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1.
The passage of Ulysses through Jupiter's magnetosphere presents a new opportunity to investigate the contribution to the Jovian magnetosphere of ions of atmospheric origin. A determination of the magnetospheric H+/He2+ flux ratio allows an estimate of the relative abundance of ionospheric material in the Jovian magnetosphere. We find that the H+/He2+ flux ratio, measured in the energy/charge range between 0.65 and 60 keV/e, steadily increases from a solar wind level of 25 at the magnetopause to a value of 700 at the point of closest approach, and then steadily decreases whilst approaching the magnetopause on the outbound path. We conclude from this that: (1) there is a significant solar wind component throughout the outer and middle magnetosphere; and (2) a significant fraction of the protons in the middle magnetosphere are of nonsolar origin.  相似文献   

2.
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   

3.
The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on-board the Mars Express spacecraft (MEX) measured penetrating solar wind plasma and escaping/accelerated ionospheric plasma at very low altitudes (250 km) in the dayside subsolar region. This implies a direct exposure of the martian topside atmosphere to solar wind plasma forcing leading to energization of ionospheric plasma. The ion and electron energization and the ion outflow from Mars is surprisingly similar to that over the magnetized Earth. Narrow “monoenergetic” cold ion beams, ion beams with broad energy distributions, sharply peaked electron energy spectra, and bidirectional streaming electrons are particle features also observed near Mars. Energized martian ionospheric ions (O+, O+2, CO+2, etc.) flow in essentially the same direction as the external sheath flow. This suggests that the planetary ion energization couples directly to processes in the magnetosheath/solar wind. On the other hand, the beam-like distribution of the energized plasma implies more indirect energization processes like those near the Earth, i.e., energization in a magnetized environment by waves and/or parallel (to B) electric fields. The general conditions for martian plasma energization are, however, different from those in the Earth's magnetosphere. Mars has a weak intrinsic magnetic field and solar wind plasma may therefore penetrate deep into the dense ionospheric plasma. Local crustal magnetization, discovered by Acuña et al. [Acuña, M.J., Connerey, J., Ness, N., Lin, R., Mitchell, D., Carlsson, C., McFadden, J., Anderson, K., Rème, H., Mazelle, C., Vignes, D., Wasilewski, P., Cloutier, P., 1999. Science 284, 790-793], provide some dayside shielding against the solar wind. On the other hand, multiple magnetic anomalies may also lead to “hot spots” facilitating ionospheric plasma energization. We discuss the ASPERA-3 findings of martian ionospheric ion energization and present evidences for two types of plasma energization processes responsible for the low- and mid-altitude plasma energization near Mars: magnetic field-aligned acceleration by parallel electric fields and plasma energization by low frequency waves.  相似文献   

4.
The Ulysses flyby of Jupiter has permitted the detection of a variety of quasiperiodic magnetospheric phenomena. In this paper, Unified Radio and Plasma Wave Experiment (URAP) observations of quasiperiodic radio bursts are presented. There appear to be two preferred periods of short-term variability in the Jovian magnetosphere, as indicated by two classes of bursts, one with 40 min periodicity, the other with 15 min periodicity. The URAP radio direction determination capability provides clear evidence that the 40 min bursts originate near the southern Jovian magnetic pole, whereas the source location of the 15 min bursts remains uncertain. These bursts may be the signatures of quasiperiodic electron acceleration in the Jovian magnetosphere; however, only the 40 min bursts occur in association with observed electron bursts of similar periodicity. Both classes of bursts show some evidence of solar wind control. In particular, the onset of enhanced 40 min burst activity is well correlated with the arrival of high-velocity solar wind streams at Jupiter, thereby providing a remote monitor of solar wind conditions at Jupiter.  相似文献   

5.
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   

6.
A theory of geomagnetic storms, auroras and associated effects is further developed. It depends on motions in the Earth's exosphere or magnetosphere initiated by a combination of pressure and frictional drag of the solar wind and modified and extended by electric fields and currents in the ionosphere. Motion may be non-divergent, streamline flow opposed only by Lorentz forces in the ionosphere and not propagating to Earth, or divergent, non-streamline motion opposed by Lorentz forces in the Earth. The two types of motion are coupled in the E region where the former is identified with free flow of Hall current and the generation of non-streamline motion. The latter is identified with blockage of Hall current, the creation of a polarization field and hence the generation of streamline motion.

A theory of all components of a geomagnetic storm is given in terms of combinations of these motions, and their distant, ionospheric and earth currents. This includes a new theory of the preliminary reverse part of the DS field and the transition from the sudden commencement to the main phase of the DS field. It is extended to introduce briefly a theory of auroras based mainly on ionospheric drifts caused by the magnetospheric motions.  相似文献   


7.
Numerical calculations for the electric current in the polar ionosphere have been made by assuming some realistic distributions of the electric field and conductivity. Two dynamo actions are taken into account; one of which is induced by ionospheric winds and the other by the solar wind. For the solar wind dynamo action, it is found that the secondary polarization field caused by non-uniform distribution of ionospheric conductivity is much larger than the primary field induced by the solar wind, suggesting its important effect on charged particles in the magnetosphere, and that the irrotational current having a source and sink is of the same order of magnitude as the solenoidal current closing its circuit in the ionosphere. It is also found that the solar wind is, in general, more effective than the ionospheric winds in producing polar current systems such as DP 1 and 2, but in some cases the ionospheric winds have a significant effect on the current distribution.  相似文献   

8.
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   

9.
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   

10.
Observations of the Unified Radio and Plasma Wave (URAP) instrument onboard the Ulysses spacecraft have been used to analyze periods inherent in the Jovian broad-banded kilometric radio emission (bKOM) between 29 and 47 kHz. It is demonstrated, by using power spectrum analysis and linear prediction time filtering that the long-term fluctuations of the bKOM signal are triggered by the solar wind, particularly by the solar wind density, while no association was found with the solar wind velocity. In addition, there seem to be some inherent periodicities in the bKOM events which cannot be fully attributed to the influence of solar wind plasma quantities by these techniques.  相似文献   

11.
DAGLIS  I. A.  AXFORD  W. I.  SARRIS  E. T.  LIVI  S.  WILKEN  B. 《Solar physics》1997,172(1-2):287-296
Particle acceleration is a prominent feature of the geomagnetic storm, which is the prime dynamic process in Geospace – the near-Earth space environment. Magnetic storms have their origin in solar events, which are transient disturbances of the solar atmosphere and radiation that propagates as variations of the solar wind fields and particles through interplanetary space to the Earth's orbit. During magnetic storms, ions of both solar wind origin and terrestrial origin are accelerated and form an energetic ring current in the inner magnetosphere. This current has global geomagnetic effects, which have both physical and technical implications. Recently, it has been shown that large magnetic storms, which exhibit an unusually energized ionospheric plasma component, are closely associated with coronal mass ejections (CMEs). This implies a cause/effect chain connecting solar events through CMEs and the solar wind with the acceleration of terrestrial ion populations which eventually constitute the main source of global geomagnetic disturbances. Here we present spacecraft observations related to storm-time particle acceleration and assess the observations within the framework of causes and effects of solar-terrestrial relationships.  相似文献   

12.
The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause.  相似文献   

13.
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   

14.
The paper presents the relations between different solar and ionospheric parameters. Variation of 5577 line intensity with the variation of solar and ionospheric parametersis also discussed. A study have been made and following important results are obtained:(i) Virtual height ofF layer is decreased exponentially with the increase of solar flare numbers, sunspot number and 10.7 cm solar flux.(ii) Linear relations between critical frequency ofF layer and different solar parameters are obtained.(iii) Empirical relations between ionospheric and solar parameters are established.(iv) It is concluded that airglow intensity will also be affected with the variation of different solar and ionospheric parameters.(v) It is concluded that airglow intensity is mainly affected by 10.7 cm solar flux among different solar parameters and virtual height plays important role than critical frequency ofF layer.  相似文献   

15.
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   

16.
An analysis of ion data from 390 Venus Express, VEX, orbits demonstrates that the flow of solar wind- and ionospheric ions near Venus is characterized by a marked asymmetry. The flow asymmetry of solar wind H+ and ionospheric O+ points steadily in the opposite direction to the planet’s orbital motion, and is most pronounced near the Pole and in the tail/nightside region. The flow asymmetry is consistent with aberration forcing, here defined as lateral forcing induced by the planet’s orbital motion. In addition to solar wind forcing by the radial solar wind expansion, Venus is also subject a lateral/aberration forcing induced by the planet’s orbital motion transverse to the solar wind flow.The ionospheric response to lateral solar wind forcing is analyzed from altitude profiles of the ion density, ion velocity and ion mass-flux. The close connection between decreasing solar wind H+ mass-flux and increasing ionospheric O+ mass-flux, is suggestive of a direct/local solar wind energy and momentum transfer to ionospheric plasma. The bulk O+ ion flow is accelerated to velocities less than 10 km/s inside the dayside/flank Ionopause, and up to 6000 km in the tail. Consequently, the bulk O+ outflow does not escape, but remains near Venus as a fast (km/s) O+ zonal wind in the Venus polar and nightside upper ionosphere. Furthermore, the total O+ mass-flux in the Venus induced magnetosphere, increases steadily downward to a maximum of 2 × 10−14 kg/(m2 s) at ≈400 km altitude, suggesting a downward transport of energy and momentum. The O+, and total mass-flux, decay rapidly below 400 km. With no other plasma mass-flux as replacement, we argue that the reduction of ion mass-flux is caused by ion-neutral drag, a transfer of ion energy and momentum to neutrals, implying that the O+ plasma wind is converted to a neutral (thermosphere) wind at Venus. Incidentally, such a neutral wind would go in the same direction as the Venus atmosphere superrotation.  相似文献   

17.
《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   

18.
This paper presents an empirical model for space-time distribution of the basic parameters of the general circulation of the atmosphere at ionospheric levels (E-and F-regions). The model is based on the results of a physico-statistical analysis of experimental data on the measurement of horizontal ionospheric drifts by close spaced receivers, carried out by the world network of stations in 1958–1970. This model allows an evaluation of the motion parameters at a given latitude, local time, season and the level of solar activity to be made. The limitations and shortcomings of the model are discussed, the results are compared with theoretical and semi-empirical schemes of the atmospheric general circulation, as well as with data of both rocket measurements of wind and drift measurements of plasma by the method of incoherent scatter of radio waves. The physics of the results obtained are stressed. The characteristics of the model are tested and defined using the materials af the coordinated program of drift measurements in the E-region from 8 stations of the northern hemisphere in 1971–1974. The characteristics of motions at higher latitudes and the longitudinal effect are discussed.  相似文献   

19.
The upper thermosphere and F-region ionosphere system at 43°N is modelled for equinox and moderate solar conditions via a series of iterative calculations employing a thermospheric wind model and a one-dimensional ionospheric model which are mutually coupled. Several feedback loops within the system involving F2-layer peak height, F2-layer peak density, zonal wind, meridional wind, and Coriolis force are investigated to better understand the interactive aspect of ionosphere-thermosphere coupling. The interplay of primary importance involves the night-time ascent/descent of the F-layer due to equatorward/poleward neutral winds, the resulting changes in ion drag presented to the meridional and zonal wind fields, and the Coriolis force modification of the ion drag coupling. Wind shear and plasma profile shape are not significantly coupled. For magnetically undisturbed conditions, self-consistent treatment of these effects modifies a non-interactive “control” calculation by 20–35 m s−1 in the wind field. During geomagnetically disturbed periods interactive processes play a more crucial role in determining thermospheric and ionospheric storm responses. Our calculations reveal wind enhancements of up to 100 m s−1 associated with the lifting and negative-phase depletion of the F-region for prolonged magnetic disturbance conditions, the former mechanism accounting for a major portion of the effect.  相似文献   

20.
A time-dependent, nonplanar, two-dimensional magnetohydrodynamic computer model is used to simulate a series, separately examined, of solar flare-generated shock waves and their subsequent disturbances in interplanetary space between the Sun and the Earth's magnetosphere. The ‘canonical’ or ansatz series of shock waves include initial velocities near the Sun over the range 500 to 3500 km s?1. The ambient solar wind, through which they propagate, is taken to be a steady-state homogeneous plasma (that is, independent of heliolongitude) with a representative set of plasma and magnetic field parameters. Complete sets of solar wind plasma and magnetic field parameters are presented and discussed. Particular attention is addressed to the MHD model's ability to address fundamental operational questions vis-à-vis the long-range forecasting of geomagnetic disturbances. These questions are: (i) will a disturbance (such as the present canonical series of solar flare shock waves) produce a magnetospheric and ionospheric disturbance, and, if so, (ii) when will it start, (iii) how severe will it be, and (iv) how long will it last? The model's output is used to compute various solar wind indices of current interest as a demonstration of the model's potential for providing ‘answers’ to these questions.  相似文献   

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