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  • 151.
    Meisel, David D.
    et al.
    SUNY Geneseo, NY, USA.
    Kero, Johan
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Szasz, Csilla
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Sidorov, Vladimir
    Kazan State University, Russia.
    Briczinski, Stan
    Penn State University, PA, USA.
    Physical Characteristics of Kazan Minor Showers as Determined by Correlations with the Arecibo UHF Radar2008Ingår i: Earth, moon, and planets, ISSN 0167-9295, E-ISSN 1573-0794, Vol. 102, nr 1-4, s. 315-322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position and velocity. Although some may be chance associations, only those events with probabilities of association[0.5 have been kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from the AO results. By comparing these histograms with those of the ‘‘background’’ in which the minor showers are found, a qualitative scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual ‘‘apex’’ sporadic source areas where it is easiest to detect discrete showers with less confusion from the background.

  • 152.
    Meisel, David D.
    et al.
    SUNY Geneseo, NY, USA.
    Szasz, Csilla
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Kero, Johan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Quantitative Comparison of a New Ab Initio Micrometeor Ablation Model with an Observationally Verifiable Standard Model2008Ingår i: Advances in Meteoroid and Meteor Science, 2008, s. 411-415Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height range of 80–140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere

    properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over the mass range 10-16 kg to 10-7 kg, but the faint end

    of this range cannot be observed by any other method and so direct verification is not possible. On the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations can be fit to a ‘‘standard’’ ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the

    features of the ab initio model that are different from the ‘‘standard’’ model are: (1) uses the experimentally based low pressure vaporization theory of O’Hanlon (A users’s guide to

    vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from experimental data on heat transfer, luminosity and ionization efficiencies measured by

    Friichtenicht and Becker (NASA Special Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids and

    ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits (as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical Quantities 2000). This utilization of mostly experimentally determined data is the main reason for calling this an ab initio model and is made necessary by the fact that individual average meteoroid mass densities are now derivable from Arecibo observations.

  • 153.
    Meisel, David D.
    et al.
    SUNY Geneseo, NY, USA.
    Szasz, Csilla
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Kero, Johan
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Quantitative Comparison of a New Ab Initio Micrometeor Ablation Model with an Observationally Verifiable Standard Model2008Ingår i: Earth, moon, and planets, ISSN 0167-9295, E-ISSN 1573-0794, Vol. 102, nr 1-4, s. 411-415Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height range of 80–140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over the mass range 10-16 kg to 10-7 kg, but the faint end of this range cannot be observed by any other method and so direct verification is not possible. On the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations can be fit to a ‘‘standard’’ ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the features of the ab initio model that are different from the ‘‘standard’’ model are: (1) uses the experimentally based low pressure vaporization theory of O’Hanlon (A users’s guide to vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from experimental data on heat transfer, luminosity and ionization efficiencies measured by Friichtenicht and Becker (NASA Special Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids and ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits (as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical Quantities 2000). This utilization of mostly experimentally determined data is the main reason for calling this an ab initio model and is made necessary by the fact that individual average meteoroid mass densities are now derivable from Arecibo observations.

  • 154. Mendoca, JT
    et al.
    Ribeiro, JE
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK.
    Wave kinetic description of quantum pair plasmas2008Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 74, nr 1, s. 91-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dispersion relation for a quantum pair plasma is derived, by using a wave kinetic description. A general form of the kinetic dispersion relation for eleetrostatic waves in a two-component quantum plasma is established. The particular case of an electron positron pair plasma is considered in detail. Exact expressions for Landau damping are derived, and the quasi-classical limit is discussed.

  • 155. Mendonca, J T
    et al.
    Bingham, R
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780, Bochum, Germany.
    A kinetic approach to Bose-Einstein condensates: self-phase modulation and Bogoliubov oscillations2005Ingår i: Journal of Experimental and Theoretical Physics, ISSN 1063-7761, E-ISSN 1090-6509, Vol. 101, nr 5, s. 942-948Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A kinetic approach to Bose-Einstein condensates (BECs) is proposed based on the Wigner-Moyal equation (WME). In the semiclassical limit, the WME reduces to the particle-number conservation equation. Two examples of applications are (i) a self-phase modulation of a BE condensate beam, where we show that part of the beam is decelerated and eventually stops as a result of the gradient of the effective self-potential, and (ii) the derivation of a kinetic dispersion relation for sound waves in BECs, including collisionless Landau damping.

  • 156. Mendonca, J T
    et al.
    Shukla, Nitin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Also at GoLP/Instituto de Plasmas Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica do Lisboa, Portugal.
    Shukla, P K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Germany; Scottish Universities Physics Alliance (SUPA), Department of Physics, University of Strathclyde, Glasgow, UK; GoLP/Instituto de Plasmas Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica do Lisboa, Portugal; School of Physics, University of KwaZulu-Natal, Durban, South Africa; Max-Planck Institut für Extraterrestrische Physik und Plasmaphysik, Garching, Germany.
    Magnetization of Rydberg plasmas by electromagnetic waves2010Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, s. 19-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is shown that the ponderomotive force of a large-amplitude electro-magnetic wave in Rydberg plasmas can generate quasi-stationary magnetic fields. The present result can account for the origin of seed magnetic fields in the ultracold Rydberg plasmas when they irradiated by the high-frequency electromagnetic wave.

  • 157. Mendonca, JT
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Centre for Fundamental Physics (CfFP), STFC Rutherford Appleton Laboratory, Chilton, Didcot, UK; Institut für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany; SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK .
    Bingham, R
    Nonlinear excitation of zonal flows by Rossby wave turbulence2009Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11, artikel-id 073038Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We apply the wave-kinetic approach to study nonlinearly coupled Rossby wave-zonal flow fluid turbulence in a two-dimensional rotating fluid. Specifically, we consider for the first time nonlinear excitations of zonal flows by a broad spectrum of Rossby wave turbulence. Short-wavelength Rossby waves are described here as a fluid of quasi-particles, and are referred to as the 'Rossbyons'. It is shown that Reynolds stresses of Rossbyons can generate large-scale zonal flows. The result should be useful in understanding the origin of large-scale planetary and near-Earth atmospheric circulations. It also provides an example of a turbulent wave background driving a coherent structure.

  • 158. Meyer-Vernet, Nicole
    et al.
    Mann, Ingrid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. EISCAT Scientific Association, Kiruna, Sweden .
    Le Chat, G
    Schippers, P
    Belheouane, S
    Issautier, K
    Lecacheux, A
    Maksimovic, M
    Pantellini, F
    Zaslavsky, A
    The physics and detection of nanodust in the solar system2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 1, artikel-id 014015Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mass distribution of small bodies in the solar system extends over more than 35 orders of magnitude, from asteroids to nanodust, which bridge the gap between molecules and macroscopic submicron grains. The small size of nanograins compared to the relevant basic scales gives them peculiar properties. Some of these properties affect their electric charging and their large charge-to-mass ratio drives their acceleration to very high speeds in moving magnetised plasmas, as the solar wind and rotating planetary magnetospheres. The electric charge and/or high speed of nanograins have enabled them to be detected serendipitously in various parts of the solar system by several instruments designed to study larger dust, plasma particles, or waves, on a number of spacecraft. These discoveries have opened an emerging field of research, in which many open questions remain, in particular concerning the lower size limit of the particles.

  • 159.
    Misra, A. P.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, P. K.
    Stability and evolution of wave packets in strongly coupled degenerate plasmas2012Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, nr 2, s. 026409-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the nonlinear propagation of electrostatic wave packets in a collisional plasma composed of strongly coupled ions and relativistically degenerate electrons. The equilibrium of ions is maintained by an effective temperature associated with their strong coupling, whereas that of electrons is provided by the relativistic degeneracy pressure. Using a multiple-scale technique, a (3 + 1)-dimensional coupled set of nonlinear Schrodinger-like equations with nonlocal nonlinearity is derived from a generalized viscoelastic hydrodynamic model. These coupled equations, which govern the dynamics of wave packets, are used to study the oblique modulational instability of a Stoke's wave train to a small plane-wave perturbation. We show that the wave packets, though stable to the parallel modulation, become unstable against oblique modulations. In contrast to the long-wavelength carrier modes, the wave packets with short wavelengths are shown to be stable in the weakly relativistic case, whereas they can be stable or unstable in the ultrarelativistic limit. Numerical simulation of the coupled equations reveals that a steady-state solution of the wave amplitude exists together with the formation of a localized structure in (2 + 1) dimensions. However, in the (3 + 1)-dimensional evolution, a Gaussian wave beam self-focuses after interaction and blows up in a finite time. The latter is, however, arrested when the dispersion predominates over the nonlinearities. This occurs when the Coulomb coupling strength is higher or a choice of obliqueness of modulation, or a wavelength of excitation is different. Possible application of our results to the interior as well as in an outer mantle of white dwarfs are discussed.

  • 160.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Banerjee, S.
    Upper-hybrid wave-driven Alfvenic turbulence in magnetized dusty plasmas2011Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, nr 3, artikel-id 037401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear dynamics of coupled electrostatic upper-hybrid (UH) and Alfven waves (AWs) is revisited in a magnetized electron-ion plasma with charged dust impurities. A pair of nonlinear equations that describe the interaction of UH wave envelopes (including the relativistic electron mass increase) and the density as well as the compressional magnetic field perturbations associated with the AWs are solved numerically to show that many coherent solitary patterns can be excited and saturated due to modulational instability of unstable UH waves. The evolution of these solitary patterns is also shown to appear in the states of spatiotemporal coherence, temporal as well as spatiotemporal chaos, due to collision and fusion among the patterns in stochastic motion. Furthermore, these spatiotemporal features are demonstrated by the analysis of wavelet power spectra. It is found that a redistribution of wave energy takes place to higher harmonic modes with small wavelengths, which, in turn, results in the onset of Alfvenic turbulence in dusty magnetoplasmas. Such a scenario can occur in the vicinity of Saturn's magnetosphere as many electrostatic solitary structures have been observed there by the Cassini spacecraft.

  • 161.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Banerjee, S
    Haas, F
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, P K
    Assis, L P G
    Temporal dynamics in the one-dimensional quantum Zakharov equations for plasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 3, artikel-id 032307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The temporal dynamics of the quantum Zakharov equations in one spatial dimension, which describes the nonlinear interaction of quantum Langmuir waves and quantum ion-acoustic waves, is revisited by considering their solution as a superposition of three interacting wave modes in Fourier space. Previous results in the literature are modified and rectified. Periodic, chaotic, and hyperchaotic behaviors of the Fourier-mode amplitudes are identified by the analysis of Lyapunov exponent spectra and the power spectrum. The periodic route to chaos is explained through a one-parameter bifurcation analysis. The system is shown to be destabilized via a supercritical Hopf-bifurcation. The adiabatic limits of the fully spatiotemporal and reduced systems are compared from the viewpoint of integrability properties.

  • 162.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Generation of wakefields by whistlers in spin quantum magnetoplasmas2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 12, artikel-id 122306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The excitation of electrostatic wakefields in a magnetized spin quantum plasma by the classical and the spin-induced ponderomotive force (CPF and SPF, respectively) due to whistler waves is reported. The nonlinear dynamics of the whistlers and the wakefields is shown to be governed by a coupled set of nonlinear Schrodinger and driven Boussinesq-like equations. It is found that the quantum force associated with the Bohm potential introduces two characteristic length scales, which lead to the excitation of multiple wakefields in a strongly magnetized dense plasma (with a typical magnetic field strength B(0)greater than or similar to 10(9) T and particle density n(0)greater than or similar to 10(36) m(-3)), where the SPF strongly dominates over the CPF. In other regimes, namely, B(0)less than or similar to 10(8) T and n(0)less than or similar to 10(35) m(-3), where the SPF is comparable to the CPF, a plasma wakefield can also be excited self-consistently with one characteristic length scale. Numerical results reveal that the wakefield amplitude is enhanced by the quantum tunneling effect; however, it is lowered by the external magnetic field. Under appropriate conditions, the wakefields can maintain high coherence over multiple plasma wavelengths and thereby accelerate electrons to extremely high energies. The results could be useful for particle acceleration at short scales, i.e., at nanometer and micrometer scales, in magnetized dense plasmas where the driver is the whistler wave instead of a laser or a particle beam.

  • 163. Misra, Amar P.
    et al.
    Chatterjee, Debjani
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Effects of group velocity and multiplasmon resonances on the modulation of Langmuir waves in a degenerate plasma2017Ingår i: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, nr 5, artikel-id 053209Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the nonlinear wave modulation of Langmuir waves (LWs) in a fully degenerate plasma. Using the Wigner-Moyal equation coupled to the Poisson equation and the multiple scale expansion technique, a modified nonlocal nonlinear Schrodinger (NLS) equation is derived which governs the evolution of LW envelopes in degenerate plasmas. The nonlocal nonlinearity in the NLS equation appears due to the group velocity and multiplasmon resonances, i.e., resonances induced by the simultaneous particle absorption of multiple wave quanta. We focus on the regime where the resonant velocity of electrons is larger than the Fermi velocity and thereby the linear Landau damping is forbidden. As a result, the nonlinear wave-particle resonances due to the group velocity and multiplasmon processes are the dominant mechanisms for wave-particle interaction. It is found that in contrast to classical or semiclassical plasmas, the group velocity resonance does not necessarily give rise the wave damping in the strong quantum regime where hk similar to mv(F) with _ h denoting the reduced Planck's constant, m the electron mass, and v(F) the Fermi velocity; however, the three-plasmon process plays a dominant role in the nonlinear Landau damping of wave envelopes. In this regime, the decay rate of the wave amplitude is also found to be higher compared to that in the modest quantum regime where the multiplasmon effects are forbidden.

  • 164.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma K
    RUB International Chair, International Centre for Advanced Studies in Physical Sciences, Faculty of Physics and Astronomy, Ruhr University Bochum, Bochum, Germany.
    Stability of two-dimensional ion-acoustic wave packets in quantum plasmas2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 4, s. 042102-042109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear propagation of two-dimensional (2D) quantum ion-acoustic waves (QIAWs) is studied in a quantum electron–ion plasma. By using a 2D quantum hydrodynamic model and the method of multiple scales, a new set of coupled nonlinear partial differential equations is derived which governs the slow modulation of the 2D QIAW packets. The oblique modulational instability (MI) is then studied by means of a corresponding nonlinear Schrödinger equation derived from the coupled nonlinear partial differential equations. It is shown that the quantum parameter H (ratio of the plasmon energy density to Fermi energy) shifts the MI domains around the kθ -plane, where k is the carrier wave number and θ is the angle of modulation. In particular, the ion-acoustic wave (IAW), previously known to be stable under parallel modulation in classical plasmas, is shown to be unstable in quantum plasmas. The growth rate of the MI is found to be quenched by the obliqueness of modulation. The modulation of 2D QIAW packets along the wave vector k is shown to be described by a set of Davey–Stewartson-like equations. The latter can be studied for the 2D wave collapse in dense plasmas. The predicted results, which could be important to look for stable wave propagation in laboratory experiments as well as in dense astrophysical plasmas, thus generalize the theory of MI of IAW propagations both in classical and quantum electron–ion plasmas.

  • 165.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Mathematics, Siksha Bhavana, Visva-Bharati University, India.
    Samanta, S
    Double-layer shocks in a magnetized quantum plasma2010Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 82, nr 3, artikel-id 037401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio delta. The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.

  • 166.
    Misra, Amar P
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, PK
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nonlinear wave-wave interactions in quantum plasmas2010Ingår i: New frontiers in advanced plasma physics, American Institute of Physics (AIP), 2010, s. 103-110Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wave-wave interaction in plasmas is a topic of important research since the 16th century. The formation of Langmuir solitons through the coupling of high-frequency (hf) Langmuir and low-frequency (If) ion-acoustic waves, is one of the most interesting features in the context of turbulence in modern plasma physics. Moreover, quantum plasmas, which are ubiquitous in ultrasmall electronic devices, micromechanical systems as well as in dense astrophysical environments are a topic of current research. In the light of notable interests in such quantum plasmas, we present here a theoretical investigation on the nonlinear interaction of quantum Langmuir waves (QLWs) and quantum ion-acoustic waves (QIAWs), which are governed by the one-dimensional quantum Zakharov equations (QZEs). It is shown that a transition to spatiotemporal chaos (STC) occurs when the length scale of excitation of linear modes is larger than that of the most unstable ones. Such length scale is, however, to be larger (compared to the classical one) in presence of the quantum tunneling effect. The latter induces strong QIAW emission leading to the occurrence of collision and fusion among the patterns at an earlier time than the classical case. Moreover, numerical simulation of the QZEs reveals that many solitary patterns can be excited and saturated through the modulational instability (MI) of unstable harmonic modes. In a longer time, these solitons are seen to appear in the state of STC due to strong QIAW emission as well as by the collision and fusion in stochastic motion. The energy in the system is thus strongly redistributed, which may switch on the onset of Langmuir turbulence in quantum plasmas.

  • 167.
    Misra, Amar Prasad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Modulational instability and nonlinear evolution of two-dimensional electrostatic wave packets in ultra-relativistic degenerate dense plasmas2011Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 18, nr 4, artikel-id 042308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the nonlinear propagation of electrostatic wave packets in an ultra-relativistic (UR) degenerate dense electron-ion plasma, whose dynamics is governed by the nonlocal two-dimensional nonlinear Schrodinger-like equations. The coupled set of equations is then used to study the modulational instability (MI) of a uniform wave train to an infinitesimal perturbation of multidimensional form. The condition for the MI is obtained, and it is shown that the nondimensional parameter, beta proportional to lambda(C)n(0)(1/3) (where lambda(C) is the reduced Compton wavelength and n(0) is the particle number density) associated with the UR pressure of degenerate electrons, shifts the stable (unstable) regions at n(0) similar to 10(30)cm(-3) to unstable (stable) ones at higher densities, i.e., n(0) greater than or similar to 7 x 10(33). It is also found that the higher the values of n(0), the lower is the growth rate of MI with cut-offs at lower wave numbers of modulation. Furthermore, the dynamical evolution of the wave packets is studied numerically. We show that either they disperse away or they blowup in a finite time, when the wave action is below or above the threshold. The results could be useful for understanding the properties of modulated wave packets and their multidimensional evolution in UR degenerate dense plasmas, such as those in the interior of white dwarfs and/or pre-Supernova stars.

  • 168. Misra, AP
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik and Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa; Nonlinear Physics Centre, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior T’ecnico, 1049-001 Lisboa, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, United Kingdom; SUPA Department of Physics, University of Strathclyde, Glasgow G40NG, United Kingdom; Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan.
    Modulational instability of magnetosonic waves in a spin 1/2 quantum plasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 5, artikel-id 052105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The modulational instability (MI) of magnetosonic waves (MSWs) is analyzed, by using a two-fluid quantum magnetohydrodynamic model that includes the effects of the electron-1/2 spin and the plasma resistivity. The envelope modulation is then studied by deriving the corresponding nonlinear Schrodinger equation from the governing equations. The plasma resistivity is shown to play a dissipative role for the onset of MI. In the absence of resistivity, the microscopic spin properties of electrons can also lead to MI. In such a situation, the dominant spin contribution corresponds to a dense quantum plasma with the particle number density, n(0)greater than or similar to 10(28) m(-3). Also, in such a dissipative (absorbing) medium, where the group velocity vector is usually complex for real values of the wave vector, the role of the real group velocity in the propagation of one-dimensional MSW packets in a homogeneous absorbing medium is reported. The effects of quantum spin on the stability/instability conditions of the magnetosonic envelope are obtained and examined numerically. From the nonlinear dispersion relation of the modulated wave packet it is found that the effect of the spin (plasma resistivity) is to decrease (increase) the instability growth rate provided the normalized Zeeman energy does not exceed a critical value. The theoretical results may have relevance to astrophysical (e.g., magnetars) as well as to ultracold laboratory plasmas (e.g., Rydberg plasmas).

  • 169. Misra, AP
    et al.
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultät für Physik and Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; School of Physics, University of KwaZulu-Natal, 4000 Durban, South Africa; Nonlinear Physics Centre, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior T’ecnico, 1049-001 Lisboa, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G40NG, UK; Department of Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan.
    Relativistic modulational instability of electron-acoustic waves in an electron-pair ion plasma2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 12, artikel-id 122107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The modulational instability of finite amplitude electron-acoustic waves (EAWs) along the external magnetic field is studied in an electron-pair ion plasma. Accounting for the relativistic electron mass variation nonlinearity and the Boltzmann distribution of both positive and negative ions, new regimes for the relativistic modulational instability (MI) for the low frequency (below the electron gyrofrequency) short-wavelength (in comparison with the ion gyroradius) modes are obtained numerically. It is found that the presence of a significant fraction of negative ions suppresses the MI growth/decay rate for the modulated EAW packets. The results could be of important for understanding the origin of amplitude modulated EAW packets in space (e.g., Earth's magnetotail) as well as in laboratory plasmas.

  • 170. Modestov, M.
    et al.
    Bychkov, Vitaly
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Brodin, Gert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Marklund, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Brandenburg, A.
    Evolution of the magnetic field generated by the Kelvin-Helmholtz instability2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 7, s. 072126-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kelvin-Helmholtz instability in an ionized plasma is studied with a focus on the magnetic field generation via the Biermann battery (baroclinic) mechanism. The problem is solved by using direct numerical simulations of two counter-directed flows in 2D geometry. The simulations demonstrate the formation of eddies and their further interaction and merging resulting in a large single vortex. In contrast to general belief, it is found that the instability generated magnetic field may exhibit significantly different structures from the vorticity field, despite the mathematically identical equations controlling the magnetic field and vorticity evolution. At later stages of the nonlinear instability development, the magnetic field may keep growing even after the hydrodynamic vortex strength has reached its maximum and started decaying due to dissipation.

  • 171.
    Modestov, Mikhail
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Fronts and instabilities in laser ablation, organic semiconductors and quantum media2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Konceptet med en utbredningsfront spelar en avgörande roll inom många olika områden i fysik. I denna avhandling studeras centrala aspekter av utbredningsfronters dynamik och deras stabilitet i för laser-plasmaväxelverkan, organiska halvledare samt kvantmedier. 

    För laser-plasmaväxelverkan har vi undersökt de hydrodynamiska instabiliteter, som t ex Rayleigh-Taylor-instabiliteten, vilka utvecklas vid deflagrationsfronter (under så kallad laserablation). Med hjälp av direkta numeriska simuleringar har vi hittat en märkbar hastighetökning av Rayleigh-Taylor bubblan i en deaflgrationsfront jämfört med det som kan ses vid ett inert gränssnitt. Vi har även studerat Darrieus-Landau-instabiliteten vid laserdeflagration, speciellt hur denna påverkas av de specifika egenskaperna hos ett fusionsplasma: ett starkt temperaturberoende hos värmeledningen samt plasmaflödet som uppnår ljudhastighet.

    Vi har funnit att dessa egenskaper hos laser-plasmasystem gör Darrieus-Landau instabilitet starkare jämfört med det vanliga fallet av långsamma flammor. Vi har även klargjort de experimentella förutsättningar som krävs för observationer av Darrieus-Landau instabilitet i laser-plasmasystem. 

    Vi har studerat samspelet mellan klassiska och kvantmekaniska aspekter i kvantplasmor. Specifikt har vi undersökt chockvågors utbredning och dynamik samt instabiliteter i pseudo-ferrofluider. För chocker i kvantplasmor har vi visat att en övergång från Burgers klassiska monotona chockstruktur till ett vågtåg av solitoner sker i kvantgränsen. Vi för också en motsvarighet till ferrofluidinstabiliter i magnetiserade plasmor  på grund av dess kollektiva spinn-dynamik i ett yttre magnetfält. Vi har diskuterar instabilitetens roll för termonukleära explosioner hos vita dvärgar i supernovor av typ Ia.  

    I organiska halvledare har vi utvecklat en teoretisk och numerisk modell av elektrokemiska dopningsfronter. Studien är baserad på en modifierade drift-diffusiondmodell för komplexa dopade halvledare, vilka består av hål, elektroner, positiva och negativa joner. Modellen beskriver dopningsstrukturen och gör det möjligt att beräkna dopningsfrontens hastighet med värden som överensstämmer mycket väl med experimenten. Vi har även upptäckt en ny grundläggande instabilitet, vilket gör dopningsfronter anisotrop och snabbar upp processen betydligt. Vi visar hur instabilitet kan styras och användas för att förbättra optoelektronisk utrustning.  

    Slutligen studerar vi laviner av spin-växlingar i kristaller bestående av nanomagneter. Denna process kan beskrivas i termer av ett nytt analogt koncept, så kallad magnetiska deflagration och detonation, på grund av de slående likheter dessa har till motsvarande förbränningsfenomen. Vi har funnit att magnetiska deflagration blir instabil och propagerar i en pulserande regim när potentialbarriären för spin-växling är tillräckligt hög i jämförelse med frigörelsen av energi i processen. Vi visar också möjlighet till magnetisk detonation i dessa  kristaller, vilket förklarar de ultrasnabba spin-laviner man stött på under vid experiment helt nyligen. Denna magnetiska detonation förstör inte de unika egenskaperna hos kristallerna, en mycket viktig slutsats med tanke på möjliga tillämpningar av nanomagneter i kvantdatorer.

  • 172.
    Modestov, Mikhail
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Bychkov, Vitaly
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Betti, Riccardo
    Fusion Science Center and Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623, USA .
    Eriksson, Lars-Erik
    Department of Applied Mechanics, Chalmers University of Technology, 412 96 Göteborg, Sweden.
    Bubble velocity in the nonlinear Rayleigh-Taylor instability at a deflagration front2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 4, s. 042703-042715Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Rayleigh-Taylor instability at a deflagration front is studiedsystematically using extensive direct numerical simulations.  Itis shown that, for a sufficiently large gravitational field, theeffects of bubble rising dominate the deflagration dynamics. Itis demonstrated both analytically and numerically that thedeflagration speed is described asymptotically by the Layzertheory in the limit of large acceleration. In the opposite limitof small and zero gravitational field, intrinsic properties of thedeflagration front become important. In that case, the deflagrationspeed is determined by the velocity of a planar front and by theDarrieus-Landau instability. Because of these effects, thedeflagration speed is larger than predicted by theLayzer theory. An analytical formula for the deflagration speedis suggested, which matches two asymptotic limits of large andsmall acceleration. The formula is in good agreement withthe numerical data in a wide range of Froude numbers. Thepresent results are also in agreement with previous numericalsimulations on this problem.

  • 173. Moslem, W M
    et al.
    Sabry, R
    Shukla, P K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Germany; School of Physics, University of Kwazulu-Durban, South Africa; Max-Planck Institut für Extraterrestrische Physik, Garching, Germany; GoLP/Instituto Superior Técnico, Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK; SUPA Department of Physics, University of Strathclyde, Glasgow, UK.
    Three dimensional cylindrical Kadomtsev-Petviashvili equation in a very dense electron-positron-ion plasma2010Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 3, artikel-id 032305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By using the hydrodynamic equations of ions, Thomas-Fermi electron/positron density distribution, and Poisson equation, a three-dimensional cylindrical Kadomtsev-Petviashvili (CKP) equation is derived for small but finite amplitude ion-acoustic waves. The generalized expansion method is used to analytically solve the CKP equation. New class of solutions admits a train of well-separated bell-shaped periodic pulses is obtained. At certain condition, the latter degenerates to solitary wave solution. The effects of physical parameters on the solitary pulse structures are examined. Furthermore, the energy integral equation is used to study the existence regions of the localized pulses. The present study might be helpful to understand the excitation of nonlinear ion-acoustic waves in a very dense astrophysical objects such as white dwarfs.

  • 174. Moslem, WM
    et al.
    Ali, S
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; School of Physics, University of KwaZulu-Natal, Durban 4000, South Africa; Max-Planck Institut für Extraterrestrische Physik, D-45741 Garching, Germany; CCLRC Center for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 OQX, United Kingdom; SUPA Department of Physics, University of Strathclyde, Glasgow G4 ONG, United Kingdom; GoLP/Centro de Fisica de Plasmas, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049 Lisboa, Portugal.
    Tang, XY
    Rowlands, G
    Solitary, explosive, and periodic solutions of the quantum Zakharov-Kuznetsov equation and its transverse instability2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 8, artikel-id 082308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By employing the quantum hydrodynamic model and the reductive perturbation technique, a quantum Zakharov-Kuznetsov (QZK) equation is derived for finite but small amplitude ion-acoustic waves in a quantum magnetoplasma. The extended Conte's truncation method is used to obtain the solitary, explosive, and periodic solutions of the QZK equation. Furthermore, the stability of the solitary wave solution of the QZK equation is investigated by using the small-k perturbation expansion method.

  • 175. Moslem, WM
    et al.
    Lazar, M
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Nonlinear Physics Centre & Center for Plasma Science and Astrophysics, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G 40NG, UK; School of Physics, Faculty of Science & Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa; and Department of Physics, CITT, Islamabad, Pakistan.
    Finite amplitude envelope surface solitons2008Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 4, artikel-id 042301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Known results on the nonlinear coupling of surface plasma waves with quasistationary ion density perturbations are generalized to include finite amplitude density modulations. A more rigorous analytical criterion is provided for the existence of the surface soliton, by using the pseudopotential formalism. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The present results are useful in understanding the nonlinear dynamics and the periodic oscillatory structures on plasma surfaces.

  • 176. Moslem, WM
    et al.
    Sabry, R
    Abdelsalam, UM
    Kourakis, I
    Shukla, Padma Kant
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, D-44780 Bochum, Germany; Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany; GoLP/Instituto Superior Técnico, 1049-001 Lisbon, Portugal; CCLRC Centre for Fundamental Physics, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, UK; SUPA Department of Physics, University of Strathclyde, Glasgow G 40NG, UK; School of Physics, Faculty of Science and Agriculture, University of Kwazulu-Natal, Durban 4000, South Africa; Department of Physics, CITT, Islamabad, Pakistan.
    Solitary and blow-up electrostatic excitations in rotating magnetized electron-positron-ion plasmas2009Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11, artikel-id 033028Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear dynamics of a rotating magnetoplasma consisting of electrons, positrons and stationary positive ions is considered. The basic set of hydrodynamic and Poisson equations are reduced to a Zakharov-Kuznetsov (ZK) equation for the electric potential. The ZK equation is solved by applying an improved modified extended tanh-function method (2008 Phys. Lett. A 372 5691) and its characteristics are investigated. A set of new solutions are derived, including localized solitary waves, periodic nonlinear waveforms and divergent (explosive) pulses. The characteristics of these nonlinear excitations are investigated in detail.

  • 177.
    Moslem, WM
    et al.
    Department of Physics, Faculty of Science, Port Said University, Port Said, Egypt .
    Sabry, R
    Theoretical Physics Group, Department of Physics, Faculty of Science, Mansoura University, Damietta Branch, New Damietta 34517, Egypt.
    Shukla, Padma K
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. UB International Chair, International Center for Advanced Studies in Physical Sciences, Faculty of Physics & Astronomy, Ruhr University Bochum, D-44780 Bochum, Germany.
    The optimum shielding around a test charge in plasmas containing two negative ions2011Ingår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 77, nr 5, s. 663-673Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper focuses on the progress in understanding the shielding around a test charge in the presence of ion-acoustic waves in multispecies plasmas, whose constituents are positive ions, two negative ions, and Boltzmann distributed electrons. By solving the linearized Vlasov equation with Poisson equation, the Debye-Huckel screening potential and wakefield (oscillatory) potential distribution around a test charge particle are derived. It is analytically found that both the Debye-Huckel potential and the wakefield potential are significantly modified due to the presence of two negative ions. The present results might be helpful to understand and to form new materials from plasmas containing two negative ions such as Xe(+) - F(-) - SF(6)(-) and Ar(+) - F(-) - SF(6)(-) plasmas, as well as to tackle extension of the test charge problem in multinegative ions' coagulation/agglomeration.

  • 178. Nemecek, Z.
    et al.
    Pavlu, J.
    Richterova, T.
    Safrankova, J.
    Vaverka, Jakub
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Secondary Electron Emission And Its Role in the Space Environment2018Ingår i: DIVERSE WORLD OF DUSTY PLASMAS / [ed] Nemecek, Z Pavlu, J Safrankova, J, AMER INST PHYSICS , 2018, Vol. 1925, artikel-id UNSP 020002Konferensbidrag (Refereegranskat)
    Abstract [en]

    The role of dust in the space environment is of increasing interest in recent years and also the fast development of fusion devices with a magnetic confinement brought new issues in the plasma surface interaction. Among other processes, secondary electron emission plays an important role for dust charging in interplanetary space and its importance increases at and above the surfaces of airless bodies like planets, moons, comets or asteroids. A similar situation can be found in many industrial applications where the dust is a final product or an unintentional impurity. The present paper reviews the progress in laboratory investigations of the secondary emission process as well as an evolution of the modeling of the interaction of energetic electrons with dust grains of different materials and sizes. The results of the model are discussed in view of latest laboratory simulations and they are finally applied on the estimation of an interaction of the solar wind and magnetospheric plasmas with the dust attached to or levitating above the lunar surface.

  • 179. Nilsson, Hans
    et al.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Pitkänen, Timo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, Tomas
    Slapak, Rikard
    Andersson, Laila
    Gunell, Herbert
    Schillings, Audrey
    Vaivads, Andris
    Oxygen ion response to proton bursty bulk flows2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 8, s. 7535-7546Artikel i tidskrift (Refereegranskat)
    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+.

  • 180.
    Norberg, Carol
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Pellinen-Wannberg, Asta
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Active Dust Experiment in the Mesosphere2008Ingår i: AIP Conference Proceedings vol. 1041: Multifacets of Dusty Plasmas: Fifth International Conference on Physics of Dusty Plasmas, 2008, s. 291-292Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The mesosphere stretches from an altitude of about 50 to 90 km above the Earth’s surface. Meteors entering the Earth’s atmosphere are believed to ablate and hence give rise to a thin layer of dust particles in the upper part of the Earth’s mesosphere. It seems that the dust is most dense in a layer that lies between 80 and 90 km. The dust particles are thought to have sizes of a few to tens of nanometers. Efforts have been made to measure these particles using rockets and radar techniques with limited success. We propose to release dust into the mesosphere over northern Sweden at a height of about 90 km and observe the released dust using the EISCAT radar system. The dust will be launched from the Swedish Space Corporation Esrange Space Centre on a single-stage Improved Orion rocket that will be launched so that its flight path will be in the radar field of view.

  • 181.
    Nyberg, Markus
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Lizana, Ludvig
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Persistence of non-Markovian Gaussian stationary processes in discrete time2018Ingår i: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, nr 4, artikel-id 040101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The persistence of a stochastic variable is the probability that it does not cross a given level during a fixed time interval. Although persistence is a simple concept to understand, it is in general hard to calculate. Here we consider zero mean Gaussian stationary processes in discrete time n. Few results are known for the persistence P0(n) in discrete time, except the large time behavior which is characterized by the nontrivial constant θ through P0(n)∼θn. Using a modified version of the independent interval approximation (IIA) that we developed before, we are able to calculate P0(n) analytically in z-transform space in terms of the autocorrelation function A(n). If A(n)→0 as n→∞, we extract θ numerically, while if A(n)=0, for finite n>N, we find θ exactly (within the IIA). We apply our results to three special cases: the nearest-neighbor-correlated "first order moving average process", where A(n)=0 for n>1, the double exponential-correlated "second order autoregressive process", where A(n)=c1λn1+c2λn2, and power-law-correlated variables, where A(n)∼n−μ. Apart from the power-law case when μ<5, we find excellent agreement with simulations.

  • 182.
    Olsson, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dissipation and velocity distribution at the shear-driven jamming transition2016Ingår i: Physical Review E, ISSN 2470-0045, Vol. 93, nr 4, artikel-id 042614Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate energy dissipation and the distribution of particle velocities at the jamming transition for overdamped shear-driven frictionless disks in two dimensions at zero temperature. We find that the dissipation is caused by the fastest particles and that the fraction of particles responsible for the dissipation decreases towards zero as jamming is approached. These particles belong to an algebraic tail of the velocity distribution that approaches similar to v(-3) as jamming is approached. We further find that different measures of the velocity diverge differently, which means that concepts such as typical velocity may no longer be used, a finding that should have implications for analytical approaches to shear-driven jamming.

  • 183.
    Paulsson, Joakim
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Three-wave Interaction and Manley-Rowe Relations in Spin Plasmas2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis we present a fluid model for plasmas which include spin contributions. Also, how to use the model is discussed. We then consider non-linear theories, such as coupled mode theory. The main theory considered is the Manley-Rowe relations for the coupling coefficients. It is easier to work with wave energy densities rather than amplitudes to show Manley-Rowe relations. Manley-Rowe relations are used, both as a test for a theory, showing that the theory has an underlying Hamiltonian structure, and when considering parametric instabilities of the waves. We define a linearised wave energy density for spin plasmas and demonstrate a Manley-Rowe relation for a given geometry for the waves.

  • 184.
    Pellinen-Wannberg, Asta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Rymdfysik.
    Auroral and meteor applications of the EISCAT incoherent scatter radar1995Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 185.
    Pellinen-Wannberg, Asta
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    The Radio Physics of Meteors: High Resolution Radar Methods Offering New Insights2011Ingår i: Radio Science Bulletin, ISSN 1024-4530, Vol. 339, s. 32-45Artikel i tidskrift (Övrigt vetenskapligt)
  • 186.
    Pellinen-Wannberg, Asta
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Box 812, S-98128 Kiruna, Sweden.
    Carrillo Sanchez, Juan Diego
    Haggstrom, Ingemar
    Plane, John M. C.
    Westman, Assar
    E region ionization enhancement over northern Scandinavia during the 2002 Leonids2014Ingår i: 2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS), IEEE , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Intensive E-region ionization was observed with the EISCAT UHF radar during the 2002 Leonids meteor shower. The levels of the geomagnetic disturbance were low during the event. Thus the ionization cannot be explained by intensive precipitation. The layer was 30-40 km thick, so it cannot be classified as a sporadic E-layer (often associated to ions of meteoric origin). These are typically only about km-wide. Incoherent scatter radars have never so far reported any notable meteor shower-related increases in the average background ionization. The 2002 Leonid storm flux, however, was so high that it, if any, might be able to induce such an event. Whether meteors in general can cause such an excess E-region ionization during an intensive shower is discussed. The University of Leeds CABMOD model is used to estimate deposition rates of individual meteors and to relate the results to the predicted Leonid flux values in free space and observed ionization on November 19, 2002.

  • 187.
    Pellinen-Wannberg, Asta K.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Haggstrom, Ingemar
    Sanchez, Juan Diego Carrillo
    Plane, John M. C.
    Westman, Assar
    Strong E region ionization caused by the 1767 trail during the 2002 Leonids2014Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 9, s. 7880-7888Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intensive E region ionization extending up to 140 km altitude and lasting for several hours was observed with the European Incoherent Scatter (EISCAT) UHF radar during the 2002 Leonids meteor shower maximum. The level of global geomagnetic disturbance as well as the local geomagnetic and auroral activity in northern Scandinavia were low during the event. Thus, the ionization cannot be explained by intensive precipitation. The layer was 30-40 km thick, so it cannot be classified as a sporadic E layer which are typically just a few kilometers wide. Incoherent scatter radars have not to date reported any notable meteor shower-related increases in the average background ionization. The 2002 Leonids storm flux, however, was so high that it might have been able to induce such an event. The Chemical Ablation Model is used to estimate deposition rates of individual meteors. The resulting electron production, arising from hyperthermal collisions of ablated atoms with atmospheric molecules, is related to the predicted Leonid flux values and observed ionization on 19 November 2002. The EISCAT Svalbard Radar (ESR) located at some 1000 km north of the UHF site did not observe any excess ionization during the same period. The high-latitude electrodynamic conditions recorded by the SuperDARN radar network show that the ESR was within a strongly drifting convection cell continuously fed by fresh plasma while the UHF radar was outside the polar convection region maintaining the ionization.

  • 188.
    Pellinen-Wannberg, Asta
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Swedish Institute of Space Physics, Kiruna, Sweden.
    Kero, Johan
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Häggström, Ingemar
    EISCAT Scientific Association, Kiruna, Sweden.
    Mann, Ingrid
    EISCAT Scientific Association, Kiruna, Sweden.
    Tjulin, Anders
    EISCAT Scientific Association, Kiruna, Sweden.
    The forthcoming EISCAT_3D as an extra-terrestrial matter monitor2016Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 123, s. 33-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is important to monitor the extra-terrestrial dust flux in the Earth’s environment and into the atmosphere. Meteoroids threaten the infrastructure in space as hypervelocity hits by micron-sized granules continuously degrade the solar panels and other satellite surfaces. Through their orbital elements meteoroids can be associated to the interplanetary dust cloud, comets, asteroids or the interstellar space. The ablation products of meteoroids participate in many physical and chemical processes at dierent layers inthe atmosphere, many of them occurring in the polar regions.

    High-power large-aperture (HPLA) radars, such as the tristatic EISCAT UHF together with the EISCAT VHF, have been versatile instruments for studying many properties of the meteoroid population, even though they were not initially designed for this purpose. The future EISCAT_3D will comprise a phased-array transmitter and several phased-array receivers distributed in Northern Scandinavia. These will work at 233 MHz centre frequency with power up to 10 MW and run advanced signal processing systems. The facility will in many aspects be superior to its predecessors as the first radar to combine volumetric-, aperture synthesis- and multistatic imaging as well as adaptive experiments. The technical design goals of the radar respond to the scientific requests from the user community. The VHF frequency and the volumetric imaging capacity will increase the collecting volume compared to the earlier UHF, the high transmitter power will increase the sensitivity of the radar, and the interferometry will improve the spatial resolution of the orbit estimates. The facility will be able to observe and define orbits to about 10% of the meteors from the established mass flux distribution that are large or fast enough to produce an ionization mantle around the impacting meteoroid within the collecting volume. The estimated annual mean of about 190 000 orbits per day with EISCAT_3D gives many orders of magnitude higher detected orbit rates than the earlier tristatic UHF radar.

  • 189.
    Pellinen-Wannberg, Asta
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Murad, Edmond
    AFRL, retired.
    Brosch, Noah
    The Wise Observatory and Tel Aviv University.
    Häggström, Ingemar
    EISCAT Headquarters.
    Khayrov, Timur
    Luleå University of Technology and Julius Maximilians Universitä Würzburg.
    The solar cycle effect on the atmosphere as a scintillator for meteor observations2010Ingår i: Icy Bodies of the Solar System: proceedings of the international astronomical union / [ed] J.A. Fernández, D. Lazzaro, D. Prialnik & R. Schulz, Cambridge: Cambridge University Press, 2010, s. 249-252Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We discuss using high solar cycle atmospheric conditions as sensors for observing meteors and their properties. High altitude meteor trails (HAMTs) have sometimes been observed with HPLA (High Power Large Aperture) radars. At other times they are not seen. In the absence of systematic studies on this topic, we surmise that the reason might be differing atmospheric conditions during the observations. At EISCAT HAMTs were observed in 1990 and 1991. Very high meteor trails were observed with Israeli L-band radars in 1998, 1999 and 2001. Through the Leonid activity, around the latest perihelion passage of comet Tempel-Tuttle, optical meteors as high as 200 km were reported. This was partly due to new and better observing methods. However, all the reported periods of high altitude meteors seem to correlate with solar cycle maximum. The enhanced atmospheric and ionospheric densities extend the meteoroid interaction range with the atmosphere along its path, offering a better possibility to distinguish differential ablation of the various meteoric constituents. This should be studied during the next solar maximum, due within a few years.

  • 190.
    Pellinen-Wannberg, Asta
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Wannberg, Gudmund
    Institutet för rymdfysik.
    Kero, Johan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Szasz, Csilla
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik. Institutet för rymdfysik.
    Westman, Assar
    EISCAT Scientific Association.
    The impact of high resolution radar on meteor studies: the EISCAT perspective2008Ingår i: URSI Radio Science Bulletin, ISSN 1024-4530, nr 324, s. 17-28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Meteors, i.e. meteoroids interacting with the atmosphere, provided a vast amount of knowledge about interplanetary matter already long before the space era. Using what is today known as specular meteor radars (SMR), a great body of data on meteors was accumulated, mainly through recording echoes from the meteor trails. However, due to the specularity requirement and the ceiling effect, this method only detects a subset of the meteor population. By contrast, the High Power Large Aperture (HPLA) radar method can observe head echoes from meteors passing through the radar beam at almost arbitrary aspect angles. The very high power densities available at typical HPLA installations allow millisecond time resolution and spatial resolution in the range of tens of meters to be achieved routinely. In special cases, interference between echoes from two meteors has made it possible to achieve centimetre scale spatial resolution, thus allowing the deduction of an upper limit on the effective target size. Vector quantities such as meteor velocity and deceleration, providing mass and orbit estimates, can be recorded by phased arrays with interferometric capability, as well as by multi-static radars. A case in point is the tri-static EISCAT UHF radar system, which provides a unique capability of monitoring head echoes over a very wide range of aspect angles. A recent analysis of data from the UHF system confirms that head echo targets are essentially spherical in the forward direction. The next generation of HPLA systems is exemplified by the EISCAT_3D multistatic phased array radar concept. We discuss how this system will affect temporal and spatial resolution, sensitivity and rate of statistics in meteor observations.

  • 191. Persson, M.
    et al.
    Futaana, Y.
    Nilsson, H.
    Wieser, G. Stenberg
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Fedorov, A.
    Zhang, T. L.
    Barabash, S.
    Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole2019Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 6, s. 4597-4607Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June-July 2014, covering the aerobraking campaign with lowered altitude measurements (similar to 130 km). The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400-km altitude. A clear trend of dusk-to-dawn heavy ion flow across the polar ionosphere was found, with speeds of similar to 2-10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow. Plain Language Summary We have calculated the ion density and velocities in the Venusian polar ionosphere using measurements from the Ion Mass Analyzer on board the Venus Express spacecraft. During June-July 2014 the periapsis was lowered to similar to 130 km, which allowed for measurements down to low altitudes of the ionosphere near the North Pole. The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400 km, which is similar to what was found near the equatorial region by the Pioneer Venus mission. In addition, there is a clear trend of dusk-to-dawn flow, along the terminator, for the heavy ions. This is surprising, as a general flow from day-to-night is expected for the Venusian ionosphere due to the long nights and significant heating of the dayside upper atmosphere. The interplanetary magnetic field direction does not appear to affect the ion flow pattern. Instead, we propose a thermal pressure gradient as the dominant accelerating mechanism, induced by the decrease in density from the equator toward the pole.

  • 192. Pitkänen, Timo
    et al.
    Aikio, Anita T.
    Amm, Olaf
    Kauristie, Kirsti
    Nilsson, Hans
    Kaila, Kari U.
    Conjugate EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere2010Ingår i: URSI Finnish XXXII Convention on Radio Science and Electromagnetism 2010 meeting, Oulu, Finland, 26 August 2010, 2010Konferensbidrag (Övrigt vetenskapligt)
  • 193. Pitkänen, Timo
    et al.
    Aikio, Anita T.
    Amm, Olaf
    Kauristie, Kirsti
    Nilsson, Hans
    Kaila, Kari U.
    EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere2011Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 29, s. 299-319Artikel i tidskrift (Refereegranskat)
  • 194. Pitkänen, Timo
    et al.
    Aikio, Anita T.
    Juusola, Liisa
    Observations of polar cap flow channel and plasma sheet flow bursts during substorm expansion2013Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 118, s. 774-784Artikel i tidskrift (Refereegranskat)
  • 195. Pitkänen, Timo
    et al.
    Aikio, Anita T.
    Kozlovsky, Alexander
    Amm, Olaf
    Corrigendum to “Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm” published in Ann. Geophys., 27, 2157-2171, 20092009Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, s. 3007-3007Artikel i tidskrift (Refereegranskat)
  • 196. Pitkänen, Timo
    et al.
    Aikio, Anita T.
    Kozlovsky, Alexander
    Amm, Olaf
    Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm2009Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, s. 2157-2171Artikel i tidskrift (Refereegranskat)
  • 197.
    Pitkänen, Timo
    et al.
    Department of Physical Sciences, University of Oulu, Finland.
    Aikio, Anita T.
    Department of Physical Sciences, University of Oulu, Finland.
    Kozlovsky, Alexander
    Sodankylä Geophysical Observatory, Sodankylä, Finla.
    Amm, Olaf
    Finnish Meteorological Institute, Helsinki, Finland.
    Reconnection electric field estimates and dynamics of high-latitude boundaries during a substorm2009Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, s. 2157-2171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamics of the polar cap and the auroral oval are examined in the evening sector during a substorm period on 25 November 2000 by using measurements of the EISCAT incoherent scatter radars, the north-south chain of the MIRACLE magnetometer network, and the Polar UV Imager.

    The location of the polar cap boundary (PCB) is estimated from electron temperature measurements by the mainland low-elevation EISCAT VHF radar and the 42m antenna of the EISCAT Svalbard radar. A comparison to the poleward auroral emission (PAE) boundary by the Polar UV Imager shows that in this event the PAE boundary is typically located 0.7 of magnetic latitude poleward of the PCB by EISCAT. The convection reversal boundary (CRB) is determined from the 2-D plasma drift velocity extracted from the dual-beam VHF data. The CRB is located 0.5–1 equatorward of the PCB indicating the existence of viscous-driven antisunward convection on closed field lines.

    East-west equivalent electrojets are calculated from the MIRACLE magnetometer data by the 1-D upward continuation method. In the substorm growth phase, electrojets together with the polar cap boundary move gradually equatorwards. During the substorm expansion phase, the Harang discontinuity (HD) region expands to the MLT sector of EISCAT. In the recovery phase the PCB follows the poleward edge of the westward electrojet.

    The local ionospheric reconnection electric field is calculated by using the measured plasma velocities in the vicinity of the polar cap boundary. During the substorm growth phase, values between 0 and 10 mV/m are found. During the late expansion and recovery phase, the reconnection electric field has temporal variations with periods of 7–27 min and values from 0 to 40 mV/m. It is shown quantitatively, for the first time to our knowledge, that intensifications in the local reconnection electric field correlate with appearance of auroral poleward boundary intensifications (PBIs) in the same MLT sector. The results suggest that PBIs (typically 1.5 h MLT wide) are a consequence of temporarily enhanced longitudinally localized magnetic flux closure in the magnetotail.

  • 198.
    Pitkänen, Timo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, Tomas
    Space and Plasma Physics, EES, KTH, Stockholm, Sweden.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Kullen, Anita
    Space and Plasma Physics, EES, KTH, Stockholm, Sweden.
    On IMF By-induced dawn-dusk asymmetries in earthward convective fast flows2017Ingår i: Dawn-dusk asymmetries in planetary plasma environments / [ed] Stein Haaland, Andrei Runov, Colin Forsyth, American Geophysical Union (AGU), 2017, 1st, s. 95-106Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Studies of earthward plasma and magnetic field transport in the Earth’s magnetotail plasma sheet have shown that, on the average, Earthward ion flows in the premidnight and midnight sectors exhibit a duskward component while flows in the postmidnight sector are dawnward. The flow pattern is more pronounced for slower flows (<100 km/s) and alters gradually to a more symmetric one with respect to midnight for increasing flow speeds. However, recent ionospheric and magnetospheric studies have suggested that a nonzero By component in the interplanetary magnetic field (IMF) may significantly influence the earthward transport, creating previously unnoticed dawn‐dusk asymmetries between the hemispheres. In this article, we give a short overview of the present understanding of the topic, present new results, and briefly discuss the importance of the IMF By component for the Earthward transport processes in the magnetotail plasma sheet.

  • 199.
    Pitkänen, Timo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kullen, A.
    Maggiolo, R.
    Karlsson, T.
    Nilsson, H.
    Norqvist, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Response of magnetotail twisting to variations in IMF B-y: a THEMIS case study 1-2 January 20092016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 15, s. 7822-7830Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theoretical considerations, observations, and simulations have shown that the B-y component of the interplanetary magnetic field (IMF) may cause twisting of the magnetotail. However, the fundamental issues, the temporal and spatial responses of the magnetotail in the twisting process, are still unresolved. We report unique multipoint observations of the response of the magnetotail to the variations in IMF B-y on 1-2 January 2009. For the first time, estimates of the tail twisting response time at different (Time History of Events and Macroscale Interactions during Substorms, THEMIS) distances in the same event are inferred. Using cross-correlation and timing analyses, we find that the tail twisting propagates from farther out toward the Earth and the response time increases significantly to the inner magnetosphere.

  • 200.
    Pitkänen, Timo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Norqvist, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, Tomas
    Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna, Sweden.
    IMF dependence of the azimuthal direction of earthward magnetotail fast flows2013Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, nr 21, s. 5598-5604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cluster magnetotail data together with ACE solar wind data from 2001 to 2009 are used to investigate the dependence of the azimuthal flow direction of earthward magnetotail fast flows on the interplanetary magnetic field (IMF). We find an indication that fast flows have favored azimuthal directions that have dependence on the IMF. Our results suggest that for positive IMF By, the favored azimuthal direction of the fast flows is dawnward in the northern plasma sheet and duskward in the southern plasma sheet. For negative IMF By, an opposite situation takes place, the favored azimuthal flow directions are then duskward and dawnward in the northern and southern plasma sheet, respectively. As a possible explanation for the results, it is suggested that the untwisting reconnected magnetic field lines may direct the fast flows in the magnetotail, the field line twist itself being dependent on the IMF.

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