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1.
A solar wind parameter ε, known as the energy coupling function, has been shown to correlate with the power consumption in the magnetosphere. It is shown in the present paper that the parameter ε can be identified semi-quantitatively as the dynamo power delivered from the solar wind to an open magnetosphere. This identification not only provides a theoretical basis for the energy coupling function, but also constitutes an observational verification of the solar wind-magnetosphere dynamo along the magnetotail. Moreover, one can now conclude that a substorm results when the dynamo power exceeds 1018 ergs ?1.  相似文献   

2.
A high time resolution study of the relationship between the solar wind-magnetosphere energy coupling function ? and the total energy dissipation rate UT of the magnetosphere is made using 5-min average values of solar wind data and of the geomagnetic indices AE and Dst. All the results are essentially the same as those obtained by the earlier studies which were based on the hourly average data set. Therefore, we confirm that the magnetosphere is primarily a driven system.  相似文献   

3.
The energy coupling function between the solar wind and the magnetosphere can be obtained for two extreme situations, in which the magnetospheric geometry is determined primarily by either (i) the interplanetary magnetic field, or (ii) the solar wind pressure. In this paper, we obtained an expression for the energy coupling function by assuming a simple interpermeation of the interplanetary and geomagnetic fields. Two important quantities in this case are the potential difference between the two neutral points and the amount of open flux. From these two overall quantities, the voltage and the current of the magnetospheric dynamo are calculated. The dynamo power output represents the rate at which energy is transferred from the solar wind to the magnetosphere. The derived functional dependence on the interplanetary conditions provides a theoretical basis for the energy coupling function previously deduced from observations.  相似文献   

4.
The outer regions (r > 2.3 Rj; Rj = radius of Jupiter) of the magnetosphere of Jupiter will systematically accumulate plasma. If sufficient plasma accumulates, the field lines must open to allow the plasma to escape. Available energy sources appear able to supply plasma at a high enough rate to keep the field lines constantly open beyond about 60 RJ. We suggest that the solar wind interaction with Jupiter may be essentially different from that with the Earth, with the Jovian magnetosphere opening up to form a planetary wind.  相似文献   

5.
Reconnection involves singular lines called X-lines on the day and night sides of the magnetosphere, and the reconnection rate is proportional to the component of the electric field along the X-line. Although there is some indirect support for this model, nevertheless direct support is totally lacking. However, there are two distinct pieces of clearly contradictory observational evidence on the dayside. First is the failure to account for the implied energy dissipation by the magnetopause current, over 1011 W, which should be easily observable as heating or enhanced flow of the plasma near the magnetopause. In marked contrast to this prediction, HEOS-2 satellite data reveal a plasma with decreased energy density and reduced flow. Second, the boundary of closed magnetic field lines is in the wrong location. In the reconnection process the plasma outflow would cut across open field lines toward higher latitudes; there should be a band of open field lines equatorward of the cleft. Observations of trapped energetic particles indicate closed field lines within the entry layer and cleft. Either one of these pieces of evidence is sufficient by itself to require drastic revision, even rejection, of the reconnection model. There is also contradictory evidence on the night side. The last closed field line capable of trapping energetic particles is poleward of auroral arcs. The implication is that the X-line is at the distant magnetopause, and not in the plasma sheet. Consequently, even if the reconnection process were operative at the nightside X-line, it would be isolated from steady state plasma sheet and auroral processes. On the other hand, substorm phenomena, in which stored magnetic energy is converted into particle kinetic energy, necessarily involve an induced electric field; that is excluded in theories of the reconnection process in which it is assumed that curl E = 0. Nevertheless, the observed easy access of energetic solar flare particles to the polar caps, and especially the preservation of interplanetary anisotropies as differences between the two polar caps, argues strongly for an open magnetosphere, with interconnection between geomagnetic and inter-planetary magnetic field lines. It is suggested that the resolution of this apparent paradox involves electric fields parallel to the magnetic field lines somewhere on the dawn and dusk sides of the magnetosphere, with an equipotential dayside magnetopause.  相似文献   

6.
We present results from a theoretical model which has been used to investigate the modulation of the magnetosphere-ionosphere coupling currents in the Jovian middle magnetosphere by solar wind-induced compressions and expansions of the magnetosphere. We consider an initial system in which the current sheet field lines extend to 50RJ in the equatorial plane, and where the iogenic plasma in the current sheet undergoes steady outward radial diffusion under the influence of the ionospheric torque which tends to maintain corotation with the planet. We show using typical Jovian parameters that the upward-directed field-aligned currents flowing throughout the middle magnetosphere region in this system peak at values requiring the existence of significant field-aligned voltages to drive them, resulting in large precipitating energy fluxes of accelerated electrons and bright ‘main oval’ UV auroras. We then consider the changes in these parameters which take place due to sudden expansions or compressions of the magnetosphere, resulting from changes in the solar wind dynamic pressure. Two cases are considered and compared, these being first the initial response of the system to the change, determined approximately from conservation of angular momentum of the radially displaced plasma and frozen-in field lines, and second the subsequent steady state of steady outward radial diffusion applied to the compressed or expanded system. We show that moderate inward compressions of the outer boundary of the current sheet field lines, e.g. from 50 to 40RJ, are effective in significantly reducing the coupling currents and precipitation in the initial state, the latter then recovering, but only partly so, during the evolution to the steady state. Strong inward compressions, e.g. to 30RJ cause significant super-corotation of the plasma and a reversal in sense of the current system in the initial state, such that bright auroras may then be formed poleward of the usual ‘main auroral oval’ due to the ‘return’ currents. The sense of the currents subsequently reverts back to the usual direction as steady-state conditions are restored, but they are weak, and so is the consequent electron precipitation. For outward expansions of the current sheet, however, the field-aligned currents and electron precipitation are strongly enhanced, particularly at the poleward border mapping to the outer weak field region of the current sheet. In this case there is little evolution of the parameters between the initial expansion and the subsequent steady state. Overall, the results suggest that the Jovian middle magnetosphere coupling currents and resulting ‘main oval’ auroral acceleration and precipitation will be strongly modulated by the solar wind dynamic pressure in the sense of anti-correlation, through the resulting compressions and expansions in the size of the magnetosphere.  相似文献   

7.
The functional dependence on solar wind parameters of the rate of energy transfer from the solar wind into the magnetosphere is subject to constraints imposed by dimensional analysis. The form and extent of the constraints depend on assumption about the energy coupling mechanisms, specifically on the relative importance of electromagnetic coupling (MHD flows effects), ionospheric conductivity effects (through Birkeland currents), and the viscous coupling. The effective viscosity coefficient scales in a well-defined manner with solar wind parameters, and its effect is dimensionally the same as that of more general finite-gyroradius mechanisms. We obtain the general form of the expression for energy transfer which takes all these effects into account and which can then be specialized to specific assumptions about the coupling mechanism. We point out the needed changes in energy transfer formulas previously used in the littrature, which make them conform to the requirements of dimensional analysis. Electromagnetic coupling yields the most restrictive formulas for energy transfer, although a unique expression cannot be obtained either on solely dimensional grounds or from presently available theory. Modifications required by the addition of viscous or finite-gyroradius effects are well defined but small and likely to be difficult to detect in practice. Assumptions of energy transfer by solar wind plasma entry leads to expressions equivalent, as far as dimensional arguments go, to those based on assumptions of electromagnetic or viscous coupling. Ionospheric conductivity effects are likely to be minor since Joule heating in the ionosphere is a relatively small fraction of the magnetospheric energy budget. All energy transfer formulas discussed presuppose a well-defined set of solar wind parameters and hence can be valid only on time scales longer than the solar wind flow time past the magnetosphere, which is also the expected time scale for energy storage (if any) in the magnetotail.  相似文献   

8.
The medium energy particle spectrometer (electrons of energy > 20 keV, protons > 25 keV) on board ISEE-2 has measured very similar pitch angle distributions and intensities during “flux transfer” events in the magnetosheath and events previously designated as “inclusion” events in the magnetosphere on a single pass through the magnetopause. This is interpreted as strong evidence that magnetic field lines in the magnetosphere can connect to field lines in the magnetosheath, at least locally and for brief times, allowing the same population ofparticles to be observed on both sides of the boundary. In addition, a simple mathematical model is provided incorporating a time constant for the process re-supplying particles to the open flux tube. The observed data are satisfactorily reproduced using a time constant of 46 s, which is comparable to the half-bounce time of protons at this position.  相似文献   

9.
S Massetti  S Orsini  A Mura  H Lammer 《Icarus》2003,166(2):229-237
The presence of a magnetosphere around Mercury plays a fundamental role on the way the solar wind plasma interacts with the planet. Since the observations suggest that Mercury should occupy a large fraction of its magnetosphere and because of lack of an atmosphere, significant differences in solar wind-magnetosphere coupling are expected to exist with respect to the Earth case. On the basis of a modified Tsyganenko T96 model we describe the geometry of the magnetic field that could characterize Mercury, and its response to the variations of the impinging solar wind and of the interplanetary magnetic field. The investigation is focused on the shape and dimension of the open magnetic field regions (cusps) that allow the direct penetration of magnetosheath plasma through the exosphere of Mercury, down to its surface. The precipitating particle flux and energy are evaluated as a function of the open field line position, according to different solar wind conditions. A target of this study is the evaluation of the sputtered particles from the crust of the planet, and their contribution to the exospheric neutral particle populations. Such estimates are valuable in the frame of a neutral particle analyser to be proposed on board of the ESA/BepiColombo mission.  相似文献   

10.
This paper summarizes a study of the development of a large number of geomagnetic storms in terms of the solar wind—magnetosphere energy coupling function ε, the AE and Dst indices. It is shown that the maximum magnitude of the main phase decrease (¦Dst¦) is determined primarily by the peak value of ε; for ε < 1019 erg s?1, ~1019 erg s?1, 1019–1020 erg s?1, ? 1020 erg s?1, the maximum values of ¦Dst¦ are < 50γ, ~50γ, ~100γ and ? 200γ, respectively. A few examples for different peak values of ε (and thus of ¦Dst¦) are presented and examined in detail. Substorm activity during storms is well controlled by ε.  相似文献   

11.
Observations made by the ASPERA-3 experiment onboard the Mars Express spacecraft found within the martian magnetosphere beams of planetary ions. In the energy (E/q)-time spectrograms these beams are often displayed as dispersive-like, ascending or descending (whether the spacecraft moves away or approach the planet) structures. A linear dependence between energy gained by the beam ions and the altitude from the planet suggests their acceleration in the electric field. The values of the electric field evaluated from ion energization occur close to the typical values of the interplanetary motional electric field. This suggests an effective penetration of the solar wind electric field deep into the martian magnetosphere or generation of large fields within the magnetosphere. Two different classes of events are found. At the nominal solar wind conditions, a ‘penetration’ occurs near the terminator. At the extreme solar wind conditions, the boundary of the induced magnetosphere moves to a more dense upper atmosphere that leads to a strong scavenging of planetary ions from the dayside regions.  相似文献   

12.
The geometry of the open flux area in the polar region is computed by superposing a uniform interplanetary magnetic field (IMF) with various orientation angles to a model of the magnetosphere. It is confirmed that the IMF By component is as important as the Bz component in “opening” the magnetosphere. It is also shown that the computed area of open field lines is remarkably similar to the observed ones which were determined by using the entry of solar electrons. In particular, when the IMF vector is confined in the X-Z-plane and the Bz component has a large positive value, the open area becomes crescent-shaped, coinciding approximately with the cusp region.  相似文献   

13.
A.J. Dessler 《Icarus》1980,44(2):291-295
Theoretical arguments have been presented to the effect that both plasma and energy are supplied to the Jovian magnetosphere primarily from internal sources. If we assume that Io is the source of plasma for the Jovian magnetosphere and that outward flow of plasma from the torus is the means of drawing from the kinetic energy of rotation of Jupiter to drive magnetospheric phenomena, we can obtain a new, independent estimate of the rate of mass injection from Io into the Io plasma torus. We explicitly assume the solar wind supplies neither plasma nor energy to the Jovian magnetosphere in significant amounts. The power expended by the Jovian magnetosphere is supplied by torus plasma falling outward through the corotational-centrifugal-potential field. A lower limit to the rate of mass injection into the torus, which on the average must equal the rate of mass loss from the torus, is therefore derivable if we adopt a value for the power expended to drive the various magnetospheric phenomena. This method yields an injection rate of at least 103 kg/sec, a value in agreement with the results obtained by two other independent methods of estimating mass injection rate. If this injection rate from Io and extraction of energy from Jupiter's kinetic energy of rotation has been maintained over geologic time, then approximately 0.1% of Io's mass (principally in the form of sulfur and oxygen) has been lost to the Jovian magnetosphere, and Jupiter's spin rate has been reduced by less than 0.1%.  相似文献   

14.
With the aid of the Akasofu's energy coupling function between the solar wind and the magnetosphere, we have made in this paper an analysis of about 20 geomagnetic storms recorded at Beijing during the period of years 1966 to 1972. There is a close correlation between the energy coupling function ? and the geomagnetic indices ap and Kp. All in all an empirical formula as ? ～ 1?2 × 1017ap has been found for the geomagnetic storms occurred in a low latitude station, i.e. Beijing of China. Comparisons of the horizontal component Hmax (in γ) and ?(1018 erg s?1) in Table 1 indicate that the development of storm main phase at Beijing depends very much on the ? values thus involved. Also, these are well illustrated for several individual storms as mentioned in the second section of the paper. In concluding this paper some brief discussions are made and included. It is hoped that geomagnetic observations in the middle and low latitudes from our vast country should make further contributions to the study of solar wind-magnetosphere coupling, including the Akasofu's energy coupling function.  相似文献   

15.
The reflection and refraction of MHD waves through an “open” magnetopause (rotational discontinuity) is studied. It is found that most of the incident wave energy can be transmitted through the open magnetopause. A transverse Alfvén wave (or a compressional magnetosonic wave) from the solar wind incident upon the open magnetopause would generally lead to the generation of both the transverse Alfvén and compressional magnetosonic waves in the magnetosphere. Transmission of Alfvén waves in the coplanar rotational discontinuity is studied in detail. The integral power of the Alfvén-wave transfer is found to be proportional to the open magnetic flux of the magnetosphere and is typically ～ 1% of the power of the total electromagnetic energy transfer through the open magnetopause. The transmitted wave power may contribute significantly to the geomagnetic pulsations observed on the ground, especially in the open-field-line region.  相似文献   

16.
The solar wind is a magnetized flowing plasma that intersects the Earth's magnetosphere at a velocity much greater than that of the compressional fast mode wave that is required to deflect that flow. A bow shock forms that alters the properties of the plasma and slows the flow, enabling continued evolution of the properties of the flow on route to its intersection with the magnetopause. Thus the plasma conditions at the magnetopause can be quite unlike those in the solar wind. The boundary between this “magnetosheath” plasma and the magnetospheric plasma is many gyroradii thick and is surrounded by several boundary layers. A very important process occurring at the magnetopause is reconnection whereby there is a topological change in magnetic flux lines so that field lines can connect the solar wind plasma to the terrestrial plasma, enabling the two to mix. This connection has important consequences for momentum transfer from the solar wind to the magnetosphere. The initiation of reconnection appears to be at locations where the magnetic fields on either side of the magnetopause are antiparallel. This condition is equivalent to there being no guide field in the reconnection region, so at the reconnection point there is truly a magnetic neutral or null point. Lastly reconnection can be spatially and temporally varying, causing the region of the magnetopause to be quite dynamic.  相似文献   

17.
This paper is an exploration of the possibility that the large-scale equilibrium of plasma and magnetic fields in the solar corona is a minimum energy state. Support for this conjecture is sought by considering the simplest form of that equilibrium in a dipole solar field, as suggested by the observed structure of the corona at times of minimum solar activity. Approximate, axisymmetric solutions to the MHD equations are constructed to include both a magnetically closed, hydrostatic region and a magnetically open region where plasma flows along field lines in the form of a transonic, thermally-driven wind. Sequences of such solutions are obtained for various degrees of magnetic field opening, and the total energy of each solution is computed, including contributions from both the plasma and magnetic field. It is shown that along a sequence of increasingly closed coronal magnetic field, the total energy curve is a non-monotonic function of the parameter measuring the degree of magnetic field opening, with a minimum occurring at moderate field opening.For reasonable choices of model parameters (coronal temperature, base density, base magnetic field strength, etc.), the morphology of the minimum energy solution resembles the observed quiet, solar minimum corona. The exact location energy minimum along a given sequence depends rather sensitively on some of the adopted parameter values. It is nevertheless argued that the existence of an energy minimum along the sequences of solutions should remain a robust property of more realistic coronal wind models that incorporate the basic characteristics of the equilibrium corona- the presence of both open and closed magnetic regions.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

18.
The recent finding of the solar wind-magnetosphere energy coupling function ε has advanced significantly our understanding of magnetospheric disturbances. It is shown that the magnetosphere-ionosphere coupling system responds somewhat differently to three different input energy flux levels of ε. As ε increases from < 1017 erg s?1 to > 019 erg s?1, typical responses of the magnetosphere-ionosphere coupling system are:ε < 1017 erg s?1: an enhancement of the Sqp, etc,ε ≈ 1018 erg s?1: substorm onset,1018 erg s?1 < ε < 1019 erg s?1f: a typical substorm,ε >1019 erg s?1: an abnormal growth of the ring current belt, resulting in a magnetospheric storm.It is stressed that the magnetospheric substorm results as a direct response of the magnetosphere to a rise and fall of ε above ≈ 1018 erg s?1, so that it is not caused by a sudden conversion of magnetic energy accumulated prior to substorm onset. The variety of the development of the main phase of geomagnetic storms is also primarily controlled by ε.  相似文献   

19.
It is found that from the viewpoint of the magnetic field configuration there are only two types of solar wind: streams with closed field lines (flare-induced streams) and streams with open field lines (M-streams of various velocity and lifetime, and quiet solar wind). We emphasize that in the absence of flare-induced streams the Earth's magnetosphere is, as a rule, circum-flown not by a quiet but by a variably disturbed solar wind—M-streams. An important feature of M-streams is that within a given interplanetary magnetic field sector the sign (+ or −) of the stream magnetic field almost always coincides with that of the sector. These facts lead to the conclusion that M-streams are mainly responsible for the sector structure.  相似文献   

20.
Flapping motions of the magnetotail with an amplitude of several earth radii are studied by analysing the observations made in the near (x = ?25 ~ ?30 RE and the distant (x? ?60 RE) tail regions. It is found that the flapping motions result from fluctuations in the interplanetary magnetic field, especially Alfvénic fluctuations, when the magnitude of the interplanetary magnetic field is larger than ~10 γ and they propagate behind the Earth with the solar wind flow. Flappings tend to be observed in early phases of the magnetospheric substorm, and they have two fundamental modes with periods of ~200 and ~500 sec. In some limited cases a good correspondence with the long period micropulsations (Pc5) in the polar cap region is observed. These observational results are explained by the model in which the Alfvénic fluctuations in the solar wind penetrate into the magnetosphere along the connected interplanetary-magnetospheric field lines. The characteristics of the flapping reveal that the geomagnetic tail is a good resonator for the hydromagnetic disturbances in the solar wind.  相似文献   

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