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  • 1
    Electronic Resource
    Electronic Resource
    Spatial transport and spectral transfer of solar wind turbulence composed of Alfvén waves and convective structures I: The theoretical model (1995)
    Springer
    Annales geophysicae 13 (1995), S. 459-474 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this paper we give a survey of detailed algebraic developments of a solar wind turbulence model. The numerical solution of the coupled system of spectral transfer equations for turbulence composed of Alfvén waves and convective structures or two-dimensional turbulence is prepared. The underlying theory of spectral transfer equations was established by several authors in the early 1990s. The related numerical turbulence model which is elaborated in detail in this paper is based on a rotationally symmetric solar wind model for the background magnetic and flow velocity fields with the full geometry of Parker’s spiral which has to be inserted into the transfer equations. Various sources and sinks for turbulent energy are included and appropriately modelled analytically. Spherical expansion terms related to radial gradients of the background velocity fields are considered as far as possible within a rotational symmetric solar wind model, which excludes vorticity effects. Furthermore, nonlinear interaction terms are considered, justified by phenomenological arguments and evaluated by dimensional analysis. Moreover, parametric conversion terms for Alfvén waves and wave-structure interactions are modelled and a generalized spectral flux function for the residual energy eR is introduced. In addition, we compensate the spectra for WKB trends and f-5/3-slopes in order to prepare a convenient form of the equations for numerical treatment. The modelling of source and sink terms includes a special analytical treatment for correlation tensors. This first part presents a summary of the main ideas and the special approximations used for all these terms, together with details on the basic steps of the algebraic calculations. The description of the numerical scheme and a survey of the numerical results of our model, as well as a discussion of the main physical results are contained in a companion paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0459-3
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  • 2
    Electronic Resource
    Electronic Resource
    Multifractal scaling of the kinetic energy flux in solar wind turbulence (1996)
    Springer
    Annales geophysicae 14 (1996), S. 259-269 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The geometrical and scaling properties of the energy flux of the turbulent kinetic energy in the solar wind have been studied. Using present experimental technology in solar wind measurements we cannot directly measure the real volumetric dissipation rate, 〈varepsilon〉(t), but are constrained to represent it by its surrogate the energy flux near the dissipation range at the proton gyro scale. There is evidence for the multifractal nature of the so defined dissipation field 〈varepsilon〉(t), a result derived from the scaling exponents of its statistical moments. The generalized dimension Dq has been determined and reveals that the dissipation field has a multifractal structure, which is not compatible with a scale-invariant cascade. The related multifractal spectrum f(〈alpha〉) has been estimated for the first time for MHD turbulence in the solar wind. Its features resemble those obtained for turbulent fluids and other nonlinear multifractal systems. The generalized dimension Dq can for turbulence in high-speed streams be fitted well by the functional dependence of the p-model with a comparatively large parameter p1=0.87, indicating a strongly intermittent multifractal energy cascade. The experimental value for Dp/3 used in the scaling exponent s(p) of the velocity structure function gives an exponent that can describe some of the observations. The scaling exponent 〈mu〉 of the autocorrelation function of 〈varepsilon〉(t) has also been directly evaluated, being 0.37. Finally, the mean dissipation rate was determined, which could be used in solar wind heating models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0259-4
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  • 3
    Electronic Resource
    Electronic Resource
    Non-Gaussian probability distributions of solar wind fluctuations (1994)
    Springer
    Annales geophysicae 12 (1994), S. 1127-1138 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The probability distributions of field differences 〈Delta〉x(〈tau〉)=x(t+〈tau〉)-x(t), where the variable x(t) may denote any solar wind scalar field or vector field component at time t, have been calculated from time series of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is found that for comparatively long time lag 〈tau〉, ranging from a few hours to 1 day, the differences are normally distributed according to a Gaussian. For shorter time lags, of less than ten minutes, significant changes in shape are observed. The distributions are often spikier and narrower than the equivalent Gaussian distribution with the same standard deviation, and they are enhanced for large, reduced for intermediate and enhanced for very small values of 〈Delta〉x. This result is in accordance with fluid observations and numerical simulations. Hence statistical properties are dominated at small scale 〈tau〉 by large fluctuation amplitudes that are sparsely distributed, which is direct evidence for spatial intermittency of the fluctuations. This is in agreement with results from earlier analyses of the structure functions of 〈Delta〉x. The non-Gaussian features are differently developed for the various types of fluctuations. The relevance of these observations to the interpretation and understanding of the nature of solar wind magnetohydrodynamic (MHD) turbulence is pointed out, and contact is made with existing theoretical concepts of intermittency in fluid turbulence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-1127-8
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  • 4
    Electronic Resource
    Electronic Resource
    An extended structure-function model and its application to the analysis of solar wind intermittency properties (1996)
    Springer
    Annales geophysicae 14 (1996), S. 270-285 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An extended structure-function model is developed by including the new effect in the p-model of Meneveau and Sreenivasan which shows that the averaged energy cascade rate changes with scale, a situation which has been found to prevail in nonfullydeveloped turbulence in the inner solar wind. This model is useful for the small-scale fluctuations in the inner heliosphere, where the turbulence is not fully developed and cannot be explained quantitatively by any of the previous intermittency turbulence models. With two model parameters, the intrinsic index of the energy spectrum 〈alpha〉, and the fragmentation fraction P1, the model can fit, for the first time, all the observed scaling exponents of the structure functions, which are calculated for time lags ranging from 81 s to 0.7 h from the Helios solar wind data. From the cases we studied we cannot establish for P1 either a clear radial evolution trend, or a solar-wind-speed or stream-structure dependence or a systematic anisotropy for both the flow velocity and magnetic field component fluctuations. Generally, P1 has values between 0.7 and 0.8. However, in some cases in low-speed wind P1 has somewhat higher values for the magnetic components, especially for the radial component. In high-speed wind, the inferred intrinsic spectral indices (〈alpha〉) of the velocity and magnetic field components are about equal, while the experimental spectral indices derived from the observed power spectra differ. The magnetic index is somewhat larger than the index of the velocity spectrum. For magnetic fluctuations in both high- and low-speed winds, the intrinsic exponent 〈alpha〉 has values which are near 1.5, while the observed spectral exponent has much higher values. In the solar wind with considerable density fluctuations near the interplanetary current sheet near 1 AU, it is found that P1 has a comparatively high value of 0.89 for Vx. The impact of these results on the understanding of the nature of solar wind fluctuations is discussed, and the limitations in using structure functions to study intermittency are also described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0270-9
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  • 5
    Electronic Resource
    Electronic Resource
    Pressure enhancement associated with meridional flow in high-speed solar wind: possible evidence for an interplanetary magnetic flux rope (1997)
    Springer
    Annales geophysicae 15 (1997), S. 137-142 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A sizable total-pressure (magnetic pressure plus kinetic pressure) enhancement was found within the high-speed wind stream observed by Helios 2 in 1976 near 0.3 AU. The proton density and temperature and the magnetic magnitude simultaneously increased for about 6 h. This pressure rise was associated with a comparatively large southward now velocity component (with Vz ≈ − 100 km · s−1) and magnetic-field rotation. The pressure enhancement was associated with unusual features in the electron distribution function. It shows a wide angular distribution of electron counting rates in the low-energy (57.8 eV) channel, while previous to the enhancement it exhibits a wide angular distribution of electron count rate in the high-energy (112, 221 and 309 eV) channels, perhaps indicating the mirroring of electrons in the converging field lines of the background magnetic field. These fluid and kinetic phenomena may be explained as resulting from an interplanetary magnetic flux rope which is not fully convected by the flow but moves against the background wind towards the Sun.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0137-8
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical conductivity of a doubly-degenerate hubbard-model
    Amsterdam : Elsevier
    Physics Letters A 59 (1976), S. 293-294 
    Details
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0375-9601(76)90797-0
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  • 7
    Electronic Resource
    Electronic Resource
    Coulomb collision rates for self-similar and kappa distributions (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1379-1386 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Coulomb collision operator for two nonthermal particle distributions, the self-similar and kappa distribution, is investigated theoretically. Associated friction and diffusion rates are evaluated and calculated numerically as a function of velocity. It is shown that the full collision term can be cast into a relaxation time form with an effective collision rate that differs drastically from the smooth overall diffusion rates and is very sensitive to the shape of the distribution. Numerical results for the effective rates are presented and the relevance of our analysis with respect to observed distributions in space plasmas and for quasilinear turbulence is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.864971
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  • 8
    Electronic Resource
    Electronic Resource
    Are structures in high-speed streams signatures of coronal fine structures?
    Amsterdam : Elsevier
    Advances in Space Research 9 (1989), S. 127-130 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0273-1177(89)90105-1
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical models for the solar wind
    Amsterdam : Elsevier
    Advances in Space Research 14 (1994), S. 103-121 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0273-1177(94)90170-8
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  • 10
    Electronic Resource
    Electronic Resource
    Ions of martian origin and plasma sheet in the martian magnetosphere: initial results of the TAUS experiment (1989)
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 612-614 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The instruments previously used for investigating the martian plasma environment were either plasma cups or curved electrostatic analysers by which different types of ions generally cannot be distinguished. To resolve this deficiency, the TAUS spectrometer, which uses electric and magnetic fields ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/341612a0
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