Interhemispheric flow of thermal plasma in a closed magnetic flux tube at mid-latitudes under sunspot minimum conditions     

G.J. Bailey  R.J. Moffett  J.A. Murphy 《Planetary and Space Science》1978,26(8):753-765

The coupled H⁺ and O⁺ time-dependent continuity and momentum equations are solved within a region of the L = 3 magnetic flux tube lying between (and including) the F2-layers of conjugate hemispheres. The method of solution is an extended and modified version of the Murphy et al. (1976) method. The model is used to study the coupling between the F2-layers of conjugate hemispheres during magnetically quiet periods.The results of the calculations strongly indicate that the protonosphere acts as a reservoir, with variable H⁺ content, which prevents direct coupling between the F2-layers of conjugate hemispheres. However there is generally a significant interhemispheric flow of plasma. This flow is caused by conditions in the summer and winter topside ionospheres and it maintains continuity in the plasma concentration within the protonosphere. There are times when the direction of flow is from the winter hemisphere to the summer hemisphere. It is suggested that maintenance of the winter F2-layer at night is not assisted directly by the F2-layer of the conjugate summer hemisphere.It is shown that during the first few days of protonosphere replenishment after a magnetic storm there is an upflow of H⁺ in the topside ionosphere at all times in the summer hemisphere. There is also an upflow of H⁺ during the daytime in both hemispheres. A comparison with the results obtained when the interhemispheric H⁺ flux is held permanently at zero shows that both F2-layers are little affected by the interhemispheric H⁺ flux. Nevertheless both F2-layers are affected by the H⁺ tube content of the protonosphere. When the H⁺ flux at 1000 km in one hemisphere is much greater than the H⁺ flux at 1000 km in the conjugate hemisphere, there is a corresponding signature in the interhemispheric H⁺ flux.The results suggest that there is insufficient time between magnetic storms for complete replenishment of the protonosphere to occur.  相似文献   

Mid-latitude electron content modelling: The role of interhemispheric coupling     

G.C. Sethia  G.J. Bailey  R.J. Moffett  J.K. Hargreaves 《Planetary and Space Science》1985,33(3):321-332

A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O⁺, H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content (N_p). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content (N_T) and F2 region peak electron density (N_max) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on N_T of the neutral air wind are not much different in winter from those in summer.  相似文献   

The influence of convection electric fields on thermal proton outflow from the ionosphere     

W.J. Raitt  R.W. Schunk  P.M. Banks 《Planetary and Space Science》1977,25(3):291-301

The continuity, momentum and energy hydrodynamic equations for an O⁺-H⁺ ionosphere have been solved self-consistently for steady state conditions when a perpendicular (convection) electric field is present. Comparison of the H⁺ temperature profiles obtained with and without the electric field show that the effect of the electric field is to enhance the H⁺ temperature at high altitudes from about 3600 to 6400 K. Due to ion heating by the electric field, there is a net reduction of O⁺ in the F2-region as compared with the case of a non-convecting ionosphere. When the reduction of O⁺ is neglected, the electric field acts to increase the H⁺ outward flux from 8.3 × 10⁷ to 2.7 × 10⁸ cm^?2 sec^?1 for average ionospheric conditions. However, when the reduction of O⁺ is included, there is a net reduction in the outward H⁺ flux. Nevertheless, the convection electric field still results in an increase in the rate of depletion of the F-re m^?1 electric field.  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   

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   

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   

The role of ion-molecule reactions in the conversion of N₂O₅ to HNO₃ in the stratosphere     

H. Böhringer  D.W. Fahey  F.C. Fehsenfeld  E.E. Ferguson 《Planetary and Space Science》1983,31(2):185-191

We have investigated the role of several ion-molecule reactions in the conversion of N₂O₅ to HNO₃. In the proposed conversion, an N₂O₅ molecule would react with an H₂O molecule clustered to an inert ion to produce two HNO₃ molecules. Subsequent clustering of an H₂O molecule to the inert ion would make the reaction catalytic. If such an ion-catalysed conversion of N₂O₅ to HNO₃ occurs, it would probably play a role in the stratospheric chemistry at high latitudes in winter. In this paper we present reaction rate constant measurements made in a flowing afterglow apparatus for hydrated H₃O⁺, H⁺(CH₃CN)_m (m = 1, 2, 3), and several negative ions reacting with N₂O₅. Slow rate constants were found for these ions for hydration levels that are predominant in the stratosphere. With the known stratospheric ion density, these slow rate constants preclude significant N₂O₅ conversion by ion-molecule reactions.  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   

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   

Theoretical ion densities in the lower ionosphere     

R.W. Schunk  J.C.G. Walker 《Planetary and Space Science》1973,21(11):1875-1896

We have solved the coupled momentum and continuity equations for NO⁺, O₂⁺, and O⁺ions in the E- and F-regions of the ionosphere. This theoretical model has enabled us to examine the relative importance of various processes that affect molecular ion densities. We find that transport processes are not important during the day; the molecular ions are in chemical equilibrium at all altitudes. At night, however, both diffusion and vertical drifts induced by winds or electric fields are important in determining molecular ion densities below about 200 km. Molecular ion densities are insensitive to the O⁺ density distribution and so are little affected by decay of the nocturnal F-region or by processes, such as a protonospheric flux, that retard this decay. The O⁺ density profile, on the other hand, is insensitive to molecular ion densities, although the O⁺ diffusion equation is formally coupled to molecular ion densities by the polarization electrostatic field. Nitric oxide plays an important role in determining the NO⁺ to O₂⁺ ratio in the E-region, particularly at night. Nocturnal sources of ionization are required to maintain the E-region through the night. Vertical velocities induced by expansion and contraction of the neutral atmosphere are too small to affect ion densities at any altitude.  相似文献   

Ion composition in the E- and lower F- region above kiruna during sunset and sunrise     

E. Kopp  P. Eberhardt  J. Geiss 《Planetary and Space Science》1973,21(2):227-238

A magnetic type mass spectrometer has been flown on two ESRO sounding rockets from ESRANGE (Kiruna 68°N) on February 25 and 26, 1970. The first launch was at sunset (16:33 UT) and the second the next morning, during sunrise (04:47 UT). For both flights the solar zenith angle was approximately 98°. The instrument was measuring simultaneously the neutral gas and positive ion composition and the total ion density. In this paper the results of the ion composition measurements are presented. For both flights the main ion constituents measured between approximately 110–220 km were O⁺, NO⁺ and O₂⁺. Only at sunset were N⁺ and N₂⁺ detected above 200 km. In spite of the identical solar UV-radiation, pronounced sunset/sunrise variations in the positive ion composition were found. The total ion densities at sunrise were between 5×10³ and 5 × 10⁴ ions cm^?3 and therefore too high to be explained without a night-time ionization by precipitated particles. At sunrise the NO⁺ and O₂⁺ profiles show a correlated wavelike structure with three pronounced almost equally spaced layers in the E-region. Only the highest layer is present in the O⁺ profile. Locally enhanced field aligned ionization originated by particle precipitation and an E × B instability are the most likely source for this structure. In the E- and lower F-regions the $\text{NO}{}^{\mathrm{+}}\text{O}{}_2{}^{\mathrm{+}}$ ration increased overnight from values around 7 at sunset to 15 at sunrise, correlated with an increase of the local magnetic activity index K from 0⁺ to 2°. This could be explained if the NO density and magnetic activity are correlated.  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   

Ion and neutral composition changes in the thermospheric region during magnetic storms     

S. Chandra 《Planetary and Space Science》1971

The structural differences of the ion and neutral composition in the thermospheric region are studied by solving a system of basic ionospheric and atmospheric equations. The study shows that the compositional changes during a magnetic storm arise largely as a result of changes in the neutral composition at the turbopause. A decrease in [O]/[N₂] in the lower atmosphere triggers a complex chain of events which results in an increase of the neutral gas temperature, depletion of the O⁺ layer and enhancement of NO⁺. The relative changes in these layers occasionally produce a sequence of electron density profiles giving rise to the so-called G condition. It is shown that, compared to the neutral atmosphere, the ionosphere is much more sensitive to the changes in [O]/[N₂] in the lower thernaospheric region. Since the ionospheric parameters can be measured much more accurately than the atmospheric parameters, it is argued that they should form an integral part of the observational data required to construct the atmospheric models.  相似文献   

Temperature and solar zenith angle control of D-region positive ion chemistry     

Jeffrey M. Forbes 《Planetary and Space Science》1982,30(10):1065-1072

A numerical model is utilized to investigate the temperature (T) and solar zenith angle (χ) control of D-region positive ion chemistry between 75 and 90 km. It is assumed that NO^? is the precursor ion in a chain which involves three-body formation of the intermediary cluster ions NO⁺(H₂O)_m?1(X) (m = 1–3), where X can be N₂,O₂, H₂O, or CO₂, switching reactions which convert these weakly bound clusters to hydrates of NO⁺ and reaction of the third hydrate of NO⁺ with H₂O to initiate the chain to form H⁺(H₂O)_n (n = 1–7). Zonal mean and tidal temperatures from rocket observations and theory are synthesized to obtain the best available estimate of mean latitudinal, seasonal and local time variations of temperature in this height region. Relative compositions of NO⁺(H₂O)_m and H⁺(H₂O)_n are found to vary widely over the complete range of realistic conditions; however, the relative ion populations are entirely explicable in terms of the effects of χ and T on the relative life-times of the intermediary ion clusters with respect to recombination, switching and thermal decomposition. For instance, as χ increases (and electron production decreases) beyond 60° for a given temperature, the recombination times of the intermediate ion cluster species lengthen with respect to the formation time of the H⁺ water clusters, causing the relative H⁺ water cluster population to increase and thus raise the level where the cluster ion and NO⁺ concentrations are equal from about 85 km (normal midday) to 90 km. For a given χ the concentrations of NO⁺H₂O and H⁺(H₂O)₄ increase (decrease) for temperatures less than (greater than) 190 and 205 K, respectively. The transition occurs when the temperature becomes sufficiently high that the lifetimes of intermediary ion clusters with respect to thermal decomposition become less than their lifetimes with respect to H₂O switching (which ultimately leads to the third hydrate of NO⁺ and entry into the water chain). At this point, the formation time of H⁺(H₂O)₄ becomes long compared with its lifetime with respect to thermal decomposition and its relative concentration decreases also. Implications of these results with respect to studies of the D-region are discussed.  相似文献   

Collisional vibrational quenching of O2+(v) and other molecular ions in planetary atmospheres     

H. Böhringer  M. Durup-Ferguson  E.E. Ferguson  D.W. Fahey 《Planetary and Space Science》1983,31(4):483-487

New experimental techniques have yielded several thermal energy vibrational quenching rate constants for O₂⁺(v). Rates for quenching of O₂⁺(v = 1) by O₂, N₂, Ar, CO₂, H₂, and CH₄ are 3(?10), 2(?12), 1(?12), 1(?10), 2.5(?12), and 6(?10) cm³s^?1 at 300 K. The quenching is somewhat faster for O₂⁺(v = 2). The triatomic ions CO₂⁺, NO₂⁺, N₂O⁺, SO₂⁺, and H₂O⁺ are all vibrationally deexcited with an efficiency greater than 10^?3 in Ar or Ne collisions. A theoretical rationalization of the experimental results leads to the prediction that vibrational quenching in planetary atmospheres will generally be efficient, k > 1(?12) cm³s^?1 for almost all ion and neutral gas pairs.  相似文献   

Electronic Sputtering Analysis of Astrophysical Ices     

L. S. Farenzena  P. Iza  R. Martinez  F. A. Fernandez-Lima  E. Seperuelo Duarte  G. S. Faraudo  C. R. Ponciano  M. G. P. Homem  A. Naves de Brito  K. Wien  E. F. da Silveira 《Earth, Moon, and Planets》2005,97(3-4):311-329

Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. ²⁵²Cf fission fragments projectiles were used to induce ejection of ionized material from H₂O, CO₂, CO, NH₃, N₂, O₂ and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure X_nR^±, where X is the neutral ice molecule and R^± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H₂O)_nH₃O⁺ and the negative ion spectrum by the series (H₂O)_nOH⁻ and (H₂O)_nO⁻. The positive ion CO₂ ice spectrum is characterized by R⁺ = C⁺, O⁺, CO⁺, O₂⁺ or CO₂⁺ and the negative one by R⁻ = CO₃⁻. The dominant series for ammonia ice correspond to R⁺ = NH₄⁺ and to R⁻ = NH₂⁻. The oxygen series are better described by (O₃)_nO_m⁺ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N₂ ice: (N₂)_nN₂⁺ and (N₂)_nN⁺. For argon positive secondary ions, only the (Ar)_nAr⁺ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation.  相似文献   

A theoretical evaluation of the lunar tidal variations in the ionospheric F2-layer     

M.F.K. Abur-Robb  E. Dunford 《Planetary and Space Science》1975,23(7):1071-1080

Time-varying solutions of the full continuity equation for electrons in the F2-region are obtained. The effects of production, loss, diffusion and electrodynamic ‘E × B’ drift are taken into account. The ‘E × B’ drift term consists of a solar and a lunar component. The solar component of drift is assumed diurnal with 14.6m/sec maximum upward speed at mid-day. The lunar component is assumed sinusoidal with period of half lunar day and amplitude one tenth of the solar drift; the phase is assumed to remain constant in lunar time, in accordance with Chapman's phase law.The results show that the lunar variations in the F2-region are markedly dependent on solar time and latitude. It is also shown that the average semi-diurnal lunar variations in N_mF2 and h_mF2 at any particular lunar time are almost opposite in phase to each other (i.e. out of phase by 6 hr) in the magnetic equatorial zone, and out of phase by 2 hr at moderate latitudes. The phase of δh_mF2 is 10 hr at low latitudes and 9 hr at moderate latitudes. The phase of δN_mF2 is 4 hr at low latitudes and 11 lunar hr at moderate latitudes.The results also show that the phase of the lunar semi-monthly oscillations in N_mF2 undergoes a rapid shift of about 5 lunar hr in going from 8 to 12° and the so called phase reversal occurs at about 10° lat at which the amplitude of N_mF2. becomes extremely small.These and other results are in good agreement with observations. Thus it is shown that the main features of the observed lunar tidal variations of the F2-region within 20° of the magnetic equator can be explained satisfactorily by the superposition of a small lunar drift on a large solar drift.  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   

Nighttime proton fluxes at Millstone Hill     

J.V. Evans  J.M. Holt 《Planetary and Space Science》1978,26(8):727-744

Incoherent scatter measurements of electron density and vertical O⁺ fluxes over Millstone Hill (42.6°N, 71.5°W) previously have been used to study the exchange of plasma between the ionosphere and the magnetosphere. During the daytime there is usually an upward flux of O⁺ ions above about 450 km that can be measured readily and equated to the escaping proton flux. At night the O⁺ fluxes usually are downwards everywhere owing to the decay of the F-layer, and it becomes difficult to detect effects due an arriving proton flux. In a new study of the nighttime fluxes, appeal was made to the estimated abundance of the H⁺ ions in the upper F-region which can be extracted from the observations. From a study of the behavior on 25 days over the interval 1969–1973, we conclude that in the daytime the flux always is upwards and close to its limiting value. This situation persists throughout the night in summer at times of high sunspot activity (e.g., 1969). There is a period of downward flux prior to ionospheric sunrise on winter nights whose duration increases with decreasing sunspot number. As sunspot minimum is approached (e.g., in 1973) downward fluxes are encountered for a brief period prior to ionospheric sunrise in summer also. Thus, over most parts of sunspot cycle, it appears that the protonosphere supplies ionization to the winter night ionosphere, while being maintained from the summer hemisphere. This helps explain the smallness of the day-to-night variations reported for the electron content of magnetospheric flux tubes near L = 4 in the American sector.  相似文献   

Ion composition and chemistry in the coma of Comet 1P/Halley—A comparison between Giotto's Ion Mass Spectrometer and our ion-chemical network     

Martin Rubin  Kenneth C. Hansen  Michael R. Combi  Hans Balsiger 《Icarus》2009,199(2):505-519

In order to understand the cometary plasma environment it is important to track the closely linked chemical reactions that dominate ion evolution. We used a coupled MHD ion-chemistry model to analyze previously unpublished Giotto High Intensity Ion Mass Spectrometer (HIS-IMS) data. In this way we study the major species, but we also try to match some minor species like the CH_x and the NH_x groups. Crucial for this match is the model used for the electrons since they are important for ion-electron recombination. To further improve our results we included an enhanced density of supersonic electrons in the ion pile-up region which increases the local electron impact ionization. In this paper we discuss the results for the following important ions: C⁺, CH⁺, CH⁺₂, CH⁺₃, N⁺, NH⁺, NH⁺₂, NH⁺₃, NH⁺₄, O⁺, OH⁺, H₂O⁺, H₃O⁺, CO⁺, HCO⁺, H₃CO⁺, and CH₃OH⁺₂. We also address the inner shock which is very distinctive in our MHD model as well as in the IMS data. It is located just inside the contact surface at approximately 4550 km. Comparisons of the ion bulk flow directions and velocities from our MHD model with the data measured by the HIS-IMS give indication for a solar wind magnetic field direction different from the standard Parker angle at Halley's position. Our ion-chemical network model results are in a good agreement with the experimental data. In order to achieve the presented results we included an additional short lived inner source for the C⁺, CH⁺, and CH⁺₂ ions. Furthermore we performed our simulations with two different production rates to better match the measurements which is an indication for a change and/or an asymmetric pattern (e.g. jets) in the production rate during Giotto's fly-by at Halley's comet.  相似文献