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1.
The level of wave geomagnetic activity in the morning and daytime sectors of auroral latitudes during strong magnetic storms with Dst min varying from ?100 to ?150 nT in 1995–2002 have been studied using a new ULF index of wave activity proposed in [Kozyreva et al., 2007]. It has been detected that daytime Pc5 pulsations (2–6 mHz) are most intense during the main phase of a magnetic storm rather than during the recovery phase as was considered previously. It has been indicated that morning geomagnetic pulsations during the substorm recovery phase mainly contribute to daytime wave activity. The appearance of individual intervals with the southward IMF B z component during the magnetic storm recovery phase results in increases in the ULF index values.  相似文献   

2.
The geomagnetic observations, performed at the global network of ground-based observatories during the recovery phase of the superstrong magnetic storm of July 15–17, 2000 (Bastille Day Event, Dst = ?301 nT), have been analyzed. It has been indicated that magnetic activity did not cease at the beginning of the storm recovery phase but abruptly shifted to polar latitudes. Polar cap substorms were accompanied by the development of intense geomagnetic pulsations in the morning sector of auroral latitudes. In this case oscillations at frequencies of 1–2 and 3–4 mHz were observed at geomagnetic latitudes higher and lower than ～62°, respectively. It has been detected that the spectra of variations in the solar wind dynamic pressure and the amplitude spectra of geomagnetic pulsations on the Earth’s surface were similar. Wave activity unexpectedly appeared in the evening sector of auroral latitudes after the development of near-midnight polar substorms. It has been established that the generation of Pc5 pulsations (in this case at frequencies of 3–4 mHz) was spatially asymmetric about noon during the late stage of the recovery phase of the discussed storm as took place during the recovery phase of the superstrong storms of October and November 2003. Intense oscillations were generated in the morning sector at the auroral latitudes and in the postnoon sector at the subauroral and middle latitudes. The cause of such an asymmetry, typical of the recovery phase of superstrong magnetic storms, remains unknown.  相似文献   

3.
The spatial dynamics of geomagnetic variations and pulsations, auroras, and riometer absorption during the development of the main phase of the extremely strong magnetic storm of November 7–8, 2004, has been studied. It has been indicated that intense disturbances were observed in the early morning sector of auroral latitudes rather than in the nighttime sector, as usually takes place during magnetic storms. The unusual spatial dynamics was revealed at the beginning of the storm main phase. A rapid poleward expansion of disturbances from geomagnetic latitudes of 65°–66° to 74°–75° and the development of the so-called polar cap substorm with a negative bay amplitude of up to 2500 nT, accompanied by precipitation of energetic electrons (riometer absorption) and generation of Pi2–Pi3 pulsations, were observed when IMF B z was about ?45 nT. The geomagnetic activity maximum subsequently sharply shifted equatorward to 60°–61°. The spatial dynamics of the westward electrojet, Pi2–Pi3 geomagnetic pulsations, and riometer absorption was similar, which can indicate that the source of these phenomena is common.  相似文献   

4.
The analysis results of a complex of phenomena that were developing in the evening and morning magnetospheric and ionospheric sectors during two events (January 18 and February 19, 2008) are presented. The analysis is based on the observation data in the magnetotail from the THEMIS satellites and ground-based observations in the morning (MIRACLE network) and nighttime (THEMIS ground-based network) sectors. The events with moderate substorms in the nighttime sector were preceded by strong geomagnetic Pc5 pulsations in the morning sector, the regime of which changed during the development of auroral disturbances. The substorms were accompanied by dipolizations in the magnetotail at distances of ~10 Re and unexpected jump-like fluxes of ～200-keV electrons. The fluxes appeared within several minutes after a breakup at three central THEMIS satellites simultaneously spaced up to 1.7 Re. According with the ASC data at the NAL observatory (3 frames/min) and with the THEMIS network of ASC data, onset of auroral activations in the night and morning sectors occurred simultaneously. Probable reasons for the sudden suppression or intensification of Pc5 pulsations are discussed.  相似文献   

5.
Based on the data of the ground observations, the global distributions of the Pc5 geomagnetic pulsation amplitudes during the recovery phase of the superstorm of October 31, 2003, have been mapped, and an unusually deep penetration of these pulsations into the inner magnetosphere has been found out. Thus, two more zones with identical dynamic spectra and oscillation amplitudes from the polar to equatorial latitudes have been detected in the postnoon sector simultaneously with morning classical Pc5 pulsations in the narrow (～63°–68° CGM) latitudinal band extended along longitude. The higher-latitude zone as if continues the morning band, and the lower-latitude zone is characterized by the maximal intensity at latitudes of ～50°–57° CGM. The oscillation amplitudes are of the same order of magnitude in both zones. The zones are spatially separated by a very narrow latitudinal amplitude minimum and by a change in the phase and sense of rotation of the wave polarization vector. The pulsation spectra in the morning and daytime sectors are different, which indicates that the nature of the morning and postnoon oscillations is different.  相似文献   

6.
A very strong magnetic storm of May 15, 2005, was caused by an interplanetary magnetic cloud that approached the Earths’ orbit. The sheath region of this cloud was characterized by a high solar wind density (～25–30 cm?3) and velocity (～850 km/s) and strong variations (to ～20 nT) in the interplanetary magnetic field (IMF). It has been indicated that an atypical bay-like geomagnetic disturbance was observed during the initial phase of this storm in a large longitudinal region at high latitudes: from the morning to evening sectors of the geomagnetic local time. Increasing in amplitude, the magnetic bay rapidly propagated to the polar cap latitudes up to the geomagnetic pole. An analysis of the global space-temporal dynamics of geomagnetic pulsations in the frequency band 1–6 mHz indicated that most intense oscillations were observed in the morning sector in the region of the equivalent ionospheric current at latitudes of about 72°–76°. The wavelet structure of magnetic pulsations in the polar cap and fluctuations in IMF was generally similar to the maximum at frequencies lower than 4 mHz. This can indicate that waves directly penetrated into the polar cap from the solar wind.  相似文献   

7.
The dynamics of the auroral precipitation boundaries in the daytime (0900–1200 MLT) and nighttime (2100–2400 MLT) sectors during two strong magnetic storms of February 8–9, 1986, and March 13–14, 1989, with a Dst value at a maximum of approximately ?300 and ?600 nT, respectively, are studied using the DMSP satellite data. It is shown that, during the main phase of a storm, a shift to lower latitudes of the poleward and equator ward boundaries of the daytime precipitation is observed. In the nighttime sector, the equatorward boundary of the precipitation also shifts to lower latitudes, whereas the position of the poleward boundary depends weakly on the magnetic activity level even in the periods of very strong magnetic disturbances. The increase in the polar cap area occurs mainly due to the equatorward shift of the daytime precipitation. A high correlation degree between the equatorward shift of the poleward boundary of the daytime precipitation and the position of the equatorward boundary of the precipitation at the nighttime side of the Earth is demonstrated. The analysis of the events shows that (1) the magnetic activity level in the nighttime sector of the auroral zone influences considerably the position of the daytime precipitation boundaries during magnetic storms and that (2) the ring current inputs considerably into the value of the Dst variations.  相似文献   

8.
A complex of geophysical phenomena (geomagnetic pulsations in different frequency ranges, VLF emissions, riometer absorption, and auroras) during the initial phase of a small recurrent magnetic storm that occurred on February 27–March 2, 2008, at a solar activity minimum has been analyzed. The difference between this storm and other typical magnetic storms consisted in that its initial phase developed under a prolonged period of negative IMF B z values, and the most intense wave-like disturbances during the storm initial phase were observed in the dusk and nighttime magnetospheric sectors rather than in the daytime sector as is observed in the majority of cases. The passage of a dense transient (with N p reaching 30 cm−3) in the solar wind under the southward IMF in the sheath region of the high-speed solar wind stream responsible for the discussed storm caused a great (the AE index is ∼1250 nT) magnetospheric substorm. The appearance of VLF chorus, accompanied by riometer absorption bursts and Pc5 pulsations, in a very long longitudinal interval of auroral latitudes (L ∼ 5) from premidnight to dawn MLT hours has been detected. It has been concluded that a sharp increase in the solar wind dynamic pressure under prolonged negative values of IMF B z resulted in the global (in longitude) development of electron cyclotron instability in the Earth’s magnetosphere.  相似文献   

9.
We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution.  相似文献   

10.
A planetary pattern of substorm development in auroral precipitation has been constructed on the basis of the F6 and F7 satellite observations. The behavior of the auroral injection boundaries and characteristics of precipitating electrons in various precipitation regions during all phases of a statistically mean magnetospheric substorm with an intensity of AL ～ ?400 nT at a maximum is considered in detail. It is shown that during a substorm, the zone of structured auroral oval precipitation AOP and the diffuse auroral zone DAZ are the widest in the nighttime and daytime sectors, respectively. In the daytime sector, all precipitation regions synchronously shift equatorward not only at the origination phase but during the substorm development phase. The strongest shift to low latitudes of the daytime AOP region is observed at a maximum of the development phase. As a result of this shift, the area of the polar cap increases during the phases of substorm origination and development. It is shown that the average position of the precipitation boundaries and the energy fluxes of precipitating electrons at each phase are linearly related to the intensity of a magnetic disturbance. This makes it possible to develop a model of auroral precipitation development during each phase of substorms of any intensity.  相似文献   

11.
This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13–17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF) Bz component was ready to turn southward. From 14–17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4～6 MHz) and total electron content (TEC) (～30TECU, 1TECU=1×1016el/m2) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120°E. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047–24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm.  相似文献   

12.
A new type of high-latitude magnetic bays is revealed at geomagnetic latitudes higher than 71°, called ??polar substorms.?? It is shown that polar substorms differ from both classical substorms and high-latitude geomagnetic disturbances of the type of polar boundary intensifications (PBIs). While classical substorms start at latitudes below 67° and then expand poleward, polar substorms start almost simultaneously in the evening-night polar region of the oval. In contrast to PBIs, accompanied by auroral streamers expanding southward, polar substorms are accompanied by auroral arcs quickly traveling northward. It is shown that polar substorms are observed before midnight (20?C22 MLT) under weak geomagnetic activity (Kp ?? 2) during the late recovery phase of a magnetic storm. It is shown that a typical feature of polar substorms is the simultaneous excitation of highly intensive Pi2 and Pi3 geomagnetic pulsations at high latitudes, which exceed the typical amplitude of these pulsations at auroral latitudes by more than an order of magnitude. The duration of pulsations is determined by the substorm duration, and their amplitude decreases sharply at geomagnetic latitudes below ??71°. It is suggested that pulsations reflect fluctuations in ionospheric currents connected with polar substorms.  相似文献   

13.
The observations of the variations in the vertical component of the atmospheric electric field (E z ) at Swider midlatitude Poland observatory (geomagnetic latitude 47.8°) under the conditions of fair weather during 14 magnetic storms have been analyzed. The effect of the magnetic storm main phase in the daytime midlatitude variations in E z in the absence of local geomagnetic disturbances has been detected for the first time. Considerable (～100–300 V m?1) decreases in the electric field strength (E z ) at Swider observatory were observed in daytime simultaneously with the substorm onset in the nighttime sector of auroral latitudes (College observatory). The detected effects indicate that an intensification of the interplanetary electric field during the magnetic storm main phase, the development of magnetospheric substorms, and precipitation of energetic electrons into the nighttime auroral ionosphere can result in considerable disturbances in the midlatitude atmospheric electric field.  相似文献   

14.
During an interaction of the Earth’s magnetosphere with the interplanetary magnetic cloud on October 18–19, 1995, a great magnetic storm took place. Extremely intense disturbances of the geomagnetic field and ionosphere were recorded at the midlatitude observatory at Irkutsk (Φ′≈45°, Λ′≈177°, L≈2) in the course of the storm. The most important storm features in the ionosphere and magnetic field are: a significant decrease in the geomagnetic field Z component during the storm main phase; unusually large amplitudes of geomagnetic pulsations in the Pi1 frequency band; extremely low values of critical frequencies of the ionospheric F2-layer; an appearance of intense Es-layers similar to auroral sporadic layers at the end of the recovery phase. These magnetic storm manifestations are typical for auroral and subauroral latitudes but are extremely rare in middle latitudes. We analyze the storm-time midlatitude phenomena and attempt to explore the magnetospheric storm processes using the data of ground observations of geomagnetic pulsations. It is concluded that the dominant mechanism responsible for the development of the October 18–19, 1995 storm is the quasi-stationary transport of plasma sheet particles up to L≈2 shells rather than multiple substorm injections of plasma clouds into the inner magnetosphere.  相似文献   

15.
Geomagnetic pulsations of the Pc4–5 type at the Barentsburg Observatory for December 2007 to January 2008 are compared with the auroral intensity variations based on the photometric records at the same observatory. In all cases, auroral pulsations similar in shape are also observed simultaneously with geomagnetic pulsations. In the morning and daytime hours, the pulsation radiance maxima fall on the positive half-periods in the H component at the observation point; in the evening and nighttime hours, they fall on the negative half-periods.  相似文献   

16.
The effect of auroral electrojets on the variations in the low-latitude geomagnetic disturbances and Dst during a strong magnetic storm of November 20–21, 2003, with Dst ≈ ?472 nT has been studied based on the global magnetic observations. It has been indicated that the magnetospheric storm expansive phase with Δt ≈ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 30–100 nT in the premidnight-dawn sector. A growth of negative low-latitude ΔH values and Dst is mainly caused by regular convection electrojets with Δt ≥ 10 h, the centers of which shift to latitudes of ～ 50°–55° during the storm development. It has been established that the maximal low-latitude values of the field ΔH component at 1800–2400 MLT are observed when the auroral luminosity equatorward boundary shifts maximally southward during an increase in the negative values of the IMF B z component. It has been assumed that, during this storm, a magnetic field depression at low latitudes was mainly caused by an enhancement of the partially-ring current which closes through field-aligned currents into the ionosphere at the equatorward boundary of the auroral luminosity zone.  相似文献   

17.
The substorm characteristics during the main phase of a large magnetic storm of November 20, 2003, are studied based on the data of TV observations of auroras and auroral absorption at Tixie Bay station and at the global network of magnetic stations. The contribution of auroral particles, responsible for the emission of discrete auroras, has been estimated based on an analysis of the spatial-time variations in the auroral luminosity intensity. This contribution accounted for ～40% of the total luminous flux, which is approximately twice as large as was previously observed in substorm disturbances. Responses of the solar wind and IMF parameters in substorms and variations in the magnetic indices, characterizing geomagnetic activity in the northern polar cap and ring current (PCN, ASY-H and SYM-H), have been detected. The spatial-time distribution of the equivalent ionospheric currents has been constructed, and the total value of these currents along the meridian has been determined based on the [Popov et al., 2001] method and using the IMAGE magnetic data. It has been obtained that the maximal total equivalent ionospheric current in the premidnight sector (～2000 MLT) leads the minimal value of the SYM-H index by ～1.5 h.  相似文献   

18.
Simultaneous morning Pc5 pulsations (f ~ 3–5 mHz) in the geomagnetic field, aurora intensities (in the 557.7 and 630.0 nm oxygen emissions and the 471.0 nm nitrogen emission), and riometer absorption, were studied based on the CARISMA, CANMOS, and NORSTAR network data for the event of January 1, 2000. According to the GOES-8 satellite observations, these Pc5 geomagnetic pulsations are observed as incompressible Alfvén waves with toroidal polarization in the magnetosphere. Although the Pc5 pulsation frequencies in auroras, the geomagnetic field, and riometer absorption are close to one another, stable phase relationships are not observed between them. Far from all trains of geomagnetic Pc5 pulsations are accompanied by corresponding auroral pulsations; consequently, geomagnetic pulsations are primary with respect to auroral pulsations. Both geomagnetic and auroral pulsations propagate poleward, and the frequency decreases with increasing geomagnetic latitude. When auroral Pc5 pulsations appear, the ratio of the 557.7/630.0 nm emission intensity sharply increases, which indicates that auroral pulsations result from not simply modulated particle precipitation but also an additional periodic acceleration of auroral electrons by the wave field. A high correlation is not observed between Pc5 pulsations in auroras and the riometer absorption, which indicates that these pulsations have a common source but different generation mechanisms. Auroral luminosity modulation is supposedly related to the interaction between Alfvén waves and the region with the field-aligned potential drop above the auroral ionosphere, and riometer absorption modulation is caused by the scattering of energetic electrons by VLF noise pulsations.  相似文献   

19.
Intense quasimonchromatic geomagnetic pulsations with a period of ～15 min, observed on the Earth’s surface in the near-noon sector at the beginning of the recovery phase of a very strong (Dst min = ?260 nT) magnetic storm of May 15, 2005, are analyzed. The variations were registered at auroral latitudes only in the X field component, and wave activity shifted into the postnoon sector of the polar cap an hour later; in this case pulsations were observed in the X and Y field components. Within the magnetosphere the source of magnetic pulsations could be the surface waves on the magnetopause caused by the pulse of the solar wind magnetic pressure. Geomagnetic pulsations in the polar cap, observed in phase at different latitudes, could apparently reflect quasiperiodic variations in the NBZ system of field-aligned currents. Such variations can originate due to the series of pulsed reconnections in the postnoon outer cusp at large (～20 nT) positive B z values and large (about ?40 nT) negative values of IMF B x .  相似文献   

20.
The data of the DMSP F7 spacecraft are used for studying the influence of the geomagnetic dipole tilt angle on the latitudinal position of auroral precipitation boundaries in the nighttime (2100–2400 MLT) and daytime (0900–1200 MLT) sectors. It is shown that, in the nighttime sector, the high-latitude zone of soft diffuse precipitation (SDP) and the boundary of the polar cap (PC) at all levels of geomagnetic activity are located at higher and lower latitudes relative to the equinox period in winter and summer, respectively. The position of boundaries of the diffuse auroral precipitation zone (DAZ) located equatorward from the auroral oval does not depend on the season. In the daytime sector, the inverse picture is observed: the SDP precipitation zone takes the most low-latitude and high-latitude positions in the winter and summer periods, respectively. The total value of the displacements from winter to summer of both the nighttime and daytime boundaries of the PC is ∼2.5°. A diurnal wave in the latitudinal position of the nighttime precipitation boundaries is detected. The wave is most pronounced in the periods of the winter and fall seasons, is much weaker in the spring period, and is almost absent in summer. The diurnal variations of the position of the boundaries are quasi-sinusoidal oscillations with the latitude maximum and minimum at 0300–0500 and 1700–2100 UT, respectively. The total value of the diurnal displacement of the boundaries is ∼2.5° of latitude. The results obtained show that, undergoing seasonal and diurnal variations, the polar cap is shifted as a whole in the direction opposite to the changes in the tilt angle of the geomagnetic dipole. The seasonal displacements of the polar cap and its diurnal variations in the winter period occur without any substantial changes in its area.  相似文献   

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