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: The electron-cyclotron maser is a process that generates coherent radiation from plasma as mentioned in this paper, and it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural high-temperature magnetized plasmas.
Abstract: The electron–cyclotron maser is a process that generates coherent radiation from plasma. In the last two decades, it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural high-temperature magnetized plasmas. Originally proposed as a somewhat exotic idea and subsequently applied to include non-relativistic plasmas, the electron–cyclotron maser was considered as an alternative to turbulent though coherent wave–wave interaction which results in radio emission. However, when it was recognized that weak relativistic corrections had to be taken into account in the radiation process, the importance of the electron–cyclotron maser rose to the recognition it deserves. Here we review the theory and application of the electron–cyclotron maser to the directly accessible plasmas in our immediate terrestrial and planetary environments. In situ access to the radiating plasmas has turned out to be crucial in identifying the conditions under which the electron–cyclotron maser mechanism is working. Under extreme astrophysical conditions, radiation from plasmas may provide a major energy loss; however, for generating the powerful radiation in which the electron–cyclotron maser mechanism is capable, the plasma must be in a state where release of susceptible amounts of energy in the form of radiation is favorable. Such conditions are realized when the plasma is unable to digest the available free energy that is imposed from outside and stored in its particle distribution. The lack of dissipative processes is a common property of collisionless plasmas. When, in addition, the plasma density becomes so low that the amount of free energy per particle is large, direct emission becomes favorable. This can be expressed as negative absorption of the plasma which, like in conventional masers, leads to coherent emission even though no quantum correlations are involved. The physical basis of this formal analogy between a quantum maser and the electron–cyclotron maser is that in the electron–cyclotron maser the free-space radiation modes can be amplified directly. Several models have been proposed for such a process. The most famous one is the so-called loss-cone maser. However, as argued in this review, the loss-cone maser is rather inefficient. Available in situ measurements indicate that the loss-cone maser plays only a minor role. Instead, the main source for any strong electron–cyclotron maser is found in the presence of a magnetic-field-aligned electric potential drop which has several effects: (1) it dilutes the local plasma to such an extent that the plasma enters the regime in which the electron–cyclotron maser becomes effective; (2) it generates energetic relativistic electron beams and field-aligned currents; (3) it deforms, together with the magnetic mirror force, the electron distribution function, thereby mimicking a high energy level sufficiently far above the Maxwellian ground state of an equilibrium plasma; (4) it favors emission in the free-space RX mode in a direction roughly perpendicular to the ambient magnetic field; (5) this emission is the most intense, since it implies the coherent resonant contribution of a maximum number of electrons in the distribution function to the radiation (i.e., to the generation of negative absorption); (6) it generates a large number of electron holes via the two-stream instability, and ion holes via the current-driven ion-acoustic instability which manifest themselves as subtle fine structures moving across the radiation spectrum and being typical for the electron–cyclotron maser emission process. These fine structures can thus be taken as the ultimate identifier of the electron–cyclotron maser. The auroral kilometric radiation of Earth is taken here as the paradigm for other manifestations of intense radio emissions such as the radiation from other planets in the solar system, from exoplanets, the Sun and other astrophysical objects.
358 citations
Cites background from "Io Jupiter interaction, millisecond..."
...Recently, Zarka et al. (2005) argued that S-bursts are the result of loss-cone maser activity inside the Io flux tube....
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...…extrasolar planets has immediately stimulated the idea that in analogy to the strongly magnetized planets in the solar system, exoplanets could also radiate in the radio band, possibly emitting maser radiation (Farrell et al. 1999; Bastian et al. 2000; Zarka et al. 2001b; Winterhalter et al. 2005)....
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...Application to Jupiter and radiation from the other magnetized planets followed, and speculations about radiation emitted from extrasolar planets when they are magnetized strongly enough have been published as well (Bastian et al. 2000; Zarka et al. 2001a,b)....
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...Searches have been going on at the Very Large Array (VLA) in New Mexico (Bastian et al. 2000) and a comparable array UTR-2 in Kharkov (Ukraine) (Zarka et al. 2001b)....
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...From the knowledge of the emissivities of Earth and Jupiter under solar-wind conditions, one may scale emissivities up to exoplanets of the family of ‘hot Jupiters’ close to their mother stars (Zarka et al. 2001b)....
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University of Colorado Boulder1, INAF2, Southwest Research Institute3, University of Texas at San Antonio4, University of Liège5, University of Leicester6, Goddard Space Flight Center7, Planetary Science Institute8, University of Iowa9, Jet Propulsion Laboratory10, Johns Hopkins University11, University of California, Los Angeles12, Centre national de la recherche scientifique13
TL;DR: Junior as discussed by the authors is the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere, where it carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter's radiation belts.
Abstract: In July 2016, NASA’s Juno mission becomes the first spacecraft to enter polar orbit of Jupiter and venture deep into unexplored polar territories of the magnetosphere. Focusing on these polar regions, we review current understanding of the structure and dynamics of the magnetosphere and summarize the outstanding issues. The Juno mission profile involves (a) a several-week approach from the dawn side of Jupiter’s magnetosphere, with an orbit-insertion maneuver on July 6, 2016; (b) a 107-day capture orbit, also on the dawn flank; and (c) a series of thirty 11-day science orbits with the spacecraft flying over Jupiter’s poles and ducking under the radiation belts. We show how Juno’s view of the magnetosphere evolves over the year of science orbits. The Juno spacecraft carries a range of instruments that take particles and fields measurements, remote sensing observations of auroral emissions at UV, visible, IR and radio wavelengths, and detect microwave emission from Jupiter’s radiation belts. We summarize how these Juno measurements address issues of auroral processes, microphysical plasma physics, ionosphere-magnetosphere and satellite-magnetosphere coupling, sources and sinks of plasma, the radiation belts, and the dynamics of the outer magnetosphere. To reach Jupiter, the Juno spacecraft passed close to the Earth on October 9, 2013, gaining the necessary energy to get to Jupiter. The Earth flyby provided an opportunity to test Juno’s instrumentation as well as take scientific data in the terrestrial magnetosphere, in conjunction with ground-based and Earth-orbiting assets.
192 citations
TL;DR: In this paper, it was shown that the Alfven waves need to be filamented by a turbulent cascade process and accelerate the electrons at high latitude in order to explain the observations and to form a consistent scheme of the Io-Jupiter interaction.
Abstract: [1] Io's motion relative to the Jovian magnetic field generates a power of about 1012 W, which is thought to propagate as an Alfven wave along the magnetic field line. This power is transmitted to the electrons, which will then precipitate and generate the observed auroral phenomena from UV to radio wavelengths. A more detailed look at this hypothesis shows some difficulties: Can the Alfven waves escape the torus or are they trapped inside? Where and how are the particles accelerated? In which direction? Is there enough power transmitted to the particles to explain the strong brightness of the auroral emissions in UV, IR, visible, and radio? In other words, can we make a global, consistent model of the Io-Jupiter interaction that matches all the observations? To answer these questions, we review the models and studies that have been proposed so far. We show that the Alfven waves need to be filamented by a turbulent cascade process and accelerate the electrons at high latitude in order to explain the observations and to form a consistent scheme of the Io-Jupiter interaction.
98 citations
TL;DR: In this article, the ionospheric response to auroral precipitation at the giant planets is reviewed, using models and observations The emission processes for aurorae at radio, infrared, visible, ultraviolet, and X-ray wavelengths are described, and exemplified using ground-and space-based observations Comparisons between the emissions at different wavelengths are made, where possible, and interpreted in terms of precipitating particle characteristics or atmospheric conditions.
Abstract: The ionospheric response to auroral precipitation at the giant planets is reviewed, using models and observations The emission processes for aurorae at radio, infrared, visible, ultraviolet, and X-ray wavelengths are described, and exemplified using ground- and space-based observations Comparisons between the emissions at different wavelengths are made, where possible, and interpreted in terms of precipitating particle characteristics or atmospheric conditions Finally, the spatial distributions and dynamics of the various components of the aurorae (moon footprints, low-latitude, main oval, polar) are related to magnetospheric processes and boundaries, using theory, in situ, and remote observations, with the aim of distinguishing between those related to internally-driven dynamics, and those related to the solar wind interaction
95 citations
TL;DR: In this article, a good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥ 80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤ 1°.
Abstract: [1] The electrodynamic interaction between Io and Jupiter causes electron acceleration in/near the Io flux tube (IFT), which in turn produces intense radio emissions in the hecto-decameter range, displaying arc shapes in the time-frequency plane. The shapes depend on the hemisphere of origin of the emission and on the Io-Jupiter-observer geometry. Assuming radio wave generation by the cyclotron-maser instability, we simulate t-f arc shapes as a function of emission beaming, lead angle between the radio emitting field line and the instantaneous Io field line, and electron energy. A good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤1°. The lead angle is found between a few degrees and ∼40° in both hemispheres. Resonant electron energies are about a few keV. Implications on the absence of a plasma cavity at IFT footprints and on Jupiter's internal magnetic field model are discussed.
73 citations
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Additional excerpts
...The adiabatic motion of the emitting electrons without acceleration by parallel electric fields is the baseline model proposed by Ellis (1965). Its main characteristic is the kinetic energy conservation along the electrons trajectory....
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31 citations
CNET1
TL;DR: In this article, the predictions of different theories proposed for explaining the auroral planetary radio emissions are compared with the observations, and the most developed theory is certainly the cyclotron maser instability.
21 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 paper, high-resolution spectra of Jupiter's decametric S-storms are studied with an acousto-optical radio spectrograph operating over the frequency range 20-30 MHz.
Abstract: High-resolution spectra of Jupiter's decametric S-storms are studied with an acousto-optical radio spectrograph operating over the frequency range 20–30 MHz. In 1985–1989 20 S-storms were recorded in the Io-B region. There is only a slight average zoning effect of certain types of fine structure in the Io-B region, with sporadic S-bursts occurring most often in the early CML values, and S-trains in the late values. Emissions of type N and its variants occur at lower values of the Io phase than S-emissions and their variants. There is no exact storm-to-storm correspondence, nor any Io-B-centered zones in which the various types of fine structure could be accurately placed. Every storm is different and has a ‘signature’ of its own. An important exception is formed by the wide-range quasi-periodic FDS-S storms that occur at the edge of the Io-B region with Io phase values greater than 80 ‡. These are outstanding storms in which the individual bursts may extend across the full spectral width of 20–30 MHz and be repeated in rapid succession at quasi-periodic rates of 20–40 s−1. It is suggested that these be referred to as type Q storms. It is estimated that only 10% of the S-burst types are recorded so far.
19 citations
"Io Jupiter interaction, millisecond..." refers background in this paper
...Moreover, S-bursts shape studies have shown the presence of breaks of the bursts drift in the time–frequency plane (Riihimaa, 1991)....
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