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1.
The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Alien belt is attributed to solar wind particles diffused in towards the planet by dynamo electric fields from ionospheric neutral winds and consequences of this theory are given.  相似文献   

2.
This paper emphasizes an effort to link processes which relate solar activity and magnetospheric disturbances in terms of energy transfer through a chain of four elements. In this view, each element is explicitly thought to be powered by a dynamo, namely the solar wind generation dynamo, the solar flare dynamo, the solar wind-magnetosphere dynamo and the auroral dynamo, respectively. Each dynamo powers a plasma acceleration process by the Lorentz force and the plasma flows thus generated are the solar wind, the flare-generated solar wind disturbance, the magnetospheric plasma convection and the ionospheric convection, respectively. Each plasma flow conveys the energy from one element to the next in the chain. Some of the kinetic energy of the photospheric plasma is eventually deposited in the polar ionosphere as heat energy.  相似文献   

3.
In order to envisage the circulation pattern of the magnetospheric plasma produced by the dynamo action in the ionosphere, the distribution of the dynamo-induced electrostatic field resulting from basic ionospheric wind systems is studied. It is then shown by use of Maeda's field distribution that there exists a remarkable large-scale circulation of the magnetospheric plasma, inward (earthward) on the evening side of the magnetosphere and outward on the morning side. This motion is comparable to the motion produced by the Earth's rotation and by zonal winds in the ionosphere. It is shown also that the electrostatic field can cause a considerable radial motion of some of the energetic particles in the radiation belt.  相似文献   

4.
The electric currents induced in the atmosphere of a non-magnetic planet such as Venus by the interaction of the solar wind satisfy a generalized Ohm's Law relationship with tensor conductivity. The distribution of these currents within the planetary ionosphere may be calculated by a variational technique which minimizes the Joule heating over the ionospheric volume. In this paper, we present the development of the variational technique, and apply it to a model of the solar wind interaction with Venus.Potential and current distributions are shown, and the use of these distributions in determining convective transport patterns of planetary ions is discussed.  相似文献   

5.
The distributions of the current and the neutral winds driven by the electric field of convection are calculated in the dynamo-region of the ionosphere. At high latitudes the convection field drives the current and wind systems which consist of two cells with the centres at about 6 and 18 hours LT. In the northern hemisphere in the dawn cells winds and currents are clockwise, in the dusk cells they are counterclockwise. The appearance of the wind system shows that the upper atmosphere moves in the direction inverse to the displacement of the ionospheric ends of the magnetic flux tubes taking part in the convection. In the disturbed conditions the calculated wind system has the directions and velocities of the winds which are in a satisfactory agreement with the data of the irregularity drifts in the lower ionosphere in the winter season.  相似文献   

6.
In a steady-state model for the interaction of the solar wind with the atmosphere of a non-magnetic planet, the magnetized solar wind acts as a dynamo over the dayside of the planet and induces Ohmic currents in the planet's ionosphere. A model for the dynamo mechanism and for the induced current configuration is developed. Based on this model and assumed model atmospheres of Mars and Venus, the distribution of currents entering the ionosphere through the ionopause is calculated. The requirement that the total current be of such a magnitude as to cancel the shock-compressed interplanetary magnetic field fixes the ionopause altitude. The calculations for Venus are in reasonable agreement with observations. The calculations for Mars indicate the possibility of an observable ionopause in the altitude range from 325 to 425 km.  相似文献   

7.
《Planetary and Space Science》2006,54(13-14):1482-1495
Venus has no internal magnetic dynamo and thus its ionosphere and hot oxygen exosphere dominate the interaction with the solar wind. The solar wind at 0.72 AU has a dynamic pressure that ranges from 4.5 nPa (at solar max) to 6.6 nPa (at solar min), and its flow past the planet produces a shock of typical magnetosonic Mach number 5 at the subsolar point. At solar maximum the pressure in the ionospheric plasma is sufficient to hold off the solar wind at an altitude of 400 km above the surface at the subsolar point, and 1000 km above the terminators. The deflection of the solar wind occurs through the formation of a magnetic barrier on the inner edge of the magnetosheath, or shocked solar wind. Under typical solar wind conditions the time scale for diffusion of the magnetic field into the ionosphere is so long that the ionosphere remains field free and the barrier deflects almost all the incoming solar wind. Any neutral atoms of the hot oxygen exosphere that reach the altitude of the magnetosheath are accelerated by the electric field of the flowing magnetized plasma and swept along cycloidal paths in the antisolar direction. This pickup process, while important for the loss of the Venus atmosphere, plays a minor role in the deceleration and deflection of the solar wind. Like at magnetized planets, the Venus shock and magnetosheath generate hot electrons and ions that flow back along magnetic field lines into the solar wind to form a foreshock. A magnetic tail is created by the magnetic flux that is slowed in the interaction and becomes mass-loaded with thermal ions.The structure of the ionosphere is very much dependent on solar activity and the dynamic pressure of the solar wind. At solar maximum under typical solar wind conditions, the ionosphere is unmagnetized except for the presence of thin magnetic flux ropes. The ionospheric plasma flows freely to the nightside forming a well-developed night ionosphere. When the solar wind pressure dominates over the ionospheric pressure the ionosphere becomes completely magnetized, the flow to the nightside diminishes, and the night ionosphere weakens. Even at solar maximum the night ionosphere has a very irregular density structure. The electromagnetic environment of Venus has not been well surveyed. At ELF and VLF frequencies there is noise generated in the foreshock and shock. At low altitude in the night ionosphere noise, presumably generated by lightning, can be detected. This paper reviews the plasma environment at Venus and the physics of the solar wind interaction on the threshold of a new series of Venus exploration missions.  相似文献   

8.
Some new ideas on the interaction of the solar wind with the magnetosphere are brought forward. The mechanism of reflection of charged particles at the magnetopause is examined. It is shown that in general the reflection is not specular but that a component of momentum of the particle parallel to the magnetopause changes. A critical angle is derived such that particles whose trajectories make an angle less than it with the magnetopause enter the magnetosphere freely, so transferring their forward momentum to it. Spatially or temporally non-uniform entry of charged particles into the magnetosphere causes electric fields parallel to the magnetopause which either allow the free passage of solar wind across it or vacuum reconnection to the interplanetary magnetic field depending on the direction of the latter. These electric fields can be discharged in the ionosphere and so account qualitatively for the dayside agitation of the geomagnetic field observed on the polar caps. The solar wind wind plasma which enters the magnetosphere creates (1) a dawn-dusk electric field across the tail (2) enough force to account for the geomagnetic tail and (3) enough current during disturbed times to account for the auroral electrojets. The entry of solar wind plasma across the magnetosphere and connection of the geomagnetic to interplanetary field can be assisted by wind generated electric field in the ionosphere transferred by the good conductivity along the geomagnetic field to the magnetopause. This may account for some of the observed correlations between phenomena in the lower atmosphere and a component of magnetic disturbance.  相似文献   

9.
We propose a mechanism whereby the solar wind flowing past the magnetosphere of Uranus causes a Faraday disc dynamo topology to be established and power to be extracted from the kinetic energy of rotation of Uranus. An immediate consequence of this dynamo is the generation of Birkeland currents that flow in and out of the sunlit polar cap with the accompanying production of polar aurora. We calculate the power extracted from planetary rotation as a function of planetary dipole magnetic moment and the ionospheric conductivity of Uranus. For plausible values of ionospheric conductivity, the observed auroral power requires a magnetic moment corresponding to a surface equatorial field of the order of 4 Gauss, slightly larger than the value 1.8 Gauss given by the empirical “magnetic Bodes law”.  相似文献   

10.
Strong ultraviolet radiation from the Sun ionizes the upper atmosphere of Venus, creating a dense ionosphere on the dayside of the planet. In contrast to Earth, the ionosphere of Venus is not protected against the solar wind by a magnetic field. However, the interaction between charged ionospheric particles and the solar wind dynamic and magnetic pressure creates a pseudo-magnetosphere which deflects the solar wind flow around the planet (Schunk and Nagy, 1980). The combination of changing solar radiation and solar wind intensities leads to a highly variable structure and plasma composition of the ionosphere. The instrumentation of the Venus Express spacecraft allows to measure the magnetic field (MAG experiment) as well as the electron energy spectrum and the ion composition (ASPERA-4 experiment) of the upper ionosphere and ionopause. In contrast to the earlier Pioneer Venus Orbiter (PVO) measurements which were conducted during solar maximum, the solar activity was very low in the period 2006-2009. A comparison with PVO allows for an investigation of ionospheric properties under different solar wind and EUV radiation conditions. Observations of MAG and ASPERA have been analyzed to determine the positions of the photoelectron boundary (PEB) and the “magnetopause” and their dependence on the solar zenith angle (SZA). The PEB was determined using the ELS observations of ionospheric photoelectrons, which can be identified by their specific energy range. It is of particular interest to explore the different magnetic states of the ionosphere, since these influence the local plasma conductivity, currents and probably the escape of electrons and ions. The penetration of magnetic fields into the ionosphere depends on the external conditions as well as on the ionospheric properties. By analyzing a large number of orbits, using a combination of two different methods, we define criteria to distinguish between the so-called magnetized and unmagnetized ionospheric states. Furthermore, we confirm that the average magnetic field inside the ionosphere shows a linear dependence on the magnetic field in the region directly above the PEB.  相似文献   

11.
A model for the production and loss of energetic electrons in Jupiter's radiation belt is presented. It is postulated that the electrons originate in the solar wind and are diffused in toward the planet by perturbations which violate the particles' third adiabatic invariant. At large distances, magnetic perturbations, electric fields associated with magnotospheric convection, or interchange instabilities driven by thermal plasma gradients may drive the diffusion. Inside about 10 RJ the diffusion is probably driven by electric fields associated with the upper atmosphere dynamo which is driven by neutral winds in the ionosphere. The diurnal component of the dynamo wind fields produces a dawn-dusk asymmetry in the decimetric radiation from the electrons in the belts, and the lack of obvious measured asymmetries in the decimetric radiation measurements provides estimates of upper limits for these Jovian ionospheric neutral winds. The average diurnal winds are less than or comparable to those on earth, but only modest fluctuating winds are required to drive the energetic electron diffusion referred to above.The winds required to diffuse the energetic particles across the orbit of the satellite lo in a time equal to their drift period are also estimated. If Io is non-conducting, modest winds are required, but if Io is conducting, only small winds are needed. It is concluded that both protons and electrons are diffused in from the solar wind to small distances without serious losses occurring due to the particles being swept up by the satellites.Consideration of proton and electron diffusion in energy shows that once the electrons become relativistic, the ratio of proton to electron energy increases. Thus, if protons and electrons have the same energy in the solar wind, when the electrons reach nMeV, the protons will be nMeV if n ? 1 or n2 MeV if n ? 1. If the proton-to-electron energy ratio is initially, e.g., 5, then these figures are 5n and 5n2, respectively.  相似文献   

12.
We present estimates of the day-side ionospheric conductivities at Mars based on magnetic field measurements by Mars Global Surveyor (MGS) at altitudes down to ∼100 km during aerobraking orbits early in the mission. At Mars, the so-called ionospheric dynamo region, where plasma/neutral collisions permit electric currents perpendicular to the magnetic field, lies between 100 and 250 km altitude. We find that the ionosphere is highly conductive in this region, as expected, with peak Pedersen and Hall conductivities of 0.1-1.5 S/m depending on the solar illumination and induced magnetospheric conditions. Furthermore, we find a consistent double peak pattern in the altitude profile of the day-side Pedersen conductivity, similar to that on Titan found by Rosenqvist et al. (2009). A high altitude peak, located between 180 and 200 km, is equivalent to the terrestrial peak in the lower F-layer. A second and typically much stronger layer of Pedersen conductivity is observed between 120 and 130 km, which is below the Hall conductivity peak at about 130-140 km. In this altitude region, MGS finds a sharp decrease in induced magnetic field strength at the inner magnetospheric boundary, while the day-side electron density is known to remain high as far down as 100 km. We find that such Titan-like behaviour of the Pedersen conductivity is only observed under regions of strongly draped magnetospheric field-lines, and negligible crustal magnetic anomalies below the spacecraft. Above regions of strong crustal magnetic anomalies, the Pedersen conductivity profile becomes more Earth-like with one strong Pedersen peak above the Hall conductivity peak. Here, both conductivities are 1-2 orders of magnitude smaller than the above only weakly magnetised crustal regions, depending on the strength of the crustal anomaly field at ionospheric altitudes. This nature of the Pedersen conductivity together with the structured distribution of crustal anomalies all over the planet should give rise to strong conductivity gradients around such anomalies. Day-side ionospheric conductivities on Mars (in regions away from the crustal magnetic anomalies) and Titan seem to behave in a very similar manner when horizontally draped magnetic field-lines partially magnetise a sunlit ionosphere. Therefore, it appears that a similar double peak structure of strong Pedersen conductivity could be a more general feature of non-magnetised bodies with ionised upper atmospheres, and thus should be expected to occur also at other non-magnetised terrestrial planets like Venus or other planetary bodies within the host planet magnetospheres.  相似文献   

13.
Cassini’s Titan flyby on 16 April, 2005 (T5) is the only encounter when the two main ionizing sources of the moon’s atmosphere, solar radiation and corotating plasma, align almost anti-parallel. In this paper a single-fluid multi-species 3D MHD model of the magnetospheric plasma interaction for T5 conditions is analyzed. Model results are compared to observations to investigate the ionospheric dynamics at Titan as well as to understand the deviations from a typical solar wind interaction, such as Venus’ interaction with the solar wind. Model results suggest that for the T5 interaction configuration, corotating plasma is the dominant driver determining the global interaction features at high altitudes. In the lower ionosphere below ～1500 km altitude – where the control of the ionospheric composition transfers from dynamic to chemical processes – magnetic and thermal pressure gradients oppose each other locally, complicating the ionospheric dynamics. Model results also imply that the nightside ionosphere – produced only by the impact ionization in the model – does not provide enough thermal pressure to balance the incident plasma dynamic pressure. As a result, the induced magnetic barrier penetrates into the ionosphere by plasma convection down to ～1000 km altitude and by magnetic diffusion below this altitude. Moreover, strong horizontal drag forces due to ion-neutral collisions and comparable drag forces estimated from possible neutral winds in the lower ionosphere below ～1400 km altitude oppose over local regions, implying that the Titan interaction must be treated as a 3D problem. Ion and electron densities calculated from the model generally agree with the Cassini Ion Neutral Mass Spectrometer and Langmuir probe measurements; however, there are significant differences between the calculated and measured magnetic fields. We discuss possible explanations for the discrepancy in the magnetic field predictions.  相似文献   

14.
The exchange of ions between the ionosphere of a planet with negligible intrinsic magnetic field, and the solar wind is examined. It is suggested that a balance exists between the outflow of ionospheric ions at the plasmapause and ions from the solar wind in a restricted region close to the subsolar point. This results in a current system towards the subsolar point on the surface of the ionopause and a toroidal magnetic field. Simple calculations are made of the current and field configuration that might result from the system for conditions similar to those encountered on the Viking 1 and 2 transits of the Mars ionosphere.  相似文献   

15.
A mathematical theory of the three-dimensional ionospheric dynamo is described, which is exact within the context of the assumption that the magnetic field lines are perfectly conducting.Explicit formulae are obtained for the electric fields, and hence for the current systems, which are excited by the dynamo e.m.f. associated with an arbitrary given wind field.They can also be applied to determine the fields arising from an external source of e.m.f., originating for example in the magnetosphere.The convergence properties of the solution are investigated for a simple symmetric wind field; it is found that inclusion of spherical harmonics up to degree 80 is sufficient to yield the features of the electrojet region, now fully coupled to the global current system.  相似文献   

16.
A comparative study of the viscous transport of solar wind momentum to the upper layers of the Venus ionosphere with that occurring within the trans-terminator flow leads to estimates of the ratio of the viscosity coefficients that are applicable to both cases. Support for viscous forces between the solar wind and the ionospheric plasma in the trans-terminator flow derives from the momentum flux balance between the momentum flux in the latter flow and the deficiency of solar wind momentum along the flanks of the ionosheath. By comparing the relative width of the viscous boundary layer in the Venus ionosheath and the width of the trans-terminator flow we find that the transport of momentum within the upper ionosphere proceeds at a rate similar to that at which momentum is delivered to the upper ionosphere from the solar wind. Comparable values are obtained for the viscosity coefficient of the solar wind that streams over the ionosphere and that implied from momentum transport within the ionospheric trans-terminator flow. It is further suggested that despite the different nature of the processes that give place to the viscous transport of the solar wind momentum to the upper ionosphere (wave-particle interactions) and those responsible for its distribution within the ionosphere (through coulombian collisions) there is a similar response in the behavior of both plasmas to momentum transport. Calculations show that with comparable values of the viscosity coefficient in the ionosheath and in the upper ionospheric plasma the mean free path suitable to wave-particle interactions in the ionosheath is of the same order of magnitude as the mean free path of the planetary O+ ions that interact through coulombian collisions in the upper ionosphere. The effects of this similarity are considered in the discussion.  相似文献   

17.
The declining phases of solar cycles are known for their high speed solar wind streams that dominate the geomagnetic responses during this period. Outstanding questions about these streams, which can provide the fastest winds of the solar cycle, concern their solar origins, persistence, and predictability. The declining phase of cycle 23 has lasted significantly longer than the corresponding phases of the previous two cycles. Solar magnetograph observations suggest that the solar polar magnetic field is also ～?2?–?3 times weaker. The launch of STEREO in late 2006 provided additional incentive to examine the origins of what is observed at 1 AU in the recent cycle, with the OMNI data base at the NSSDC available as an Earth/L1 baseline for comparisons. Here we focus on the year 2007 when the solar corona exhibited large, long-lived mid-to-low latitude coronal holes and polar hole extensions observed by both SOHO and STEREO imagers. STEREO provides in situ measurements consistent with rigidly corotating solar wind stream structure at up to ～?45° heliolongitude separation by late 2007. This stability justifies the use of magnetogram-based steady 3D solar wind models to map the observed high speed winds back to their coronal sources. We apply the WSA solar wind model currently running at the NOAA Space Weather Prediction Center with the expectation that it should perform its best at this quiet time. The model comparisons confirm the origins of the observed high speed streams expected from the solar images, but also reveal uncertainties in the solar wind source mapping associated with this cycle’s weaker solar polar fields. Overall, the results illustrate the importance of having accurate polar fields in synoptic maps used in solar wind forecast models. At the most fundamental level, they demonstrate the control of the solar polar fields over the high speed wind sources, and thus one specific connection between the solar dynamo and the solar wind character.  相似文献   

18.
From the world distribution of geomagnetic disturbance, the connection between the electric current in the ionosphere, the field-aligned current and asymmetric equatorial ringcurrent in the magnetosphere is discussed. The partial ring-current in the afternoon-evening region, whose intensity is closely correlated with the AE-index, usually develops and decays earlier than the symmetric ring-current in the course of magnetic storms. The partial ringcurrent seems to have a direct connection with the positive geomagnetic bay in high latitudes in the evening hours through the ionizing effect of the particles leaking from the partial ringcurrent. The dawn-to-dusk electric field in the magnetospheric tail is transferred to the polar ionosphere, producing there the twin vortex Hall current responsible for polar cap geomagnetic variation. The magnetic effect of the associated Pedersen current in the ionosphere is shown to be small but still worth considering. The electrojet near midnight along the auroral oval is thought to appear when the electric conductivity of the ionosphere is locally increased under the presence of large scale dawn-to-dusk electric field. The occasional appearance of a localized abnormal geomagnetic disturbance with reversed direction near the geomagnetic pole seems to suggest the occasional reversal of electric field near the outer surface of the magnetospheric tail, especially when the interplanetary magnetic field is northward.  相似文献   

19.
We calculate electric fields and currents in the ionosphere during the solar eclipse. Three dimensional anisotropic and inhomogeneous conductivity distribution is taken into consideration. Electrical conductivity is assumed to be decreased by the solar eclipse, but winds are not altered. It is shown that the additional currents and fields due to the eclipse are essentially understood as those generated by the obstruction to Sq currents. However, the currents flow preferably in the region nearer to the noon meridian and at the Equator and partly escape through the field-aligned currents to the opposite hemisphere, and therefore the effect of the solar eclipse is also seen in the opposite hemisphere in the deformed shape.  相似文献   

20.
A detailed analysis of rapid-run magnetograms from Guam (geomagnetic latitude = 4.2°) revealed that there are two kinds of geomagnetic sudden commencement (SC) observed in nighttime. One is the ordinary SC consisting of a main impulse only which has a smooth rise of the H-component. The other is a superposition by a small positive impulse on the very beginning part of the smooth rise of the main impulse and consequently the SC starts with a small stepwise increase of the H-component. The latter type of SC occurs between 20 and 08 h L.T. and its occurrence rate takes the maximum value of about 50% around 03 h L.T. Corresponding magnetograms from a dayside equatorial station (Huancayo, geomagnetic latitude = ?0.7°) were examined and a good correlation was found between the stepwise SC at the nightside (Guam) and SC1 with a preliminary reverse impulse (PRI) at the dayside (Huancayo). Since PRI observed at the dayside equator may be interpreted as an extension of an ionospheric current due to an dusk-to-dawn electric field impressed on the polar ionosphere, our results show that a polar originating ionospheric current can extend to the nightside equator and produce a small but observable magnetic effect in spite of much reduced nighttime ionospheric conductivity.  相似文献   

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