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Author name code: trulsen
ADS astronomy entries on 2022-09-14
author:Trulsen, Jan

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Title: Dynamic models for magnetospheric oscillations on the minute
    scale
Authors: Sato, H.; Pecseli, H.; Børve, S.; Trulsen, J.
2012AGUFMSM11C2315S    Altcode:
  Sudden pulses in the model solar wind sets the Earth's magnetosphere
  into damped oscillatory motions. Oscillation periods on the order of
  5-10 min have been observed by instrumented spacecrafts. A simple model
  is capable of explaining the basic properties of these oscillations
  and give scaling laws for their characteristics in terms of the
  parameters of the problem, such as the Solar wind momentum density. The
  period of the oscillations, their damping and anharmonic nature are
  accounted for.The model has no free adjustable numerical parameters
  and can be seen as an effort to predict some dynamic properties of the
  magnetosphere on the basis of measurable steady state characteristics. A
  simple test of the model is found by comparing its prediction of
  the Earth-Magnetopause distance with observed values. The results
  agree well with observations. The analysis is supported by numerical
  simulations solving the Magneto-Hydro-Dynamic (MHD) equations in
  two spatial dimensions, where we let a solar wind interact with a
  magnetic dipole representing a magnetized Earth. Two tilt-angles of
  the magnetic dipole axis were considered. We observe the formation of a
  magnetosheath, with the magnetopause at a distance corresponding well
  to the analytical results. The analytical model seem to be robust,
  and gives good qualitative agreement with the numerical simulations
  for a range of parameters, also concerning oscillation periods and
  damping times for cases where the dynamic response to perturbations are
  considered. The analysis allows also for predicting the magnetic field
  perturbations detected on Earth due to changes in the magnetosheath
  current. In order to improve the model we study a conformal mapping
  that brings the shape of the magnetosheath model closer to observations.

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Title: Spacecraft charging in flowing plasmas; numerical simulations
Authors: Miloch, W. J.; Yaroshenko, V. V.; Vladimirov, S. V.; Pécseli,
   H. L.; Trulsen, J.
2012JPhCS.370a2004M    Altcode:
  The density and potential variations at and in the vicinity of a
  spacecraft in flowing plasmas are studied by numerical simulations. The
  spacecraft charging, wake formation, and their role for the diagnostics
  of the ambient plasma are addressed. It is demonstrated that the wake
  features, such as ion focusing, can be altered by photoemission due to
  directed sunlight. For multiple ion species, the wakes for ions with
  different ion masses can be separated, with light ions contributing
  to the ion focus, and heavy ions giving a geometrical shape of the
  wake. As a specific case, the Cassini spacecraft approaching Saturn is
  considered. The simulations are carried out with DiP2D and DiP3D codes,
  the two- and three-dimensional particle-in-cell codes.

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Title: Fluctuations in the direction of propagation of intermittent
    low-frequency ionospheric waves
Authors: Sato, H.; Pécseli, H. L.; Trulsen, J.
2012JGRA..117.3329S    Altcode: 2012JGRA..11703329S
  Low-frequency (8-28 Hz), long-wavelength electrostatic waves in the
  ionospheric E region over northern Scandinavia are studied by using
  data obtained from an instrumented rocket having four probes mounted
  on two perpendicular booms. Two data sets are available, one for upleg
  and one for downleg conditions with somewhat different ionospheric
  parameters. The ionospheric plasma is unstable with respect to the
  electrostatic Farley-Buneman instability in both cases, but the DC
  electric field is somewhat enhanced during the downleg part of the
  flight. We find that the direction of wave propagation as given by the
  local normalized fluctuating electrostatic field vector varies randomly
  within an interval of aspect angles. The distribution of the directional
  change per time unit is determined. The waves propagate predominantly in
  the electrojet direction, but significant variations in directions can
  be found, both with respect to the magnetic field (the aspect angle)
  and with respect to the electrojet direction. Some of our results are
  in variance with related radar observations in the electrojet near
  the equator. Indications of significant spatial intermittency of the
  signal is demonstrated. Large-amplitude electrostatic fluctuations
  are confined to spatially localized regions and have a narrower aspect
  angle distribution with reduced directional fluctuations. We introduce
  an intermittency measure based on average excess time statistics for
  the record for the absolute value of the detected time-varying electric
  fields. We thus determine the average of time intervals spent above a
  prescribed amplitude threshold level. The results are compared with
  an analytical expression obtained for a reference nonintermittent
  Gaussian signal. The general analysis requires the joint probability
  density of signal amplitude and its time derivative to be known. The
  analytical models for quantifying the intermittency effects were
  tested by synthetic time series allowing study of the transition from
  non-Gaussian to Gaussian random signals.

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Title: Fluctuations in the Direction of Propagation of Low Frequency
    Ionospheric Waves
Authors: Sato, H.; Pécseli, H. L.; Trulsen, J. K.
2011ESASP.700..629S    Altcode:
  No abstract at ADS

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Title: Ion acoustic double layers forming behind irradiated solid
    objects in streaming plasmas
Authors: Miloch, W. J.; Rekaa, V. L.; Pécseli, H. L.; Trulsen, J.
2010JPlPh..76..429M    Altcode:
  Small solid metallic objects in relative motion to thermal plasmas
  are studied by numerical simulations. We analyze supersonic motions,
  where a distinctive ion wake is formed behind obstacles. At these plasma
  drift velocities, ions enter the wake predominantly due to deflections
  by the electric field in the sheath around the obstacle. By irradiating
  the back side of the object by ultraviolet (UV) light, we can induce
  also an enhanced photo-electron population there. The resulting charge
  distribution gives rise to a pronounced local potential and plasma
  density well behind the object. This potential variation has the
  form of a three-dimensional ion acoustic double layer, containing
  also an ion phase space vortex. The analysis is supported also by
  one-dimensional numerical simulations to illustrate the importance of
  boundary conditions, Dirichlet and von Neumann conditions in particular.

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Title: Numerical Dissipation in RSPH Simulations of Astrophysical
    Flows with Application to Protoplanetary Disks
Authors: Børve, S.; Speith, R.; Trulsen, J.
2009ApJ...701.1269B    Altcode:
  Smoothed Particle Hydrodynamics (SPH) is widely used for astrophysical
  applications, in particular problems of self-gravitational
  hydrodynamics. However, critics have argued that inherent accuracy
  problems with the method can be identified, in particular when it
  comes to describing shocks and dynamical instabilities. Regularized
  Smoothed Particle Hydrodynamics (RSPH) has previously been proposed as
  an extension to SPH. It is an attempt to increase the accuracy of the
  hydrodynamical description without having to abandon the Lagrangian
  formulation altogether. As the name implies, the method relies on a
  regularization technique where the solution at temporal intervals is
  mapped on to a new set of regularly placed particles. This technique
  allows us to reduce the numerical noise otherwise caused by highly
  irregular particle distributions and to take advantage of a more
  flexible approach to variable resolution. The cost of introducing the
  regularization scheme lies in increased methodical complexity, and in
  increased numerical dissipation. This paper investigates the numerical
  dissipation both qualitatively and quantitatively in the context
  of two-dimensional models relevant to the study of protoplanetary
  disks. Basic hydrodynamical tests highlight key properties of the RSPH
  approach. By comparison with an analytical solution, we are also able
  to quantify the dependence of the spurious viscosity on key numerical
  parameters. To put the theoretical discussion in perspective, we also
  present results from simulations of test problems involving disk-planet
  interactions. The results are compared to published results obtained
  with other codes.

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Title: Plasma and electromagnetic wave simulations of meteors
Authors: Dyrud, Lars; Wilson, Derek; Boerve, Steiner; Trulsen, Jan;
   Pecseli, Hans; Close, Sigrid; Chen, Chen; Lee, Yoonjae
2008AdSpR..42..136D    Altcode:
  Every day billions of meteoroids impact and disintegrate in the Earth's
  atmosphere. Current estimates for this global meteor flux vary from
  2000 to 200,000 tons per year, and estimates for the average velocity
  range between 10 km/s and 70 km/s. The basic properties of this
  global meteor flux, such as the average mass, velocity, and chemical
  composition remain poorly constrained. We believe much of the mystery
  surrounding the basic parameters of the interplanetary meteor flux
  exists for the following reason, the unknown sampling characteristics
  of different radar meteor observation techniques, which are used to
  derive or constrain most models. We believe this arises due to poorly
  understood radio scattering characteristics of the meteor plasma,
  especially in light of recent work showing that plasma turbulence and
  instability greatly influences meteor trail properties at every stage
  of evolution. We present our results on meteor plasmas simulations
  of head echoes using particle in cell (PIC) ions, which show that
  electric fields strongly influence early stage meteor plasma evolution,
  by accelerating ions away from the meteoroid body. We also present the
  results of finite difference time domain electromagnetic simulations
  (FDTD), which can calculate the radar cross section of the simulated
  meteor plasmas. These simulations have shown that the radar cross
  section depends in a complex manner on a number of parameters. These
  include the angle between radar and meteor entry, a large dependence
  on radar frequency, which shows that for a given meteor plasma size
  and density, the reflectivity as a function of probing radar frequency
  varies, but typically peaks below 100 MHz.

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Title: Plasma and Electromagnetic Simulations of Meteor Head Echo
    Radar Reflections
Authors: Dyrud, Lars; Wilson, Derek; Boerve, Steiner; Trulsen, Jan;
   Pecseli, Hans; Close, Sigrid; Chen, Chen; Lee, Yoonjae
2008EM&P..102..383D    Altcode: 2007EM&P..tmp...65D
  Recently, meteor head echo detections from high powered large aperture
  radars (HPLA) have brought new measurements to bear on the study
  of sporadic interplanetary meteors. These same observations have
  demonstrated an ability to observe smaller meteoroids without some
  of the geometrical restrictions of specular radar techniques. Yet
  incorporating data from various radar reflection types and
  from different radars into a single consistent model has proven
  challenging. We believe this arises due to poorly understood radio
  scattering characteristics of the meteor plasma, especially in light
  of recent work showing that plasma turbulence and instability greatly
  influences meteor trail properties at every stage of evolution. In
  order to overcome some of the unknown relationships between meteoroid
  characteristics (such as mass and velocity) and the resulting head echo
  radar cross-sections (RCS), we present our results on meteor plasma
  simulations of head echo plasmas using particle in cell (PIC) ions,
  which show that electric fields strongly influence early stage meteor
  plasma evolution, by accelerating ions away from the meteoroid body at
  speeds as large as several kilometers per second. We also present the
  results of finite difference time domain electromagnetic simulations
  (FDTD), which can calculate the radar cross-section of the simulated
  meteor plasma electron distributions. These simulations have shown
  that the radar cross-section depends in a complex manner on a number
  of parameters. In this paper we demonstrate that for a given head echo
  plasma the RCS as a function of radar frequency peaks at sqrt (2*peak
  plasma frequency) and then decays linearly on a dB scale with increasing
  radar frequency. We also demonstrate that for a fixed radar frequency,
  the RCS increases linearly on a dB scale with increasing head echo
  plasma frequency. These simulations and resulting characterization
  of the head echo radar cross-section will both help relate HPLA radar
  observations to meteoroid properties and aid in determining a particular
  radar facility’s ability to observe various meteoroid populations.

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Title: Nonlinearly generated plasma waves as a model for enhanced
    ion acoustic lines in the ionosphere
Authors: Daldorff, L. K. S.; Pécseli, H. L.; Trulsen, J.
2007GeoRL..3418101D    Altcode:
  Observations from the EISCAT Svalbard Radar, for instance, demonstrate
  that the symmetry of the naturally occurring ion line can be broken
  by an enhanced, non-thermal, level of fluctuations, i.e., Naturally
  Enhanced Ion-Acoustic Lines (NEIALs). In a significant number of cases,
  the entire ion spectrum can be distorted, with the appearance of a
  third line, corresponding to a propagation velocity significantly below
  the ion acoustic sound speed. By numerical simulations, we consider
  one possible model accounting for the observations, suggesting that
  a primary process can be electron acoustic waves excited by a cold
  electron beam. Subsequently, an oscillating two-stream instability
  excites electron plasma waves which in turn decay to asymmetric ion
  lines. Our code solves the full Vlasov equation for electrons and ions,
  with the dynamics coupled through the electrostatic field derived from
  Poisson's equation.

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Title: Symmetry assumptions in SPH.
Authors: Omang, M.; Børve, S.; Christensen, S. O.; Trulsen, J.
2007sphe.work..103O    Altcode:
  No abstract at ADS

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Title: Challenges related to particle regularization in SPH.
Authors: Børve, S.; Speith, R.; Omang, M.; Trulsen, J.
2007sphe.work...67B    Altcode:
  No abstract at ADS

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Title: Multidimensional MHD Shock Tests of Regularized Smoothed
    Particle Hydrodynamics
Authors: Børve, S.; Omang, M.; Trulsen, J.
2006ApJ...652.1306B    Altcode:
  This paper investigates to what extent the numerical scheme regularized
  smoothed particle hydrodynamics (RSPH) is able to accurately describe
  multidimensional MHD shocks. The scheme can be viewed as an extension
  to smoothed particle hydrodynamics (SPH), which is widely used for
  astrophysical applications. In the first of two previous papers, the
  basic idea behind the RSPH scheme was introduced and tested, primarily
  on one-dimensional MHD shock problems. A new formulation of the momentum
  equation was also proposed to secure stability in the low-β regime. A
  two-dimensional, linear stability analysis of this formulation was
  presented in the second paper. The second paper also utilized recent
  developments of the RSPH scheme that improve the overall description
  of multidimensional problems in general. Based on the results from the
  linear stability analysis, adjustments to the momentum equation are
  made in the present work, which are also applicable to the nonlinear
  regime. These adjustments address the problem of asymmetries in the
  momentum equation, which in nonlinear problems can lead to small,
  yet systematic errors in postshock conditions. In addition, this
  paper describes the first application of the improved RSPH scheme to
  multidimensional MHD shocks. Comparisons are made with existing methods,
  in particular the related SPH method. Special attention is given to
  the scheme's ability to maintain the b.nabla b.dot B=0 constraint
  and to what extent redefining the particle distribution affects the
  conservation of kinetic energy and angular momentum.

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Title: Plasma and electromagnetic wave simulations of meteors
Authors: Dyrud, L.; Lee, Y.; Boerve, S.; Trulsen, J.; Pecseli, H.
2006cosp...36..160D    Altcode: 2006cosp.meet..160D
  Every day billions of meteoroids impact and disintegrate in the Earth
  s atmosphere Current estimates for this global meteor flux vary from
  2000-200 000 tons per year and estimates for the average velocity range
  between 10 km s to 70 km s The basic properties of this global meteor
  flux such as the average mass velocity and chemical composition remain
  poorly constrained We believe much of the mystery surrounding the basic
  parameters of the interplanetary meteor flux exists for the following
  reasons the unknown sampling characteristics of different radar meteor
  observation techniques which are used to derive or constrain most
  models We believe this arises due to poorly understood radio scattering
  characteristics of the meteor plasma especially in light of recent work
  showing that plasma turbulence and instability greatly influences meteor
  trail properties at every stage of evolution We present our results on
  meteor plasmas simulations of head echoes using PIC ions which show
  that electric fields strongly influence early stage meteor plasma
  evolution by accelerating ions away from the meteoroid body We also
  present the results of time domain electromagnetic simulations FDTD
  which can calculate the radar cross section of the simulated meteor
  plasmas These simulations have shown that the radar cross section
  depends in a complex manner on a number of parameters These include
  the angle between radar and meteor entry a large dependence on radar
  frequency which shows that for a given meteor plasma size and density
  the peak reflectivity for the meteor varies

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Title: On the Possibility for Action Conservation in the Solar Cycle
Authors: Pécseli, Hans; Trulsen, Jan
2004SoPh..222..363P    Altcode:
  The sunspot series are investigated in detail by use of a wavelet
  transform. By simple arguments, we present a reduced sunspot
  time-series, which can be argued to be approximately proportional to
  the magnetic flux density at the coronal surface. This reduced sunspot
  index correctly reproduces the (average) 22 year solar cycle. Closer
  scrutiny of the sunspot variation shows that the frequency of the
  solar cycle and the energy in the magnetic field vary consistently
  with conservation of action, i.e., energy divided by frequency. The
  analysis is based on the available data beginning with the year 1700,
  and analyzed by a wavelet transform. The present results relate to
  observations reported previously in the literature.

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Title: Two-dimensional MHD Smoothed Particle Hydrodynamics Stability
    Analysis
Authors: Børve, S.; Omang, M.; Trulsen, J.
2004ApJS..153..447B    Altcode:
  Smoothed particle hydrodynamics (SPH) is an N-body integration scheme
  widely used within the field of astrophysics. Unfortunately, the
  method has up until recently been facing serious problems concerning
  instabilities when applied to MHD problems. Regularized smoothed
  particle hydrodynamics (RSPH) was proposed as an extension to SPH
  with the aim of achieving high-accuracy modeling of hydrodynamic and
  magnetohydrodynamic problems. This work included a new formulation of
  the discrete MHD equations that is easily implemented into SPH and RSPH
  codes alike. In this paper, the stability properties of two-dimensional
  linear MHD waves using this formulation are investigated. The presented
  analysis shows that linear stability properties similar to that obtained
  for sound waves in the absence of a magnetic field is achieved also
  for MHD waves. This result is confirmed by the included test results
  using both standard SPH and RSPH.

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Title: Time-resolved statistical analysis of nonlinear electrostatic
    fluctuationsin the ionospheric E region
Authors: Larsen, Y.; Hanssen, A.; Krane, B.; Pécseli, H. L.;
   Trulsen, J.
2002JGRA..107.1005L    Altcode:
  Low-frequency electrostatic fluctuations detectedby the instruments
  on the Rocket and Scatter Experiment (ROSE) rockets inthe E region
  over northern Scandinavia are analyzed.It is demonstrated that the
  time-resolved statistical properties of the fluctuationsdeviate
  significantly from those associated with a Gaussian process. The
  characteristicsof the fluctuations are analyzed with particular
  attention to non-Gaussianeffects and phase-coherent mode couplings
  of electrostatic fluctuations. Non-Gaussianeffects are analyzed
  by means of the kernel estimator for probability densityfor short
  data segments. Short-time phase-coherent effects are analyzed
  andquantified by means of the squared wavelet bicoherence, which
  has desirablestatistical properties in the frequency regions of
  interest. The results arecompared with similar results from rocket
  data obtained over SøndreStrømfjord in Greenland. The results show
  a remarkable similarity,indicating that the observed phase coherence
  is a robust feature of the saturatedstage of the E region instabilities.

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Title: Regularized Smoothed Particle Hydrodynamics: A New Approach
    to Simulating Magnetohydrodynamic Shocks
Authors: Børve, S.; Omang, M.; Trulsen, J.
2001ApJ...561...82B    Altcode:
  Smoothed particle hydrodynamics (SPH) has proven to be a useful
  numerical tool in studying a number of different astrophysical
  problems. Still, used on other problems, such as the modeling of
  low-β MHD systems, the method has so far not performed as well as one
  might have hoped. The present work has been motivated by the desire to
  accurately model strong hydrodynamic and magnetohydrodynamic shocks, and
  a key issue has therefore been to achieve a near-optimal representation
  of the simulated system at all times. Using SPH, this means combining
  the Lagrangian nature of the method with a smoothing-length profile
  that varies in both space and time. In this paper, a scheme containing
  two novel features is proposed. First, the scheme assumes a piecewise
  constant smoothing-length profile. To avoid substantial errors near
  the steps in the profile, alternative forms of the SPH equations of
  motion are used. Second, a predictive attitude toward optimizing the
  particle distribution is introduced by activating a mass, momentum,
  and energy conservation regularization process at intervals. The
  scheme described has been implemented in a new code called regularized
  smoothed particle hydrodynamics (RSPH), and test results for a number
  of standard hydrodynamic and magnetohydrodynamic tests in one and two
  dimensions using this code are presented.

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Title: Low frequency waves in plasmas with spatially varying electron
    temperature
Authors: Guio, P.; Børve, S.; Pécseli, H. L.; Trulsen, J.
2000AnGeo..18.1613G    Altcode: 2001AnGeo..18.1613G
  Low frequency electrostatic waves are studied in magnetized plasmas
  with an electron temperature which varies with position in a direction
  perpendicular to the magnetic field. For wave frequencies below the ion
  cyclotron frequency, the waves need not follow any definite dispersion
  relation. Instead a band of phase velocities is allowed, with a range of
  variation depending on the maximum and minimum values of the electron
  temperature. Simple model equations are obtained for the general case
  which can be solved to give the spatial variation of a harmonically
  time varying potential. A simple analytical model for the phenomenon is
  presented and the results are supported by numerical simulations carried
  out in a 2 1/2 -dimensional particle-in-cell numerical simulation. We
  find that when the electron temperature is striated along B0 and low
  frequency waves (<omega>+/-<Omega>ci) are excited in this
  environment, then the intensity of these low frequency waves will be
  striated in a manner following the electron temperature striations. High
  frequency ion acoustic waves (<omega>≫<Omega>ci) will
  on the other hand have a spatially more uniform intensity distribution.

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Title: Smoothed Particle Hydrodynamics with Time Varying, Piecewise
    Constant Smoothing Length Profiles
Authors: Børve, S.; Omang, M.; Trulsen, J.
2000AAS...19710722B    Altcode: 2000BAAS...32.1584B
  Smoothed Particle Hydrodynamics (SPH) has proven to be a very useful
  numerical tool in studying a number of widely different astrophysical
  problems. Still, used on many other types of problems the method
  faces problems concerning efficiency and accuracy compared to that of
  modern grid-based methods. Essential to efficiency is maintaining a
  near-optimal particle distribution and smoothing length profile that
  reflects the physics of the problem. This means, directing computer
  resources towards those regions and time intervals where the action is
  taking place and not being wasted where nothing is happening. In the
  literature researchers have tried to achieve these goals by combining
  the Lagrangian nature of the SPH method with a smoothing length profile
  varying smoothly in space and time. To make the SPH method better suited
  for accurately describing a wider range of problems, a scheme containing
  two novel features is proposed. First, the scheme assumes a piecewise
  constant smoothing length profile. To avoid substantial errors near
  steps in the smoothing length profile, alternative forms of the SPH
  equations of motion is used. Secondly, a predictive attitude towards
  optimizing the particle distribution is introduced by activating
  a mass, momentum and internal energy conservation regularization
  process at intervals. The main challenge faced by the scheme has been
  to put the newly optimized smoothing length profile into use without
  severely altering the underlying physics. To achieve this, the entire
  set of particles is redefined in the process. The basic ideas behind
  this scheme is briefly described. Finally, the results from several
  hydrodynamical and magnetohydrodynamical tests in one and two dimensions
  are presented. This work is funded by the Research Council of Norway.

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Title: Spectral properties of low-frequency electrostatic waves in
    the ionospheric E region
Authors: Krane, B.; Pécseli, H. L.; Trulsen, J.; Primdahl, F.
2000JGR...10510585K    Altcode:
  The spectral properties of low frequency electrostatic waves in
  the polar cap E region over northern Scandinavia were studied
  experimentally by instruments on the Rocket and Scatter Experiment
  (ROSE) rockets. Fluctuations in plasma density were detected as
  well as potential differences between boom-mounted probes. By
  comparison of the spectral index for fluctuations in the potential
  signal and plasma density, evidence is obtained for deviations from
  Boltzmann distributions in the electron dynamics, which would predict
  fluctuations in density and potential to be proportional, with the same
  constant of proportionality at all frequencies. Investigations of the
  cross correlation between density and potential signals demonstrate
  that the phase between the two increases approximately linearly with
  frequency. Empirical relations are obtained for the frequency dependence
  of the amplitude and phase relations between fluctuations in density
  and potential.

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Title: Statistics of the lower hybrid wave cavities detected by the
    FREJA satellite
Authors: Kjus, S. H.; Pécseli, H. L.; Lybekk, B.; Holtet, J.; Trulsen,
   J.; Lühr, H.; Eriksson, A.
1998JGR...10326633K    Altcode:
  Localized electrostatic wave packets in the frequency region of lower
  hybrid waves have been detected by the instruments on the FREJA
  satellite and also earlier by instrumented rocket payloads. These
  waves are often associated with local density depletions, indicating
  that the structures can be interpreted as wave-filled cavities which
  are strongly elongated along the magnetic field. The basic features of
  the observations are discussed, providing a survey of the conditions
  for occurrence and spatial distributions. The basic properties of
  the individual cavities and associated fluctuating electric fields
  are discussed as well, and typical densities, widths, and other
  characteristics are obtained for selected orbits.

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Title: Propagation and dispersion of electrostatic waves in the
    ionospheric E region
Authors: Iranpour, K.; Pécseli, H. L.; Trulsen, J.; Bahnsen, A.;
   Primdahl, F.; Rinnert, K.
1997AnGeo..15..878I    Altcode:
  Low-frequency electrostatic fluctuations in the ionospheric E
  region were detected by instruments on the ROSE rockets. The phase
  velocity and dispersion of plasma waves in the ionospheric E region
  are determined by band-pass filtering and cross-correlating data of
  the electric-field fluctuations detected by the probes on the ROSE F4
  rocket. The results were confirmed by a different method of analysis
  of the same data. The results show that the waves propagate in the
  Hall-current direction with a velocity somewhat below the ion sound
  speed obtained for ionospheric conditions during the flight. It is
  also found that the waves are dispersive, with the longest wavelengths
  propagating with the lowest velocity.

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Title: Structure of low-frequency oscillations at substorm breakup
Authors: Holter, O.; Perraut, S.; Roux, A.; Altman, C.; Korth, A.;
   Pécseli, H. L.; Trulsen, J.; Pedersen, A.
1996ESASP.389..393H    Altcode: 1996icss.conf..393H
  No abstract at ADS

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Title: Lower hybrid wave cavities detected by the FREJA satellite
Authors: Pécseli, H. L.; Iranpour, K.; Holter, Ø.; Lybekk, B.;
   Holtet, J.; Trulsen, J.; Eriksson, A.; Holback, B.
1996JGR...101.5299P    Altcode:
  Localized electrostatic wave packets in the frequency region
  of lower hybrid waves have been detected by the instruments on
  the FREJA satellite. These waves are often associated with local
  density depletions indicating that the structures can be interpreted
  as wave filled cavities. The basic features of the observations
  are discussed. On the basis of simple statistical arguments it
  is attempted to present some characteristics which have to be
  accommodated within an ultimate theory describing the observed wave
  phenomena. An interpretation in terms of collapse of nonlinear
  lower hybrid waves is discussed in particular. It is argued that
  such a model seems inapplicable, at least in its simplest form, by
  providing a timescale and a length scale which are not in agreement
  with observations. Alternatives to this model are presented.

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Title: Velocity correlations in two-dimensional electrostatic
    turbulence in low-β plasmas
Authors: Pécseli, H. L.; Trulsen, J.
1995JPlPh..54..401P    Altcode:
  The Eulerian and Lagrangian correlation functions in low-frequency
  electrostatic turbulence in strongly magnetized plasmas are studied in
  two spatial dimensions. In this limit the ion velocity in the direction
  perpendicular to a homogeneous magnetic field is approximated by the
  E × B/B<SUP>2</SUP> velocity. For strictly flute-type fluctuations,
  a similar model is also used for the electron dynamics. Allowing, on
  the other hand, for a small B-parallel component of the perturbations,
  an isothermal Boltzmann distribution for the electrons can be justified
  while the two-dimensional ion description is retained. The present
  analysis is based on an approximation of the actual two-dimensional
  flow in terms of an autonomous system consisting of many overlapping
  and mutually convecting vortices. Simple analytical expressions for
  the full space—time-varying Eulerian correlation are derived solely
  in terms of plasma parameters. it is demonstrated that an extension of
  the arguments giving the foregoing results also allows for derivation
  of analytical expressions for the Lagrangian correlation function. The
  results are supported by a Monte Carlo simulation based on the model.

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Title: Characterization of low frequency oscillations at substorm
    breakup
Authors: Holter, Ø.; Altman, C.; Roux, A.; Perraut, S.; Pedersen,
   A.; Pécseli, H.; Lybekk, B.; Trulsen, J.; Korth, A.; Kremser, G.
1995JGR...10019109H    Altcode:
  Field and particle data recorded on the geostationary satellite GEOS
  2 are used to investigate the electric and magnetic signatures of a
  substorm characterized by a dispersionless injection of energetic
  electrons and ions. Three types of field variations are observed:
  (1) Long-period oscillations with period of ~300 s, interpreted
  as oscillations of entire field lines. These oscillations develop
  as second harmonic standing waves and correspond to coupled shear
  Alfvén-slow magnetosonic modes. They grow after the most active
  period of the breakup. (2) Short-period transient oscillations with
  periods of ~45-65 s, interpreted as wave modes trapped in a current
  layer which develops prior to the substorm breakup and is disrupted
  at breakup. These oscillations also correspond to a coupled shear
  Alfvén-slow magnetosonic mode (coupled via magnetic field curvature
  effects in a high-β plasma). The short-period transient oscillations
  are only observed during the most active period of the breakup. (3)
  A nonoscillatory sharp increase observed on both the parallel magnetic
  component and the energetic ion flux, averaged over one satellite
  rotation, interpreted as evidence for the fast magnetosonic mode which
  in view of the simultaneous large impulsive increase in the azimuthal
  electric field, appears to propagate radially outwards, transporting
  the substorm breakup downtail. .

---------------------------------------------------------
Title: Nonlinear wave interactions in two-electron-temperature plasmas
Authors: Hanssen, A.; Pécseli, H. L.; Stenflo, L.; Trulsen, J.
1994JPlPh..51..423H    Altcode:
  Dynamical equations are derived for the evolution of weakly
  nonlinear electron plasma waves when the electron distributions are
  characterized by more than one temperature component. The presence of
  electron-acoustic modes in multi- temperature plasmas opens a new decay
  channel. By considering an explicit example, it is demonstrated that
  these distributions imply significant modifications of the standard
  models for the decay spectrum of electron plasma waves. In particular,
  long-wavelength Langmuir waves can decay to shorter wavelengths. The
  results can have implications for ionospheric heating experiments.

---------------------------------------------------------
Title: Propagation and nonlinear interaction of low-frequency
    electrostatic waves in the polar cap E region
Authors: Pecseli, H. L.; Trulsen, J.; Bahnsen, A.; Primdahl, F.
1993JGR....98.1603P    Altcode:
  Low-frequency electrostatic fluctuations in the polar cap E region were
  detected by an instrumented rocket payload. The basic characteristics
  of the fluctuations, such as speed and direction of propagation, were
  obtained by a correlation analysis. The bispectrum, in particular,
  provided indications of nonlinear couplings. Harmonic wave interactions
  were observed for a wide altitude range. Evidence for cascading of
  wave energy toward small wavelengths was obtained. The accuracy of
  the statistical analysis was tested by a Monte Carlo simulation.

---------------------------------------------------------
Title: Propagation of low-frequency electrostatic waves in the
    ionospheric E-region.
Authors: Iranpour, K.; Pécseli, H. L.; Trulsen, J.; Bahnsen, A.;
   Primdahl, F.; Rose, G.; Rinnert, K.
1993wpst.conf..181I    Altcode:
  Low frequency electrostatic fluctuations in the E-region over
  northern Scandinavia were detected. Some basic characteristics of the
  fluctuations were obtained. The bispectrum in particular, provided
  indications of nonlinear couplings. Harmonic wave interactions were
  observed for a wide altitude range.

---------------------------------------------------------
Title: Equilibrium and turbulent transport in the BLAAMANN plasma
    torus.
Authors: Rypdal, K.; Grønvoll, E.; Øynes, F.; Fredriksen, Å.;
   Armstrong, R. J.; Trulsen, J.; Pécseli, H. L.
1993wpst.conf...39R    Altcode:
  A preliminary study of the plasma turbulence indicates that the
  diffusion is due to the quasiperiodic occurrence of a large vortex
  pair in which plasma particles are repeatedly trapped and detrapped.

---------------------------------------------------------
Title: Velocity correlations in two-dimensional electrostatic plasma
    turbulence.
Authors: Pécseli, H. L.; Trulsen, J.
1993wpst.conf...49P    Altcode:
  The Eulerian and Lagrangian correlation functions in low frequency
  electrostatic turbulence in strongly magnetized plasmas are studied
  in two spatial dimensions.

---------------------------------------------------------
Title: Plasma physics in the ionosphere. II. The ionosphere in the
    plasma laboratory.
Authors: Trulsen, J.
1981FFV....43...67T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Numerical simulation of Poynting-Robertson and collisional
    effects in the interplanetary dust cloud
Authors: Trulsen, J.; Wikan, A.
1980A&A....91..155T    Altcode:
  A numerical simulation model is developed to investigate the combined
  influence of the Poynting-Robertson and collisional effects on the
  dynamical evolution of an interplanetary dust population. It is shown
  that collisional effects should be taken into account when the mean free
  collision time is of the order of or shorter than the Poynting-Robertson
  effect. The individual grains still spiral inwards, but collisions now
  act to make the statistical mean eccentricity and inclination of the
  orbits decrease at comparable rates with decreasing solar distance. This
  produces an expanding fan-shaped form of the interplanetary dust cloud.

---------------------------------------------------------
Title: Nonlinear mixing in the ionosphere.
Authors: Dysthe, K. B.; Mjolhus, E.; Trulsen, J.
1980PhyS...21..122D    Altcode:
  It has been proposed to sound the ionosphere by means of nonlinear
  mixing of two VHF/UHF waves of different frequency. This paper
  studies the problem theoretically, including the earth's magnetic
  field, collisions and plasma inhomogeneity. We find that collisions,
  and sideways drift of wave packets due to perpendicular components of
  the group velocity, may seriously affect the results when the plasma
  inhomogeneity is weak. Also, the effect is favoured if the pump waves
  have lower frequencies than used in recently reported experiments.

---------------------------------------------------------
Title: Poynting-Robertson Effect and Collisions in the Interplanetary
    Dust Cloud
Authors: Trulsen, J.; Wikan, A.
1980IAUS...90..299T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Nonlinear mixing as a plasma density probe
Authors: Dysthe, K. B.; Mjolhus, E.; Trulsen, J.
1978JGR....83.1985D    Altcode:
  Nonlinear mixing of two electromagnetic waves, ω<SUB>+/-</SUB>and
  k<SUB>+/-</SUB>, in an inhomogeneous isotropic and collisionless plasma
  in the parameter range β<SUP>2/3</SUP>(KL)<SUP>1/3</SUP>&lt;&lt;1
  is studied. Here β is the ratio of electron thermal velocity to
  speed of light, K=Ω/c,Ω=ω<SUB>+</SUB>-ω<SUB>-</SUB>, and L is a
  local characteristic length for electron density variation. Langmuir
  waves, Ω and k<SUB>L</SUB>, are found to be excited in two different
  ways. When (Δk/K) β<SUP>2/3</SUP>(KL)<SUP>1/3</SUP>&gt;&gt;1, where
  Δk=k<SUB>+</SUB>-k<SUB>-</SUB>, resonant wave mixing occurs in which
  the generated Langmuir waves satisfy k<SUB>L</SUB>?Δk. When (Δk/K)
  β<SUP>2/3</SUP>(KL)<SUP>1/3</SUP>&lt;&lt;1, nonlinear conversion
  takes place at the critical surface where Ω equals the local plasma
  frequency, the Langmuir waves propagating antiparallel to the density
  gradient and not along Δk. Coherent scattering of electromagnetic
  waves off the density perturbations associated with the excited Langmuir
  waves is studied.

---------------------------------------------------------
Title: Stimulated resonance line scattering in the ionosphere
Authors: Stenflo, L.; Trulsen, J.
1978JGR....83.1154S    Altcode:
  We have found that stimulated resonance line scattering from the
  ionosphere should be possible with the planned Eiscat radar.

---------------------------------------------------------
Title: Stimulated Brillouin scattering in the ionosphere
Authors: Dysthe, K. B.; Leer, E.; Trulsen, J.; Stenflo, L.
1977JGR....82..717D    Altcode:
  We discuss the possibility of obtaining stimulated backscattering from
  the ionosphere. It is found that stimulated Brillouin scattering off
  ion modes and quasi modes may be possible with the signal power that
  is planned for the Eiscat radar.

---------------------------------------------------------
Title: The origin and properties of thermal fluctuations in a plasma.
Authors: Trulsen, J.; Bjøernå, N.
1977rpap.conf...29T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Dynamics of Interplanetary Dust and Related Topics Invited
    Paper
Authors: Trulsen, J.
1976LNP....48..416T    Altcode: 1976IAUCo..31..416T
  The problem of the effects of mutual collisions for the dynamics
  of interplanetary dust particles and grains is reviewed. Collisions
  are shown to give a rather characteristic dynamical signature, the
  importance of these effects depending mainly on the mean free collision
  time and the degree of inelasticity. Although a few attempts to look
  for collisional effects in the solar system have been made, rather
  much work remains to be done before the problem is fully understood.

---------------------------------------------------------
Title: Numerical Simulation of Jetstreams. II: The Two Dimensional
    Case
Authors: Trulsen, Jan
1972Ap&SS..18....3T    Altcode:
  The dynamics of two dimensional jetstreams have been studied
  by following the evolution of simulation particle populations for
  different collision models. Collisions, independent of details of the
  collision model, rapidly lead to the establishment of a distribution
  of perihelion vectors of the form ~exp(-α(P-η)<SUP>2</SUP>), the
  characteristic time for this process being of the order of magnitude
  equal to the mean free collision time. Under appropriate conditions a
  radial focusing takes place. In terms of the varians of semi-major axis
  a focusing exceeding a factor 2 has been achieved. Necessary conditions
  for the existence of this radial focusing are a sufficient degree of
  inelasticity and the requirement that the dominant part of the velocity
  change in a typical collision is along the pre-collisional relative
  velocity vector. The properties of grazing collisions are especially
  important in this respect.

---------------------------------------------------------
Title: On the Rings of Saturn
Authors: Trulsen, Jan
1972Ap&SS..17..330T    Altcode:
  Results from numerical simulations of jetstreams are used to
  discuss certain aspects of the dynamics of the rings of Saturn. The
  probable velocity distribution inside the ring system is strongly
  non-Maxwellian. For the rings to form and remain a minimal degree of
  inelasticity is required. The energy consumption decreases rapidly
  with decreasing thickness of the rings. As we expect the degree of
  inelasticity to decrease for very small impact velocities, a minimal
  thickness should be reached, somewhat lower than the observed value.

---------------------------------------------------------
Title: Numerical simulation of jetstreams
Authors: Trulsen, Jan
1972Ap&SS..17..241T    Altcode:
  The dynamics of jetstreams have been studied by following the evolution
  of a simulation particle population. The self-gravitational field of
  the stream has been neglected, the individual small bodies interacting
  through hard, partially inelastic collisions only, no fragmentation or
  accreaction taking place. The chosen collision model — the beta-model
  — is given by Equation (4). The collisions will quickly establish
  a Rayleigh distribution of both eccentricities and inclinations, the
  average amplitude of the oscillations associated with eccentricity
  being up by approximately a factor √2. The velocity distribution
  inside the stream is highly non-Maxwellian. If the collisions are
  sufficiently inelastic, the stream is focused, the individual orbits
  becoming more and more circular (for azimuthally symmetric streams)
  and ecliptic. In the opposite case the collisions destroy the stream
  configuration rapidly. The beta collisional model is unable to produce
  any radial focusing.

---------------------------------------------------------
Title: Theory of jet streams
Authors: Trulsen, J.
1972fpp..conf..179T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Formation of Comets in Meteor Streams
Authors: Trulsen, J.
1972IAUS...45..487T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On jetstreams (formation of planetary systems).
Authors: Trulsen, J.
1972PhyNr...6..210T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Cyclotron radiation in hot magnetoplasmas
Authors: Trulsen, Jan
1971JPlPh...6..367T    Altcode:
  The effects of thermal motions on the cyclotron radiation from test
  particles gyrating in a homogeneous magnetoplasma are studied. These
  effects take care of all singularities that exist in the theory of
  cyclotron radiation in cold magneto- plasma, e.g. the divergence in
  energy loss for small particle energies. Around the hybrid frequencies
  thermal corrections become of dominant importance. At these frequencies
  cold-plasma theory breaks down. Thermal effects arise in two ways:
  by modifying the wave modes known from cold plasma theory, and by the
  introduction of a new longitudinal wave mode, known as the Bernstein
  mode. All wave modes are damped (in stable plasmas), the damping
  increasing rapidly with the product (V/v|) (ω - s), where the wave
  frequency ω is measured in units of the gyro frequency; V is the
  thermal velocity; v| the parallel component of the particle velocity,
  and s is an integer.

---------------------------------------------------------
Title: Towards a Theory of Jet Streams
Authors: Trulsen, Jan
1971Ap&SS..12..329T    Altcode:
  A kinetic equation for a jet stream consisting of identical, partially
  inelastic grains in neighbouring orbits around a central gravitating
  body is derived and given a preliminary discussion. No nonsingular
  equilibrium state exists for the jet stream configuration. The
  Boyle-Mariotte ideal gas law does not apply. The effect of hard,
  partially inelastic collisions is to decrease the kinetic temperature
  of the stream, thereby leading to a lining-up of the orbits of the
  individual grains with a subsequent reduction in the importance of
  collisions on the dynamics of the stream.

---------------------------------------------------------
Title: Collisional Focusing of Particles in Space Causing Jetstreams
Authors: Trulsen, Jan
1971NASSP.267..327T    Altcode: 1971psmp.coll..327T; 1971IAUCo..12..327T
  No abstract at ADS

---------------------------------------------------------
Title: Radiation from a charged particle in a magnetoplasma
Authors: Trulsen, J.; Fejer, J. A.
1970JPlPh...4..825T    Altcode:
  Two expressions for the power radiated by a charged particle in a
  homogeneous magnetoplasma are derived, using a method similar to that
  of Kolomenskii, Eidman and Liemohn. The first expression is identical
  with that of Eidman. The reason for the correctness of Eidman's result
  for dispersive media, in spite of his complete neglect of dispersion
  in the derivation, is explained. Liemohn, by taking dispersion into
  account at only one stage of the derivation, obtains a result which
  disagrees with the present one, often by many orders of magnitude,
  as illustrated by computations. <P />The second expression is derived
  by several authors by different methods; it is more suitable for
  computations than the first one. The radiation bands and their limiting
  frequencies are discussed systematically.