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.
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TL;DR: In this paper, the shape of radio emissions is modeled with an empirical beaming angle function and adjust the parameters to best fit the emission arcs, based on the location of Io in the Jovian magnetic field.
Abstract: The Io-Jupiter interaction generates strong decametric radio emissions (DAM), which appear as arcs in the time-frequency plane. These emissions are beamed at an angle from the magnetic field lines, which may vary with frequency and longitude amongst other properties. Empirical models of this beaming angle describe the shape of the DAM arcs and offer insight into the emission mechanism for DAM. Several studies have investigated the variation in the emission beaming angle. The studies span a range of frequencies which depend on the observational means (spacecraft, ground-based radio telescopes) used to obtain data. Subsequently, because of the varying assumptions made (e.g. relativistic vs. non-relativistic electrons for the wave polarization), methods used (e.g. prescribing a beaming angle function vs. determining a beaming angle function from observational geometry) and frequency ranges observed, different results have been found in each study. In the present paper, we model the shape of the emission with an empirical beaming angle function and adjust the parameters to best fit the emission arcs. However, our model builds on previous models by taking into account the location of Io in the Jovian magnetic field. We also look at a broader frequency range than many of the intermediate studies. We find that a simple empirical beaming angle function describes the shape of the A, B, and D arcs and that the beaming angle function must decrease at high and low frequencies. We then propose a simple explanation for the beaming angle profile, deduced from cyclotron maser theory. Copyright 2008 by the American Geophysical Union.
26 citations
TL;DR: A review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres is provided in this paper, with a focus on the plasma supply to each region of the magnetosphere.
Abstract: The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres.
25 citations
TL;DR: In this paper, the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around the star was investigated, and it was shown that the associated current can reach the same magnitude as the Goldreich-Julian current that powers the pulsar's magnetosphere.
Abstract: We investigate the electromagnetic interaction of a relativistic stellar wind with a planet or a smaller body in orbit around the star. This may be relevant to objects orbiting a pulsar, such as PSR B1257+12 and PSR B1620-26 that are expected to hold a planetary system, or to pulsars with suspected asteroids or comets. We extend the theory of Alfv\'en wings to relativistic winds. When the wind is relativistic albeit slower than the total Alfv\'en speed, a system of electric currents carried by a stationary Alfv\'enic structure is driven by the planet or by its surroundings. For an Earth-like planet around a "standard" one second pulsar, the associated current can reach the same magnitude as the Goldreich-Julian current that powers the pulsar's magnetosphere.
24 citations
Cites background from "Io Jupiter interaction, millisecond..."
...…up to now, and it has been the object of recent studies concerning its overall structure (Chust et al. 2005; Hess et al. 2010), the possibility of particle acceleration (Hess et al. 2007b, 2009b), and its consequences on the radio emissions (Queinnec & Zarka 1998; Hess et al. 2007a, 2009a)....
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TL;DR: In this article, the authors studied the evolution of the Io UV footprints with a time resolution of a few tens of seconds using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode.
Abstract: [1] The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple ultraviolet spots near the feet of the Io flux tube. Variations of spot numbers and brightness and of inter-spot distances have been observed to be linked to Io's position in its plasma torus. We have studied the evolution of the Io UV footprints with a time resolution of a few tens of seconds using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode. We present evidence of systematic strong brightness variations of the main spots (up to 50%) with a typical growth time of 1 minute. Additionally, unanticipated simultaneous fluctuations of both primary and secondary spots have also been found in the southern hemisphere. Our findings suggest that the footprint brightness is not only actively controlled by the plasma directly interacting with Io but also by the poorly constrained electron acceleration region between Io and Jupiter.
24 citations
Cites background from "Io Jupiter interaction, millisecond..."
...However, the time scales (from 0.25 second to 0.025 second) as well as the electron energies involved ( 4 keV with 1 keV potential jumps) [Hess et al., 2007] can hardly be linked to the timescales ( 1 min) and the energies ( 50 keV) discussed here....
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...However, the time scales (from 0.25 second to 0.025 second) as well as the electron energies involved (4 keV with 1 keV potential jumps) [ Hess et al., 2007 ] can hardly be linked to the timescales (1 min) and the energies (50 keV) discussed here....
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TL;DR: The ExPRES (Exoplanetary and Planetary Radio Emission Simulator) as mentioned in this paper is able to reproduce the occurrence in time-frequency plane of CMI-generated radio emissions from planetary magnetospheres, exoplanets or star-planet interacting systems.
Abstract: All magnetized planets are known to produce intense non thermal radio emissions through a mechanism known as Cyclotron Maser Instability (CMI), requiring the presence of accelerated electrons generally arising from magnetospheric current systems. In return, radio emissions are a good probe of these current systems and acceleration processes. The CMI generates highly anisotropic emissions and leads to important visibility effects, which have to be taken into account when interpreting the data. Several studies showed that modeling the radio source anisotropic beaming pattern can reveal a wealth of physical information about the planetary or exoplanetary magnetospheres that produce these emissions. We present a numerical tool, called ExPRES (Exoplanetary and Planetary Radio Emission Simulator), which is able to reproduce the occurrence in time-frequency plane of CMI-generated radio emissions from planetary magnetospheres, exoplanets or star-planet interacting systems. Special attention is given to the computation of the radio emission beaming at and near its source. We explain what physical information about the system can be drawn from such radio observations, and how it is obtained. These information may include the location and dynamics of the radio sources, the type of current system leading to electron acceleration and their energy and, for exoplanetary systems, the magnetic field strength, the orbital period of the emitting body and the rotation period, tilt and offset of the planetary magnetic field. Most of these parameters can be remotely measured only via radio observations. The ExPRES code provides the proper framework of analysis and interpretation for past (Cassini, Voyager, Galileo), current (Juno, groundbased radiotelescopes) and future (BepiColombo, Juice) observations of planetary radio emissions, as well as for future detection of radio emissions from exoplanetary systems.
23 citations
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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