36 results on '"Hoilijoki, S."'
Search Results
2. 3D GUMICS Simulations of Northward IMF Magnetotail Structure
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Fryer, L. J., Fear, R. C., Gingell, I. L., Coxon, J. C., Palmroth, M., Hoilijoki, S., Janhunen, P., Kullen, Anita, Cassak, P. A., Fryer, L. J., Fear, R. C., Gingell, I. L., Coxon, J. C., Palmroth, M., Hoilijoki, S., Janhunen, P., Kullen, Anita, and Cassak, P. A.
- Abstract
This study presents a re-evaluation of the Kullen and Janhunen (2004, https://doi.org/10.5194/angeo-22-951-2004) global northward interplanetary magnetic field (IMF) simulation, using the Grand Unified Magnetosphere–Ionosphere Coupling Simulation version 4 (GUMICS-4), a global MHD model. We investigate the dynamic coupling between northward IMF conditions and the Earth’s magnetotail and compare the results to observation-based mechanisms for the formation of transpolar arcs. The results of this study reveal that under northward IMF conditions (and northward IMF initialization), a large closed field line region forms in the magnetotail, with similarities to transpolar arc structures observed from spacecraft data. This interpretation is supported by the simultaneous increase of closed flux measured in the magnetotail. However, the reconnection configuration differs in several respects from previously theorized magnetotail structures that have been inferred from both observations and simulations results and associated with transpolar arcs. We observe that dawn–dusk lobe regions form as a result of high-latitude reconnection during the initialization stages, which later come into contact as the change in the IMF By component causes the magnetotail to twist. We conclude that in the GUMICS simulation, transpolar arc-like structures are formed as a result of reconnection in the magnetotail, rather than high-latitude reconnection or due to the mapping of the plasma sheet through a twisted magnetotail as interpreted from previous analysis of GUMICS simulations., QC 20230901
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- 2023
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3. Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF
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Hoilijoki, S, Ganse, U, Sibeck, D. G, Cassak, P. A, Turc, L, Battarbee, M, Fear, R. C, Blanco-Cano, X, Dimmock, A. P, Kilpua, E. K. J, Jarvinen, R, Juusola, L, Pfau-Kempf, Y, and Palmroth, M
- Subjects
Geophysics - Abstract
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(sub 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(sub 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.
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- 2019
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4. Vlasiator: First global hybrid-Vlasov simulations of Earth's foreshock and magnetosheath
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von Alfthan, S., Pokhotelov, D., Kempf, Y., Hoilijoki, S., Honkonen, I., Sandroos, A., and Palmroth, M.
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- 2014
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5. Contributions to Loss Across the Magnetopause During an Electron Dropout Event
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George, H., primary, Reeves, G., additional, Cunningham, G., additional, Kalliokoski, M. M. H., additional, Kilpua, E., additional, Osmane, A., additional, Henderson, M. G., additional, Morley, S. K., additional, Hoilijoki, S., additional, and Palmroth, M., additional
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- 2022
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6. Estimating Inner Magnetospheric Radial Diffusion Using a Hybrid-Vlasov Simulation
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George, H., primary, Osmane, A., additional, Kilpua, E. K. J., additional, Lejosne, S., additional, Turc, L., additional, Grandin, M., additional, Kalliokoski, M. M. H., additional, Hoilijoki, S., additional, Ganse, U., additional, Alho, M., additional, Battarbee, M., additional, Bussov, M., additional, Dubart, M., additional, Johlander, A., additional, Manglayev, T., additional, Papadakis, K., additional, Pfau-Kempf, Y., additional, Suni, J., additional, Tarvus, V., additional, Zhou, H., additional, and Palmroth, M., additional
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- 2022
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7. Estimating Inner Magnetospheric Radial Diffusion Using a Hybrid-Vlasov Simulation
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George, H., Osmane, A., Kilpua, E. K. J., Lejosne, S., Turc, L., Grandin, M., Kalliokoski, M. M. H., Hoilijoki, S., Ganse, U., Alho, M., Battarbee, M., Bussov, M., Dubart, M., Johlander, Andreas, Manglayev, T., Papadakis, K., Pfau-Kempf, Y., Suni, J., Tarvus, V., Zhou, H., Palmroth, M., George, H., Osmane, A., Kilpua, E. K. J., Lejosne, S., Turc, L., Grandin, M., Kalliokoski, M. M. H., Hoilijoki, S., Ganse, U., Alho, M., Battarbee, M., Bussov, M., Dubart, M., Johlander, Andreas, Manglayev, T., Papadakis, K., Pfau-Kempf, Y., Suni, J., Tarvus, V., Zhou, H., and Palmroth, M.
- Abstract
Radial diffusion coefficients quantify non-adiabatic transport of energetic particles by electromagnetic field fluctuations in planetary radiation belts. Theoretically, radial diffusion occurs for an ensemble of particles that experience irreversible violation of their third adiabatic invariant, which is equivalent to a change in their Roederer L* parameter. Thus, the Roederer L* coordinate is the fundamental quantity from which radial diffusion coefficients can be computed. In this study, we present a methodology to calculate the Lagrangian derivative of L* from global magnetospheric simulations, and test it with an application to Vlasiator, a hybrid-Vlasov model of near-Earth space. We use a Hamiltonian formalism for particles confined to closed drift shells with conserved first and second adiabatic invariants to compute changes in the guiding center drift paths due to electric and magnetic field fluctuations. We investigate the feasibility of this methodology by computing the time derivative of L* for an equatorial ultrarelativistic electron population travelling along four guiding center drift paths in the outer radiation belt during a 5 minute portion of a Vlasiator simulation. Radial diffusion in this simulation is primarily driven by ultralow frequency waves in the Pc3 range (10-45 s period range) that are generated in the foreshock and transmitted through the magnetopause to the outer radiation belt environment. Our results show that an alternative methodology to compute detailed radial diffusion transport is now available and could form the basis for comparison studies between numerical and observational measurements of radial transport in the Earth's radiation belts.
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- 2022
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8. Using mutual information to investigate non-linear correlation between AE index, ULF Pc5 wave activity and electron precipitation
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Hoilijoki, S. (Sanni), Kilpua, E. K. (Emilia K. J.), Osmane, A. (Adnane), Kalliokoski, M. M. (Milla M. H.), George, H. (Harriet), Savola, M. (Mikko), Asikainen, T. (Timo), Hoilijoki, S. (Sanni), Kilpua, E. K. (Emilia K. J.), Osmane, A. (Adnane), Kalliokoski, M. M. (Milla M. H.), George, H. (Harriet), Savola, M. (Mikko), and Asikainen, T. (Timo)
- Abstract
In this study, we use mutual information from information theory to investigate non-linear correlation between geomagnetic activity indicated by auroral electrojet (AE) index with both the global ultra low frequency (ULF) Pc5 wave power and medium energy (≥30 keV) electron precipitation at the central outer radiation belt. To investigate the energy and magnetic local time (MLT) dependence of the non-linearity, we calculate the mutual information and Pearson correlation coefficient separately for three different energy ranges (30–100 keV, 100–300 keV and ≥300 keV) and four different MLT sectors (0–6, 6–12, 12–18, 18–24). We compare results from 2 years 2004 and 2007 representing geomagnetically more active and less active years, respectively. The correlation analysis between the AE index and electron precipitation shows a clear MLT and energy dependence in both active and quiet conditions. In the two lowest energy ranges of the medium energy electrons (30–100 keV and 100–300 keV) both non-linear correlation and Pearson correlation indicate strong dependence with the AE index in the dawn sector. The linear dependence indicated by the Pearson correlation coefficient decreases from dawn to dusk while the change in the non-linear correlation is smaller indicating an increase in the non-linearity from dawn to dusk. The non-linearity between the AE index and electron precipitation is larger at all MLT sectors except MLTs 6–12 during geomagnetically more active year when larger amount of the activity is driven by interplanetary coronal mass ejections (ICMEs) compared to lower activity year with high speed stream (HSS) and stream interaction region (SIR) driven activity. These results indicate that the processes leading to electron precipitation become more non-linear in the dusk and during geomagnetically more active times when the activity is driven by ICMEs. The non-linearity between the AE index and global ULF Pc5 activity is relatively low and seems not to be a
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- 2022
9. Interpreting Solar EUV Wave Observations from Different Viewing Angles Using an MHD Model
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Hoilijoki, S., Pomoell, J., Vainio, R., Palmroth, M., and Koskinen, H. E. J.
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- 2013
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10. Origin of Electron‐Scale Magnetic Fluctuations Close to an Electron Diffusion Region
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Hoilijoki, S., primary, Pucci, F., additional, Ergun, R. E., additional, Schwartz, S. J., additional, Wilder, F. D., additional, Eriksson, S., additional, Chasapis, A., additional, Ahmadi, N., additional, Webster, J. M., additional, Burch, J. L., additional, Torbert, R. B., additional, Strangeway, R. J., additional, and Giles, B. L., additional
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- 2021
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11. Observations of Particle Acceleration in Magnetic Reconnection-driven Turbulence
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Ergun, R. E., Ahmadi, N., Kromyda, L., Schwartz, S. J., Chasapis, A., Hoilijoki, S., Wilder, F. D., Stawarz, J. E., Goodrich, K. A., Turner, D. L., Cohen, I. J., Bingham, S. T., Holmes, J. C., Nakamura, R., Pucci, F., Torbert, R. B., Burch, J. L., Lindqvist, Per-Arne, Strangeway, R. J., Le Contel, O., Giles, B. L., Ergun, R. E., Ahmadi, N., Kromyda, L., Schwartz, S. J., Chasapis, A., Hoilijoki, S., Wilder, F. D., Stawarz, J. E., Goodrich, K. A., Turner, D. L., Cohen, I. J., Bingham, S. T., Holmes, J. C., Nakamura, R., Pucci, F., Torbert, R. B., Burch, J. L., Lindqvist, Per-Arne, Strangeway, R. J., Le Contel, O., and Giles, B. L.
- Abstract
The Magnetospheric Multiscale Mission observes, in detail, charged particle heating and substantial nonthermal acceleration in a region of strong turbulence (vertical bar delta B vertical bar/vertical bar B vertical bar similar to 1, where B is the magnetic field) that surrounds a magnetic reconnection X-line. Magnetic reconnection enables magnetic field annihilation in a volume that far exceeds that of the diffusion region. The formidable magnetic field annihilation breaks into strong, intermittent turbulence with magnetic field energy as the driver. The strong, intermittent turbulence appears to generate the necessary conditions for nonthermal acceleration. It creates intense, localized currents (J) and unusually large-amplitude electric fields (E). The combination of turbulence-generated E and J results in a significant net positive mean of J center dot E, which signifies particle energization. Ion and electron heating rates are such that they experience a fourfold increase from their initial temperature. Importantly, the strong turbulence also generates magnetic holes or depletions in vertical bar B vertical bar that can trap particles. Trapping considerably increases the dwell time of a subset of particles in the turbulent region, which results in significant nonthermal particle acceleration. The direct observation of strong turbulence that is enabled by magnetic reconnection with nonthermal particle acceleration has far-reaching implications, since turbulence in plasmas is pervasive and may occupy significant volumes of the interstellar medium and intergalactic space. For example, strong turbulence from magnetic field annihilation in the supernova nebulae may dominate large volumes. As such, this observed energization process could plausibly contribute to the supply and development of the cosmic-ray spectrum., QC 20201126
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- 2020
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12. Onset of fast magnetic reconnection and particle energization in laboratory and space plasmas
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Pucci, F., primary, Velli, M., additional, Shi, C., additional, Singh, K. A. P., additional, Tenerani, A., additional, Alladio, F., additional, Ambrosino, F., additional, Buratti, P., additional, Fox, W., additional, Jara-Almonte, J., additional, Ji, H., additional, Yamada, M., additional, Yoo, J., additional, Okamura, S., additional, Ergun, R., additional, Hoilijoki, S., additional, and Schwartz, S., additional
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- 2020
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13. Nascent Flux Rope Observations at Earth's Dayside Magnetopause
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Eriksson, S., primary, Souza, V. M., additional, Cassak, P. A., additional, and Hoilijoki, S., additional
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- 2020
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14. Particle Acceleration in Strong Turbulence in the Earth’s Magnetotail
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Ergun, R. E., primary, Ahmadi, N., additional, Kromyda, L., additional, Schwartz, S. J., additional, Chasapis, A., additional, Hoilijoki, S., additional, Wilder, F. D., additional, Cassak, P. A., additional, Stawarz, J. E., additional, Goodrich, K. A., additional, Turner, D. L., additional, Pucci, F., additional, Pouquet, A., additional, Matthaeus, W. H., additional, Drake, J. F., additional, Hesse, M., additional, Shay, M. A., additional, Torbert, R. B., additional, and Burch, J. L., additional
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- 2020
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15. Observations of Particle Acceleration in Magnetic Reconnection–driven Turbulence
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Ergun, R. E., primary, Ahmadi, N., additional, Kromyda, L., additional, Schwartz, S. J., additional, Chasapis, A., additional, Hoilijoki, S., additional, Wilder, F. D., additional, Stawarz, J. E., additional, Goodrich, K. A., additional, Turner, D. L., additional, Cohen, I. J., additional, Bingham, S. T., additional, Holmes, J. C., additional, Nakamura, R., additional, Pucci, F., additional, Torbert, R. B., additional, Burch, J. L., additional, Lindqvist, P.-A., additional, Strangeway, R. J., additional, Le Contel, O., additional, and Giles, B. L., additional
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- 2020
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16. Electron‐Scale Magnetic Structure Observed Adjacent to an Electron Diffusion Region at the Dayside Magnetopause
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Hoilijoki, S., primary, Ergun, R. E., additional, Schwartz, S. J., additional, Eriksson, S., additional, Wilder, F. D., additional, Webster, J. M., additional, Ahmadi, N., additional, Le Contel, O., additional, Burch, J. L., additional, Torbert, R. B., additional, Strangeway, R. J., additional, and Giles, B. L., additional
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- 2019
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17. Magnetic Reconnection in Three Dimensions: Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet
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Ergun, R. E., primary, Hoilijoki, S., additional, Ahmadi, N., additional, Schwartz, S. J., additional, Wilder, F. D., additional, Drake, J. F., additional, Hesse, M., additional, Shay, M. A., additional, Ji, H., additional, Yamada, M., additional, Graham, D. B., additional, Cassak, P. A., additional, Swisdak, M., additional, Burch, J. L., additional, Torbert, R. B., additional, Holmes, J. C., additional, Stawarz, J. E., additional, Goodrich, K. A., additional, Eriksson, S., additional, Strangeway, R. J., additional, and LeContel, O., additional
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- 2019
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18. Magnetic Reconnection in Three Dimensions: Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet
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Ergun, R. E., primary, Hoilijoki, S., additional, Ahmadi, N., additional, Schwartz, S. J., additional, Wilder, F. D., additional, Burch, J. L., additional, Torbert, R. B., additional, Lindqvist, P.‐A., additional, Graham, D. B., additional, Strangeway, R. J., additional, Le Contel, O., additional, Holmes, J. C., additional, Stawarz, J. E., additional, Goodrich, K. A., additional, Eriksson, S., additional, Giles, B. L., additional, Gershman, D., additional, and Chen, L. J., additional
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- 2019
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19. Observations of a Small-Scale Flux Rope Next to an EDR at the Dayside Magnetopause
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Hoilijoki, S., Ergun, R., Eriksson, S., Wilder, F. D., Ahmadi, N., Schwartz, S. J., Torbert, R. B., Le Contel, Olivier, Strangeway, R. J., Giles, B. L., Burch, J. L., Laboratoire de Physique des Plasmas (LPP), Université Paris-Saclay-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11)-École polytechnique (X)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
- Subjects
[PHYS.PHYS.PHYS-PLASM-PH]Physics [physics]/Physics [physics]/Plasma Physics [physics.plasm-ph] ,Physics::Space Physics ,Astrophysics::Solar and Stellar Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
International audience; Magnetic reconnection is a fundamental plasma process that converts magnetic energy to thermal and kinetic energy of the particles. Previous studies have shown that small-scale magnetic flux ropes often form in secondary magnetic reconnection inside the ion diffusion region, where ions are demagnetized. It has also been shown that these small-scale flux ropes may have a role in the particle acceleration in magnetic reconnection and they might even have an impact on the reconnection rate. With the high cadence multipoint observations provided by Magnetopsheric Multiscale (MMS) mission the details of the small-scale flux ropes and their possible impact on the reconnecting current sheet can be studied. We present results of a dayside magnetopause crossing event where MMS first encounters an electron diffusion region (EDR), where crescent shaped electron velocity distribution functions are observed. Right after the current sheet crossing MMS enters a magnetic structure that has bipolar magnetic field in the direction normal to the current sheet. Inside the structure three of the spacecraft observe an increase in the total magnetic field magnitude and dip in the density. These features suggest that the structure may be a small-scale flux rope being formed adjacent to the current sheet. During this event the MMS spacecraft separation is 8 km, which is much smaller than the ion skin depth (di 40 km) allowing us to investigate the electron scale features of this structure.
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- 2018
20. Magnetic Reconnection in Three Dimensions : Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet
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Ergun, R. E., Hoilijoki, S., Ahmadi, N., Schwartz, S. J., Wilder, F. D., Burch, J. L., Torbert, R. B., Lindqvist, P-A, Graham, Daniel B., Strangeway, R. J., Le Contel, O., Holmes, J. C., Stawarz, J. E., Goodrich, K. A., Eriksson, S., Giles, B. L., Gershman, D., Chen, L. J., Ergun, R. E., Hoilijoki, S., Ahmadi, N., Schwartz, S. J., Wilder, F. D., Burch, J. L., Torbert, R. B., Lindqvist, P-A, Graham, Daniel B., Strangeway, R. J., Le Contel, O., Holmes, J. C., Stawarz, J. E., Goodrich, K. A., Eriksson, S., Giles, B. L., Gershman, D., and Chen, L. J.
- Abstract
Magnetic reconnection at the subsolar magnetopause is persistently accompanied by strong fluctuations of the magnetic field (B), plasma density (n), and all components of the electric field (E) and current (J). The strongest fluctuations are at frequencies below the lower hybrid frequency and observed in a thin, intense current sheet adjacent to the electron diffusion region. In this current sheet, the background magnitudes of B and n are changing considerably, creating an inhomogeneous plasma environment. We show that the fluctuations in B and n are consistent with an oscillatory displacement of the current sheet in the surface normal direction. The displacement is propagating parallel to the magnetic reconnection X line. Wavelengths are on the order of or longer than the thickness of the current sheet to which they are confined, so we label these waves electromagnetic drift waves. E and J fluctuations are more complex than a simple displacement. They have significant variations in the component along B, which suggest that the drift waves also may be confined along B. The current sheet is supported by an electron drift driven by normal electric field, which, in turn, is balanced by an ion pressure gradient. We suggest that wave growth comes from an instability related to the drift between the electrons and ions. We discuss the possibility that drift waves can displace or penetrate into the electron diffusion region giving magnetic reconnection three-dimensional structure. Drift waves may corrugate the X line, possibly breaking the X line and generating turbulence.
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- 2019
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21. Magnetic Reconnection in Three Dimensions : Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet
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Ergun, R. E., Hoilijoki, S., Ahmadi, N., Schwartz, S. J., Wilder, F. D., Drake, J. F., Hesse, M., Shay, M. A., Ji, H., Yamada, M., Graham, Daniel B., Cassak, P. A., Swisdak, M., Burch, J. L., Torbert, R. B., Holmes, J. C., Stawarz, J. E., Goodrich, K. A., Eriksson, S., Strangeway, R. J., LeContel, O., Ergun, R. E., Hoilijoki, S., Ahmadi, N., Schwartz, S. J., Wilder, F. D., Drake, J. F., Hesse, M., Shay, M. A., Ji, H., Yamada, M., Graham, Daniel B., Cassak, P. A., Swisdak, M., Burch, J. L., Torbert, R. B., Holmes, J. C., Stawarz, J. E., Goodrich, K. A., Eriksson, S., Strangeway, R. J., and LeContel, O.
- Abstract
We present a model of electromagnetic drift waves in the current sheet adjacent to magnetic reconnection at the subsolar magnetopause. These drift waves are potentially important in governing 3-D structure of subsolar magnetic reconnection and in generating turbulence. The drift waves propagate nearly parallel to the X line and are confined to a thin current sheet. The scale size normal to the current sheet is significantly less than the ion gyroradius and can be less than or on the order of the wavelength. The waves also have a limited extent along the magnetic field (B), making them a three-dimensional eigenmode structure. In the current sheet, the background magnitudes of B and plasma density change significantly, calling for a treatment that incorporates an inhomogeneous plasma environment. Using detailed examination of Magnetospheric Multiscale observations, we find that the waves are best represented by series of electron vortices, superimposed on a primary electron drift, that propagate along the current sheet (parallel to the X line). The waves displace or corrugate the current sheet, which also potentially displaces the electron diffusion region. The model is based on fluid behavior of electrons, but ion motion must be treated kinetically. The strong electron drift along the X line is likely responsible for wave growth, similar to a lower hybrid drift instability. Contrary to a classical lower hybrid drift instability, however, the strong changes in the background B and n(o), the normal confinement to the current sheet, and the confinement along B are critical to the wave description.
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- 2019
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22. Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF
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Hoilijoki, S., Ganse, U., Sibeck, D. G., Cassak, P. A., Turc, L., Battarbee, M., Fear, R. C., Blanco-Cano, X., Dimmock, Andrew P., Kilpua, E. K. J., Jarvinen, R., Juusola, L., Pfau-Kempf, Y., Palmroth, M., Hoilijoki, S., Ganse, U., Sibeck, D. G., Cassak, P. A., Turc, L., Battarbee, M., Fear, R. C., Blanco-Cano, X., Dimmock, Andrew P., Kilpua, E. K. J., Jarvinen, R., Juusola, L., Pfau-Kempf, Y., and Palmroth, M.
- Abstract
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 degrees toward the Sun in the other. In the purely southward case (i.e., without B-x) the magnitude of the magnetos heath 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.
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- 2019
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23. Ion irradiation effects in silicon nanowires
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Nordlund, K., Hoilijoki, S., and Holmstr¨om, E.
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- 2011
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24. Foreshock Properties at Typical and Enhanced Interplanetary Magnetic Field Strengths
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Turc, L., Ganse, U., Pfau-Kempf, Y., Hoilijoki, S., Battarbee, M., Juusola, L., Jarvinen, R., Brito, T., Grandin, M., Palmroth, M., University of Helsinki, University of Colorado Boulder, Department of Electronics and Nanoengineering, Finnish Meteorological Institute, Aalto-yliopisto, and Aalto University
- Subjects
Plasma waves ,Bow shock ,Physics::Space Physics ,Numerical simulations ,Foreshock ,Kinetic simulations ,Astrophysics::Galaxy Astrophysics ,ULF waves - Abstract
In this paper, we present a detailed study of the effects of the interplanetary magnetic field (IMF) strength on the foreshock properties at small and large scales. Two simulation runs performed with the hybrid-Vlasov code Vlasiator with identical setup but with different IMF strengths, namely, 5 and 10 nT, are compared. We find that the bow shock position and shape are roughly identical in both runs, due to the quasi-radial IMF orientation, in agreement with previous magnetohydrodynamic simulations and theory. Foreshock waves develop in a broader region in the higher IMF strength run, which we attribute to the larger growth rate of the waves. The velocity of field-aligned beams remains essentially the same, but their density is generally lower when the IMF strength increases, due to the lower Mach number. Also, we identify in the regular IMF strength run ridges of suprathermal ions which disappear at higher IMF strength. These structures may be a new signature of the foreshock compressional boundary. The foreshock wave field is structured over smaller scales in higher IMF conditions, due to both the period of the foreshock waves and the transverse extent of the wave fronts being smaller. While the foreshock is mostly permeated by monochromatic waves at typical IMF strength, we find that magnetosonic waves at different frequencies coexist in the other run. They are generated by multiple beams of suprathermal ions, while only a single beam is observed at typical IMF strength. The consequences of these differences for solar wind-magnetosphere coupling are discussed.
- Published
- 2018
25. A Survey of Plasma Waves Appearing Near Dayside Magnetopause Electron Diffusion Region Events
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Wilder, F. D., primary, Ergun, R. E., additional, Hoilijoki, S., additional, Webster, J., additional, Argall, M. R., additional, Ahmadi, N., additional, Eriksson, S., additional, Burch, J. L., additional, Torbert, R. B., additional, Le Contel, O., additional, Strangeway, R. J., additional, and Giles, B. L., additional
- Published
- 2019
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26. Foreshock Properties at Typical and Enhanced Interplanetary Magnetic Field Strengths: Results From Hybrid-Vlasov Simulations
- Author
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Turc, L., primary, Ganse, U., additional, Pfau-Kempf, Y., additional, Hoilijoki, S., additional, Battarbee, M., additional, Juusola, L., additional, Jarvinen, R., additional, Brito, T., additional, Grandin, M., additional, and Palmroth, M., additional
- Published
- 2018
- Full Text
- View/download PDF
27. Ion Acceleration by Flux Transfer Events in the Terrestrial Magnetosheath
- Author
-
Jarvinen, R., primary, Vainio, R., additional, Palmroth, M., additional, Juusola, L., additional, Hoilijoki, S., additional, Pfau-Kempf, Y., additional, Ganse, U., additional, Turc, L., additional, and von Alfthan, S., additional
- Published
- 2018
- Full Text
- View/download PDF
28. Enhancement of irradiation-induced defect production in Si nanowires.
- Author
-
Hoilijoki, S., Holmström, E., and Nordlund, K.
- Subjects
- *
MOLECULAR dynamics , *MOLECULAR rotation , *NANOWIRES , *NANOSTRUCTURED materials , *IRRADIATION - Abstract
We performed classical molecular dynamics simulations of defect production in small-diameter hexagonal Si nanowires under Ar ion irradiation. Using irradiation energies of 30 eV to 10 keV, we find that for low energies the defect production in the nanowires may be enhanced by as much as a factor of 3 in comparison to bulk Si due to the large surface-to-volume ratio of the systems. Conversely, at higher energies the increased transmission of ions causes a significant decrease in defect production. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
29. ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared
- Author
-
Palmroth, M., Archer, O., Vainio, R., Hietala, H., Pfau-Kempf, Y., Hoilijoki, S., Hannuksela, O., Ganse, U., Sandroos, A., von Alfthan, S., and Eastwood, J.
- Published
- 2015
- Full Text
- View/download PDF
30. Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF.
- Author
-
Hoilijoki, S., Ganse, U., Turc, L., Battarbee, M., Kilpua, E. K. J., Pfau‐Kempf, Y., Juusola, L., Palmroth, M., Sibeck, D. G., Cassak, P. A., Fear, R. C., Blanco‐Cano, X., Dimmock, A. P., and Jarvinen, R.
- Subjects
MAGNETIC reconnection ,MAGNETOPAUSE ,MAGNETIC fields ,PARAMETERS (Statistics) - Abstract
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) Bx 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 Bx) 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. Key Points: Sunward IMF tilt results in a smaller tangential field at the magnetopause, slowing dayside reconnectionSmaller tangential field results from a decrease in the IMF component that is shocked up at the bow shockA positive IMF Bx component introduces north‐south asymmetries, where fewer (but larger) FTEs appear on the Southern Hemisphere [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
31. Interpreting EUV observations from different viewing angles using an MHD model
- Author
-
Hoilijoki, S, Pomoell, J, Vainio, R, Palmroth, M, and Koskinen, H. E. J.
- Published
- 2013
32. Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF BxComponent During Southward IMF
- Author
-
Hoilijoki, S., Ganse, U., Sibeck, D. G., Cassak, P. A., Turc, L., Battarbee, M., Fear, R. C., Blanco‐Cano, X., Dimmock, A. P., Kilpua, E. K. J., Jarvinen, R., Juusola, L., Pfau‐Kempf, Y., and Palmroth, M.
- Abstract
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) Bxcomponent 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 Bx) 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. Sunward IMF tilt results in a smaller tangential field at the magnetopause, slowing dayside reconnectionSmaller tangential field results from a decrease in the IMF component that is shocked up at the bow shockA positive IMF Bxcomponent introduces north‐south asymmetries, where fewer (but larger) FTEs appear on the Southern Hemisphere
- Published
- 2019
- Full Text
- View/download PDF
33. Vlasiator: Global Kinetic Magnetospheric Modeling Tool.
- Author
-
Sandroos, A., von Alfthan, S., Hoilijoki, S., Honkonen, I., Kempf, Y., Pokhotelov, D., and Palmroth, M.
- Published
- 2015
34. ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared
- Author
-
Palmroth, M., Archer, M., Vainio, R., Hietala, H., Pfau-Kempf, Y., Hoilijoki, S., Hannuksela, O., Ganse, U., Sandroos, A., Alfthan, S. von, and Eastwood, J. P.
- Full Text
- View/download PDF
35. Onset of fast magnetic reconnection and particle energization in laboratory and space plasmas
- Author
-
Hantao Ji, S. Hoilijoki, F. Ambrosino, Masaaki Yamada, S. Okamura, William Fox, P. Buratti, Robert E. Ergun, S. J. Schwartz, F. Alladio, Jongsoo Yoo, Chen Shi, Fulvia Pucci, Marco Velli, Anna Tenerani, Jonathan Jara-Almonte, K. A. P. Singh, Pucci, F., Velli, M., Shi, C., Singh, K. A. P., Tenerani, A., Alladio, F., Ambrosino, F., Buratti, P., Fox, W., Jara-Almonte, J., Ji, H., Yamada, M., Yoo, J., Okamura, S., Ergun, R., Hoilijoki, S., and Schwartz, S.
- Subjects
Physics ,Range (particle radiation) ,astrophysical plasmas ,010504 meteorology & atmospheric sciences ,Plasma parameters ,fusion plasma ,Magnetic reconnection ,Plasma ,Condensed Matter Physics ,Space (mathematics) ,01 natural sciences ,Computational physics ,Particle acceleration ,Physics::Plasma Physics ,Ionization ,Physics::Space Physics ,0103 physical sciences ,Particle ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
The onset of magnetic reconnection in space, astrophysical and laboratory plasmas is reviewed discussing results from theory, numerical simulations and observations. After a brief introduction on magnetic reconnection and approach to the question of onset, we first discuss recent theoretical models and numerical simulations, followed by observations of reconnection and its effects in space and astrophysical plasmas from satellites and ground-based detectors, as well as measurements of reconnection in laboratory plasma experiments. Mechanisms allowing reconnection spanning from collisional resistivity to kinetic effects as well as partial ionization are described, providing a description valid over a wide range of plasma parameters, and therefore applicable in principle to many different astrophysical and laboratory environments. Finally, we summarize the implications of reconnection onset physics for plasma dynamics throughout the Universe and illustrate how capturing the dynamics correctly is important to understanding particle acceleration. The goal of this review is to give a view on the present status of this topic and future interesting investigations, offering a unified approach.
- Published
- 2020
36. Vlasov methods in space physics and astrophysics.
- Author
-
Palmroth M, Ganse U, Pfau-Kempf Y, Battarbee M, Turc L, Brito T, Grandin M, Hoilijoki S, Sandroos A, and von Alfthan S
- Abstract
This paper reviews Vlasov-based numerical methods used to model plasma in space physics and astrophysics. Plasma consists of collectively behaving charged particles that form the major part of baryonic matter in the Universe. Many concepts ranging from our own planetary environment to the Solar system and beyond can be understood in terms of kinetic plasma physics, represented by the Vlasov equation. We introduce the physical basis for the Vlasov system, and then outline the associated numerical methods that are typically used. A particular application of the Vlasov system is Vlasiator, the world's first global hybrid-Vlasov simulation for the Earth's magnetic domain, the magnetosphere. We introduce the design strategies for Vlasiator and outline its numerical concepts ranging from solvers to coupling schemes. We review Vlasiator's parallelisation methods and introduce the used high-performance computing (HPC) techniques. A short review of verification, validation and physical results is included. The purpose of the paper is to present the Vlasov system and introduce an example implementation, and to illustrate that even with massive computational challenges, an accurate description of physics can be rewarding in itself and significantly advance our understanding. Upcoming supercomputing resources are making similar efforts feasible in other fields as well, making our design options relevant for others facing similar challenges.
- Published
- 2018
- Full Text
- View/download PDF
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