Io Jupiter interaction, millisecond bursts and field-aligned potentials
TL;DR: In this paper, the authors performed an automated analysis of 230 high-resolution dynamic spectra of S-bursts, providing 5 × 10 6 frequency drift measurements and confirmed over a large number of measurements that the frequency drift d f / d t (f ) is in average negative and decreases (in absolute value) at high frequencies, as predicted by the adiabatic theory.
About: This article is published in Planetary and Space Science.The article was published on 2007-01-01. It has received 61 citations till now. The article focuses on the topics: Jupiter & Jovian.
Citations
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TL;DR: In this paper, the authors analyzed the records of radio emissions obtained during an Io-A S-burst storm on 15 March 2005, and proposed a statistical model of narrow band random process for describing such features in the observed waveforms as coherent segments, phase jumps, nonlinear frequency drift, etc.
Abstract: [1] We analyze the records of Jupiter's decameter radio emissions obtained during an Io-A S-burst storm on 15 March 2005. The observations were performed at the world's largest decameter array, UTR-2, which is equipped with a digital receiver capable of catching waveforms of duration ∼3 s with temporal resolution defined by the sampling rate of ∼66 MHz. A Hilbert transform based algorithm has been applied to study narrow-band spectral patterns demonstrating quasi-linear drift over time-frequency plane. The instantaneous amplitude and phase information has been extracted from the recorded waveforms with the purpose of analyzing microsecond-scale coherent events in the S-burst emission. A statistical model of narrow band random process is proposed for describing such features in the observed waveforms as coherent segments, phase jumps, nonlinear frequency drift, etc. It is shown that the study of coherence properties in terms of instantaneous phase is equivalent to Fourier analysis of a narrowband signal. This implies that no particular mechanism (such as superimposed modulation or oscillation) is required for generating the observed coherent phase structures of S-burst emission: those, as well as the pulse-like envelope structures, emerge naturally at the output of a narrow band filter applied to a random noise. It is further suggested that probability distribution function of instantaneous amplitude gives an important insight into the underlying physical mechanism of S-burst generation. In particular, it is demonstrated that models based on the concept of “generator,” i.e., a nonlinear system with feedback, are less suitable for reproducing the observational characteristics of S-bursts at microsecond time scale resolution. On the other hand, the concept of “amplifier,” i.e., a linear system (without feedback) that enhances the fluctuations within a narrow band, fits the observational data well. This conclusion is consistent with S-burst generation mechanism via cyclotron-maser instability, which is indeed a resonant wave amplification process.
14 citations
TL;DR: In this paper, numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECMaser) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale were presented.
Abstract: We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$
u_{\rm pe}$ ($
u_{\rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$
u_{\rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.
13 citations
TL;DR: In this paper, a multimagnetofluid code is applied to the Io-Jupiter system to clarify the origin of the currentvoltage relationship, and the authors find that if the ionospheric proton density decreases at the same rate as the parallel current density, the timescale on which the transition layer disappears is consistent with the longitudinal extent of the tail aurora.
Abstract: [1] The Io tail aurora extends for approximately 100 degrees downstream in longitude from the Io footprint aurora. Observations indicate that the brightness of the Io tail aurora continuously decreases along the footpath while its peak altitude remains constant. According to the quasi-steady theoretical frame, this suggests that the field-aligned voltage is constant while the parallel current density decreases in the downstream direction. The mechanism that realizes the current-voltage relationship of the Io tail aurora remains unresolved. In this paper, we apply a new multimagnetofluid code to the Io-Jupiter system to clarify the origin of the current-voltage relationship. The code solves a set of equations that includes the electron convection term in Ohm's law, which enables us to simulate the current-driven ion acoustic instability in the fluid frame. The instability forms a transition layer at a high altitude, which accelerates the magnetospheric electrons and blocks the magnetospheric ions, leading to the formation of a density depleted region called an auroral cavity. We find that if the ionospheric proton density decreases at the same rate as the parallel current density, the timescale on which the transition layer disappears is consistent with the longitudinal extent of the tail aurora, and the potential gap is constant all along the tail. We discuss the possibility that the fringe, wideband repetitive bursts of the Io-related Jovian decametric radiation, is excited in the auroral cavity.
11 citations
TL;DR: In this article, a linear correlation coefficient r(f − fo, Δt) between the spectral intensity in the current (f ) and the reference (fo) frequency channels with Δt time shift was calculated.
Abstract: Short (S-) bursts of Jovian decametric emission show random behavior with very complicated forms in the dynamic spectrum. We first draw attention to the correlation properties of S-bursts as an indicator of their hidden regularity. Thus we calculate the linear correlation coefficient r(f − fo, Δt) between the spectral intensity in the current (f ) and the reference (fo) frequency channels with Δt time shift. The result is displayed in the form of 2D-correlation image, where the pixel brightness reflects the r estimate, and the pixel’s co-ordinates are f and Δt. The non-trivial and stabile correlation patterns are found, described, and discussed here. Apparently, there is the hidden wave-like modulation of the whole S-burst storm in the form of a correlation or anti-correlation between emissions at different radio frequencies with short time scales from 0.02 s to 0.8 s.
10 citations
Cites background from "Io Jupiter interaction, millisecond..."
...Another approach is to study the form of individual S-bursts in dynamic spectra for an average estimate of their frequency drift rate (e.g., Hess et al. 2007, and references therein)....
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TL;DR: In this paper, the first LWA1 results for the study of six Io-related events at temporal resolutions as fine as 0.25 ms were presented, showing that the Io-C starts as early as CMLIII = 230 degrees at frequencies near 11 MHz.
Abstract: New observations of Jupiter's decametric radio emissions have been made with the Long Wavelength Array Station 1 (LWA1) which is capable of making high quality observations as low as 11 MHz. Full Stokes parameters were determined for bandwidths of 16 MHz. Here we present the first LWA1 results for the study of six Io-related events at temporal resolutions as fine as 0.25 ms. LWA1 data show excellent spectral detail in Jovian DAM such as simultaneous left hand circular (LHC) and right hand circular (RHC) polarized Io-related arcs and source envelopes, modulation lane features, S-bursts structures, narrow band N-events, and interactions between S-bursts and N-events. The sensitivity of the LWA1 combined with the low radio frequency interference environment allow us to trace the start of the LHC Io-C source region to much earlier CMLIII than typically found in the literature. We find the Io-C starts as early as CMLIII = 230 degrees at frequencies near 11 MHz. This early start of the Io-C emission may be valuable for refining models of the emission mechanism. We also detect modulation lane structures that appear continuous across LHC and RHC emissions, suggesting that both polarizations may originate from the same hemisphere of Jupiter. We present a study of rare S-bursts detected during an Io-D event and show drift rates are consistent with those from other Io-related sources. Finally, S-N burst events are seen in high spectral and temporal resolution and our data strongly support the co-spatial origins of these events.
10 citations
Cites background from "Io Jupiter interaction, millisecond..."
...While the L-bursts are modulated by scintillation, the S-bursts show modulation and both simple and complex structure that is intrinsic to the source regions [Arkypov & Rucker, 2009; Hess et al., 2007; Carr & Reyes, 1999; Carr et al., 1983]....
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...Sbursts are CMI emission thought to be produced by 5 keV electrons accelerated along magnetic field lines connecting to Io [Hess et al., 2007; Zarka et al., 1996]....
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References
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TL;DR: In this paper, it was found that reflected electrons can result in the amplification of electromagnetic waves via a relativistic normal cyclotron resonance, which may explain the recently discovered terrestrial kilometric radiation.
Abstract: During magnetospheric substorms, electrons with energies of about 1 keV are injected from the plasma-sheet region into the auroral region. A fraction of these energetic electrons can precipitate into the upper atmosphere, and the rest are reflected because of the mirror effect of the convergent geomagnetic field. It is found that these reflected electrons can result in the amplification of electromagnetic waves via a relativistic normal cyclotron resonance. This process may explain the recently discovered terrestrial kilometric radiation.
951 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...The magnetic mirror at the foot of the Io flux tube (IFT) reflects a part of the electrons, whose distribution is then unstable relative to the cyclotron-maser instability and produces emission at the local cyclotron frequency (Wu and Lee, 1979; Louarn, 1992)....
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TL;DR: In this article, a polar orbiting satellite was used to measure spatially confined regions of extremely large electric fields in the auroral zone at altitudes below 8000 km, which are identified as paired electrostatic shocks which are associated with electrostatic ion cyclotron wave turbulence.
Abstract: dc and ac plasma-density and vector-electric-field detectors on a polar orbiting satellite have measured spatially confined regions of extremely large (\ensuremath{\sim}\textonehalf{} V/m) electric fields in the auroral zone at altitudes below 8000 km. Such regions frequently have double structures of opposing electric fields containing characteristic and different wave spectra internal and external to themselves. These structures are identified as paired electrostatic shocks which are associated with electrostatic ion cyclotron wave turbulence.
671 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...Potential drops like those evidenced in Section 5 are observed in situ in the terrestrial auroral zones (Mozer et al., 1977)....
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TL;DR: In this article, a nonlinear analytical model of the Alfven current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma was presented.
Abstract: We present a nonlinear analytical model of the Alfven current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. We thereby extend the linear work by Drell et al. (1965) to the fully nonlinear, sub-Alfvenic situation also including flow which is not perpendicular to the background magnetic field. The following principal results have been obtained: (1) The portion of the currents feeding Io is aligned with the Alfven characteristics at an angle θA = tan−1 MA to the magnetic field for the special case of perpendicular flow where MA is the Alfven Mach number. (2) The Alfven tubes act like an external conductance ΣA = 1/(µ0VA(1 + MA² + 2MA sin θ)1/2) where VA is the Alfven speed and θ the angular deviation from perpendicular flow towards the direction of Alfven wave propagation. Hence the Jovian ionospheric conductivity is not necessary for current closure. (3) In addition, the Alfven tubes may be reflected from either the torus boundary or the Jovian ionosphere. The efficiency of the resulting interaction with these boundaries varies with Io position. The interaction is particularly strong at extreme magnetic latitudes, thereby suggesting a mechanism for the Io control of decametric emissions. (4) The reflected Alfven waves may heat both the torus plasma and the Jovian ionosphere as well as produce increased diffusion of high-energy particles in the torus. (5) From the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites for several reasons: these include its ionosphere arising from ionized volcanic gases, a high external Alfvenic conductance ΣA, and a high corotational voltage in addition to the interaction phenomenon with a boundary. (6) We find that Amalthea is probably strongly coupled to Jupiter's ionosphere while the outer Galilean satellites may occasionally experience super-Alfvenic conditions.
538 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...This electric field induces currents and/or Alfvén waves (Goldreich and Lynden-Bell, 1969; Neubauer, 1980; Saur, 2004) which accelerate electrons from the Io torus toward Jupiter along the magnetic field...
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...As the Io–Jupiter plasma has the structure of an Alfvén wing (Neubauer, 1980; Saur, 2004), we can expect that Alfvén waves play an important role in the acceleration of the electrons....
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492 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...This electric field induces currents and/or Alfvén waves (Goldreich and Lynden-Bell, 1969; Neubauer, 1980; Saur, 2004) which accelerate electrons from the Io torus toward Jupiter along the magnetic field...
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TL;DR: In this paper, a spherical harmonic model of the magnetic field of Jupiter was derived from in situ magnetic field measurements and remote observations of the position of the foot of the Io flux tube in Jupiter's ionosphere.
Abstract: Spherical harmonic models of the planetary magnetic field of Jupiter are obtained from in situ magnetic field measurements and remote observations of the position of the foot of the Io flux tube in Jupiter's ionosphere. The Io flux tube (IFT) footprint locates the ionospheric footprint of field lines traced from Io's orbital radial distance in the equator plane (5.9 Jovian radii). The IFT footprint is a valuable constraint on magnetic field models, providing “ground truth” information in a region close to the planet and thus far not sampled by spacecraft. The magnetic field is represented using a spherical harmonic expansion of degree and order 4 for the planetary (“internal”) field and an explicit model of the magnetodisc for the field (“external”) due to distributed currents. Models fitting Voyager 1 and Pioneer 11 magnetometer observations and the IFT footprint are obtained by partial solution of the underdetermined inverse problem using generalized inverse techniques. Dipole, quadrupole, octupole, and a subset of higher-degree and higher-order spherical harmonic coefficients are determined and compared with earlier models.
426 citations
"Io Jupiter interaction, millisecond..." refers methods in this paper
...A more accurate magnetic field model is VIP4 (Connerney et al., 1998) based on Voyager and Pioneer magnetometer measurements together with IR observation of the IFT footprint at the surface of Jupiter....
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...Thus, we analyze each individual dynamic spectrum, using the more accurate VIP4 magnetic field model (Connerney et al., 1998)....
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