EXOS‐B/Siple Station VLF wave‐particle interaction experiments: 1. General description and wave‐particle correlations

Kimura, Ikuo; Matsumoto, Hiroshi; Mukai, T.; Hashimoto, K.; Bell, T. F.; Inan, U. S.; Helliwell, R. A.; Katsufrakis, J. P.

doi:10.1029/ja088ia01p00282

Cited by 29 publications

(19 citation statements)

References 25 publications

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“…With the path properties, wave frequency, and pulse length determined, the only adjustable parameters left to choice are the input wave amplitude and ambient (i.e., initial) the hot electron distribution. Although ducted Siple signals were never observed in situ, several spacecraft observations of non‐ducted obliquely propagating Siple transmissions have been observed which measured the wave magnetic field amplitude to be 0.02–0.05 pT [ Kimura et al , 1983; Rastani et al , 1985; Sonwalkar and Inan , 1986]. For the cases considered here, where long‐period saturation oscillations are active without significant triggering of free running plasma emissions, Siple transmitted at frequencies not exactly at the frequency to which the transmitter was tuned, resulting in lower radiated wave amplitudes.…”

Section: Resultsmentioning

confidence: 99%

Saturation effects in the VLF‐triggered emission process

2008

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[1] An in-depth study is performed of the saturation characteristics of the VLF-triggered emission process, a plasma instability associated with the amplification of whistler mode signals in the magnetosphere. A survey of data from the 1986 operating year of the Siple VLF wave injection experiment reveals that long-period oscillations (characterized by a pattern of growth to saturation then subsequent suppression of the wave), shortperiod oscillations (previously identified as sidebands), and generation of incoherent wave energy around the frequency of the triggering signal are all characteristics of the instability at saturation. A model is developed to study these phenomena. The model is in some respects similar to the Vlasov Hybrid Simulation but modified so that saturation is a natural consequence of the modeled growth process. Results from the model indicate that the growth and eventual saturation are caused by wave amplitude gradients, most notably gradients that indicate a transition from an amplitude where the wave cannot trap electrons in its potential in the presence of the inhomogeneous magnetospheric magnetic field to an amplitude where such trapping is possible. That is, resonant currents are enhanced in the region where the phase space electron hole created by the trapping condition is allowed to mix with the ambient energetic electrons. This growth process is found to naturally lead to saturation of the instability.

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Section: Resultsmentioning

confidence: 99%

Saturation effects in the VLF‐triggered emission process

2008

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“…Observations on the ground stations reveal that narrow band whistler‐mode waves which often consist of rising tones are periodically generated by triggering waves which are emitted from the ground station at high‐latitude region [ Helliwell and Katsufrakis , 1974; Helliwell , 1983]. Results of in situ measurements by satellites show that the triggered emissions are generated near the equatorial region of the magnetosphere and related to energetic electrons [ Inan et al , 1977; Kimura et al , 1983; Bell et al , 2000]. Several models of the generation mechanism have been proposed by previous theories and simulations (see reviews by Matsumoto [1979] and Omura et al [1991]).…”

Section: Introductionmentioning

confidence: 99%

A study of generation mechanism of VLF triggered emission by self‐consistent particle code

Katoh

Omura

2006

J. Geophys. Res.

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[1] We carry out a self-consistent particle simulation with a dipole magnetic field to study the generation mechanism of VLF triggered emissions. The evolution of a wave packet propagating along a reference magnetic field line is solved by Maxwell's equations, while the bounce motion of energetic electrons in the nonuniform magnetic field is taken into account. Simulation result demonstrates that our model can investigate the detailed physics of VLF triggered emissions. In the simulation result we find that a triggered emission with a rising tone is generated near the equatorial region after the wave packet passes through the magnetic equator, and 26% rising from the original frequency of the injected wave packet is reproduced. The generation process simulated in the present paper is explained by roles of resonant currents J E and J B in association with an electromagnetic electron hole in the phase space produced through the nonlinear interaction. It has been suggested that a negative J E contributes to the growth of whistlermode waves, while a negative J B induces the frequency rising. Simulation result shows that both negative J E and negative J B are formed at the trailing edge of the triggering wave, generating the emission with the rising tone. On the basis of the simulation result, we find that these resonant currents are formed by untrapped electrons through the nonlinear wave-particle interaction and suggest that the resonant current formation by untrapped electrons plays an essential role in the triggering mechanism.

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“…The terms on the right hand side of eq. (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) scale respectively like (dropping the fourth),…”

Section: (3-8)mentioning

confidence: 99%

“…(see also eqs. (7-12) through (7)(8)(9)(10)(11)(12)(13)(14)). The numerical difficulty associated with the phase equation can be seen rather clearly from equation (6-7).…”

Section: Numerical Implementationmentioning

confidence: 99%

“…This is a rounded-off square wave pulse with continuous first derivative. At each time step the trapping condition (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), as well as the cut-off condition equation (4-27) (evaluated using the average amplitude over the interaction region) is checked for all perpendicular velocities and grid points. If the particles in question are trapped -r, a, and L are stepped using the above schemes and the real current is accumulated.…”

Section: Numerical Implementationmentioning

confidence: 99%

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Self‐Consistent Theory of Triggered Whistler Emissions

Molvig¹,

Hilfer²,

Miller³

et al. 1988

J. Geophys. Res.

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A kinetic theory of triggered VLF whistler emissions is given that is capable of predicting from a small scale numerical implementation the observed emission forms, and frequency-time characteristics. The present paper focuses on the theoretical developments and the explanation of the triggering process, complete with a demonstration of the threshold behavior (sometimes known as the dot-dash anomaly) and the generation of specific falling frequency emissions that compare quite favorably to typical observations made in the controlled experiments based in Siple Station, Antarctica. The theory that gives these results is a fully self-consistent nonlinear treatment based on kinetic theory and valid in the asymptotic limit when several trapping periods occur within the interaction region. For a typical set of parameters, I = 4.3, n = 400 cm-3 , and amplitude, BT ~ 1.6 pT, for the input wave magnetic field, one has about seven trapping periods in the triggering signal and would expect good results from the asymptotic limit. In this limit the nonlinear dynamics can be reduced to the determination of the time, r, that the resonant particles are trapped. The nonlinear currents can be expressed in terms of this function, r, by simple integrals over the trapped particles' perpendicular velocities alone. Most of the features of the emission process can be determined analytically and properties, such as the rate of change of frequency, related to magnetospheric parameters. For more quantitative predictions such as amplitude and frequency waveforms, a small numerical code which integrates the nonlinear wave equations is used. The theoretical picture of the triggering mechanism i contains the observed threshold behavior wherein short triggering pulses of nominal amplitude BT ~ 1 pT and 100 ms in duration or less cannot generate an emission, whereas those in the 200 ms range and longer do. Similar sensitivity is found with respect to initial frequency, where in some cases 5.5 kHz signals can trigger, but 5.0 kHz signals cannot.Gains in the range of 20 -30 dB are obtained with initial temporal growth rates in the range 100 -200 dB/sec. The emission process requires an inverted population in the perpendicular velocity distribution function but not necessarily linear instability. A sufficient number of high energy electrons is required that the driven currents can offset convection, but provided this is satisfied, a sufficiently long triggering signal will always generate a self-sustaining emission. Interestingly, however, the self-sustaining emission does not depend on the number of these high energy particles or the details of the velocity distribution function but only on bulk magnetospheric parameters such as magnetic field, gradient scale length, and the plasma density in the plasmapause. Also the marginal signals generated just above the threshold are always fallers as is observed. These features have not been explained by existing theories. Unresolved issues include the mechanism of termination, the generation of ri...

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EXOS‐B/Siple Station VLF wave‐particle interaction experiments: 1. General description and wave‐particle correlations

Abstract: In situ measurements of both ener-1Department

Cited by 29 publications

References 25 publications

Saturation effects in the VLF‐triggered emission process

Saturation effects in the VLF‐triggered emission process

A study of generation mechanism of VLF triggered emission by self‐consistent particle code

Self‐Consistent Theory of Triggered Whistler Emissions

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