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1.
During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of ～5.2 Re 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
2.
Vertical profiles of electron density obtained in the vicinity of the plasmapause using the Alouette-II topside sounder have been analyzed to assess the presence of H+ flow in the topside ionosphere. The observations in the midnight sector show clearly the presence of the plasmapause; i.e. there is a sharp boundary separating the poleward regions of polar wind H+ flow and the more gentle conditions of the plasmasphere where light ions are present in abundance. In contrast, in the sunlit morning sector upwards H+ flow is deduced to be present to invariant latitudes as low as 48° (L = 2·2) in the regions normally known to be well inside the plasmasphere. The upwards H+ flux is sufficiently large (3 × 108 ions cm?2 sec?1) that the plasmapause cannot be seen in the latitudinal electron density contours of the topside ionosphere. The cause for this flow remains unknown but it may be a result of a diurnal refilling process. 相似文献
3.
K. Marubashi 《Planetary and Space Science》1979,27(5):603-615
Dynamic behavior of the coupled ionosphere-protonosphere system in the magnetospheric convection electric field has been theoretically studied for two plasmasphere models. In the first model, it is assumed that the whole plasmasphere is in equilibrium with the underlying ionosphere in a diurnal average sense. The result for this model shows that the plasma flow between the ionosphere and the protonosphere is strongly affected by the convection electric field as a result of changes in the volume of magnetic flux tubes associated with the convective cross-L motion. Since the convection electric field is assumed to be directed from dawn to dusk, magnetic flux tubes expand on the dusk side and contract on the dawn side when rotating around the earth. The expansion of magnetic flux tubes on the dusk side causes the enhancement of the upward H+ flow, whereas the contraction on the dawn side causes the enhancement of the downward H+ flow. Consequently, the H+ density decreases on the dusk side and increases on the dawn side. It is also found that significant latitudinal variations in the ionospheric structures result from the L-dependency of these effects. In particular, the H+ density at 1000 km level becomes very low in the region of the plasmasphere bulge on the dusk side. In the second model, it is assumed that the outer portion of the plasmasphere is in the recovery state after depletions during geomagnetically disturbed periods. The result for this model shows that the upward H+ flux increases with latitude and consequently the H+ density decreases with latitude in the region of the outer plasmasphere. In summary, the present theoretical study provides a basis for comparison between the equatorial plasmapause and the trough features in the topside ionosphere. 相似文献
4.
The temporal development of the latitudinal position of a 600 km midlatitude electron density trough at dawn and dusk during the period 25–27 May 1967, which encompassed a large magnetic storm, was measured by the RF capacitive probe on the polar orbiting Ariel 3 satellite. The substorm-related changes in the L coordinate of the trough minimum and the point of most rapid change of density gradient on the low latitude side of the trough are similar. Oscillations of the trough position at dusk are in phase with substorm activity whereas movement of the trough at dawn is only apparent with the onset of the large storm. Detailed model calculations of the plasmasphere dynamics assuming a spatially invariant equatorial convection E-field which varies in step with the Kp index produces a plasmapause motion which parallels the observed trough behaviour, particularly at dusk, and shows that the outer plasmasphere and possibly the trough region are characterized by complex fine structured variations due to the past history of the magnetosphere convection. 相似文献
5.
M.P. Gough 《Planetary and Space Science》1982,30(7):657-668
Energetic electron injection events result in the arrival of loss-cone distributions of electrons at energies of a few keV close to the plasmapause at local midnight. These distributions favour the growth of strong electrostatic waves with some conversion to electromagnetic nonthermal continuum emissions near to the geomagnetic equator.GEOS2 located at the geostationary orbit (L = 6.6, 3.3° South) has observed these continuum emissions for a number of electron injection events. Their unique frequency structure provides a measurement of the geomagnetic field strength at the source and hence its radial position, while direction finding measurements at GEOS2 complete the source location determination.Measurements of source locations as a function of time after the start of an electron injection event, yield typical inwards motions of 1REh?1. In this way the emissions provide a remote sensing of the plasmapause location from the geostationary orbit. 相似文献
6.
A conservative convection electric field model developed by Volland (1973) to describe the solar wind induced plasma flow within the inner magnetosphere is modified to include a noisy spatial component. Under steady state conditions such a random component will result in spatial irregularities in the thermal plasma density distribution in the vicinity of the plasmapause—particularly near dusk. Spatial irregularities in the convection can produce longitudinally restricted perturbations near the plasmapause some of which are detached from the main body of the plasmasphere. Temporal variations in the midnight to noon flow intensity are shown to produce elongated extensions of the plasmasphere known as plasmatails but even short period variations of the overall magnitude of the convection cannot produce longitudinally localized perturbations in the thermal plasma distribution. Convection models based on the 3 hr magnetic index Kp yield plasmasphere structures which are qualitatively similar to those based on shorter period variations, but the exact location at any given time of the plasmapause is dependent upon the characteristic time scale employed. 相似文献
7.
Satellite and other observations have shown that H+ densities in the mid-latitude topside ionosphere are greatly reduced during magnetic storms when the plasmapause and magnetic field convection move to relatively low L-values. In the recovery phase of the magnetic storm the convection region moves to higher L-values and replenishment of H+ in the empty magnetospheric field tubes begins. The upwards flow of H+, which arises from O+—H charge exchange, is initially supersonic. However, as the field tubes fill with plasma, a shock front moves downwards towards the ionosphere, eventually converting the upwards flow to subsonic speeds. The duration of this supersonic recovery depends strongly on the volume of the field tube; for example calculations indicate that for L = 5 the time is approximately 22 hours. The subsonic flow continues until diffusive equilibrium is reached or a new magnetic storm begins. Calculations of the density and flux profiles expected during the subsonic phase of the recovery show that diffusive equilibrium is still not reached after an elapsed time of 10 days and correspondingly there is still a net loss of plasma from the ionosphere to the magnetosphere at that time. This slow recovery of the H+ density and flux patterns, following magnetic storms, indicates that the mid-latitude topside ionosphere may be in a continual dynamic state if the storms occur sufficiently often. 相似文献
8.
William J. Burke Hans J. Braun J.W. Münch Rita C. Sagalyn 《Planetary and Space Science》1979,27(9):1175-1185
The relationship between the simultaneously observed positions of the maximum omnidirectional flux of the quiet-time ring current positive ions (Λφ) and the maximum electron temperature ΛT in the trough is studied in the midnight sector of the topside ionosphere. Λφ maps to the inner edge of the plasma sheet where ring current fluxes change from nearly isotropic to trapped. At altitudes near 2500 km, the electron temperature at trough latitudes were always sharply peaked. Although Λφ varied with the level of geomagnetic activity, (Λφ ? ΛT) did not. These observations support the hypothesis that the quiet-time ring current is the source of elevated electron temperatures found near the plasmapause. Below 1300 km, peaked electron temperature distributions in the trough were not consistent features of the data. It is shown that (Λφ ? ΛT) increased with decreasing altitude. The possible influences of a westward component to the convective electric field and ionospheric refraction of ion cyclotron waves are discussed. 相似文献
9.
The topology of the boundaries of penetration (or inversely the boundaries of the forbidden regions) of 90° pitch angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment) complex structural features are expected in the proton energy spectra detected on satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to plasmatail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large scale convection field changes may be seen in the noselike proton spectrograms observed near dusk by instrumentation on the satellite Explorer 45 (S3) (Smith and Hoffman, 1974). These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to Kp through night-time equatorial plasmapause measurements. 相似文献
10.
Additional studies of the ion composition results obtained from the OGO-6 satellite support earlier observations of irregularities in the distribution of H+ and He+ within the light ion trough near L = 4, which has been associated with the plasmapause. These irregularities are in the form of sub-troughs superimposed upon the major mid latitude decrease of the light ions. In the sub-troughs, ionization depletions and recoveries of as much as an order of magnitude are observed within a few degrees of latitude, usually exhibited in a pattern which changes significantly with longitude as the Earth rotates beneath the relatively fixed satellite orbit. The location and properties exhibited by these sub-troughs appear to be consistent with the concept of a plasmasphere distortion in the form of “plasmatails” resulting from the combined effects of magnetospheric convection plus corotation. Like the light ion trough, the “plasmatail” irregularity in H+ may be obscured on the day side by the dominant topside distribution of O+. Consequently, these light ion irregularities are seen as an important factor for studies of plasmapause-trough relationships. 相似文献
11.
All of the OGO-5 light ion density measurements (covering the period from March 1968 to May 1969) obtained from the Lockheed Light Ion Mass Spectrometer were used to determine the average global topology of the equatorial plasmasphere density distribution. The variation of the light ion equatorial density at L?3.2 with local time was deduced by determining the average density observed within one hour of a specific local time and within 0.1 of a given L coordinate. The average H+ density showed a semidiurnal variation with peaks near noon and midnight. The He+ observations also revealed multiple peaks throughout the day but with smaller amplitudes than those of H+. At L>3.2 plasma trough conditions increase the scatter of densities. The average variation of the H+ density with L within the plasmasphere is found to be steepest near midnight and can be least squares fitted equally well to either an exponential variation exp (?bL) where b is between 0.85 and 1.5 or to a power law L?a where a varies from 3.2 to 5. 相似文献
12.
Using the data obtained by means of the Alouette-1 satellite, the distribution of electron density in the region of the F2-layer maximum and topside ionosphere during different phases of two successive magnetic storms on September 13 and 16,1963 have been studied. The middle latitudes at local near noon and midnight hours have been considered mainly. It is shown that the daytime topside electron density at some altitudes did not change during the main phases of the two magnetic storms. The electron density decreases below these levels and increases above. During the recovery phases of both magnetic storms the increase in electron density remains at all altitudes from hmF2 to 1000 km. 相似文献
13.
A gridded spherical electrostatic analyzer aboard Injun 5 has been used to measure fluxes of thermal and hyperthermal electrons at subauroral latitudes in the midnight sector of the northern ionosphere between altitudes of 2500 and 850 km. Due to the offset between the geomagnetic and geographic poles hyperthermal fluxes, consisting of energetic photoelectrons that have escaped from the sunlit southern hemisphere are observed along orbits over the Atlantic Ocean and North America but not over Asia. The ambient electron temperatures (Te) near 2500 km have their highest values at trough latitudes for all longitudes. At altitudes near 1000 km elevated electron temperatures in the trough were not a consistent feature of the data. Equatorward of the trough, in the longitude sector to which conjugate photoelectrons have access, Te ～ 4000 K at 2500 km and ～ 3000 K at 1000 km. For regions with the conjugate point in darkness Te ? 2300 K over the 1000–2500 km altitude range. The effective thermal characteristics of conjugate photoelectrons are studied as functions of altitude and latitude. The observations indicate that (1) at trough latitudes elevated electron temperatures in the topside ionosphere are mostly produced by sources other than conjugate photoelectrons, and (2) at subtrough latitudes, in the Alantic Ocean-North American longitude sector, conjugate photoelectrons contribute significantly to the heating of topside electrons. Much of the conjugate photoelectron energy is deposited at altitudes >2500 km then conducted along magnetic field lines into the ionosphere. 相似文献
14.
R.J. Thomson 《Planetary and Space Science》1977,25(11):1037-1043
Simultaneous ground and satellite VLF observations together with raytracing studies clearly establishes the existence of ground observed PL whistlers. The dynamic spectrum of observed PL whistlers may be reproduced exactly by raytracing in TLG magnetospheric models consistent with lower ionosphere, topside ionosphere and equatorial density measurements. The Transition Level Gradient (TLG) model is based on the observation that the transition level altitude increases towards the plasmapause (Titheridge, 1976). PL ground whistlers (i) are observed downgoing over large latitudinal ranges, for up to 2000 km of satellite travel, by ISIS II at 1400 km altitude, (ii) have almost the same dynamic spectrum over the entire latitudinal range observed by ISIS II, (iii) are indistinguishable from ducted whistlers over the observed frequency range (i.e. linear Q for ? < 10 kHz), (iv) have nose frequencies > 16 kHz, (v) at 1400 km altitude have a lower latitudinal cutoff at L ～ 2 and a higher latitudinal cutoff between L ～ 3 and L ～ 4 and (vi) probably only occur at night-time during or immediately following disturbed magnetic activity. 相似文献
15.
A distinct feature of the ion composition results from the OGO-2, 4 and 6 satellites is the light ion trough, wherein the mid latitude concentrations of H+ and He+ decrease sharply with latitude, dropping to levels of 103 ions/cm3 or less near 60° dipole latitude (L=4). In contrast to the ‘main trough’ in electron density, Ne, observed primarily as a nightside phenomenon, the light ion trough persists during both day and night. For daytime winter hemisphere conditions and for all seasons during night, the mid latitude light ion concentration decrease is a pronounced feature. In the dayside summer and equinox hemispheres, the rate of light ion decrease with latitude is comparatively gradual, and the trough boundary is less well defined, particularly for quiet magnetic conditions. In response to magnetic storms, the light ion trough minimum moves equatorward, and deepens, consistent with earlier evidence of the contraction of the plasmasphere in response to storm time enhancements in magnetospheric plasma convection. The fact that a pronounced light ion trough is observed under conditions for which the dominant ion O+ may exhibit little or no simultaneous decrease appears to explain why earlier studies of the ‘main trough’ in topside distributions of Ne and Ni may, at times, have been inconclusive in relating the total ionization minimum with the mechanism of the plasmapause. In particular, the topside distribution of Ni appears to be the complex resultant of several variables within the ion composition, being governed by the competing processes of chemical production and loss, loss through magnetospheric convection, and large-scale dynamic transport resulting from neutral winds and electric fields. The net result is that in general, the light ion trough, rather than Ni, provides a more fundamental parameter for examining the structure and behavior of the plasmapause. 相似文献
16.
J.H. Whitteker 《Planetary and Space Science》1977,25(8):773-786
A numerical time-dependent model of the topside and F-layer ionosphere is used to describe how the density of O+ ions and the plasma temperatures change as a result of transient electron precipitation with a soft energy spectrum (ca. 100 eV per electron). The response time for electron gas heating is about 2 min; for changes in topside scale height it is from 5 to 15 min, depending on altitude; and for changes in F-layer peak density, it is more than an hour. The low-density topside ion gas is thermally isolated on a short time scale; consequently the ion temperature responds almost adiabatically to volume changes. A transient precipitation event (of, say, 10 min duration) initiates a disturbance that propagates upward at approximately the sonic upeed in the plasma (ca. 2km/s), growing in amplitude with height. Such an event has little effect on the density at the peak of the F layer. An element of ionosphere that drifts horizontally in an antisunward direction through the magnetospheric cleft and into the polar cap recieves some ionization from the cleft, but not enough to be decisive in its survival. The collapse of the topside when heating is removed increases temporarily the density of the F layer. 相似文献
17.
Ground observations of Pi 2 geomagnetic pulsations are correlated with satellite measurements of plasma density for three time intervals. The pulsations were recorded using the IGS network of magnetometer stations and the plasma density measurements were made on board GEOS-1 and ISEE-1. Using the technique of complex demodulation, the amplitude, phase and polarisation characteristics of the Pi 2 pulsations are observed along two meridional profiles; one from Eidar, Iceland (L = 6.7) to Cambridge, U.K. (L = 2.5) and the other from Tromso, Norway (tL = 6.2) to Nurmijarvi, Finland (L = 3.3). The observed characteristics of the Pi 2 pulsations are then compared with the plasma density measurements. Close relationships between the plasmapause position and the position of an ellipticity reversal and a variation in H component phase are observed. A small, secondary amplitude maximum is observed on the U.K./Iceland meridian well inside the position of the projection of the equatorial plasmapause. The primary maxima on the two meridians, in general occur close to the estimated position of the equatorward edge of a westward electrojet. Using the plasma density measurements, the periods of surface waves at the plasmapause for two intervals are estimated and found to be in good agreement with the dominant spectral peaks observed at the ground stations near the plasmapause latitude and within the plasmasphere. The polarisation reversal, together with phase characteristics, spectral evidence and the agreement between the theoretical and observed periods leads to the suggestion that on occasions a surface wave is excited on the plasmapause as an intermediate stage in the propagation of Pi 2 pulsations from the auroral zone to lower latitudes. 相似文献
18.
One prominent feature of the high latitude topside ionosphere is the existence of sharp latitudinal depletions in the total ion (electron) concentrations within the auroral/cusp regions. These high latitude troughs, as seen by the Bennett ion mass spectrometer observations on the satellite OGO 6 at altitudes between 400 and 1100km correspond to depletions in the atomic ions which are accompanied by localized enhancements of the minor molecular ion densities. All of the high latitude troughs traversed by OGO 6 (1969–1970) were recorded and the average invariant latitude-magnetic local time (M.L.T.) distribution was determined. The troughs on the average were found at all local times to be in the vicinity of the auroral oval and to move equatorward in response to increasing magnetic activity. The average trough location was compared to the average polar cap boundary as defined by the convection electric field reversal and the electron trapping boundary as well as to the maximum horizontal magnetic disturbance associated with the large scale field aligned currents. The high latitude troughs on the average best followed the maximum magnetic disturbance distribution. It is concluded that the troughs are the result predominantly of enhanced chemical 0+ losses in regions with high convection velocities. 相似文献
19.
Low altitude satellite observations of precipitated and locally mirroring protons during periods of ground-based SAR arc observations are presented. The SAR arcs are found to be located in a region with significantly enhanced proton pitch angle scattering and enhanced electron temperature, but inside the plasmapause where the proton pitch angle distribution is anisotropic. The increase in the pitch angle scattering takes place in a localized region having a width of a few tenths of a L-value. The observations can favourably be accounted for by the Cornwall et al. (1971) theory for the SAR arc formation. Using observed proton fluxes and typical energy spectra, the expected Hβ intensity in the SAR arc region is estimated to be a few Rayleighs, and the energy flux from precipitated protons above a few keV to be 10?2?10?1erg/cm2s. These estimates are in reasonable agreement with previously published theoretical and experimental values. Simultaneous groundbased observations of Hα emissions were found in the region of intense, isotropic proton precipitation located outside the plasmapause. 相似文献
20.
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