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  • 1
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observation of the adiabatic behaviour of energetic particle pitch-angle distributions in the magnetosphere (Lyons, 1977, and others) in the past indicated the development of pronounced minima or drift-loss cones on the pitch-angle distributions centred at α≃90° in connection with storm-time changes in magnetospheric convection and magnetic field. Using a model of a drift-modified loss-cone distribution (MLCD) of the butterfly type, the linear stability of electromagnetic whistler or ion-cyclotron waves propagating parallel to the magnetic field has been investigated. The instability is shown to be quenched at high frequencies ω〈ω m =A/(A+1), whereA is the thermal anisotropy. This quenching becomes stronger the higher are the respective parallel hot particle thermal velocityA h″ and cold plasma densityn c . Particles around pitch-angles α≃90° are identified as generating electromagnetic cyclotron waves near the marginally stable frequency ω m . It is concluded that the absence of electromagnetic VLF and ELF noise during times when MLCD develops is the result of the shift of the unstable spectrum to low frequencies.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 80 (1997), S. 341-367 
    ISSN: 1572-9672
    Keywords: Magnetopause ; Boundary Layer ; Reconnection ; Kelvin-Helmholtz-Instability ; Diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This is a brief overview on what we know and do not know about the low-latitude boundary layer (LLBL) at the flanks of the magnetotail. On the basis of recent observations, simulations and theories we conclude that reconnection is the dominant process in generating the LLBL and its structure probably even under northward IMF conditions. Part of the LLBL always seems to be on open field lines. Possibly the LLBL possesses a double structure with its outer part open and inner part closed. Anomalous diffusive processes cannot sustain the LLBL but provide sufficient diffusivity for reconnection. Strong diffusion is only expected in narrow localized regions and can make the transition to superdiffusion. Kelvin-Helmholtz instability (KHI) is favoured for northward IMF, producing vortices at the tail flanks. Its contribution to efficient mass transport still remains questionable. Coupling of the LLBL to the ionosphere can strongly affect the internal structure of the LLBL, causing turbulent eddies and detachments of plasma blobs as also field-aligned currents and electron heating. The structure and dynamics of the LLBL are affected by field-aligned electric potentials that decouple the LLBL from the ionosphere. Non-ideal coupling simulations suggest that the dusk flank is decoupled, favouring KHI, while the dawn flank is dominated by currents and turbulence.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Propagation of a quasi-neutral narrow ion beam across a magnetised cold plasma is investigated in slab geometry. This problem is of interest in connection with artificial beam injection experiments and with naturally appearing plasma injections into magnetic fields as astrophysical jets. Several different cases are discussed briefly where the beam is assumed either slow or fast. For fast beams it is shown that they propagate due to generation of a polarisation electric field even in the case of presence of a background plasma. Slow beams can depolarise by currents flowing into the beam along the field lines and providing the required electrons for charge neutralisation. Some implications of the model are discussed in the context of recent active beam injection experiments into space plasma.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 140 (1992), S. 149-160 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present observational evidence for simultaneous fundamental, second and third harmonic radio emission during an excessively strong type II burst on February 16, 1984. This burst was emitted from an active region behind the limb allowing for fair resolution of the wave bands. If interpreted as a triple harmonic system, three different, nearly equally probable mechanisms for higher harmonic emission are qualitatively discussed. These are a four-wave process which involves very strong Langmuir waves, a decay process first proposed by Cairns (1987) for higher harmonic emission near the Earth's bow shock, and time evolution of the emitted frequency during Langmuir wave collapse. In sufficiently strong coronal shock waves, both of the former mechanisms may be more efficient than under solar wind conditions. In the third mechanism, Langmuir wave collapse may be driven by strong electron beams as are expected to exist in quasiparallel shocks where electron reflection may be strongest. We discuss the differences between the signatures of these mechanisms.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 47 (1988), S. 175-202 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental investigations of plasma waves at the magnetopause, including recent results from the AMPTE/IRM satellite, show that both δE and δB fluctuations typically have a featureless spectrum which monotonically decreases with frequency; integrated rms amplitudes are typically a few mV m-1 for δE and 10 nT for δB, though in particular δE can be as much as an order of magnitude larger in exceptional cases. Surveys show a lack of correlation between wave parameters and the magnetopause parameters. Under the assumption that crossing the diffusion region would give a pronounced signature in the waves, the survey data allow an upper limit to be placed on the latitudinal extent of the diffusion region, which is about 1000 km — implying that it is not surprising that the wave data surveys have so far failed to detect it. The observed wave turbulence levels have been used to estimate diffusion coefficients under different assumptions for the wave mode, but the resulting diffusion coefficient is always too small to explain either reconnection or boundary layer formation. Recent work of Galeev et al. (1986) indicates that the dominant diffusion process may be ‘magnetic field migration’, which is a macroscopic process involving the interaction of tearing mode islands. Assuming this mode to be present at the observed level of δB, a particle diffusion coefficient of nearly 109 m2 s-1 is obtained. Another macroscopic diffusive process which could occur at the magnetopause is stochastic E × B scattering, which also implies a diffusion coefficient the order of 109 m2 s-1 if the observed δE spectrum is assumed to be a turbulent cascade consisting of convective cells.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 89 (1982), S. 342-346 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 65 (1978), S. 127-130 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 45 (1973), S. 215-216 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 68 (1978), S. 445-447 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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