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Träfflista för sökning "WFRF:(Pulkkinen T.I) "

Sökning: WFRF:(Pulkkinen T.I)

  • Resultat 1-11 av 11
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1.
  • Alho, Markku, et al. (författare)
  • Hybrid modeling of cometary plasma environments : II. Remote-sensing of a cometary bow shock
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 630
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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  • Andreeova, K., et al. (författare)
  • Shock propagation in the magnetosphere : Observations and MHD simulations compared
  • 2008
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A9, s. A09224-
  • Tidskriftsartikel (refereegranskat)abstract
    • We examine the propagation of disturbances in the Earth's magnetosphere caused by fast forward shock interaction with the magnetopause. Our statistical study and event analyses show that the propagation speeds are larger in the magnetosphere than in the solar wind and are larger in the nightside magnetosphere than in the dayside magnetosphere. A case study of a double shock during 9 November 2002 is examined both observationally and using the GUMICS-4 global MHD simulation. Tracing the disturbance propagation allows us to confirm that the MHD simulation results are in good agreement with the in situ observations. The simulation results show that the propagation of the disturbance occurs in the antisunward direction at all clock angles simultaneously. However, changes in the magnetosheath are largest at high latitudes, while in the magnetotail the largest variations are seen in the plasma sheet.
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4.
  • Hietala, H., et al. (författare)
  • Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock
  • 2009
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:24, s. 245001-
  • Tidskriftsartikel (refereegranskat)abstract
    • The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.
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5.
  • Hill, S. C., et al. (författare)
  • Magnetospheric Sources of Theta Aurora: A Case Study Comparing Observations With SWMF Global Simulation
  • 2024
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 51:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first high resolution global MHD with coupled inner magnetosphere simulation results of an observed theta aurora event. We use the Space Weather Modeling Framework in the Geospace configuration, which produces accurate field aligned current closure in the ionosphere that is integral to theta aurora formation. At the location of the observed theta aurora, the simulation produces a narrow channel of Joule heating along both open and closed field lines, and between a pair of oppositely directed field-aligned current sheets in the ionosphere. We demonstrate that this Joule heating pattern that we identify as theta aurora maps to a reconnection region at the magnetotail flanks as well as in the distant magnetotail. The theta aurora maps to a cross-tail current disruption and field-aligned current source region in a highly twisted magnetotail.
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6.
  • Kaurisitie, K., Syrjsuo, M., Amm, O., Viljanen, A., Pulkkinen, T.I. and Opgenoorth, H.J. (författare)
  • A statistical study of evening sectorarcs and electrojets.
  • 2001
  • Ingår i: Advances in Space Research. ; 28, s. 16045-1610
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results of a statistical study of evening sector auroral arcs associated with electrojets. The study (including similar to 1000 all-sky camera (ASC) frames) is based on data of the MIRACLE instrument network. An automatic search engine is used
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9.
  • Lakka, A., et al. (författare)
  • The Cross-Polar Cap Saturation in GUMICS-4 During High Solar Wind Driving
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:5, s. 3320-3332
  • Tidskriftsartikel (refereegranskat)abstract
    • It is well known that the Earth's ionospheric cross‐polar cap potential (CPCP) saturates as a response to the solar wind (SW) driver especially when the level of driving is high and the interplanetary magnetic field is oriented southward. Moreover, previous studies have shown that the upstream Alfvén Mach number may be an important factor in the saturation effect. While the CPCP is often viewed as a measure of the SW‐magnetosphere‐ionosphere coupling, the processes associated with the nonlinearity of the coupling remain an open issue. We use fourth edition of the Grand Unified Magnetosphere‐Ionosphere Coupling Simulation (GUMICS‐4) and artificial SW data to mimic weak and strong driving in order to study the CPCP response to a wide range of interplanetary magnetic field magnitudes (3.5–30 nT) and upstream Alfvén Mach number values (1.2–22). The results provide the first overview of the CPCP saturation in GUMICS‐4 and show that the onset of saturation is strongly dependent on the upstream Alfvén Mach number and the physical processes responsible for the saturation effect might take place both in the Earth's magnetosheath and in the upstream SW.
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10.
  • Pulkkinen, T. I., et al. (författare)
  • Magnetospheric modes and solar wind energy coupling efficiency
  • 2010
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:3, s. A03207-
  • Tidskriftsartikel (refereegranskat)abstract
    • Using observations and two different global MHD simulations, we demonstrate that the solar wind speed controls the magnetospheric response such that the higher the speed, the more dynamic and irregular is the magnetospheric response. For similar level of driving solar wind electric field, the magnetospheric modes can be organized in terms of speed: Low speed produces steady convection events, intermediate speeds result in periodic sawtooth oscillations, and high speeds drive large geomagnetic storms. We show that the control parameter of energy transfer and coupling is the electric field along the large-scale X line. We demonstrate using global MHD simulations that for slowly varying interplanetary magnetic field (IMF), the reconnection line is tilted approximately by an angle theta/2, where theta is the IMF clock angle. Then, for clock angles away from northward, the magnetospheric energy entry and response scale with the electric field along the reconnection line (E-PAR), rather than the traditionally used E-Y. If we define the energy coupling efficiency as response/E-PAR, we can show it to be independent of the IMF clock angle and only weakly dependent on the solar wind dynamic pressure. These results demonstrate the ability of the localized reconnection line to control the energy input through the entire magnetopause.
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11.
  • Syrjäsuo, M., Pulkkinen, T.I., Pellinen, R.P., Janhunen, P., Kauristie, K., Viljanen, A., Opgenoorth, H.J., Karllson, P., Wallman, S., Eglitis, P., Nielsen, E. and Thomas, C. (författare)
  • Observations of substorm electrodynamics using the miracle network.
  • 2001
  • Ingår i: The 4th International Conference on Substorms, ICS4. - : Terra Scient. Publ. Comp. Tokyo, Japan. Kaje Hamana, Japan.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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  • Resultat 1-11 av 11

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