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  • 1.
    Alho, Markku
    et al.
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Wedlund, Cyril Simon
    Department of Physics, University of Oslo, Oslo, Norway.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Jarvinen, R.
    School of Electrical Engineering, Aalto University, Aalto, Finland. Finnish Meteorological Institute, Helsinki, Finland.
    Pulkkinen, T.I
    School of Electrical Engineering, Aalto University, Aalto, Finland. Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI,USA.
    Hybrid modeling of cometary plasma environments: II. Remote-sensing of a cometary bow shock2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A45Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Lindkvist, Jesper
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Ramstad, Robin
    Swedish Institute of Space Physics, Kiruna.
    Götz, C.
    Technicsche Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Braunschweig.
    Mass-loading of the solar wind at 67P/Churyumov-Gerasimenko: Observations and modelling2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 596, article id A42Article in journal (Refereed)
    Abstract [en]

    Context. The first long-term in-situ observation of the plasma environment in the vicinity of a comet, as provided by the European Rosetta spacecraft. Aims. Here we offer characterisation of the solar wind flow near 67P/Churyumov-Gerasimenko (67P) and its long term evolution during low nucleus activity. We also aim to quantify and interpret the deflection and deceleration of the flow expected from ionization of neutral cometary particles within the undisturbed solar wind. Methods. We have analysed in situ ion and magnetic field data and combined this with hybrid modeling of the interaction between the solar wind and the comet atmosphere. Results. The solar wind deflection is increasing with decreasing heliocentric distances, and exhibits very little deceleration. This is seen both in observations and in modeled solar wind protons. According to our model, energy and momentum are transferred from the solar wind to the coma in a single region, centered on the nucleus, with a size in the order of 1000 km. This interaction affects, over larger scales, the downstream modeled solar wind flow. The energy gained by the cometary ions is a small fraction of the energy available in the solar wind. Conclusions. The deflection of the solar wind is the strongest and clearest signature of the mass-loading for a small, low-activity comet, whereas there is little deceleration of the solar wind

  • 3.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Alho, M.
    Aalto University, School of Electrical Engineering, Department of Electronics and Nanoengineering, Finland.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Germany.
    Tsurutani, B.
    Jet Propulsion Laboratory, California Institute of Technology, USA.
    The birth and growth of a solar wind cavity around a comet: Rosetta observations2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, no Suppl. 2, p. S369-S403Article in journal (Refereed)
    Abstract [en]

    The Rosetta mission provided detailed observations of the growth of a cavity in the solar wind around comet 67P/Churyumov–Gerasimenko. As the comet approached the Sun, the plasma of cometary origin grew enough in density and size to present an obstacle to the solar wind. Our results demonstrate how the initial slight perturbations of the solar wind prefigure the formation of a solar wind cavity, with a particular interest placed on the discontinuity (solar wind cavity boundary) passing over the spacecraft. The slowing down and heating of the solar wind can be followed and understood in terms of single particle motion. We propose a simple geometric illustration that accounts for the observations, and shows how a cometary magnetosphere is seeded from the gradual steepening of an initially slight solar wind perturbation. A perspective is given concerning the difference between the diamagnetic cavity and the solar wind cavity.

  • 4.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Brolles, T.W.
    Space Science and Engineering Division, Southwest Research Institute, San Antonio.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mass loading at 67P/Churyumov-Gerasimenko: A case study2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 4, p. 1411-1418Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.

  • 5.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 2, p. 1570-1575Article in journal (Refereed)
    Abstract [en]

    When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.

  • 6.
    Behar, Etienne
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Tabone, B.
    LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Saillenfest, M.
    IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris.
    Henri, P.
    LPC2E, CNRS, Orléans.
    Deca, J.
    Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder.
    Lindkvist, J.
    Umeå University, Department of Physics.
    Holmström, Mats
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Solar wind dynamics around a comet: A 2D semi-analytical kinetic model2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, article id A35Article in journal (Refereed)
    Abstract [en]

    Aims.We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometaryatmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics.Methods.We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-stateis assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced byindividual solar wind protons during the interaction.Results.A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to acomet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar winddeflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular regionis found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, togetherwith the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of theRosettamission.Conclusions.The qualitative match between the model and thein situdata highlights how dominant the motional electric field isthroughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic descriptionof how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical modelfor a systematic quantitative comparison to the data.

  • 7.
    Berecic, Laura
    et al.
    Swedish Institute of Space Physics, Kiruna.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Nicolaou, G.
    Swedish Institute of Space Physics, Kiruna.
    Stenberg-Wieser, G.
    Swedish Institute of Space Physics, Kiruna.
    Wieser, M.
    Swedish Institute of Space Physics, Kiruna.
    Goetz, C.
    Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

  • 8.
    Dieval, Catherine
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Edberg, N.J.T.
    Swedish Institute of Space Physics, Uppsala.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Reduced proton and alpha particle precipitations at Mars during solar wind pressure pulses: Mars Express results2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3421-3429Article in journal (Refereed)
    Abstract [en]

    1] We performed a statistical study of downward moving protons and alpha particles of ~keV energy (assumed to be of solar wind origin) inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package on board Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low-altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent, and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses, the occurrence frequency of observed proton precipitation events is reduced by a factor of ~3, and for He2+ events the occurrence frequency is reduced by a factor of ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pileup of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H+/He2+ precipitations.

  • 9.
    Edberg, Niklas J. T.
    et al.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Eriksson, Anders I.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Vigren, Erik
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Johansson, Fredrik L.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Goetz, Charlotte
    Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Germany.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Gilet, Nicolas
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, Orléans, France.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), CNRS, Orléans, France.
    The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P2019In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed)
    Abstract [en]

    We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov–Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the Langmuir Probe instrument and the direction of the convective electric field  conv = − ×  was determined from magnetic field () measurements inside the coma combined with an assumption of a purely radial solar wind velocity . We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the − convhemisphere) compared to when it is away from the nucleus (in the + conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the − conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.

  • 10.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Emami, Reza
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Törlind, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zorzano Mier, María-Paz
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Parida, Vinit
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dordlofva, Christo
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Mendaza de Cal, Maria Teresa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Roos, Tobias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ottemark, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nieto, Chris
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Soria Salinas, Álvaro Tomás
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vázquez Martín, Sandra
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neikter, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindwall, Angelica
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Fakhardji, Wissam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Projekt: Rymdforskarskolan2015Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The Graduate School of Space Technology

  • 11.
    Kirkwood, Sheila
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Belova, Evgenia G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Dalin, Peter A.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Mihalikova, Maria
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Mikhaylova, Daria
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Murtagh, Donal P.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Satheesan, K.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Urban, Joachim B.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Wolf, Ingemar
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: The importance of nitric oxide2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, no 2, p. 333-347Article in journal (Refereed)
    Abstract [en]

    The relationship between polar mesosphere summer echoes (PMSE) and geomagnetic disturbances (represented by magnetic I K indices) is examined. Calibrated PMSE reflectivities for the period May 2006-February 2012 are used from two 52.0/54.5 MHz radars located in Arctic Sweden (68 N, geomagnetic latitude 65 ) and at two different sites in Queen Maud Land, Antarctica (73/72 S, geomagnetic latitudes 62/63 ). In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity between quiet and disturbed geomagnetic conditions. Mean volume reflectivities are slightly lower at the SH locations compared to the NH, but the position of the peak in the lognormal distribution of PMSE reflectivities is close to the same at both NH and SH locations, and varies only slightly with magnetic disturbance level. Differences between the sites, and between geomagnetic disturbance levels, are primarily due to differences in the high-reflectivity tail of the distribution. PMSE occurrence rates are essentially the same at both NH and SH locations during most of the PMSE season when a sufficiently low detection threshold is used so that the peak in the lognormal distribution is included. When the local-time dependence of the PMSE response to geomagnetic disturbance level is considered, the response in the NH is found to be immediate at most local times, but delayed by several hours in the afternoon sector and absent in the early evening. At the SH sites, at lower magnetic latitude, there is a delayed response (by several hours) at almost all local times. At the NH (auroral zone) site, the dependence on magnetic disturbance is highest during evening-to-morning hours. At the SH (sub-auroral) sites the response to magnetic disturbance is weaker but persists throughout the day. While the immediate response to magnetic activity can be qualitatively explained by changes in electron density resulting from energetic particle precipitation, the delayed response can largely be explained by changes in nitric oxide concentrations. Observations of nitric oxide concentration at PMSE heights by the Odin satellite support this hypothesis. Sensitivity to geomagnetic disturbances, including nitric oxide produced during these disturbances, can explain previously reported differences between sites in the auroral zone and those at higher or lower magnetic latitudes. The several-day lifetime of nitric oxide can also explain earlier reported discrepancies between high correlations for average conditions (year-by-year PMSE reflectivities and indices) and low correlations for minute-to-day timescales

  • 12.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barghouthi, Imad A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Eriksson, A.I
    Swedish Institute of Space Physics, Uppsala.
    André, M.
    Swedish Institute of Space Physics, Uppsala.
    Hot and cold ion outflow: Observations and implications for numerical models2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, p. 105-117Article in journal (Refereed)
    Abstract [en]

    Cluster observations of oxygen ion outflow and low-frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low-altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high-energy O+ ions in the high-altitude cusp and mantle and cold H+ ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high-altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O+ and cold H+, if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low-altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations

  • 13.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Hamrin, Maria
    Department of Physics, Umeå University.
    Pitkänen, Timo
    Department of Physics, Umeå University.
    Karlsson, Tomas
    Space and Plasma Physics, School of Electrical Engineering Royal Institute of Technology Stockholm.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Andersson, Laila O.
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vaivads, Andris
    Swedish Institute of Space Physics, Uppsala.
    Oxygen ion response to proton bursty bulk flows2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 8, p. 7535-7546Article in journal (Refereed)
    Abstract [en]

    We have used Cluster spacecraft data from the years 2001 to 2005 to study how oxygen ions respond to bursty bulk flows (BBFs) as identified from proton data. We here define bursty bulk flows as periods of proton perpendicular velocities more than 100 km/s and a peak perpendicular velocity in the structure of more than 200 km/s, observed in a region with plasma beta above 1 in the near-Earth central tail region. We find that during proton BBFs only a minor increase in the O+ velocity is seen. The different behavior of the two ion species is further shown by statistics of H+ and O+ flow also outside BBFs: For perpendicular earthward velocities of H+ above about 100 km/s, the O+ perpendicular velocity is consistently lower, most commonly being a few tens of kilometers per second earthward. In summary, O+ ions in the plasma sheet experience less acceleration than H+ ions and are not fully frozen in to the magnetic field. Therefore, H+ and O+ motion is decoupled, and O+ ions have a slower earthward motion. This is particularly clear during BBFs. This may add further to the increased relative abundance of O+ ions in the plasma sheet during magnetic storms. The data indicate that O+ is typically less accelerated in association with plasma sheet X lines as compared to H+.

  • 14.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Barghouthi, I.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Eriksson, A.I.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    André, M.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Hot and cold ion outflow: Spatial distribution of ion heating2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    Ions apparently emanating from the same source, the ionospheric polar cap, can either end up as energized to keV energies in the high-altitude cusp/mantle, or appear as cold ions in the magnetotail lobes. We use Cluster observations of ions and wave electric fields to study the spatial variation of ion heating in the cusp/mantle and polar cap. The average flow direction in a simplified cylindrical coordinate system is used to show approximate average ion flight trajectories, and discuss the temperatures, fluxes and wave activity along some typical trajectories. It is found that it is suitable to distinguish between cusp, central and nightside polar cap ion outflow trajectories, though O+ heating is mainly a function of altitude. Furthermore we use typical cold ion parallel velocities and the observed average perpendicular drift to obtain average cold ion flight trajectories. The data show that the cusp is the main source of oxygen ion outflow, whereas a polar cap source would be consistent with our average outflow paths for cold ions observed in the lobes. A majority of the cusp O+ flux is sufficiently accelerated to escape into interplanetary space. A scenario with significant oxygen ion heating in regions with strong magnetosheath origin ion fluxes, cold proton plasma dominating at altitudes below about 8 RE in the polar cap, and most of the cusp oxygen outflow overcoming gravity and flowing out in the cusp and mantle is consistent with our observations.

  • 15.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gunell, Herbert
    Belgian Institute for Space Aeronomy, Brussels.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics.
    Lundin, Rickard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Swedish Institute of Space Physics.
    Wieser, Martin
    Swedish Institute of Space Physics.
    Carr, Chris
    Imperial College London.
    Cupido, Emanuele
    Imperial College London.
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Savaud, Jean-André
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Koskinen, Hannu
    Department of Physics, University of Helsinki.
    Kallio, Esa
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Lebreton, Jean-Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E).
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory.
    Edberg, Niklas
    Swedish Institute of Space Physics, Ångström Laboratory.
    Goldstein, Raymond
    Belgian Institute for Space Aeronomy, Brussels.
    Henri, Pierre
    Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E).
    Coenders, Christoph
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Richter, Ingo
    Technische Universität–Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
    Rubin, Martin
    Physikalisches Institut, University of Bern.
    Birth of a comet magnetosphere: A spring of water ions2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, no 6220, article id aaa0571Article in journal (Refereed)
    Abstract [en]

    The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (

  • 16.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wedlund, Cyril Simon
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Edberg, N.J.T.
    Swedish Institute of Space Physics, Uppsala.
    Eriksson, Anders
    Swedish Institute of Space Physics, Ångström Laboratory.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics.
    Koenders, Christoph
    Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig.
    Wieser, Martin
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Lundin, Rickard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Mandt, Kathleen E.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Burch, James L.
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Goldstein, Raymond M.
    Space Science and Engineering Division, Southwest Research Institute (SwRI).
    Mokashi, Prachet
    Southwest Research Institute, 6220 Culebra Road, San Antonio.
    Carr, Chris
    Imperial College London.
    Cupido, Emanuele
    Imperial College London.
    Fox, P.T.
    Imperial College London.
    Szego, Karoly
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Nemeth, Zoltan
    Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest.
    Fedorov, Andrei
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Sauvaud, J.A.
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Koskinen, Hannu
    Department of Physics, University of Helsinki.
    Geiger, B.
    Rosetta Science Ground Segment, Science and Robotic Exploration (SRE-OOR).
    Evolution of the ion environment of comet 67P/Churyumov-Gerasimenko2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 583, article id A20Article in journal (Refereed)
    Abstract [en]

    Context. The Rosetta spacecraft is escorting comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, where the comet activity was low, until perihelion at 1.24 AU. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation. Aims. Using the Rosetta Plasma Consortium Ion Composition Analyzer (RPC-ICA), we study the gradual evolution of the comet ion environment, from the first detectable traces of water ions to the stage where cometary water ions accelerated to about 1 keV energy are abundant. We compare ion fluxes of solar wind and cometary origin. Methods. RPC-ICA is an ion mass spectrometer measuring ions of solar wind and cometary origins in the 10 eV-40 keV energy range. Results. We show how the flux of accelerated water ions with energies above 120 eV increases between 3.6 and 2.0 AU. The 24 h average increases by 4 orders of magnitude, mainly because high-flux periods become more common. The water ion energy spectra also become broader with time. This may indicate a larger and more uniform source region. At 2.0 AU the accelerated water ion flux is frequently of the same order as the solar wind proton flux. Water ions of 120 eV-few keV energy may thus constitute a significant part of the ions sputtering the nucleus surface. The ion density and mass in the comet vicinity is dominated by ions of cometary origin. The solar wind is deflected and the energy spectra broadened compared to an undisturbed solar wind.

  • 17.
    Nordström, T.
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Zhang, T.L.
    Austrian Academy of Sciences, Space Research Institute, Graz.
    Venus ion outflow estimates at solar minimum: Influence of reference frames and disturbed solar wind conditions2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3592-3601Article in journal (Refereed)
    Abstract [en]

    Recent estimates of ion escape rates from Venus, based on ASPERA-4 data, differ by more than a factor of 4. Whereas the ASPERA-4 instrument provides state-of-the art observations, the limited field of view of the instrument and the strongly limited geographical coverage of the spacecraft orbit means that significant assumptions must be used in the interpretation of the data. We complement previous studies by using a method of average distribution functions to obtain as good statistics as possible while taking the limited field of view into account. We use more than 3 years of data, more than any of the previous studies, and investigate how the choice of a geographical reference frame or a solar wind electric field oriented reference frame affects the results. We find that the choice of reference frame cannot explain the difference between the previously published reports. Our results, based on a larger data set, fall in between the previous studies. Our conclusion is that the difference between previous studies is caused by the large variability of ion outflow at Venus. It matters significantly for the end result which data are selected and which time period is used. The average escape rates were found to be 5.2±1.0×1024 s−1for heavy ions (m/q ≥16) and 14±2.6×1024 s−1for protons. We also discuss the spatial distribution of the planetary ion outflow in the solar wind electric field reference frame.

  • 18.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics.
    Gunell, Herbert
    Department of Physics, Umeå University, Umeå, Sweden. Belgian Institute for Space Aeronomy, Brussels, Belgium.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    De Spiegeleer, Alexandre
    Department of Physics, Umeå University, Umeå, Sweden.
    Ebihara, Yusuke
    Research Institute for Sustainable Humanosphere, Kyoto University, Japan, Gokasho, Uji, Kyoto.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Slapak, Rikard
    EISCAT Scientific Association, Kiruna, Sweden.
    The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations2019In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Article in journal (Refereed)
  • 19.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Gunell, Herbert
    Department of Physics, Umeå University, Umeå, Sweden. Belgian Institute for Space Aeronomy, Brussels, Belgium.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    De Spiegeleer, Alexandre
    Department of Physics, Umeå University, Umeå, Sweden.
    Ebihara, Yusuke
    EISCAT Scientific Association, Kiruna, Sweden.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Slapak, Rikard
    Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan.
    The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations2019Manuscript (preprint) (Other academic)
    Abstract [en]

    Ion escape is of particular interest for studying the evolution of the atmosphere on geological time scales. Previously, using Cluster-CODIF data, we investigated the oxygen ion outflow from the plasma mantle for different solar wind conditions and geomagnetic activity. We found significant correlations between solar wind parameters, geomagnetic activity (Kp index) and the O+ outflow. From these studies, we suggested that O+ ions observed in the plasma mantle and cusp have enough energy and velocity to escape the magnetosphere and be lost into the solar wind or in the distant magnetotail. Thus, this study aims to investigate where do the ions observed in the plasma mantle end up. In order to answer this question, we numerically calculate the trajectories of O+ ions using a tracing code to further test this assumption and determine the fate of the observed ions. Our code consists of a magnetic field model (Tsyganenko T96) and an ionospheric potential model (Weimer 2001) in which particles initiated in the plasma mantle and cusp regions are launched and traced forward in time. We analysed 136 observations of plasma mantle or cusp events in Cluster data between 2001 and 2007, and for each event 200 O+ particles were launched with an initial parallel and perpendicular velocity corresponding to the bulk velocity observed by Cluster. From the observations, our results show that 93 % of the events have an initial parallel velocity component twice the initial perpendicular velocity. After the tracing, we found that 96 % of the particles are lost into the solar wind or in the distant tail. Out of these 96 %, 20 % escape into the dayside magnetosphere.

  • 20.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Slapak, R.
    EISCAT Scientific Association, Kiruna, Sweden.
    Wintoft, P.
    Swedish Institute of Space Physics, Lund, Sweden.
    Yamauchi, M.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Wik, M.
    Swedish Institute of Space Physics, Lund, Sweden.
    Dandouras, I.
    IRAP, Université de Toulouse, CNRS, UPS, CNES, France.
    Carr, C.M.
    Department of Physics, Imperial College London, London, United Kingdom.
    O+ Escape During the Extreme Space Weather Event of 4–10 September 20172018In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, no 9, p. 1363-1376Article in journal (Refereed)
    Abstract [en]

    We have investigated the consequences of extreme space weather on ion outflow from the polar ionosphere by analyzing the solar storm that occurred early September 2017, causing a severe geomagnetic storm. Several X-flares and coronal mass ejections were observed between 4 and 10 September. The first shock—likely associated with a coronal mass ejection—hit the Earth late on 6 September, produced a storm sudden commencement, and began the initial phase of the storm. It was followed by a second shock, approximately 24 hr later, that initiated the main phase and simultaneously the Dst index dropped to Dst = −142 nT and Kp index reached Kp = 8. Using COmposition DIstribution Function data on board Cluster satellite 4, we estimated the ionospheric O+ outflow before and after the second shock. We found an enhancement in the polar cap by a factor of 3 for an unusually high ionospheric O+ outflow (mapped to an ionospheric reference altitude) of 1013 m−2 s−1. We suggest that this high ionospheric O+ outflow is due to a preheating of the ionosphere by the multiple X-flares. Finally, we briefly discuss the space weather consequences on the magnetosphere as a whole and the enhanced O+ outflow in connection with enhanced satellite drag.

  • 21.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Slapak, Rikard
    EISCAT Scientifc Association, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Dandouras, Iannis
    IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Earth atmospheric loss through the plasma mantle and its dependence on solar wind parameters2019In: Earth, Planets and Space, Vol. 71, no 70Article in journal (Refereed)
    Abstract [en]

    Atmospheric loss and ion outfow play an important role in the magnetospheric dynamics and in the evolution of the atmosphere on geological timescales—an evolution which is also dependent on the solar activity. In this paper, we investigate the total O+ outfow [s−1 ] through the plasma mantle and its dependency on several solar wind param‑ eters. The oxygen ion data come from the CODIF instrument on board the spacecraft Cluster 4 and solar wind data from the OMNIWeb database for a period of 5 years (2001–2005). We study the distribution of the dynamic pressure and the interplanetary magnetic feld for time periods with available O+ observations in the plasma mantle. We then divided the data into suitably sized intervals. Additionally, we analyse the extreme ultraviolet radiation (EUV) data from the TIMED mission. We estimate the O+ escape rate [ions/s] as a function of the solar wind dynamic pressure, the interplanetary magnetic feld (IMF) and EUV. Our analysis shows that the O+ escape rate in the plasma mantle increases with increased solar wind dynamic pressure. Consistently, it was found that the southward IMF also plays an important role in the O+ escape rate in contrast to the EUV fux which does not have a signifcant infuence for the plasma mantle region. Finally, the relation between the O+ escape rate and the solar wind energy transferred into the magnetosphere shows a nonlinear response. The O+ escape rate starts increasing with an energy input of approxi‑ mately 1011W.

  • 22.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics (IRF), Kiruna, Sweden .
    Slapak, Rikard
    EISCAT Scientific Association, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics (IRF), Kiruna.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics (IRF), Kiruna.
    Dandouras, Iannis
    Université de Toulouse, CNRS, UPS, CNES, Toulouse, France.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Earth atmospheric loss through the plasma mantle and its dependence onsolar wind parameters2019Conference paper (Refereed)
  • 23.
    Schillings, Audrey
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Atmospheric loss during major geomagnetic storms: Cluster observations2017Conference paper (Refereed)
  • 24.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Hamrin, Maria
    Department of Physics, Umeä University.
    Pitkänen, Timo
    Department of Physics, Umeä University.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Karlsson, Tomas
    Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Quantification of the total ion transport in the near-Earth plasma sheet2017In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 4, p. 869-877Article in journal (Refereed)
    Abstract [en]

    Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001-2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s -1, respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0. 5 × 1025 s -1, which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows ( < 100kms -1) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

  • 25.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna.
    Schillings, Audrey
    Swedish Institute of Space Physics, Kiruna.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dandouras, Iannis
    CNSR, Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Atmospheric outflow from the terrestrial magnetosphere: implications forescape on evolutionary time scales2017Conference paper (Refereed)
  • 26.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A statistical study on O+ flux in the dayside magnetosheath2013In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 31, p. 1005-1010Article in journal (Refereed)
    Abstract [en]

    Studies on terrestrial oxygen ion (O+) escape into the interplanetary space have considered a number of different escape paths. Recent observations however suggest a yet insufficiently investigated additional escape route for hot O+: along open magnetic field lines in the high altitude cusp and mantle. Here we present a statistical study on O+ flux in the high-latitude dayside magnetosheath. The O+ is generally seen relatively close to the magnetopause, consistent with observations of O+ flowing primarily tangentially to the magnetopause. We estimate the total escape flux in this region to be ~ 7 × 1024 s−1, implying this escape route to significantly contribute to the overall total O+ loss into interplanetary space.

  • 27.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eriksson, Anders
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Observations of oxygen ions in the dayside magnetosheath associated with southward IMF2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    We present a case study of high energy oxygen ions (O+) observed in the dayside terrestrial magnetosheath, in the southern hemisphere. It is shown that the presence of O+ is strongly correlated to the IMF direction: O+ is observed only for Bz<0. Three satellites observe O$^+ immediately at both sides of the magnetopause and about 2 RE outside the magnetopause. These conditions indicate escape along open magnetic field lines. We show that if outflowing O+ is heated and accelerated sufficiently in the cusp, it takes 15-20 minutes for it to reach the magnetopause, allowing the ions to escape along newly opened field lines on the dayside. Earlier studies show evidence of strong heating and high velocities in the cusp and mantle at high altitudes, strengthening our interpretation. The observed magnetosheath O+ fluxes are of the same order as measured in the ionospheric upflow, which indicates that this loss mechanism is significant when it takes place.

  • 28.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Richard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    O+ transport in the dayside magnetosheath and its dependence on the IMF direction2015In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, p. 301-307Article in journal (Refereed)
    Abstract [en]

    Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

  • 29.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales2017In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 3, p. 721-731Article in journal (Refereed)
  • 30.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Yamauchi, Masatoshi
    Swedish Institute of Space Physics, Kiruna.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,20172018In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Article in journal (Refereed)
  • 31.
    Waara, Martin
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Slapak, Rikard
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    André, Mats
    Institutet för rymdfysik, Uppsala.
    Stenberg, Gabriella
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Oxygen ion energization by waves in the high altitude cusp and mantle2012In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, p. 1309-1314Article in journal (Refereed)
  • 32.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, AL, USA.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Gronoff, Guillaume
    Science Directorate, Chemistry & Dynamics Branch, NASA Langley Research Center, Hampton, VA, USA. SSAI, Hampton, VA, USA.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Solar wind charge exchange in cometary atmospheres: II. Analytical model2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A36Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided a unique opportunity to study charge-changing processes in situ.

    Aims. To understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

    Methods. An extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. It is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas.

    Results. After presenting a general 1D solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (He2+, He+, He0) and (H+, H0, H) on solar wind parameters at comet 67P. We show that double charge exchange for the He2+−H2O system plays an important role below a solar wind bulk speed of 200 km s−1, resulting in the production of He energetic neutral atoms, whereas stripping reactions can in general be neglected. Retrievals of outgassing rates and solar wind upstream fluxes from local Rosetta measurements deep in the coma are discussed. Solar wind ion temperature effects at 400 km s−1 solar wind speed are well contained during the Rosetta mission.

    Conclusions. As the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of Rosetta, forming in effect a solar wind ion cavity. This study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67P and the Rosetta mission.

  • 33.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, USA.
    Heritier, Kevin
    Department of Physics, Imperial College London, London, UK.
    Galand, Marina
    Department of Physics, Imperial College London, London, UK.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Rubin, Martin
    Space Research and Planetary Sciences, University of Bern, Bern, Switzerland.
    Altwegg, Kathrin
    Space Research and Planetary Sciences, University of Bern, Bern, Switzerland.
    Volwerk, Martin
    Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
    Gronoff, Guillaume
    Science directorate, Chemistry & Dynamics branch, NASA Langley Research Center, Hampton, Virginia, USA. SSAI, Hampton, Virginia, USA.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Solar wind charge exchange in cometary atmospheres: III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A37Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ.

    Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

    Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas.

    Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions.

    Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

  • 34.
    Wedlund, Cyril Simon
    et al.
    Department of Physics, University of Oslo, Oslo, Norway.
    Bodewits, Dennis
    Physics Department, Auburn University, Auburn, USA.
    Alho, Markku
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Hoekstra, Ronnie
    Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Gronoff, Guillaume
    Science directorate, Chemistry & Dynamics branch, NASA Langley Research Center, Hampton, Virginia, USA. SSAI, Hampton, Virginia, USA.
    Gunell, Herbert
    Royal Belgian Institute for Space Aeronomy, Brussels, Belgium. Department of Physics, Umeå University, Umeå, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna, Sweden.
    Kallio, Esa
    Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Aalto, Finland.
    Beth, Arnaud
    Department of Physics, Imperial College London, London, UK.
    Solar wind charge exchange in cometary atmospheres: I. Charge-changing and ionization cross sections for He and H particles in H2O2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A35Article in journal (Refereed)
    Abstract [en]

    Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet, mass-loading the solar wind through an effective conversion of fast light solar wind ions into slow heavy cometary ions.

    Aims. To understand these processes and place them in the context of a solar wind plasma interacting with a neutral atmosphere, numerical or analytical models are necessary. Inputs of these models, such as collision cross sections and chemistry, are crucial.

    Methods. Book-keeping and fitting of experimentally measured charge-changing and ionization cross sections of hydrogen and helium particles in a water gas are discussed, with emphasis on the low-energy/low-velocity range that is characteristic of solar wind bulk speeds (<20 keV u−1/2000 km s−1).

    Results. We provide polynomial fits for cross sections of charge-changing and ionization reactions, and list the experimental needs for future studies. To take into account the energy distribution of the solar wind, we calculated Maxwellian-averaged cross sections and fitted them with bivariate polynomials for solar wind temperatures ranging from 105 to 106 K (12–130 eV).

    Conclusions. Single- and double-electron captures by He2+ dominate at typical solar wind speeds. Correspondingly, single-electron capture by H+ and single-electron loss by H dominate at these speeds, resulting in the production of energetic neutral atoms (ENAs). Ionization cross sections all peak at energies above 20 keV and are expected to play a moderate role in the total ion production. However, the effect of solar wind Maxwellian temperatures is found to be maximum for cross sections peaking at higher energies, suggesting that local heating at shock structures in cometary and planetary environments may favor processes previously thought to be negligible. This study is the first part in a series of three on charge exchange and ionization processes at comets, with a specific application to comet 67P/Churyumov-Gerasimenko and the Rosetta mission.

  • 35.
    Wedlund, Cyril Simon
    et al.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Kallio, Esa
    Finnish Meteorological Institute, Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Alho, Markku
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wieser, Gabriella Stenberg
    Swedish Institute of Space Physics.
    Gunell, Herbert
    Swedish Institute of Space Physics / Institutet för rymdfysik , Belgian Institute for Space Aeronomy, Brussels.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Pusa, J.
    Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering.
    Gronoff, Guillaume
    Science Directorate, Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, Virginia.
    The atmosphere of comet 67P/Churyumov-Gerasimenko diagnosed by charge-exchanged solar wind alpha particles2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A154Article in journal (Refereed)
    Abstract [en]

    Context. The ESA/Rosetta mission has been orbiting comet 67P/Churyumov-Gerasimenko since August 2014, measuring its dayside plasma environment. The ion spectrometer onboard Rosetta has detected two ion populations, one energetic with a solar wind origin (H+, He2+, He+), the other at lower energies with a cometary origin (water group ions such as H2O+). He+ ions arise mainly from charge-exchange between solar wind alpha particles and cometary neutrals such as H2O. Aims. The He+ and He2+ ion fluxes measured by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA) give insight into the composition of the dayside neutral coma, into the importance of charge-exchange processes between the solar wind and cometary neutrals, and into the way these evolve when the comet draws closer to the Sun. Methods. We combine observations by the ion spectrometer RPC-ICA onboard Rosetta with calculations from an analytical model based on a collisionless neutral Haser atmosphere and nearly undisturbed solar wind conditions. Results. Equivalent neutral outgassing rates Q can be derived using the observed RPC-ICA He+/He2+ particle flux ratios as input into the analytical model in inverse mode. A revised dependence of Q on heliocentric distance Rh in AU is found to be Rh -7.06Rh-7.06 between 1.8 and 3.3 AU, suggesting that the activity in 2015 differed from that of the 2008 perihelion passage. Conversely, using an outgassing rate determined from optical remote sensing measurements from Earth, the forward analytical model results are in relatively good agreement with the measured RPC-ICA flux ratios. Modelled ratios in a 2D spherically-symmetric plane are also presented, showing that charge exchange is most efficient with solar wind protons. Detailed cometocentric profiles of these ratios are also presented. Conclusions. In conclusion, we show that, with the help of a simple analytical model of charge-exchange processes, a mass-capable ion spectrometer such as RPC-ICA can be used as a "remote-sensing" instrument for the neutral cometary atmosphere.

  • 36.
    Yamauchi, M
    et al.
    Swedish Institute of Space Physics (IRF), Kiruna, Sweden.
    Sergienko, T
    Swedish Institute of Space Physics (IRF), Kiruna, Sweden .
    Enell, C-F
    EISCAT Scientific Association, Kiruna, Sweden.
    Schillings, Audrey
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics (IRF), Kiruna, Sweden.
    Slapak, Rikard
    EISCAT Scientific Association, Kiruna, Sweden.
    Johnsen, M G
    Tromsø Geophysical Observatory (TGO), UiT the Arctic University of Norway, Tromsø, Norway.
    Tjulin, A
    EISCAT Scientific Association, Kiruna, Sweden.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics (IRF), Kiruna, Sweden .
    Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview2018In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, no 9, p. 1437-1450Article in journal (Refereed)
    Abstract [en]

    We present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner magnetosphere, and an AL < −2,000 substorm took place. (1) Both X flares caused enhancement of ionospheric electron density for about 10 min. The X9.3 flare also increased temperatures of both electrons and ions over 69°–75° geomagnetic latitude until the X‐ray flux decreased below the level of X‐class flares. However, the temperature was not enhanced after the previous X2.2 flare in the prenoon sector. (2) At around 75° geomagnetic latitude, the prenoon ion upflow flux slightly increased the day after the X9.3 flare, which is also after the first ICME and a SEP event, while no outstanding enhancement was found at the time of these X flares. (3) The upflow velocity sometimes decreased when the interplanetary magnetic field (IMF) turned southward. (4) Before the first ICME arrival after the SEP event under weak IMF with Bz ~0 nT, a substorm‐like expansion of the auroral arc signature took place without local geomagnetic signature near local midnight, while no notable change was observed after the ICME arrival. (5) AL reached <−2,000 nT only after the arrival of the second ICME with strongly southward IMF. Causality connections between the solar/solar wind event and the ionospheric responses remain unclear.

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