and IMF situation: the near region where the wave period is 71-83 s and the far region where the wave period is 25-28 s. The near foreshock region waves transmit downstream through the bow shock and affect dynamics of the solar wind and planetary ion populations. Especially, ion precipitation rate into the exobase and planetary ion escape rates fluctuate at the ULF wave period corresponding to the near foreshock region. The peak-to-peak amplitude of the modulation is few percent or less. Interestingly, ionospheric oxygen ion escape fluxes show more than two orders of magnitude local modulations in the heavy plume at the same period. Finally, the escape rates of the ionospheric oxygen ion populations are enhanced by 60-70% under flow-aligned IMF compared to nominal upstream conditions.
  • Ultra-low frequency waves in the Hermean magnetosphere: On the role of the morphology of the magnetic field and the foreshock
    (2022-12-28) Kallio, Esa; Järvinen, Riku; Massetti, Stefano; Alberti, Tommaso; Milillo, Anna; Orsini, S; De Angelis, Enrico; Laky, G.; Slavin, J.A.; Raines, J. M.; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Ultra-low frequency (ULF) waves have been observed in the Mercury's magnetosphere by the Mariner 10 and MErcury Surface, Space ENvironment, GEochemistry and Ranging missions. The observed ∼2 s (∼0.6 Hz) period waves in the magnetic field are proposed to be generated by dynamic processes in the Mercury's magnetosphere. We investigate the Hermean ULF waves with a global hybrid model. We found evidence for ∼2-s circularly polarized right-handed waves in Mercury's magnetosphere at the closest approach of BepiColombo mission's first Mercury flyby in the model. The most intense wave power occurs on the dawn side closed magnetic field lines. These waves were found to be generated on the hemisphere which is magnetically directly connected to the interplanetary magnetic field on the dayside and to the foreshock region. It is therefore possible that the generation mechanism of these waves is associated with the precipitating ion flux or with the wave activity in the foreshock region.
  • Ultra-low frequency waves in the ion foreshock of Mercury: A global hybrid modeling study
    (2020-01-01) Järvinen, Riku; Alho, Markku; Kallio, Esa; Pulkkinen, Tuija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study the solar wind interaction with Mercury using a global three-dimensional hybrid model. In the analysed simulation run, we find a well-developed, dynamic Hermean ion foreshock ahead of the quasi-parallel bow shock under upstream solar wind and interplanetary magnetic field (IMF) conditions corresponding to the orbital perihelion of the planet. A portion of the incident solar wind ion flux is scattered back upstream near the quasi-parallel bow shock including both major solar wind ion species, protons and alphas. The scattered particles form the Hermean suprathermal foreshock ion population. A significant part of the suprathermal population is backstreaming with a velocity component towards the Sun in the near-foreshock at the planetocentric distance of few planetary radii in the plane of the IMF. The ion foreshock is associated with large-scale, oblique fast magnetosonic waves in the ultra-low-frequency (ULF) range convecting downstream with the solar wind. The ULF wave period is about 5 s in the analysed upstream condition case at Mercury, which corresponds to the 30-s foreshock waves at Earth when scaled by the IMF magnitude.