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1.
Autospectra in the 2–13 month range, computed from mean monthly horizontal intensity on quiet days at Trivandrum, situated close to the dip equator, suggest an exceedingly large semi-annual modulation of the field confined to an interval of about 5 hr centred at 1000 LT. The amplitude of the semi-annual oscillation at this station, derived from power density, is greater than 19 γ at 1000 LT. Between 1900 and 0500 LT, spectral lines, corresponding to a period of six months, are not observed above the continuum. Spectral densities from observations at two other electrojet stations in India, Kodaikanal and Annamalainagar, and at Alibag, outside the electrojet, establish the existence of an appreciable enhancement of the semi-annual oscillation of the field in the equatorial electrojet belt. Similar computations of spectra using observations on all days, however, suggest a secondary component in the evening sector. This component is not enhanced in the equatorial electrojet belt. It is concluded that while in low latitudes the daytime component is largely associated with the modulation of Sq currents, in the electrojet belt it appears to be due entirely to a semi-annual modulation of the equatorial electrojet. It is also concluded that the secondary component, observed in the evening sector in low latitude and equatorial stations, is associated purely with the modulation of the ring current by disturbance. The two components of the semi-annual variation observed at the Indian stations have also been noticed at several stations between geomagnetic latitudes N54.6° and S41.8°. It is also observed that the association of the semi-annual component with geomagnetic latitude is confined to the evening-night component.  相似文献   

2.
It is suggested that the quiet day daily magnetic variation in the polar cap region, Sqp, results partly from the short-circuit effect of the magnetotail current by the polar ionosphere. This implies that there is an inward field-aligned current from the dawnside magnetopause to the forenoon sector of the auroral oval (positively charged) and an outward field-aligned current to the duskside magnetopause from the afternoon sector of the oval (negatively charged), together with the ionospheric (Pedersen and Hall) currents. The distribution of the magnetic field vectors of both combined current systems agrees with the observed Sqpvector distribution. The space charges provide an electric field distribution which is similar to that which has been observed by polar orbiting satellites.  相似文献   

3.
Density distribution of plasmaspheric particles in the equatorial plane is derived from a model of plasmaspheric streaming, which may produce Sq current system in the lower ionosphere, and from one integral of motion, which seems to be generally valid for steady-state magnetospheric convection. The results satisfy not only the observed features of Sq variation but also the observed pattern of the density distribution in the magnetospheric equatorial plane during quiet periods.  相似文献   

4.
The paper describes the phenomenon of afternoon depression of the geomagnetic H field on quiet days near the magnetic equator in the Indian zone. These events occur most frequently around 1600 solar hr and are localized in longitude; sometimes, not seen at stations separated by even 2 hr LT. The geomagnetic disturbance tends to decrease or destroy the identity of the phenomenon. The latitudinal extent of these events is confined to the equatorial electrojet region. The events do not seem to be caused mainly by the Moon, but their occurrences are modified by the lunar age, being most frequent around new and full Moon. These events are associated with the disappearance of the q type of Es over the Equator for periods during which the H field is below the night-time level. The currents responsible for these events flow westward in the E-region and are within few degrees centred near the magnetic equator.  相似文献   

5.
From an analysis of published geomagnetic data of stations in the Indian equatorial region, it is shown that on days with an abnormal Sq (H) phase limited to the electrojet belt, conditions characteristic of complete or partial counter-electrojet prevail around the usual time interval of the diurnal maximum of the H-field.  相似文献   

6.
The paper describes a comparison of vertical electron drift in the F-region (Vz) measured by VHP incoherent scatter radar at Jicamarca with the corresponding variations of geomagnetic horizontal field (H) and the maximum frequency reflected from The Es layer (Es) at Huancayo during the geomagnetic storm period 7–9 March, 1970. The Vz is generally upward during the daytime at the equator, but during 7–9, March, 1970, Vz was negative for brief periods associated with negative bays in H. These periods of abnormally low or of downward Vz correspond closely with the period of complete disappearance of the q type of Es layer. The magnetic bays associated with the intensification of ring current do not affect the equatorial Es- q and it is only the negative bays in H at the equator due to the ionospheric current flowing westward, that cause sudden disappearance of Es? q. It is suggested that the q type of Es is due to cross-field instability created in the electrojet region due to interaction of northward magnetic field and vertical upward Hall polarization electric field when the plasma density gradient is upward. The sudden disappearances of Es? q are due to the reversal of the horizontal electric field in the equatorial ionosphere and thereby due to the reversal of the equatorial electrojet currents. These reversals of electric field may be due to the imposition on the normal Sq field of another westward electric field.  相似文献   

7.
The magnetic perturbation patterns in the polar cap and auroral zone regions are obtained for extremely quiet days using two different techniques. It is shown that the form of the equivalent current flow pattern is extremely sensitive to the level of quietness, and that even so-called quiet days are at times disturbed by substorm activity. Certain characteristic equivalent flow not typically observed during substorms is noted in the polar cap, and this flow appears to be associated with effects associated with polar cap perturbations discussed by Svalgaard (1973). As well a region of equatorward flow appears at high latitudes near the dawn meridian, which appears to be Hall current driven by an eastward electric field. The dayside sub-auroral zone is dominated by the Sq-current system, while the nightside shows no significant current flow in the absence of substorm activity.  相似文献   

8.
A method of analysis has been developed making it possible to obtain electrojet parameters from vertical profiles of the POGO electrojet data. This has provided an unprecedented quantity of electrojet parameters—about 500 each of its peak eastward current intensity J0, its total eastward current I+, and its half width w—spanning through 360° longitude round the Earth, 5 h of daytime and September equinoctial months of the years 1967, 1968 and 1969. The daytime all-longitude averages of the parameters for the 3 years are 235 ± 14 km for w, 232 ± 63A km?1 for J0 and (54 ± 11) × 103A for I+. This first coverage round the globe shows that J0 and I+ vary considerably with longitude unlike w. While confirming the expected maximum of J0 and I+ at about 280°E longitude, we find that each of them also has an unexpected major maximum at about 100°E and a subsidiary maximum at 190°E longitude. The major maxima are found to be prominent only at hours near local noon. It is argued that the surprising longitudinal variations of J0 and I+ cannot be explained satisfactorily by variations in the upper mantle conductivity along the dip equator but possibly by longitudinal variations of wind systems and gradients at electrojet altitudes.  相似文献   

9.
The magnitude of the equatorial electrojet signature, S, is a measure of its magnetic field at the location of the satellite recording the signature. The general features of the large quantity of the magnetic field data of the electrojet observed by the series of POGO satellites from 1967 to 1970 have been studied here. We have compared the position of the axis of the electrojet as indicated by the position of the minimum of the electrojet signature with the position of the dip equator on the Earth's surface, and we find no significant latitudinal shift of the electrojet axis from the dip equator on the Earth. Apart from the expected decrease of the magnetic field of the electrojet with altitude above the electrojet, we have found unexpected cases in which the field increases with altitude. More surprisingly, we have discovered that the magnitude of S oscillates with altitude having maxima at about 460km and 635km and minima at about 580km and 725km, with a mean wavelength of 160 ± 29 km. It is suggested that this could be caused by additional weak current layers flowing above the main electrojet at about 110 km altitude. It is also pointed out that Onwumechili's model based on a single current system of the equatorial electrojet predicts field oscillation with altitude. The model therefore shows that a field oscillating with altitude can also result from a single complicated system of current unaided by additional current layers.  相似文献   

10.
Magnetic field intensity of the horizontal component (H) data measured from Magnetic Data Acquisition System (MAGDAS) at Ilorin (geographic latitude: 8.47°N, geographic longitude: 4.68°E, geomagnetic latitude: 1.82°S, geomagnetic longitude: 78.6°S), Nigeria in the year 2009 (a low activity year) was used to study the diurnal, monthly-median and standard deviation of the solar quiet of the horizontal component (S q H). The diurnal variation of S q H and its corresponding monthly median variation (MS q H) shows minima values at pre-sunrise hours between 0500 and 0600 LT. The S q H value shows a daytime maximum variation range between 20 and 91 nT and a nighttime minimum variation range from 1 to 4 nT. The occurrences of daytime maxima of the S q H values that were observed in all the months are between the hours of 1000 and 1200 LT. The daytime maximum of the MS q H values from the entire months were seen at 1100 LT with exceptions of January and December. The month of October has the highest value (61 nT) and the lowest value was observed in December (35 nT). It is clearer that the range in maximums of S q H and MS q H variations during the daytime period in all the months is greater than the range in minimums observed at nighttime period (post-sunset and pre-sunrise). The monthly standard deviation (STD) depicts the index of variability of all the day-to-day variations in each month. Counter electrojet (CEJ) events were observed in the morning and as well during the evening hours. The magnitudes and frequencies of CEJ events during the evening hours are greater than that of the morning hours. CEJ seen during the morning period around 0500–0600 LT is the consequence of late reversals of nighttime westward currents to daytime eastward currents. A semi-annual variation with peak values during March, April, September and October was observed. Seasonal variation that was characterized with CEJ was also investigated.  相似文献   

11.
In order to investigate Pc3-4 geomagnetic pulsations at very low and equatorial latitudes, L=1.0 to 1.2, we analyzed simultaneous geomagnetic data from Brazilian stations for 26 days during October-November 1994. The multitaper spectral method based on Fourier transform and singular value decomposition was used to obtain pulsation power spectra, polarization parameters and phase. Eighty-one (81) simultaneous highly polarized Pc3-4 events occurring mainly during daytime were selected for the study. The diurnal events showed enhancement in the polarized power density of about 3.2 times for pulsations observed at stations close to the magnetic equator in comparison to the more distant ones. The phase of pulsation observed at stations near the magnetic equator showed a delay of 48-62° in relation to the most distant one. The peculiarities shown by these Pc3-4 pulsations close to the dip equator are attributed to the increase of the ionospheric conductivity and the intensification of the equatorial electrojet during daytime that regulates the propagation of compressional waves generated in the foreshock region and transmitted to the magnetosphere and ionosphere at low latitudes. The source mechanism of these compressional Pc3-4 modes may be the compressional global mode or the trapped fast mode in the plasmasphere driving forced field line oscillations at very low and equatorial latitudes.  相似文献   

12.
A variety of astronomical phenomena appear to not satisfy the ergodic hypothesis in the relevant stationary state, if any. As such, there is no reason for expecting the applicability of Boltzmann–Gibbs (BG) statistical mechanics. Some of these phenomena appear to follow, instead, nonextensive statistical mechanics. In the same manner that the BG formalism is based on the entropy S BG=?k∑ i p i ln p i, the nonextensive one is based on the form S q=k(1 ?∑ i p i q)/(q? 1) (with S 1=S BG). The stationary states of the former are characterized by an exponential dependence on the energy, whereas those of the latter are characterized by an (asymptotic) power law. A brief review of this theory is given here, as well as of some of its applications, such as the solar neutrino problem, polytropic self-gravitating systems, galactic peculiar velocities, cosmic rays and some cosmological aspects. In addition to these, an analogy with the Keplerian elliptic orbits versus the Ptolemaic epicycles is developed, where we show that optimizing S q with a few constraints is equivalent to optimizing S BG with an infinite number of constraints.  相似文献   

13.
Some years ago Nishida (1966) identified an equivalent current system which appeared to reflect a coherent magnetic field fluctuation observed at the equator and at high latitudes. This equivalent current system was subsequently labelled DP2, and since its existence was proposed it has been a topic of some controversy. In this paper we utilize the fact that DP2 intensity is regulated by the Bz component of the interplanetary magnetic field to decouple the DP2 variation from the very similar Sq perturbation pattern. We demonstrate how DP2 can arise as a manifestation of the overall three-dimensional magnetospheric-ionospheric current system which couples the magnetosphere to the high latitude ionosphere, and suggest how ionospheric conductivity is a major factor in regulating the strength of DP2 disturbances.  相似文献   

14.
The Retarding Potential Analyzer aboard OGO-6 sometimes recorded marked depressions of ion temperature as the satellite crossed the equatorial region. These “Ti troughs” occur at heights between about 700 km and the satellite apogee at 1100 km. At the centre of a trough, close to the dip equator, Ti is frequently 500–1000 K below its value at the northern and southern edges, which are usually 15°–20° in latitude from the centre of the trough. At a given season and local time, the occurrence, symmetry, depth and position of the troughs often vary markedly with longitude. The troughs have no particular association with equatorial troughs of ion concentration Ni.As suggested by Hanson, Nagy and Moffett, the Ti troughs appear to be caused by transequatorial winds that drive F region plasma along geomagnetic field lines. The plasma is adiabatically cooled as it is driven upwards on the “upwind” side of the dip equator, and heated as it descends on the “downwind” side. The available data on the occurrence of troughs at different longitudes, local times and seasons are reasonably consistent with wind directions deduced from Jacchia's model and the OGO-6 thermospheric model of Hedin et al., and with the north-south asymmetries of the tropical 630 nm airglow observed by OGO-4 and OGO-6. Factors determining the latitudinal extent of the troughs are discussed and some questions for further study are listed.  相似文献   

15.
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   

16.
During very intense geomagnetic storm of November 7–8, 2004 simultaneous presence of storm time disturbance dynamo and eastward and westward directed prompt penetration electric fields inferred from the ground based magnetometer data in the 75° E sector is presented. Magnetometer observations show that, on the whole, average ΔH variation on 8 November remains below the night time level compared to its quiet day variation. A number of upward and downward excursions have been observed between 0130 UT and 0800 UT in the ΔH variation on 8 November. These excursions in ΔH have been attributed to the episodes of eastward and westward prompt penetrating electric fields. Ionospheric response in the equatorial ionization anomaly region along 75° E has also been studied using the total electron content data recorded at five GPS stations, namely Udaipur, Bengaluru (IISC), Hyderabad (HYDE), Maldives (MALD) and Diego Garcia (DGAR). Observation of markedly suppressed EIA, in conjunction with ΔH variation which was m negative during the daytime on 8 November, indicates the presence of an external field of opposite polarity (the disturbance dynamo electric field) that either undermined, or overshadowed the daytime ambient (eastward) electric field to the extent that the equatorial plasma fountain could not become effective.  相似文献   

17.
The existence of the dynamo region is identified in the atmosphere of Jupiter. It is found that the dynamo region extends from an altitude of 130 km (0.153 mbar) to 330 km (0.027 μbar) reckoned from zero altitude corresponding to 43.8 mbar pressure level. Physical features of the equatorial electrojet in the ionosphere of Jupiter are modelled in detail. The Jovian equatorial electrojet has a maximum eastward current density of about 1.5 Akm?2 at an altitude of 270km (0.33 μbar) with a latitudinal half width of about ±11°. The thickness of the equatorial half width is 100 km in altitude range. The type I instability in the electrojet can exist only if the electron streaming velocity exceeds the value of about 250 m s?1.  相似文献   

18.
When observed noontime values of the maximum electron density, NMAX(F2), in the ionospheric F2 region are plotted as a function of magnetic latitude, a curve is produced which has two peaks, one on either side of the dip equator at ±16° dip latitude. This paper theoretically investigates the daily variation of this latitudinal distribution in NMAX(F2) (the so-called Appleton or equatorial anomaly) and specifically attempts to account for the longitudinal differences observed between the American and Asian sectors.In Part II, models of the neutral atmosphere, production, loss and diffusion rates, neutral wind, and electric field are described and the electron densities obtained by solving the continuity equation utilizing these models are presented. In each sector, the extent to which the equatorial anomaly's daily variation is affected by changes in the geomagnetic field configuration, neutral wind, and E × B drift is examined. It is found that development of the anomaly is most sensitive to the electric field model assumed, and that the observed differences at the magnetic equator between the American and Asian sectors could be accounted for by an upward E × B drift which commences an hour or two earlier in the Asian sector.  相似文献   

19.
As a Philippine contribution to the International Heliophysical Year, we propose to use the MAGnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network (MAGDAS/CPMN), installed by the Space Environment Research Center (SERC), Kyushu University along the 210° magnetic meridian and the magnetic equator, to study the equatorial electrojet (EEJ) and counter electrojet (CEJ). Through this installation, it is made possible to observe geomagnetic field variations in real time. By utilizing this network of ground-based instruments, we hope to elucidate their regular day-to-day and seasonal variabilities and variations during magnetic storms and substorms. We also want to study the behavior of this ionospheric current system before, during, and after the occurrence of an earthquake.  相似文献   

20.
Atmospheric densities at 169 km have been obtained for the period 19 August–3 September 1970 from the measurements of an accelerometer on a low altitude satellite and from the orbital decay of the same satellite. Three different sets of local time and latitude conditions were provided by the data; two from the accelerometer measurements, before and after perigee, and one at perigee, from the orbital decay data. Under the generally quiet magnetic activity conditions that prevailed during the data-taking period, the short term density fluctuations were found to be poorly correlated with the small Kp variations. However, on the greater time scale of a day, a definite relationship was found between the daily average density and the daily geomagnetic index Ap. Further, the increase in the density corresponding to Ap was largest at the highest latitude. The high latitude accelerometer data exhibited a quasi-daily periodicity, with maximum densities occurring when the satellite was within the dayside cusp. This effect also appeared to depend on the degree of auroral electrojet activity as defined by the AE index. Comparisons of the data with the Jacchia?70 and ?71 models indicated that these models may give density values which are too small for the conditions and time period corresponding to the data.  相似文献   

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