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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 2.5-dimensional particle-in-cell numerical simulation. We find that when the electron temperature is striated along B0 and low frequency waves (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 (ci) will on the other hand have a spatially more uniform intensity distribution. 相似文献
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Jan Trulsen 《Astrophysics and Space Science》1972,17(2):330-337
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. 相似文献
3.
K. Iranpour H. L. Pecseli J. Trulsen A. Bahnsen F. Primdahl K. Rinnert 《Annales Geophysicae》1997,15(7):878-889
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. 相似文献
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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. 相似文献
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Jan Trulsen 《Astrophysics and Space Science》1971,12(2):329-348
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.Most of the work done while at the University of California, San Diego.Receipt delayed by postal strike in Great Britain. 相似文献
6.
The paper starts with a discussion of the linear stochastic theory of ocean waves and its various nonlinear extensions. The directional spectrum, with its unique dispersion relation connecting frequency (ω) and wavenumber (k), is no longer valid for nonlinear waves, and examples of $\left( \mathbf{k},\omega\right) The paper starts with a discussion of the linear stochastic theory of ocean waves and its various nonlinear extensions. The
directional spectrum, with its unique dispersion relation connecting frequency (ω) and wavenumber (k), is no longer valid for nonlinear waves, and examples of ( k,w)\left( \mathbf{k},\omega\right) -spectra based on analytical expressions and computer simulations of nonlinear waves are presented. Simulations of the dynamic
nonlinear evolution of unidirectional free waves using the nonlinear Schr?dinger equation and its generalizations show that
components above the spectral peak have larger phase and group velocities than anticipated by linear theory. Moreover, the
spectrum does not maintain a thin well-defined dispersion surface, but rather develops into a continuous distribution in ( k,w)\left( \mathbf{k,}\omega\right) -space. The majority of existing measurement systems rely on linear theory for the interpretation of their data, and no measurement
systems are currently able to measure the full spectrum in the open ocean with high accuracy. Nevertheless, there exist a
few low-resolution systems where data may be interpreted within a minimal assumption of a non-restricted ( k,w)\left( \mathbf{k,}\omega\right) -spectrum. The theory is reviewed, and analyses based on conventional spectral analysis as well as a directional wavelet analysis
are carried out on data from a compact laser array at the Ekofisk field in the North Sea. The investigation confirms the strong
impact of the second order spectrum below the spectral peak, but is non-conclusive about the off-set in the support of the
first order spectrum seen in the dynamical simulations. 相似文献
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Lars Dyrud Derek Wilson Steiner Boerve Jan Trulsen Hans Pecseli Sigrid Close Chen Chen Yoonjae Lee 《Earth, Moon, and Planets》2008,102(1-4):383-394
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. 相似文献
8.
Jan Trulsen 《Astrophysics and Space Science》1972,18(1):3-20
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(–(P–)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. 相似文献
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