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1.
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   

2.
A statistical study using data from four geomagnetic recording stations with McIlwain parameters from L = 2.5 to 6.6, suggests that the general source location of Pc 1 micropulsations lies close to the plasmapause.For each station a contour plot of the number of Pc 1 events occurring at specific Kp, and LT intervals is constructed and a curve representing the plasmapause being overhead at this station is superimposed. The relative positions of the plasmapause curve and the contour maxima are taken to indicate the position of the Pc 1 source location.  相似文献   

3.
Digital spectrograms have been computed for 18 days of geomagnetic pulsation activity at three UK Earth current stations (L = 2.6?3.6).Three main conclusions are drawn: (1) There are days when the period of the dominant spectral amplitude is ordered according to the observatory latitude. The most frequently observed large amplitude spectral peaks are centred on 80, 60 and 45s for South Uist (L = 3.6), Eskdalemuir (L = 3.1) and East Anglia (L = 2.6). respectively. (2) There are other days when the period of the dominant spectral amplitude is the same at all the observatories. (3) When Pc 3 and 4 period waves have been detected together, the latitude dependence of the amplitudes supports the theory that the shorter period pulsation is enhanced in the plasmatrough while the longer period wave is enhanced within the plasmasphere.  相似文献   

4.
Based on the observational data obtained at eleven stations along a geomagnetic meridian (Φm = 45–63°), the characteristics of pc 3, 4 pulsations are investigated. It has been shown that pc 3, 4 pulsations possess two amplitude maxima: one in the high latitudes and the other in middle latitudes. Consequently, the amplitude minimum between the two maxima is observed in subauroral latitudes (Φm ≈ 60°). Examining the peculiarities of the polarization behaviour of pc 3, 4 pulsations along the meridian array, two different regions, where the pulsations are generated, are noticed. One is situated in the middle latitudes of about 55–60°, and the other in the auroral area of about 65–70° in geomagnetic latitude. The former region corresponds to a projection of an area inside the plasmapause and the latter of an area of the outer radiation belt in the magnetosphere. The dependence of the pc 3, 4 periods on the position of the plasmapause is clarified. It is also shown that both the position of the pc 3 amplitude maximum in the middle latitudes and the position of pc 4 minimum in the subauroral area shift according to the variation in the magnetic activity and the position of plasmapause.The dynamic spectra of the simultaneous wave-packets of Pc-pulsations are investigated along the meridional profile. The maximum time delay of the Pc-signals is found at a latitude of about 57°, corresponding to the region of low values of Alfvén velocity inside the plasmasphere. On the other hand, a sharp decrease in the time delay is observed at a latitude of about 60°, the region of the rapid increase of Alfvén velocity at the plasmaspheric boundary in the magnetosphere.  相似文献   

5.
For 4 months of synoptic records whistlers have been analyzed in two groups, high latitude (HL) whistlers with fn?8 kHz and low latitude (LL) whistlers with fn?8 kHz. A decrease in percentage occurrence of HL whistlers with increasing Kp is interpreted as being due to equatorwards movement of the plasmapause in the vicinity of SANAE, Antarctica (L=4). The diurnal variation in HL and LL whistler occurrence reveals an average behaviour of the plasmapause, namely, an equatorwards movement beginning at around 2000 LT followed by a return movement from 0400 LT to 0800 LT.  相似文献   

6.
Several substorms were observed at Explorer 45 in November and December 1971, and January and February 1972, while the satellite was in the evening quadrant near L = 5. These same substorms were identified in ground level magnetograms from auroral zone and low latitude stations. The satellite vector magnetic field records and rapid run ground magnetograms were examined for evidence of simultaneous occurrence of Pi2 magnetic pulsations. Pulsations which began abruptly were observed at the satellite during 7 of the 13 substorms studied and the pulsations occurred near the estimated time of substorm onset. These 7 pulsation events were also observed on the ground and 6 were identified in station comments as Pi2. All of the events observed were principally compressional waves, that is, pulsations in field magnitude. There were also transverse components elliptically polarized counter-clockwise looking along the field line. Periods observed ranged from 40 to 200 sec with 80 sec often the dominant period.  相似文献   

7.
The polarization method of source location has been used on data from two low latitude stations (L = 1.9) to determine the exit region of structured Pc1 emissions from the magnetosphere into the ionosphere. Propagation directions in the ionospheric F2 duct can be inferred from measurements of polarization parameters made at the low latitude recording station. Measurements on six events indicated an average source L value of 3.2, which represented the sources being on the average 1.0 ± 0.5 Re inside the corresponding statistical plasmapause position.  相似文献   

8.
On 26 July 1967, a magnetically quiet day (ΣKp = 12?) with high whistler activity at Halley Bay, it was found possible, by measurement of whistler nose-frequency and dispersion and the bearings of the whistler exit points, to make a detailed study of the magnetospheric structure associated with the whistler ducts.During the period 0509–2305 UT most of the exit points of whistlers inside the plasmasphere were situated along a strip about 100km wide passing through Halley Bay in an azimuthal direction 30°E of N between 57° and 62° invariant latitude. A mechanism which can give rise to such a well-defined locus which co-rotates with the Earth is not clear. Nevertheless, it does appear that the locus coincides with the contour of solar zenith angle 102° at 1800 UT 25 July. This was also the time of occurrence of a sub-storm and it is suggested that the magnetospheric structure was initiated by proton precipitation along the solar zenith angle 102° contour.At mid-day knee-whistlers observed outside the plasmapause had exit points which were closely aligned along an L-shell at an invariant latitude of 62.5°. They exhibited a marked variation (~ 3:1) in electron tube content over about 12° of invariant longitude and a drift of about 8 msec?1 to lower L-shells.Throughout the period of observation the plasmapause lay about 2° polewards of the mean position found by Carpenter (1968) for moderately disturbed days.  相似文献   

9.
The plasmapause position is determined by the innermost equipotential surface which is tangent to the ‘Roche-Limit’ surface of the ionospheric plasma filling the magnetosphere. When the thermal particles corotate with the Earth's angular velocity, the ‘Roche-Limit’ equatorial distance is Lc=5.78 [RE]. When the angular convection velocity is evaluated from the quiet time electric field distribution E3 of McIIwain (1972), Lc depends on the local time. Its minimum value is then LC=4.5Near 2400 LT, and the plasmapause shape and position satisfactorily fit the observations. The diffusive equilibrium dnesity distribution appropriated inside the plasmasphere, becomes convectively unstable beyond L = Lc, where the collisions type of model satisfactorily represents the observations. In the intermediate region between the plasmapause and the last closed magnetic field line, contimues ionization fluxes are expected to flow out of the midlatitude ionosphere  相似文献   

10.
There is a magnetosonic waveguide under the arch of the plasmasphere. This channel, in the form of a ring with radius L～4, surrounds the Earth. It is shown that in this region of the magnetosphere the flute-like electromagnetic disturbances (k6 = 0) with frequencies ω = sωp can be excited by energetic protons, with non-monotonic dependence on transverse energy (??/?ε⊥ > 0). The interpretation of magnetic pulsations which have been observed in the equatorial vicinity of the plasmapause on the satellite OGO-3 in the frequency range ～102 cps (Russell et al., 1970) is given. In particular the origin of discrete structure of the observed spectra (narrow band spikes for a rather broad range of frequency) is discussed.  相似文献   

11.
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   

12.
A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high Ap, index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly Kp indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.  相似文献   

13.
Values of plasma temperature and vertical temperature gradient were obtained by fitting theoretical models to 60,000 observed electron density profiles, at heights of 400–1000 km. Results show the diurnal and seasonal changes in temperature from 75°S to 85°N near solar minimum. At night the temperature and temperature gradient are both low inside the plasmapause and high outside. Day-time temperatures increase almost linearly with latitude, from 1500 K at the magnetic equator to a maximum of 3500 K at the plasmapause. There is also a sharp peak at 77° latitude, beneath the magnetospheric cleft. Mean vertical temperature gradients are ca. 0.5 Kkm at night, and 1–4 K/km during the day. The downwards flow of heat, during the day, increases from about zero at 10° latitude to a maximum of 4 × 109eVcm2sec at the plasmapause. Night-time flows are 5–20 times less, inside the plasmasphere. Increases in magnetic activity cause a temperature increase at 400 km, of about 70 K per unit increase in Kp at all latitudes greater than 65°. The temperature peaks at the plasmapause and the magnetospheric cleft show little increase with magnetic activity, but move equatorwards by ca. 2° in latitude per unit Kp.  相似文献   

14.
Observation of ionograms recorded at about fifteen high latitude stations shows there the same morphological types of F-lacunae (disappearance of echoes from the F1, the F2 or the complete F-layer) as in Terre Adélie. The phenomenon is aestival and diurnal everywhere, but the shape of occurrence histograms varies from one station to another. A statistical study shows that the occurrence in the various stations (of the same hemisphere) is correlated, all the more as the considered stations have similar invariant latitudes. Occurrence is correlated with the daily index of magnetic activity Ap, a correlation which is maximum at about 75° invariant latitude and decreases on both sides. A study of particular events shows a clear relation between lacunae occurrence and the position and moving of the cleft (as deduced empirically from the Kp index), results which can be interpreted in terms of a previously described model.  相似文献   

15.
Digital dynamic spectra of micropulsations recorded at SANAE (L ～ 4) show that Pc 3 pulsations have frequencies which decrease throughout the day. Both the onset frequency and the rate of decrease of frequency depend on the level of magnetic activity during the previous night. The variation of Pc 3 amplitudes and frequencies is explained in terms of the position of the plasmapause and the associated Pc 3 resonance region in the plasmatrough.For Pc 4 pulsations a constant frequency is observed on most days and it is not possible to infer the presence of a Pc 4 resonance region.  相似文献   

16.
The records of the pulsations of Ez(air) and magnetic components during a pc 1 event are discussed.  相似文献   

17.
Computerized spherical harmonic analysis is applied to the morphology of the southern auroral oval. Records from 23 All Sky Camera stations together with visual observation reports for the period 1957–1959 constitute the raw data set. The mode of the derived auroral occurrence distribution function F(Kp, θ, φ) is regarded as the maximum probability contour and yields a set of auroral ovals. These 10 contours, one for each Kp level, are expressed in the invariant magnetic co-ordinates of Bond (1968).  相似文献   

18.
Explorer 45 traversed the plasmapause (determined approximately via the saturation of the d.c. electric field experiment) at near-equatorial latitudes on field lines which were crossed by Ariel 4 (~600km altitude) near dusk in May 1972 and on field lines which were crossed by Isis II (~1400km altitude) near midnight in December 1971 and January 1972. Many examples were found in which the field line through the near-equatorial plasmapause was traversed by Explorer 45 within one hour local time and one hour universal time of Ariel and Isis crossings of the same L coordinate. For the coincident passes near dusk, the RF electron density probe on Ariel detected electron density depletions near the plasmapause L coordinates when Ariel was in darkness. When the Ariel passes were in sunlight, however, electron depletions were not discernable near the plasmapause field line. On the selected near-midnight passes of Isis II, electron density depressions were typically detected (via the topside sounder) near the plasmapause L coordinate. The dusk Ariel electron density profiles are observed to reflect O+ density variations. Even at the high altitude of Isis near midnight, O+ is found to be the dominant ion in the trough region whereas H+ is dominant at lower latitudes as is evident from the measured electron density scale heights. In neither local time sector was it possible to single out a distinctive topside ionosphere feature as an indicator of the plasmapause field line as identified near the equator. At both local times the equator-determined plasmapause L coordinate showed a tendency to lay equatorward of the trough minimum.  相似文献   

19.
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   

20.
A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high Ap index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly kp indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.  相似文献   

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