Keywords: Jupiter; Magnetosphere; Radio emission; Radio astronomy; LOFAR; Solar system; Planetology 相似文献
共查询到20条相似文献，搜索用时 31 毫秒
1.
Philippe Zarka Rudolf A. Treumann Boris P. Ryabov Vladimir B. Ryabov 《Astrophysics and Space Science》2001,277(1-2):293-300
At least six intense nonthermal planetary radio emissions are known in our solar system: the auroral radio emissions from
the Earth, Jupiter, Saturn, Uranus and Neptune, and the radio bursts from the Io-Jupiter flux tube. The former are thought
to be driven by the solar wind flow pressure or energy flux on the magnetospheric cross-section, while the latter is a consequence
of the Io-Jupiter electrodynamic interaction. Although in the solar wind, the flow ram pressure largely dominates the magnetic
one, we suggest that the incident magnetic energy flux is the driving factor for all these six radio emissions, and that it
can be estimated in the same way in all cases. Consequences for the possible radio emission from extrasolar planets are examined.
‘Hot Jupiters’, if they are magnetized, might possess a radio emission several orders of magnitude stronger than the Jovian
one, detectable with large ground-based low-frequency arrays. On the other hand, `giants' analogous to the Io-Jupiter interaction
in the form of a pair star/hot-Jupiter are unlikely to produce intense radio emissions, unless the star is very strongly magnetized.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
H. B. Liemohn 《Astrophysics and Space Science》1973,20(2):417-429
The magnetosphere of Jupiter has been the subject of extensive research in recent years due to its detectable radio emissions. Observations in the decimetric radio band have been particular helpful in ascertaining the general shape of the Jovian magnetic field, which is currently believed to be a dipole with minor perturbations. Although there is no direct evidence for thermal plasma in the magnetosphere of Jupiter, theoretical considerations about the physical processes that must occur in the ionosphere and magnetosphere surrounding Jupiter have lead to estimates of the thermal plasma distribution. These models of the Jovian magnetic field and thermal plasma distribution, specify the characteristic plasma and cyclotron frequencies in the magnetosplasma and thereby provide a basis for estimating thelocal electromagnetic and hydromagnetic noise around Jupiter. Spatial analogs of the well-known Clemmow-Mullaly-Allis (CMA) diagrams have been constructed to identify the loci of electron and ion resonances and cutoffs for the different field and plasma models. Regions of reflection, mode coupling, and probable amplification are readily identified. The corresponding radio noise properties may be estimated qualitatively on the basis of these various electromagnetic and hydromagnetic wave mode regions. Frequency bands and regions of intense natural noise may be estimated. On the basis of the models considered, the radio noise properties around Jupiter are quite different from those encountered in the magnetosphere around the Earth. Wave particle interactions are largely confined to the immediate vicinity of the zenographic equatorial plane and guided propagation from one hemisphere to the other apparently does not occur, except for hydromagnetic modes of propagation. The characteristics of these local signals are indicative of the physical processes occurring in the Jovian magnetosphere. Thus, as a remote sensing tool, their observation will be a vital asset in the exploration of Jupiter. 相似文献
3.
H.O. Rucker M.Y. Boudjada M. Leitner A. Lecacheux M. Aubier A. Konovalenko P.H.M. Galopeau V. Shaposhnikov 《Astrophysics and Space Science》2001,277(1-2):325-328
Jupiter radio emission is known to be the most powerful nonthermal planetary radiation. In recent years specifically space-based
observations allow us to permanently cover a large frequency band(from 100 kHz up to 40 MHz combined with ground-based telescopes)of
the Jovian spectrum. The Plasma and Wave Science experiment onboard Galileo enables the observation of Jovian kilometric and
hectometric emissions; Wind/WAVES and ground-based telescopes (mainly Decametric Array in Nancay, France, and UTR-2 in Kharkov,
Ukraine) cover also hectometric and mainly decametric emissions. Specific geometrical configurations between Cassini approaching
Jupiter and Wind spacecraft orbiting Earth, with Galileo orbiting Jupiter and Wind, in combination with ground-based observations
provide a new approach to perform Jovian radio tomography. The tomography technique is used to analyze ray paths of Jovian
radio emission observed in different directions (e.g. solar and anti-solar direction) and for different declination of Earth.
The developments of Jovian radio emission tomography in recent years treated refraction effects and its connection to the
local magnetic field in the radio source as well as the radio wave propagation through the Io torus and the terrestrial ionosphere.
Most recently ground-based multi-site and simultaneous Jupiter decametric radio observations by means of digital spectropolarimeter
and waveform receiver provide the basis of a new data analysis treatment. The above addressed topics are without exemption
deeply connected to the plasma structures the radio waves are generated in and propagating through.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
S. S. Sazhin 《Astrophysics and Space Science》1987,138(1):99-103
An analytical solution of the dispersion equation for electrostatic waves propagating in a plasma consisting of cold electrons and the electrons with the loss cone distribution function is obtained for wave frequencies close to the harmonics of electron gyrofrequency. Electrostatic emissions at these frequencies were observed in the magnetospheres of the Earth, Jupiter, and Saturn. 相似文献
5.
The transmission of Alfvén waves from Io to the Jovian ionosphere is discussed. Various simplified laws for the variation of plasma density are analyzed and juxtaposed to simulate a realistic density variation along the Io-Jupiter flux line. Apparently the ionosphere is previously only to frequencies in excess of 1 Hz. The ionosphere participates in tilting the flux tube trapped by Io leading to the formation of a neutral point in the vicinity of the satellite. 相似文献
6.
Oscillations of magnetic flux tubes are of great importance as they contain information about the geometry and fine structure
of the flux tubes. Here we derive and analytically solve in terms of Kummer’s functions the linear governing equations of
wave propagation for sausage surface and body modes (m=0) of a magnetically twisted compressible flux tube embedded in a compressible uniformly magnetized plasma environment in cylindrical geometry. A general dispersion relation is obtained for such flux
tubes. Numerical solutions for the phase velocity are obtained for a wide range of wavenumbers and for varying magnetic twist.
The effect of magnetic twist on the period of oscillations of sausage surface modes for different values of the wavenumber
and vertical magnetic field strength is calculated for representative photospheric and coronal conditions. These results generalize
and extend previous studies of MHD waves obtained for incompressible or for compressible but nontwisted flux tubes. It is
found that magnetic twist may change the period of sausage surface waves of the order of a few percent when compared to counterparts
in straight nontwisted flux tubes. This information will be most relevant when high-resolution observations are used for diagnostic
exploration of MHD wave guides in analogy to solar-interior studies by means of global eigenoscillations in helioseismology. 相似文献
7.
G. A. Dulk 《Solar physics》1990,130(1-2):139-150
The purpose of this paper is to review the observations of particle beams of the kind that are frequently observed in the interplanetary medium, usually but not always accompanying a solar flare. Most frequent are beams of electrons. They are generally associated with radio bursts of type III and only sometimes with flares and X-ray bursts. The properties of these electron beams have been well studied using quasi-linear and nonlinear theory, in situ observations of electrons and of plasma waves, and remote observations of radio waves Thanks to the interaction between theory and observation, the decade of the 1980s has been one of great progress in understanding the main features of these beams and their associated plasma waves and radio bursts. However, uncertainties remain in terms of (1) whether fine scale features, filamentary structures or wave condensations, occur together with the beams, (2) whether quasi-linear or nonlinear wave emission is the dominant process, and (3) if wave condensations are important, what is the mechanism of conversion of some Langmuir wave energy into radio emission.Other particle beams are composed of protons, of neutrons, of helium ions (sometimes with a large excess of 3He), and of heavy ions with varying concentrations. Sometimes the observations seem to require the fractionation of certain ions, followed by resonant acceleration of certain species.Objects other than the Sun that are the source of interplanetary particle beams include comets and planets, especially the Earth and Jupiter. 相似文献
8.
The Io-controlled radio arcs are emissions in the decametric radio range which appear arc shaped in the time-frequency plane. Their occurrence is controlled by Io's position, so it has been for long inferred that they are powered by the Io-Jupiter electrodynamic interaction. Their frequency ranges correspond to the electron cyclotron frequencies along the Io Flux tube, so they are expected to be generated by cyclotron maser instability (CMI). The arc shape was proposed to be a consequence of the strong anisotropy of the decametric radio emissions beaming, combined with the topology of the magnetic field in the source and the observation geometry. Recent papers succeeded at reproducing the morphologies of a few typical radio arcs by modeling in three dimensions the observation geometry, using the best available magnetic field model and a beaming angle variation consistent with a loss-cone driven CMI. In the continuation of these studies, we present here the systematic modeling of a larger number of observations of the radio arcs emitted in Jupiter's southern hemisphere (including multiple arcs or arcs exhibiting abrupt changes of shape), which permits to obtain a statistical determination of the emitting field line localization (lead angle) relative to the instantaneous Io field line, and of the emitting particle velocities or energies. Variations of these parameters relative to Io's longitude are also measured and compared to the location of the UV footprints of the Io-Jupiter interaction. It is shown that the data are better organized in a reference frame attached to the UV spot resulting from the main Alfvén wing resulting from the Io-Jupiter interaction. It is proposed that the radio arcs are related to the first reflected Alfvén wing rather than to the main one. 相似文献
9.
Ikuro Suzuki 《Astrophysics and Space Science》1983,97(1):145-150
The relationship between the X-ray flux and the radio flux from cosmic objects is investigated. We consider the emission from energetic electrons on the condition in which a plasma and a magnetic field exist. As energetic electrons under the circumstances emit both X-rays by the bremsstrahlung mechanism and radio waves by the gyrosynchrotron mechanism simultaneously, it is shown that the radio flux density is closely related to the X-ray flux density. Solving an integral equation describing the X-ray flux density at Earth, we obtain the energy spectrum of electrons in the emitting region. Inserting the result into equation of the radio flux density at Earth, we obtain the direct formula between the X-ray flux density and the radio flux density. The relation is independent of the distance between Earth and cosmic sources. Assuming a power-law X-ray spectrum, we evaluate the numerical relation between two flux densities. 相似文献
10.
V. N. Melnik A. A. Konovalenko H. O. Rucker V. V. Dorovskyy E. P. Abranin A. Lecacheux A. S. Lonskaya 《Solar physics》2010,264(1):103-117
Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 – 2002 are studied. The bursts chosen for a detailed
analysis occurred in the periods 23 – 26 May 2001, 13 – 16 and 27 – 39 July 2002 during three solar radio storms. More than
800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 – 30 MHz. All bursts
were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts,
drift pairs and spikes. Moreover, S-bursts were observed during days when the active region was situated near the central
meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 – 0.6 s for the May and July storms, respectively.
For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence
of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts
based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves,
whose phase and group velocities are equal. 相似文献
11.
The Io flux tube (IFT), along which Io interacts with the Jovian magnetosphere, is the place of plasma acceleration processes resulting in auroral like emissions, in UV, IR and Radio emissions in the decameter range. At Earth, the study of the acceleration processes is mainly made by in situ measurements. Acceleration processes at Jupiter were first deduced from the observation of a particular kind of decameter radio emissions from the IFT: the short (S-)bursts. These radio bursts present a negative drift in the time-frequency domain, which is related to the motion of the energetic electrons which produce them. The measure of their drift thus permits the kinetic energy of the electrons to be obtained, as well as its variations along the IFT which have been interpreted as electric potential jumps. Using an enhanced S-burst detection and drift measurement method, more than 1 h of quasi-continuous decametric emissions recorded at the Kharkov UTR-2 radiotelescope have been analyzed. We observe the evolution of the electron kinetic energy with the longitude of Io with a resolution of , and detect the presence of acceleration structures with characteristics being consistent with electric potential jumps of few hundred volts, and moving along the IFT in the upward direction (toward Io) at the local sound velocity. 相似文献
12.
Jupiter emits intense decameter (DAM) radio waves, detectable from the ground in the range 10–40 MHz. They are produced by energetic electron precipitations in its auroral regions (auroral-DAM), as well as near the magnetic footprints of the Galilean satellite Io (Io-DAM). Radio imaging of these decameter emissions with arcsecond angular resolution and millisecond time resolution should provide:
- (1) an improved mapping of the surface planetary magnetic field, via imaging of instantaneous cyclotron sources of highest frequency;
(2) measurements of the beaming angle of the radiation relative to the local magnetic field, as a function of frequency;
(3) detailed information on the Io–Jupiter electrodynamic interaction, in particular the lead angle between the Io flux tube and the radio emitting field line;
(4) direct information on the origin of the sporadic drifting decameter S-bursts, thought to be electron bunches propagating along magnetic field lines, and possibly revealing electric potential drops along these field lines;
(5) direct observation of DAM emission possibly related to the Ganymede–Jupiter, Europa–Jupiter and/or Callisto–Jupiter interactions, and their energetics;
(6) information on the magnetospheric dynamics, via correlation of radio images with ultraviolet and infrared images of the aurora as well as of the Galilean satellite footprints, and study of their temporal variations;
(7) an improved mapping of the Jovian plasma environment (especially the Io torus) via the propagation effects that it induces on the radio waves propagating through it (Faraday rotation, diffraction fringes, etc.);
(8) possibly on the long-term a better accuracy on the determination of Jupiter's rotation period.
13.
Seismology is the best tool for investigating the interior structure of stars and giant planets. This paper deals with a photometric study of jovian global oscillations. The propagation of acoustic waves in the jovian troposphere is revisited in order to estimate their effects on the planetary albedo. According to the standard model of the jovian cloud structure there are three major ice cloud layers (e.g., [Atreya et al., 1999. A comparison of the atmospheres of Jupiter and Saturn: Deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet Space Sci. 47, 1243-1262]). We consider only the highest layers, composed of ammonia ice, in the region where acoustic waves are trapped in Jupiter's atmosphere. For a vertical wave propagating in a plane parallel atmosphere with an ammonia ice cloud layer, we calculate first the relative variations of the reflected solar flux due to the smooth oscillations at about the ppm level. We then determine the phase transitions induced by the seismic waves in the clouds. These phase changes, linked to ice particle growth, are limited by kinetics. A Mie model [Mishchenko et al., 2002. Scattering, Absorption, and Emission of Light by Small Particles. Cambridge Univ. Press, Cambridge, pp. 158-190] coupled with a simple radiation transfer model allows us to estimate that the albedo fluctuations of the cloud perturbed by a seismic wave reach relative variations of 70 ppm for a 3-mHz wave. This albedo fluctuation is amplified by a factor of ∼70 relative to the previously published estimates that exclude the effect of the wave on cloud properties. Our computed amplifications imply that jovian oscillations can be detected with very precise photometry, as proposed by the microsatellite JOVIS project, which is dedicated to photometric seismology [Mosser et al., 2004. JOVIS: A microsatellite dedicated to the seismic analysis of Jupiter. In: Combes, F., Barret, D., Contini, T., Meynadier, F., Pagani, L. (Eds.), SF2A-2004, Semaine de l'Astrophysique Francaise, Les Ulis. In: EdP-Sciences Conference Series, pp. 257-258]. 相似文献
14.
We consider a model of a coronal loop in the form of a cord surrounded by a coaxial shell. Two slow magnetosonic waves longitudinally propagate within a thin flux tube on the m=0 cylindrical mode with velocities close to the tube velocities in the cord and the shell. One wave propagates inside the cord, while the other propagates inside the shell. A peculiar feature of the second wave is that the plasma in the cord and the shell oscillates with opposite phases. There are two fast magnetosonic waves on each of the cylindrical modes with m>0. If the plasma density in the shell is lower than that in the surrounding corona, then one of the waves is radiated into the corona, which causes the loop oscillations to be damped, while the other wave is trapped by the cord, but can also be radiated out under certain conditions. If the plasma density in the shell is higher than that in the cord, then one of the waves is trapped by the shell, while the other wave can also be trapped by the shell under certain conditions. In the wave trapped by the shell and the wave radiated by the tube, the plasma in the cord and the shell oscillates with opposite phases. 相似文献
15.
S. S. Hasan 《Journal of Astrophysics and Astronomy》2000,21(3-4):283-287
We model the dynamical interaction between magnetic flux tubes and granules in the solar photosphere which leads to the excitation
of transverse (kink) and longitudinal (sausage) tube waves. The investigation is motivated by the interpretation of network
oscillations in terms of flux tube waves. The calculations show that for magnetic field strengths typical of the network,
the energy flux in transverse waves is higher than in longitudinal waves by an order of magnitude. But for weaker fields,
such as those that might be found in internetwork regions, the energy fluxes in the two modes are comparable. Using observations
of footpoint motions, the energy flux in transverse waves is calculated and the implications for chromospheric heating are
pointed out. 相似文献
16.
Sanjay Tyagi 《Astrophysics and Space Science》1993,209(2):229-235
The problem of surface wave propagation on a magnetised cylindrical plasma is investigated allowing for different axial magnetic fields inside and outside the flux tube. Properties of surface waves for symmetric and asymmetric modes of perturbations are investigated idealising the material inside and outside the cylinder to be insulator or infinitely conducting both in compressible and incompressible approximations for the tube material. 相似文献
17.
T. Takakura 《Solar physics》1979,61(1):161-186
A simulation of normal type III radio bursts has been made in a whole frequency range of about 200 MHz to 30 kHz by the usage of the semi-analytical method as developed in previous papers for the plasma waves excited by a cloud of fast electrons. Three-dimensional plasma waves are computed, though the velocities of fast electrons are assumed to be one-dimensional. Many basic problems about type III radio bursts and associated solar electrons have been solved showing the following striking or unexpected results.Induced scattering of plasma waves, by thermal ions, into the plasma waves with opposite wave vectors is efficient even for a solar electron cloud of rather low number density. Therefore, the second harmonic radio emission as attributed to the coalescence of two plasma waves predominates in a whole range from meter waves to km waves. Fundamental radio emission as ascribed to the scattering of plasma waves by thermal ions is negligibly small almost in the whole range. On the other hand, third harmonic radio emission can be strong enough to be observed in a limited frequency range.If, however, the time integral of electron flux is, for example, 2 × 1013 cm–2 (>5 keV) or more at the height of 4.3 × 1010 cm (
p = 40 MHz) above the photosphere, the fundamental may be comparable with or greater than the second harmonic, but an effective area of cross-section of the electron beam is required to be very small, 1017 cm2 or less, and hence much larger sizes of the observed radio sources must be attributed to the scattering alone of radio waves.The radio flux density expected at the Earth for the second harmonic can increase with decreasing frequencies giving high flux densities at low frequencies as observed, if x-dependence of the cross-sectional area of the electron beam is x
1.5 or less instead of x
2, at least at x 2 × 1012 cm.The second harmonic radio waves are emitted predominantly into forward direction at first, but the direction of emission may reverse a few times in a course of a single burst showing a greater backward emission at the low frequencies.In a standard low frequency model, a total number of solar electrons above 18 keV arriving at the Earth orbit reduces to 12% of the initial value due mainly to the collisional decay of plasma waves before the waves are reabsorbed by the beam electrons arriving later. However, no deceleration of the apparent velocity of exciter appears. A change in the apparent velocity, if any, results from a change in growth rate of the plasma waves instead of the deceleration of individual electrons.Near the Earth, the peak of second harmonic radio flux as emitted from the local plasma appears well after the passage of a whole solar electron cloud through this layer. This is ascribed to the secondary and the third plasma waves as caused in non-resonant regions by the induced scattering of primary plasma waves in a resonant region. 相似文献
18.
Jorma J. Riihimaa 《Astrophysics and Space Science》1977,51(2):363-383
Dynamic spectra of Jupiter's S-bursts are observed with sweep-frequency and multi-channel receivers operating at frequency ranges 21–30 and 20.85–23.20 MHz, respectively. Spectra obtained with time resolutions of 0.2, 0.02, and 0.004 s are compared, the frequency resolution being 50 kHz. The most normal appearance of S-bursts is in trains with a frequency range of the order of 1 MHz. Narrow-band Strains also occur. Narrow-band L-emissions in region B are often associated with S-bursts, obviously in the manner described by Flagget al. (1976). Synoptic spectral observations indicate that region B for S-bursts exhibits a drift in longitude similar to that for L-bursts. The Io phase profile for S-bursts has a maximum in the vicinity of 80° in region B and 230° in region C. S-bursts observed in 1976 have higher drift rates than those compiled by Krauscheet al. (1976). Region C bursts have simpler spectra and lower drift rates than region B bursts. 相似文献
19.
On July 20, 1994, before the Q fragments of Comet Shoemaker-Levy 9 fell to Jupiter, more than 200 spectra of the Jovian features were obtained at the Crimean Astrophysical Observatory in the wavelength range 5700–7600 Å with a 26 s exposure time and a spectral resolution of 20 Å. We found a time-varying Na D line emission in the form of two components with Doppler shifts of about 30 Å. The brightest and most frequent sodium flares were detected when the Q fragments passed through the Jovian inner magnetosphere at a distance of about three the Jovian radii (3RJ) from its center, where they crossed the Io-Jupiter current tube. A frequency analysis of our data revealed a flare recurrence time scale of 1 min. We conclude that sodium was released from the cometary dust and from the surfaces of numerous cometary debris and that its amount was enough to produce the observed emission. The observed high-speed clouds of sodium atoms are assumed to have been formed through ionization, ion acceleration by the bidirectional electric fields of Alfvén waves in the Io-Jupiter current tube, and their neutralization. 相似文献
20.
J. D. Mihalov 《Astrophysics and Space Science》1973,20(2):483-490
X-ray fluxes at Earth estimated from hypothetical fluxes and spectra of energetic particles trapped in Jupiter's magnetic field are found to be 1/170000 times the upper limit X-ray flux from Jupiter based on published results from a rocket experiment. Detection of the calculated X-ray flux from Jupiter does not necessarily provide information on an energetic trapped proton component because the X-ray flux due to the hypothetical trapped energetic proton fluxes alone is comparable in magnitude to that due alone to trapped energetic electron fluxes at Jupiter. 相似文献