Generation of Bernstein waves by ion shell distributions in the auroral region

Janhunen, P.; Olsson, A.; Vaivads, A.; Peterson, W. K.

doi:10.5194/angeo-21-881-2003

Cited by 26 publications

(50 citation statements)

References 32 publications

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“…One interpretation is that the satellite is just on the top of the region where waves consume energy. The ion bowl is consistent with this interpretation, since at least, if the waves are ion Bernstein waves, they can both increase the parallel energy of the electrons and the perpendicular energy of the ions (Janhunen et al, 2003a).…”

Section: Partly Consumed Psbl and Bps Ion Shellssupporting

confidence: 67%

“…The results of Janhunen et al (2003a) have motivated this investigation. The existence of the Polar database makes it possible to systematically investigate correlations between ion shell distributions, electron anisotropy and waves.…”

Section: Instrumentationmentioning

confidence: 99%

“…Some more discussion of the prodeduce and an example is given in Janhunen et al (2003a). The procedure results in an upper limit estimate of the free energy available.…”

Section: Data Processingmentioning

confidence: 99%

“…Janhunen et al (2003a) have shown that wave modes exist in the region which can tap this free energy. They have also developed a technique to estimate the available free energy from in-situ data.…”

Section: Introductionmentioning

confidence: 99%

“…They noted that these double loss cone distributions (which have been called toroidal by some investigators) at sub-auroral latitudes are maintained by transport from the plasma sheet and are possibly the free energy source of various pulsation modes. Janhunen et al (2003a) provided examples of shell distributions in auroral latitudes at ∼4-5 R E radial distance (geocentric distance) using Polar/TIMAS data and showed with the help of solving the linear dispersion relation numerically and by using a two-dimensional particle simulation that the observed shell distribution is unstable to a broad range of ion Bernstein wave modes. It was also shown in the paper that the generated Bernstein waves accelerate ∼100 eV electrons at a rate of ∼80 eV/s.…”

Section: Introductionmentioning

confidence: 99%

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Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

2004

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Abstract. Ion shell distributions are hollow spherical shells in velocity space that can be formed by many processes and occur in several regions of geospace. They are interesting because they have free energy that can, in principle, be transmitted to ions and electrons. Recently, a technique has been developed to estimate the original free energy available in shell distributions from in-situ data, where some of the energy has already been lost (or consumed). We report a systematic survey of three years of data from the Polar satellite. We present an estimate of the free energy available from ion shell distributions on auroral field lines sampled by the Polar satellite below 6 R E geocentric radius. At these altitudes the type of ion shells that we are especially interested in is most common on auroral field lines close to the polar cap (i.e. field lines mapping to the plasma sheet boundary layer, PSBL). Our analysis shows that ion shell distributions that have lost some of their free energy are commonly found not only in the PSBL, but also on auroral field lines mapping to the boundary plasma sheet (BPS), especially in the evening sector auroral field lines. We suggest that the PSBL ion shell distributions are formed during the so-called Velocity Dispersed Ion Signatures (VDIS) events. Furthermore, we find that the partly consumed shells often occur in association with enhanced wave activity and middle-energy electron anisotropies. The maximum downward ion energy flux associated with a shell distribution is often 10 mW m −2 and sometimes exceeds 40 mW m −2 when mapped to the ionosphere and thus may be enough to power many auroral processes. Earlier simulation studies have shown that ion shell distributions can excite ion Bernstein waves which, in turn, energise electrons in the parallel direction. It is possible that ion shell distributions are the link between the X-line and the auroral wave activity and electron acceleration in the energy transfer chain for stable auroral arcs.

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Section: Partly Consumed Psbl and Bps Ion Shellssupporting

confidence: 67%

Section: Instrumentationmentioning

confidence: 99%

“…Some more discussion of the prodeduce and an example is given in Janhunen et al (2003a). The procedure results in an upper limit estimate of the free energy available.…”

Section: Data Processingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

2004

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Interpreting ~1 Hz magnetic compressional waves in Mercury's inner magnetosphere in terms of propagating ion‐Bernstein waves

et al. 2015

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We show that~1 Hz magnetic compressional waves observed in Mercury's inner magnetosphere could be interpreted as ion-Bernstein waves in a moderate proton beta~0.1 plasma. An observation of a proton distribution with a large planetary loss cone is presented, and we show that this type of distribution is highly unstable to the generation of ion-Bernstein waves with low magnetic compression. Ray tracing shows that as these waves propagate back and forth about the magnetic equator; they cycle between a state of low and high magnetic compression. The group velocity decreases during the high-compression state leading to a pileup of compressional wave energy, which could explain the observed dominance of the highly compressional waves. This bimodal nature is due to the complexity of the index of refraction surface in a warm plasma whose upper branch has high growth rate with low compression, and its lower branch has low growth/damping rate with strong compression. Two different cycles are found: one where the compression maximum occurs at the magnetic equator and one where the compression maximum straddles the magnetic equator. The later cycle could explain observations where the maximum in compression straddles the equator. Ray tracing shows that this mode is confined within ±12°magnetic latitude which can account for the bulk of the observations. We show that the Doppler shift can account for the difference between the observed and model wave frequency, if the wave vector direction is in opposition to the plasma flow direction. We note that the Wentzel-Kramers-Brillouin approximation breaks down during the pileup of compressional energy and that a study involving full wave solutions is required.

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Fast magnetosonic waves driven by shell velocity distributions

Min

Liu

2015

JGR Space Physics

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Using linear dispersion theory and particle‐in‐cell simulations, we explore the ion Bernstein instability driven by the shell‐type ion velocity distribution which is related to the excitation of fast magnetosonic waves in the terrestrial magnetosphere. We first demonstrate a novel idea to construct the shell velocity distribution out of multiple Maxwellian ring‐beam velocity distributions. Applying this technique, we find that the convergence of the linear theory instability can be achieved with only a moderate number of ring‐beam components. In order to prove that such an approximation is legitimate and the linear theory instabilities evaluated are indeed valid, we use the exact shell distribution to carry out a number of one dimensional particle‐in‐cell simulations corresponding to multiple wave propagation angles adjacent to the direction at which the most unstable waves are expected to grow. The agreement between the linear dispersion analysis and the simulation results is generally very good: enhanced waves are organized along the linear theory dispersion curves in the frequency‐wave number space, and relative wave amplitudes are ordered as the linear theory growth rates very well. However, the simulations show a few extra branches that are not expected from the linear dispersion analysis. A close examination of these extra branches suggests that they are not simulation artifacts and particularly related to the ring/shell‐type distributions with large ring/shell speed (v>∼1.5 vA, where vA is the Alfvén speed). In addition, our results show that substantial wave growth can occur at nonintegral harmonics of the proton cyclotron frequency at wave normal angles substantially far away from the perpendicular direction, which may provide an alternative explanation of the off‐harmonic peaks of some fast magnetosonic waves observed in space.

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Generation of Bernstein waves by ion shell distributions in the auroral region

Cited by 26 publications

References 32 publications

Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

Ion shell distributions as free energy source for plasma waves on auroral field lines mapping to plasma sheet boundary layer

Interpreting ~1 Hz magnetic compressional waves in Mercury's inner magnetosphere in terms of propagating ion‐Bernstein waves

Fast magnetosonic waves driven by shell velocity distributions

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