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  • 1
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In situ satellite observations of type III burst exciters at 1 AU show that the beam does not evolve into a plateau in velocity space, contrary to the prediction quasilinear theory. The observations can be explained by a theory that includes mode coupling effects due to excitation of the parametric oscillating two-stream instability and its saturation by anomalous resistivity. The time evolution of the beam velocity distribution is included in the analysis.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 436 (2005), S. 782-783 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Turbulence is ubiquitous. It can be seen by gently stirring cream into coffee, or by observing the white caps and surf at the beach, and it causes the drag on cars and aeroplanes. The phenomenon is also widespread in magnetized plasmas — ionized gases that contain a magnetic field — ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 258 (1975), S. 175-175 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN a recent series of papers, Runcorn1'2 has maintained that the observation of a very small lunar surface dipole field (〈 0.05y) implies that there used to be a fairly strong interior lunar dipole moment (〉 3.2xl09yr ago). He contends that if such a field had disappeared in the past 3.2 x ...
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  • 4
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1437-1446 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quasifluid formalism designed to capture some effects of cyclotron interactions is presented. Starting from the contractions of exact moments of the Vlasov equation, a closure for cyclotron interactions is achieved by using kinetic information directly. This nonperturbative approach does not require a priori assumptions about zeroth-order particle velocity distributions. The nonlinear coupling between field-aligned particle thermal velocities and transverse cyclotron wave and thermal motions are described by off-diagonal elements of the pressure tensor. These elements are related to the growth and damping of cyclotron wave energy. A functional form for an effective wave–particle momentum transport coefficient is derived from the requirement of consistency between the energy and momentum moment equations, but its specific magnitude and sign, determined by threshold temperature anisotropy levels, must be input from kinetic theory. This effective transport coefficient has a nondefinite sign, reminiscent of the gyroviscous coefficients of classical transport, and is consistent with the time reversibility of the Vlasov equation. A coupled set of cyclotron equations of state for the evolution of the parallel and perpendicular pressures are derived. This formalism provides a connection between known kinetic solutions of cyclotron interactions and fluid plasma equations. © 1996 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 4154-4160 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low frequency fluctuations in the solar wind magnetic field and plasma velocity are often highly correlated, so much so that the fluctuations may be thought of as originating near the Sun as nearly perfect Alfvén waves. Power spectra of these fluctuations from 10−7 Hz to several Hz to suggest that the medium is turbulent. Near 1 AU, fluctuations below 10−5 Hz have a relatively flat slope (∼−1) and contain most of the energy in the fluctuating fields. From 10−5 Hz to ∼0.1 Hz, the spectra exhibit a power law inertial range similar to that seen in ordinary fluid turbulence. At the highest frequencies, the rapid fall-off of the power suggests that strong dissipation is occurring. From in situ measurements, it is clear that the fluctuations emanate from the solar corona. The turbulent cascade appears to evolve most rapidly in the vicinity of velocity shears and current sheets. Numerical solutions of both the compressible and incompressible equations of magnetohydrodynamics in both Cartesian and spherical geometry corroborate this interpretation. There are conflicting interpretations of observations suggesting that much of the power in magnetic field fluctuations resides in quasi-two-dimensional structures and simulations have helped to elucidate some of these issues. © 1999 American Institute of Physics.
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  • 7
    Publication Date: 2011-08-19
    Description: Voyager 2 magnetic field and plasma data are examined over time intervals of 1 to 12 hours in the heliospheric range of 1 to 10 AU to study the evolution of the anisotropy of solar wind fluctuations. Consistent with previous results, the directions of minimum variance vectors of magnetic fluctuations are found to be close to the mean magnetic field direction with an increasing component along the field at larger scales. At large radial distances there is more spread in the minimum variance directions than at smaller radial distances. The power in smaller-scale fluctuations in the magnetic field components perpendicular to the local mean field B(0) is in the ratio of about 5:1 near 1 AU at the scale of 1 hour but decreases to about 3:1 further out. No evidence for selective enhancement of out-of-the-ecliptic components of fluctuations is found. In contrast to results for field fluctuations, analysis of velocity fluctuations shows that the minimum variance direction systematically remains more radially oriented and becomes increasingly less oriented along B(0) with increasing heliocentric distance. The velocity fluctuations are generally more isotropic than the magnetic fluctuations. The observations cannot be explained by a superposed wave picture, and thus are consistent with the view that nonlinear turbulent evolution is responsible for the anisotropy in the fluctuations.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 3779-378
    Format: text
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  • 8
    Publication Date: 2011-08-19
    Description: The theoretical model of Tu (1988) for the turbulent evolution of solar wind fluctuations assumed the constancy of the ratio alpha(1) between the energy in inward and outward propagating Alfven waves. Here, this model is extended to reflect the observed evolution in the propagation directions of the interplanetary fluctuations. The radial dependence of alpha(1) is determined by direct time domain correlations of the normalized cross helicity. The theoretical results match the observations at least as well as those of the previous, constant alpha(1), model. Measured values of alpha(1) are then used to find the value of the cascade constant that determines the overall level of the energy spectrum. The value of 1.25 for this constant is very close to the value observed in fluid turbulence if it is assumed that the correspondence between fluid and magnetofluid theories should be made for uncorrelated (zero cross helicity) MHD turbulence.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 13575-13
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  • 9
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: Studies of turbulence and waves in the solar wind is discussed. Consideration is given to the observations and theory concerning the origin and evolution of interplanetary MHD fluctuations and to the observations, theory, and simulations of compressive fluctuations. Particular attention is given to extrapolations to near-sun and polar fields regions. Results obtained on turbulence at comets and magnetic turbulence of low-frequency waves excited by unstable distributions of ions are discussed.
    Keywords: SOLAR PHYSICS
    Type: Reviews of Geophysics Supplement (ISSN 8755-1209); 29; 932-943
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  • 10
    Publication Date: 2011-08-19
    Description: A recent theory holds that high-intensity, long-duration, continuous auroral activity (HILDCAA) is caused by interplanetary Alfven waves propagating outward from the sun. A survey of Alfvenic intervals in over a year of ISEE 3 data shows that while Alfvenic intervals often accompany HILDCAAs, the reverse is often not true. There are many Alfvenic intervals during which auroral activity (measured by high values of the AE index) is very low, as well as times of high auroral activity that are not highly Alfvenic. This analysis supports the common conclusion that large AE values are associated with a southward interplanetary field of sufficient strength and duration. This field configuration is independent of the presence of Alfven waves (whether solar generated or not) and is expected to occur at random intervals in the large-amplitude stochastic fluctuations in the solar wind.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4327-433
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