Author name code: trulsen ADS astronomy entries on 2022-09-14 author:Trulsen, Jan ------------------------------------------------------------------------ Title: Dynamic models for magnetospheric oscillations on the minute scale Authors: Sato, H.; Pecseli, H.; Børve, S.; Trulsen, J. Bibcode: 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. Title: Spacecraft charging in flowing plasmas; numerical simulations Authors: Miloch, W. J.; Yaroshenko, V. V.; Vladimirov, S. V.; Pécseli, H. L.; Trulsen, J. Bibcode: 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. Title: Fluctuations in the direction of propagation of intermittent low-frequency ionospheric waves Authors: Sato, H.; Pécseli, H. L.; Trulsen, J. Bibcode: 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. Title: Fluctuations in the Direction of Propagation of Low Frequency Ionospheric Waves Authors: Sato, H.; Pécseli, H. L.; Trulsen, J. K. Bibcode: 2011ESASP.700..629S Altcode: No abstract at ADS 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. Bibcode: 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. Title: Numerical Dissipation in RSPH Simulations of Astrophysical Flows with Application to Protoplanetary Disks Authors: Børve, S.; Speith, R.; Trulsen, J. Bibcode: 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. 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 Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: Symmetry assumptions in SPH. Authors: Omang, M.; Børve, S.; Christensen, S. O.; Trulsen, J. Bibcode: 2007sphe.work..103O Altcode: No abstract at ADS Title: Challenges related to particle regularization in SPH. Authors: Børve, S.; Speith, R.; Omang, M.; Trulsen, J. Bibcode: 2007sphe.work...67B Altcode: No abstract at ADS Title: Multidimensional MHD Shock Tests of Regularized Smoothed Particle Hydrodynamics Authors: Børve, S.; Omang, M.; Trulsen, J. Bibcode: 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. Title: Plasma and electromagnetic wave simulations of meteors Authors: Dyrud, L.; Lee, Y.; Boerve, S.; Trulsen, J.; Pecseli, H. Bibcode: 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 Title: On the Possibility for Action Conservation in the Solar Cycle Authors: Pécseli, Hans; Trulsen, Jan Bibcode: 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. Title: Two-dimensional MHD Smoothed Particle Hydrodynamics Stability Analysis Authors: Børve, S.; Omang, M.; Trulsen, J. Bibcode: 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. 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. Bibcode: 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. Title: Regularized Smoothed Particle Hydrodynamics: A New Approach to Simulating Magnetohydrodynamic Shocks Authors: Børve, S.; Omang, M.; Trulsen, J. Bibcode: 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. Title: Low frequency waves in plasmas with spatially varying electron temperature Authors: Guio, P.; Børve, S.; Pécseli, H. L.; Trulsen, J. Bibcode: 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. Title: Smoothed Particle Hydrodynamics with Time Varying, Piecewise Constant Smoothing Length Profiles Authors: Børve, S.; Omang, M.; Trulsen, J. Bibcode: 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. Title: Spectral properties of low-frequency electrostatic waves in the ionospheric E region Authors: Krane, B.; Pécseli, H. L.; Trulsen, J.; Primdahl, F. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 1996ESASP.389..393H Altcode: 1996icss.conf..393H No abstract at ADS 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. Bibcode: 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. Title: Velocity correlations in two-dimensional electrostatic turbulence in low-β plasmas Authors: Pécseli, H. L.; Trulsen, J. Bibcode: 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/B2 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1980IAUS...90..299T Altcode: No abstract at ADS Title: Nonlinear mixing as a plasma density probe Authors: Dysthe, K. B.; Mjolhus, E.; Trulsen, J. Bibcode: 1978JGR....83.1985D Altcode: Nonlinear mixing of two electromagnetic waves, ω+/-and k+/-, in an inhomogeneous isotropic and collisionless plasma in the parameter range β2/3(KL)1/3<<1 is studied. Here β is the ratio of electron thermal velocity to speed of light, K=Ω/c,Ω=ω+-ω-, and L is a local characteristic length for electron density variation. Langmuir waves, Ω and kL, are found to be excited in two different ways. When (Δk/K) β2/3(KL)1/3>>1, where Δk=k+-k-, resonant wave mixing occurs in which the generated Langmuir waves satisfy kL?Δk. When (Δk/K) β2/3(KL)1/3<<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. Bibcode: 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. Bibcode: 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. Bibcode: 1977rpap.conf...29T Altcode: No abstract at ADS Title: Dynamics of Interplanetary Dust and Related Topics Invited Paper Authors: Trulsen, J. Bibcode: 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 Bibcode: 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)2), 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 Bibcode: 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 Bibcode: 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. Bibcode: 1972fpp..conf..179T Altcode: No abstract at ADS Title: Formation of Comets in Meteor Streams Authors: Trulsen, J. Bibcode: 1972IAUS...45..487T Altcode: No abstract at ADS Title: On jetstreams (formation of planetary systems). Authors: Trulsen, J. Bibcode: 1972PhyNr...6..210T Altcode: No abstract at ADS Title: Cyclotron radiation in hot magnetoplasmas Authors: Trulsen, Jan Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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.

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.