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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. .
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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.
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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.
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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.
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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.
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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.
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Title: Plasma physics in the ionosphere. II. The ionosphere in the
plasma laboratory.
Authors: Trulsen, J.
1981FFV....43...67T Altcode:
No abstract at ADS
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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.
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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.
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Title: Poynting-Robertson Effect and Collisions in the Interplanetary
Dust Cloud
Authors: Trulsen, J.; Wikan, A.
1980IAUS...90..299T Altcode:
No abstract at ADS
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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><<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>>>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><<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.
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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.
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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.
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Title: The origin and properties of thermal fluctuations in a plasma.
Authors: Trulsen, J.; Bjøernå, N.
1977rpap.conf...29T Altcode:
No abstract at ADS
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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.
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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.
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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.
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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.
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Title: Theory of jet streams
Authors: Trulsen, J.
1972fpp..conf..179T Altcode:
No abstract at ADS
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Title: Formation of Comets in Meteor Streams
Authors: Trulsen, J.
1972IAUS...45..487T Altcode:
No abstract at ADS
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Title: On jetstreams (formation of planetary systems).
Authors: Trulsen, J.
1972PhyNr...6..210T Altcode:
No abstract at ADS
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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.
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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.
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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
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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.