The topside equatorial ionosphere during daytime: Elevated plasma temperatures,the transequatorial O⁺ breeze and the dynamics of minor ions     

G.I. Bailey  R.I. Moffett 《Planetary and Space Science》1979,27(8):1075-1085

Steady-state calculations are performed for the daytime equatorial F2-region and topside ionosphere. Values are calculated of the electron and ion temperatures and the concentrations and field-aligned velocities of the ions O⁺, H⁺ and He⁺. Account is taken of upward $\text{E × B}$ drift, a summer-winter horizontal neutral air wind and heating of the electron gas by thermalization of fast photoelectrons.The calculated plasma temperatures are in accord with experiment: at the equator there is an isothermal region from about 400–550 km altitude, with temperatures of about 2400 K around 800 km altitude. The transequatorial O⁺ breeze flux from summer to winter in the topside ionosphere is not greatly affected by the elevated plasma temperatures. The field-aligned velocities of H⁺ and He⁺ depend strongly on the O⁺ field-aligned velocity and on the presence of large temperature gradients. For the minor ions, ion-ion drag with O⁺ cannot be neglected for the topside ionosphere.  相似文献   

Effects of photoelectron heating and interhemisphere transport on day-time plasma temperatures at low latitudes     

G.J. Bailey  R.J. Moffett  W.E. Swartz 《Planetary and Space Science》1975,23(4):599-610

The thermal balance of the plasma in the day-time equatorial F region is examined. Steady-state solutions of electron and ion temperatures are obtained, assuming the ions are O⁺ and H⁺. The theoretical concentrations of O⁺ and H⁺ and the field-aligned velocity were obtained following Moffett and Hanson (1973), while theoretical photoelectron heating rates of the electron gas were taken from Swartz et al. (1975).The results demonstrate the gross features in the electron and ion temperatures as observed at the Jicamarca Observatory and in the ion temperatures observed on the OGO-6 satellite. The rapid increase in electron temperature above 500 km at the magnetic equator is due to heating by photoelectrons created at higher latitudes and travelling up along the field lines. The rapid increase in ion temperature is due to good thermal contact with the electrons rather than the neutrals. It is shown that field-aligned interhemispheric thermal plasma flows appreciably affect these temperatures, and that, with a net plasma flow from the summer hemisphere to the winter hemisphere, the temperatures are higher in the winter hemisphere. These effects are related to the character of the ion temperature minimum observed by OGO-6 near the magnetic equator.  相似文献   

Thermal balance of the mid-latitude F2-region at night     

G.J. Bailey  R.I. Footitt  R.I. Moffett 《Planetary and Space Science》1979,27(8):1063-1073

The thermal balance of the plasma in the night-time mid-latitude F2-region is examined using solutions of the steady-state O⁺ and electron heat balance equations. The required concentrations and field-aligned velocities are obtained from a simultaneous solution of the time-dependent O⁺ continuity and momentum equations.The results demonstrate the systematic trend for the O⁺ temperature to be 10–20 K greater than the electron temperature during the night at around 300 km, as observed at St. Santin by Bauer and Mazaudier. It is shown that frictional heating between the O⁺ and neutral gases is the cause of the O⁺ temperature being greater than the electron temperature; the greater the importance of frictional heating in the thermal balance the greater is the difference in the O⁺ and electron temperatures. A study is made of the roles played in the thermal balance of the plasma by the thermal conductivity of the O⁺ and electron gases; collisional heat transfer between O⁺ electrons and neutrals; frictional heating between the O⁺ and neutral gases; and advection and convection due to field-aligned O⁺ and electron motions. The results of the study show that, at around 300 km, electron cooling by excitation of the fine structure of the ground state of atomic oxygen plays a major role in the thermal balance of the electrons and, since the temperature of the ions is little affected by this electron cooling process, in determining the difference between the ion and electron temperatures.  相似文献   

Ion temperature troughs induced by a meridional neutral air wind in the night-time equatorial topside ionosphere     

G.J. Bailey  R.A. Heelis 《Planetary and Space Science》1980,28(9):895-906

A mathematical model has been developed to calculate consistent values for the O⁺ and H⁺ concentrations and field-aligned velocities and for the O⁺, H⁺ and electron temperatures in the night-time equatorial topside ionosphere. Using the results of the model calculations a study is made to establish the ability of F-region neutral air winds to produce observed ion temperature distributions and to investigate the characteristics of ion temperature troughs as functions of altitude, latitude and ionospheric composition. Solar activity conditions that give exospheric neutral gas temperatures 600 K, 800 K and 1000 K are considered.It is shown that the O⁺-H⁺ transition height represents an altitude limit above which ion cooling due to adiabatic expansion of the plasma is extremely small. The neutral atmosphere imposes a lower altitude limit since the neutral atmosphere quenches any ion cooling which field-aligned transport tends to produce. The northern and southern edges of the ion temperature troughs are shown to be restricted to a range of dip latitudes, the limiting dip latitudes being determined by the magnetic field line geometry and by the functional form of the F-region neutral air wind velocity. Both these parameters considerably influence the interaction between the neutral air and the plasma within magnetic flux tubes.  相似文献   

Relative flow of H⁺ and O⁺ ions in the topside ionosphere at mid-latitudes     

G.I. Bailey  R.J. Moffett  J.A. Murphy 《Planetary and Space Science》1977,25(10):967-972

Theoretical results on the daily variation of O⁺ and H⁺ field-aligned velocities in the topside ionosphere are presented. The results are for an L = 3 magnetic field tube under sunspot minimum conditions at equinox. They come from calculations of time-dependent O⁺ and H⁺ continuity and momentum balance in a magnetic field tube which extends from the lower F2 region to the equatorial plane (Murphy et al., 1976).There are occasions when ion counterstreaming occurs, with the O⁺ velocity upward and H⁺ velocity downward. The conditions causing this counterstreaming are described: the H⁺ layer is descending whilst O⁺ is supplied from below either to increase the O⁺ concentration at fixed heights or to replace O⁺ ions lost by charge exchange with neutral H. It is suggested that the results of observations at Arecibo by Vickrey et al. (1976) of O⁺ and H⁺ concentrations and counterstreaming velocities are significantly affected by $\text{E}\text{×}\text{B}$ drift.  相似文献   

A theoretical study of downward H⁺ field-aligned velocities at mid-latitudes     

I.A. Murphy  A.A. Naghmoosh 《Planetary and Space Science》1979,27(3):297-302

This paper examines the magnitude of downward H⁺ field-aligned velocities at mid-latitudes. For the isothermal, collisionless, steady-state case an analytical form is derived for the critical temperature, below which the plasma temperature must lie for there to be a possibility of supersonic H⁺ flow. Some simple equations are presented which yield velocity profiles and an aid to the understanding of energy distribution in the H⁺ gas. Very little gravitational potential energy is converted to kinetic energy. For the general case the situation is far more complicated, but we note in particular the importance of the O⁺ contribution to the electrostatic field. For the simpler case the flow is always subsonic regardless of the plasma temperature and it appears unlikely that supersonic flow will occur in the more general case.  相似文献   

On the diurnal and seasonal variations of H⁺, He⁺, N⁺, O⁺, and Ne at 1400-km altitude     

W. Köhnlein 《Planetary and Space Science》1981,29(7):775-782

The diurnal and seasonal variations of H⁺, He⁺, N⁺, O⁺ and Ne are analyzed at 1400-km altitude. Using longitudinally averaged observations of ISIS-2 (April 1971 to December 1972), the ion and electron densities are decomposed via spherical harmonics and Fourier series into time-independent, seasonal and diurnal terms. The time-independent terms of H⁺ and He⁺ show a plateauor trough-like structure at medium to low latitudes and a strong decrease towards the poles; N⁺ and O⁺, on the other hand, yield an almost inverse picture with a density increase at high latitudes. All constituents, except He⁺, show at polar latitudes an enhancement during local summer conditions and a depletion during local winter conditions; He⁺, however, exhibits a winter bulge and a density minimum during local summer. The diurnal variations are strongly latitude dependent; while the amplitudes (relative) of H⁺, He⁺, and Ne are rather small, the heavier ions N⁺ and O⁺ show a deep minimum early in the morning and a high but flat maximum during daytime.  相似文献   

Geomagnetic storm effects on the thermosphere and the ionosphere revealed by in situ measurements from OGO 6     

K. Marubashi  C.A. Reber  H.A. Taylor 《Planetary and Space Science》1976,24(11):1031-1041

The temporal response of ion and neutral densities to a geomagnetic storm has been investigated on a global scale with data from consecutive orbits of OGO-6 (>400km) for 4 days covering both magnetically quiet and disturbed conditions. The first response of the neutral atmosphere to the storm takes place in the H and He densities which start to decrease near the time of the storm sudden commencement. The maximum decreases in H and He were more than 40% of the normal density at high latitudes. A subsequent increase in O and N₂ densities occurs about 8 hours later than the change in H and He densities, while the relative O and N₂ density changes indicate a depletion of atomic oxygen in the lower thermosphere by more than a factor of two. The overall features of the change in the neutral atmosphere, especially the patterns of change for individual species, strongly support the physical picture that energy is deposited primarily at high latitudes during the storm, and the thermosphere structure changes through (1) heating of the lower thermosphere and (2) generation of large scale circulation in the atmosphere with upwelling at high latitudes and subsidence at the equator. The storm-time response of H⁺ occurs in two distinct regions separated by the low latitude boundary of the light ion trough. While on the poleward side of the boundary the H⁺ density decreases in a similar manner to the decrease in H density, on the equatorward side of the boundary the H⁺ decrease occurs about half a day later. It is shown that the decrease of H⁺ density is principally caused by the decrease in H density for both regions. The difference in H⁺ response between the two regions is interpreted as the difference in H⁺ dynamics outside and inside the plasmasphere. The O⁺ density shows an increase, the pattern of which is rather similar to that for O. Two possibilities for explaining the observed change in O⁺ density are suggested. One attributes the observed increase in O⁺ density to an increase in the plasma temperature during the storm. The other possibility is that the increase in the production rate of O⁺ due to an increase in O density exceeds the increase in the loss rate of O⁺ due to an increase in N₂ density, especially around the time of sunrise. Hence the change in O⁺ density in the F-region may actually be controlled by the change in O density.  相似文献   

Laboratory investigation of the ionospheric O₂⁺(X²π_g, v ≠ 0) reaction with NO     

W. Lindinger  E.E. Ferguson 《Planetary and Space Science》1983,31(10):1181-1182

Laboratory measurements of the reaction of O₂⁺ with NO from thermal energy to 0.6 eV in an Ar buffered flow drift tube agree with similar measurements made earlier in the same drift tube with He buffer. Since the O₂⁺ ions are substantially vibrationally excited in Ar and not in He it follows that the reaction is not enhanced by vibrational excitation of the O₂⁺.  相似文献   

The effect of a meridional E × B drift on the thermal plasma at L = 1.4     

G.J. Bailey 《Planetary and Space Science》1983,31(4):389-409

A fully time dependent mathematical model of the thermal plasma at L = 1.4 is described. In the mathematical model account is taken of a quiet-time E × B drift in the meridional plane. Atmospheric conditions appropriate to equinox at sunspot minimum and at sunspot maximum are considered. Results of the model calculations are presented. Emphasis is placed on the effects on the thermal plasma of a quiet-time E × B drift in the meridional plane. A comparison of the model calculations which include an E × B drift with those in which there is no E × B drift shows than an E × B drift significantly affects the plasma concentration and temperature distributions during the day at both sunspot minimum and sunspot maximum; the effects at night are very small. An upward E × B drift during the day increases both NmF2 and hmF2 and decreases the plasma temperature. The decrease in plasma temperature is due primarily to the increase in plasma concentration. It is more pronounced in the electron temperature than in the ion temperature and it varies considerably with altitude, time and atmospheric conditions. The changes in plasma concentration and temperature brought about by an E × B drift also change the O⁺-H⁺ transition height and the O⁺ and H⁺ tube contents. For the E × B drifts considered the O⁺-H⁺ transition height is raised during the morning and lowered during the afternoon. The changes in O⁺ tube content roughly follow the changes in NmF2. The changes in H⁺ tube content, however, are small since the H⁺ tube content is controlled by the H⁺ concentration at the higher altitudes of the tube of plasma and these concentration values are only slightly affected by the E × B drifts considered.  相似文献   

The topside ionosphere above Arecibo at equinox during sunspot maximum     

G.J. Bailey 《Planetary and Space Science》1980,28(1):47-59

The coupled time-dependent O⁺ and H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved simultaneously within the L = 1.4 (Arecibo) magnetic flux tube between an altitude of 120 km and the equatorial plane. The results of the calculations are used in a study of the topside ionosphere above Arecibo at equinox during sunspot maximum. Magnetically quiet conditions are assumed.The results of the calculations show that the L = 1.4 magnetic flux tube becomes saturated from an arbitrary state within 2–3 days. During the day the ion content of the magnetic flux tube consists mainly of O⁺ whereas O⁺ and H⁺ are both important during the night. There is an altitude region in the topside ionosphere during the day where ion-counterstreaming occurs with H⁺ flowing downward and O⁺ flowing upward. The conditions causing this ion-counterstreaming are discussed. There is a net chemical gain of H⁺ at the higher altitudes. This H⁺ diffuses both upwards and downwards whilst O⁺ diffuses upwards from its solar e.u.v. production source which is most important at the lower altitudes. During the night the calculated O⁺ and H⁺ temperatures are very nearly equal whereas during the day there are occasions when the H⁺ temperature exceeds the O⁺ temperature by about 300 K.  相似文献   

Induced proton flow in a collapsing post-sunset ionosphere and protonosphere     

J.A. Murphy  R.J. Moffett 《Planetary and Space Science》1978,26(3):281-288

The effect of the onset of post-sunset conditions on thermal proton flow is examined for mid-latitudes by numerical solution of the equations of continuity, momentum and energy balance for H⁺ and O⁺. Results are calculated for a dipole magnetic field tube situated at L = 4 and acceleration terms are included in the momentum equations. Proton flow into the ionosphere results from decay of the F2-layer. Changes in temperatures and temperature gradients following sunset may not enhance the H⁺ flow. Under extreme conditions the H⁺ flow remains subsonic. It seems unlikely that an interhemispheric flux of protons can directly maintain the nighttime F2-layer.  相似文献   

Temperatures in the polar wind     

G.J. Bailey  R.J. Moffett 《Planetary and Space Science》1974,22(8):1193-1199

The thermal structure of the plasma in the polar wind is examined. With O⁺H⁺ Joule heating as the mechanism for heating the plasma, it is found that O⁺ and H⁺ temperatures are significantly greater than the electron temperature. With the adopted input parameters the O⁺H⁺ temperature difference is relatively small.  相似文献   

Effect of diffusion-thermal processes on the high-latitude topside ionosphere     

R.W. Schunk  W.J. Raitt  A.F. Nagy 《Planetary and Space Science》1978,26(2):189-191

We have studied the extent to which diffusion-thermal heat flow affects H⁺ temperatures in the high-latitude topside ionosphere. Such a heat flow occurs whenever there are H⁺?O⁺ relative drifts. From our study we have found that at high-latitudes, where H⁺ flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H⁺ temperatures by 500–600 K at altitudes above about 900 km.  相似文献   

Ionospheric composition in SAR-arcs     

W.J. Raitt  R.W. Schunk  P.M. Banks 《Planetary and Space Science》1976,24(2):105-114

The high electron temperatures existing within SAR-arcs can result in enhanced vibrational excitation of atmospheric N₂ molecules and, as a consequence, increase the rate coefficient of the reaction, O⁺ + N₂ → NO⁺ + N. This results in a change in the relative abundance of O⁺ and NO⁺+ in the SAR-arc region compared with that in the undisturbed ionosphere. Theoretical ion density profiles were computed by a triple ion analysis solving the mass, momentum and energy equations for O⁺, NO⁺ and O⁺₂ ions self-consistently. Although the electron temperature dependence of the recombination rate of NO⁺ is not well known, the results show that for a range of expected recombination rates NO⁺ still remains the dominant ion up to ca. 320 km at night within a bright SAR-arc. Studies were also made of the relative importance of a downward O⁺ flux and an upward ion drift in maintaining the F-region under SAR-arc conditions. It was found that the upward drift caused a marked increase in the NO⁺/O⁺ transition altitude as high as 460 km at night. However, for typical drift speeds up to 50 m sec^?1 the peak electron density was lower than experimental observations. The effect of a large, short-duration perpendicular electric field on the SAR-arc ion and electron density profiles was found to be small. In all cases considered the magnitude of the enhanced NO⁺ density as a result of vibrationally excited N₂ molecules was sufficient to prevent the electron density within the night-time SAR-arc from becoming vanishingly small.  相似文献   

Observations of outflowing ion beams on auroral field lines at altitudes of many earth radii     

R. Lunpin  B. Hultqvist  E. Dubinin  A. Zackarov  N. Pissarenko 《Planetary and Space Science》1982,30(7):715-726

The composition, energy and angular characteristics of upward flowing ionospheric ions at altitudes greater than ～ 20,000 km have been studied by means of the PROGNOZ-7 ion composition experiment. Very narrow beams, having widths corresponding to a mirroring altitude of the order a few thousand kilometers or less, may be found up to altitudes exceeding 30,000 km on the nightside. At much higher altitudes and in regions connected to the dayside/flank boundary layer and plasma mantle, the beams are much broader than expected from adiabatic particle motions from an ionospheric source/acceleration region, suggesting that pitch angle scattering or transverse acceleration processes are present there. Considerable mass dispersion effects have also been observed in some upward flowing ionospheric ion beams. The peak energy for the O⁺ ions may differ by several keV compared to that for the H⁺ ions in one and the same ion beam at altitudes above ～ 20,000 km. The O⁺ ions in these beams have gained considerably more energy than H⁺ in the acceleration process. Many examples with a much higher O⁺ than H⁺ content in the beam have been observed. Possible mechanisms giving rise to the observed effects are discussed, one being several kV of potential drop below the neutral H, O-crossover altitude (500–1500 km). At altitudes where the upflowing ionospheric ions are intermixed with magnetosheath ions, mass dispersion effects are also observed. This dispersion often appears to be the result of a velocity filtering effect caused by the dawn-dusk electric field (earthward convection).  相似文献   

Ion flow and momentum transfer in the Venus plasma environment     

R. Lundin  S. Barabash  J.-A. Sauvaud  H. Perez-de-Tejada 《Icarus》2011,215(2):751-758

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   

Ionospheric and magnetospheric “plasmapauses”     

Joseph M. Grebowsky  I.H. Hoffman  Nelson C. Maynard 《Planetary and Space Science》1978,26(7):651-660

During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of ～5.2 R_e traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2.0–5.4. The locations of the Explorer 45 plasmapause crossings (determined by the saturation of the d.c. electric field double probe) during this month were compared to the latitudinal decreases of the H⁺ density observed on ISIS 2 (by the magnetic ion mass spectrometer) near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Hence, the abruptly decreasing H⁺ density on the low latitude side of the ionospheric trough is not a near earth signature of the equatorial plasmapause. Vertical flows of the H⁺ ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 km s^?1 near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H⁺ trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause. The existence of upward accelerated H⁺ flows to possibly supersonic speeds during the refilling of magnetic flux tubes in the outer plasmasphere could produce an equatorial plasmapause whose field lines map into the ionosphere at latitudes which are poleward of the H⁺ density decrease.  相似文献   

A model of the terrestrial ionosphere in the altitude interval 50–4000 km I. Atomic ions (H+, He+, N+, O+)     

W. Köhnlein 《Earth, Moon, and Planets》1989,45(1):53-100

An empirical model of atomic ion densities (H⁺, He⁺, N⁺, O⁺) is presented up to 4000 km altitude as a function of time (diurnal, annual), space (position, altitude) and solar flux (F10.7) — using observations of satellites (AE-B, AE-C, AE-D, AE-E, ISIS-2, OGO-6) and rockets during quiet geophysical conditions (K _p 3). The numerical treatment is based upon harmonic functions for the horizontal pattern and cubic splines for the vertical structure.The ion densities increase with increasing height up to a maximum (depending roughly on the ion mass) and decrease beyond that with increasing altitude. Above 200 km, O⁺ is the main ionic constituent being replaced at approximately 800 km (depending on latitude, local time, etc.) by H⁺. Around polar regions the light ions, H⁺ and He⁺, are depleted (polar wind) and the heavier ones enhanced. During local summer conditions the ion densities increase around polar latitudes and correspondingly decrease during local winter, except He⁺ which reflects the opposite pattern. Diurnal variations are intrinsically coupled to the individual plasma layers: N⁺ and O⁺ peak, in general, during daytime, while the amplitudes and phases of H⁺ and He⁺ change strongly with altitude and latitude. Earth, Moon and Planets Review article.  相似文献   

Helium ion outflow from the terrestrial ionosphere     

W.J. Raitt  R.W. Schunk  P.M. Banks 《Planetary and Space Science》1978,26(3):255-268

Extensive calculations have been made of the behaviour of He⁺ for situations where ion outflow occurs from the topside ionosphere. For these circumstances, steady state solutions for the He⁺ continuity, momentum and energy equations have been obtained self-consistently, yielding density, velocity and temperature profiles of He⁺ from 200 to 2000 km altitude. To model the high latitude topside ionosphere, a range of background H⁺O⁺ ionospheres was considered with variations in the H⁺ outflow velocity, the presence of a perpendicular electric field and different peak O⁺ densities. In addition, the atmospheric density of neutral helium was chosen to model typical observed winter and summer densities. From our studies we have found that: (a) The outflowing He⁺ has density profiles of similar shape to those of H⁺, for basically different reasons; (b) The effect of the perpendicular electric field differs considerably for H⁺ and He⁺. This difference stems from the fact that an electric field acts to alter significantly the O⁺ density at high altitudes and this, in turn, changes the H⁺ escape flux through the O⁺+H charge exchange reaction. A similar situation does not occur for He⁺ and therefore the He⁺ escape flux exhibits a negligibly small change with electric field; (c) The fractional heating of He⁺ due to the He⁺O⁺ relative flow is not as effective in heating He⁺ as the H⁺O⁺ relative flow is in heating H⁺; (d) During magnetospheric disturbances when the N₂ density at the altitude of the He⁺ peak (600 km) can increase by a factor as large as 50, the He⁺ peak density decreases only by approximately a factor of 2; and (e) The He⁺ escape flux over the winter pole is approximately a factor of 20 greater than the He⁺ escape flux over the summer pole. Consequently, on high latitude closed field lines there could be an interhemispheric He⁺ flux from winter to summer.  相似文献