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1.
Spatial-temporal and spectral features of ground geomagnetic pulsations in the frequency range of 1–5 mHz at the initial phase of a strong magnetic storm of the 24th cycle of solar activity (August 5–6, 2011, with a Dst-variation in the storm maximum of ?110 nT) are analyzed. Large opposite in sign amplitudes of variations in IMF parameters (from ?20 to +20 nT) at a high velocity of the solar wind (～650 km/s) accompanied by intense bursts in solar-wind density (up to ～50 cm?3) were distinctive feature of interplanetary medium conditions causing the storm. Geomagnetic Pi3 pulsations global in longitude and latitude and in-phase in the middle and equatorial latitudes were found. The onset of pulsation generation was caused by a pulse of dynamic pressure of the solar wind (～20 nPa), i.e., by a considerable compression of the magnetosphere. The maximum (2–3 mHz) in the amplitude spectrum of near-equatorial pulsations coincided with the maximum of pulsations in the daytime polar cap. After the next jump of the dynamic pressure of the solar wind (～35 nPa), an additional maximum appeared in the pulsation spectrum in the frequency band of ～3.5–4.5 mHz. Global pulsations suddenly stopped after a sharp decrease in the solar-wind dynamic pressure and corresponding extension of the magnetosphere. The obtained results are compared with the time dynamics of the position and shape of the plasmapause.  相似文献   

2.
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   

3.
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   

4.
Based on the observations in six pairs of almost conjugate high-latitude stations in the Arctic and Antarctic regions, the spectral and spatial-temporal structures of long-period geomagnetic pulsations (f = 2–5 mHz) during the magnetic storm of April 16–17, 1999, which is characterized by a high (up to 20 nPa) solar wind dynamic pressure, have been studied. It has been indicated that the magnetic storm sudden commencement is accompanied by a symmetrical excitation of np pulsations near the dayside polar cusps with close amplitudes. Under the conditions when IMF B z > 0 and B y < 0, strong magnetic field variations with the periods longer than 15–20 min were observed only in the northern polar cap. When IMF B z and B y became close to zero, geomagnetic pulsation bursts in both hemispheres were registered simultaneously but differed in the spectral composition and spatial distribution. In the Northern Hemisphere, pulsations were as a rule observed in a more extensive latitude region than in the Southern Hemisphere. In the Northern Hemisphere, the oscillation amplitude maximum was observed at higher latitudes than in the Southern Hemisphere. The pulsation amplitude at geomagnetic latitude lower than 74° was larger in the Arctic Regions than in the Antarctic Regions. This can be explained by sharply different geographic longitudes in the polar cap and latitudes in the auroral zone, which results in a different ionospheric conductivity affecting the amplitude of geomagnetic pulsations.  相似文献   

5.
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   

6.
Ground-based geomagnetic Pc5 (2–7 mHz) pulsations, caused by the passage of dense transients (density disturbances) in the solar wind, were analyzed. It was shown that intensive bursts can appear in the density of the solar wind and its fluctuations, up to Np ～ 30–50 cm3, even during the most magnetically calm year in the past decades (2009). The analysis, performed using one of the latest methods of discrete mathematical analysis (DMA), is presented. The energy functional of a time-series fragment (called “anomaly rectification” in DMA terms) of two such events was calculated. It was established that fluctuations in the dynamic pressure (density) of the solar wind (SW) cause the global excitation of Pc5 geomagnetic pulsations in the daytime sector of the Earth’s magnetosphere, i.e., from polar to equatorial latitudes. Such pulsations started and ended suddenly and simultaneously at all latitudes. Fluctuations in the interplanetary magnetic field (IMF) have turned up to be less geoeffective in exciting geomagnetic pulsations than fluctuations in the SW density. The pulsation generation mechanisms in various structural regions of the magnetosphere were probably different. It was therefore concluded that the most probable source of ground-based pulsations are fluctuations of the corresponding periods in the SW density.  相似文献   

7.
The level of wave geomagnetic activity in the morning, afternoon, and nighttime sectors during strong magnetic storms with Dst varying from ?100 to ?150 nT has been statistically studied based on a new ULF wave index. It has been found out that the intensity of geomagnetic pulsations at frequencies of 2–7 mHz during the magnetic storm initial phase is maximal in the morning and nighttime sectors at polar and auroral latitudes, respectively. During the magnetic storm main phase, wave activity is maximal in the morning sector of the auroral zone, and the pulsation intensity in the nighttime sector is twice as low as in the morning sector. It has been indicated that geomagnetic pulsations excited after substorms mainly contribute to a morning wave disturbance during the magnetic storm main phase. During the storm recovery phase, wave activity develops in the morning and nighttime sectors of the auroral zone; in this case nighttime activity is also observed in the subauroral zone.  相似文献   

8.
The high-latitude geomagnetic effects of an unusually long initial phase of the largest magnetic storm (SymH ~–220 nT) in cycle 24 of the solar activity are considered. Three interplanetary shocks characterized by considerable solar wind density jumps (up to 50–60 cm–3) at a low solar wind velocity (350–400 km/s) approached the Earth’s magnetosphere during the storm initial phase. The first two dynamic impacts did not result in the development of a magnetic storm, since the IMF Bz remained positive for a long time after these shocks, but they caused daytime polar substorms (magnetic bays) near the boundary between the closed and open magnetosphere. The magnetic field vector diagrams at high latitudes and the behaviour of high-latitude long-period geomagnetic pulsations (ipcl and vlp) made it possible to specify the dynamics of this boundary position. The spatiotemporal features of daytime polar substorms (the dayside polar electrojet, PE) caused by sudden changes in the solar wind dynamic pressure are discussed in detail, and the singularities of ionospheric convection in the polar cap are considered. It has been shown that the main phase of this two-stage storm started rapidly developing only when the third most intense shock approached the Earth against a background of large negative IMF Bz values (to–39 nT). It was concluded that the dynamics of convective vortices and the related restructing of the field-aligned currents can result in spatiotemporal fluctuations in the closing ionospheric currents that are registered on the Earth’s surface as bay-like magnetic disturbances.  相似文献   

9.
The variations in the daily average energy of geomagnetic pulsations and noise in the Pc3 (20–60 mHz) and Pc4 (10–19 mHz) frequency bands in the polar cap have been studied based on the data from P5 Antarctic station (corrected geomagnetic latitude ?87°) from November 1998 to November 1999. The daily average pulsation energy has been calculated using the method for detecting the wave packets, the spectral amplitude of which is higher than the threshold level, from the dynamic spectrum. A spectral analysis of the energy of pulsations and noise in the Pc3 and Pc4 bands, performed using the maximal entropy method, has revealed periodicities of 18 days in the local winter and 26, 13, and 7–9 days during the local summer. The simultaneous and coherent variations with periods of 26, 13, and 7–9 days in the solar wind velocity and IMF orientation indicate that the variations in the Pc3–4 wave energy in the polar cap at a sunlit ionosphere are mainly controlled by the parameters of the interplanetary medium. The variations in the Pc3–4 wave energy with a period of 18 days are observed only during the local winter and are supposedly related to the variations in the ionospheric conductivity modulated by planetary waves.  相似文献   

10.
The diumal variations in the parameters of Pc3 (20–60 mHz) and Pc4 (10–19 mHz) pulsations at latitudes of the dayside cusp and polar cap have been studied using data of the magnetic stations of the trans-Antarctic meridional profile for the time interval from January to March 1997 (local summer) under weakly disturbed geomagnetic conditions (AE ≤ 250 nT). The technique for estimating pulsation parameters is based on the separation of the wave packets and noise. The diumal variations in the hourly average parameters of the wave packets in the Pc3 and Pc4 bands and noise in the Pc3-4 band (10–60 mHz)—the average number of wave packets, energy of wave packets and noise, and energy of a single wave packet—turned out to be different for the stations located deep in the polar cap (Φ ～ 87°) and at the latitudes of the dayside polar cusp (Φ ～ 70°) and auroral oval (Φ ～ 66°). Several sources of pulsations caused by different channels of wave energy penetration into the magnetosphere through the dayside cusp, dayside magnetopause, and dawn flank of the magnetotail apparently exist at high latitudes.  相似文献   

11.
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   

12.
The features of daytime high-latitude geomagnetic variations and geomagnetic pulsations in the Рс5 range during the recent, large, two-stage magnetic storm of September 7–8, 2017 are studied. The discussed disturbances were observed at the recovery phase of the first stage of the storm after the interplanetary magnetic field (IMF) turned northward. It is shown that the large sign-alternating variations in Ву and Bz components of the IMF caused intense geomagnetic disturbances up to 300–400 nT with a quasi-period of ~20 min in the daytime sector of polar latitudes, probably in the region of the daytime polar cusp. These disturbances may have reflected quasi-period motions of the daytime magnetopause and may have resulted from nonlinear transformation of the variations in the interplanaterary magnetic field in the magnetosheath or in the magnetospheric entry layers. The appearance of high-latitude long-period variations was accompanied by the excitation of bursts (wave packets) of geomagnetic Pc5 pulsations. The onset of Pc5 pulsation bursts often coincided with a sudden northward turn of the IMF. It was discovered for the first time that the development of a “daytime polar substorm,” i.e., a negative magnetic bay in the daytime sector of polar latitudes, led to a sudden termination of the generation of geomagnetic Pc5 pulsations over the entire latitude range in which these oscillations were recorded before the appearance of the daytime bay.  相似文献   

13.
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   

14.
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   

15.
Polar and high latitude substorms and solar wind conditions   总被引：1，自引：0，他引：1  
All substorm disturbances observed in polar latitudes can be divided into two types: polar, which are observable at geomagnetic latitudes higher than 70° in the absence of substorms below 70°, and high latitude substorms, which travel from auroral (<70°) to polar (>70°) geomagnetic latitudes. The aim of this study is to compare conditions in the IMF and solar wind, under which these two types of substorms are observable on the basis of data from meridional chain of magnetometers IMAGE and OMNI database for 1995, 2000, and 2006–2011. In total, 105 polar and 55 high latitude substorms were studied. It is shown that polar substorms are observable at a low velocity of solar wind after propagation of a high-speed recurrent stream during the late recovery phase of a magnetic storm. High latitude substorms, in contrast, are observable with a high velocity of solar wind, increased values of the Bz component of the IMF, the Ey component of the electric field, and solar wind temperature and pressure, when a high-speed recurrent stream passes by the Earth.  相似文献   

16.
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   

17.
Long-period geomagnetic pulsations during the SSC of July 14, 2012, are studied. The prenoon longitudinal sector (09:20–11:30) MLT, from the boundaries of which pulsations propagate azimuthally onto the dawn and dusk sides with an opposite polarization direction and increased amplitude, has been distinguished. The position of this sector relative to noon (a shift to the dawn side) depends on the front azimuthal inclination. It has been found that the polarization direction reverses in going from low (<30°) to middle/subauroral (≥50°) latitudes on the entire dayside. The geomagnetic pulsations mainly fluctuate near the f1 = 2.9 and f2 = 4.4 mHz frequencies. Fluctuations with frequency f1, which coincide with the fluctuation frequency of the IMF х component, predominate at the polar cap latitudes (the open field line region) in the form of rapidly attenuating impulses and at low latitudes with a much smaller amplitude. Fluctuations with frequency f2 are globally registered at all latitudes in the dayside sector below the magnetopause projection as a train of several fluctuations. It is assumed that fluctuations with frequency f1 penetrate from the solar wind, and fluctuations with frequency f2 are radial magnetopause oscillations.  相似文献   

18.
Two cases when Pc5 geomagnetic pulsations were registered at the IMAGE Scandinavian network of stations and with STARE radars in the afternoon sector (1700–1800 MLT) during the recovery phase of the moderate magnetic storm are analyzed in detail. Using the ground-based observations, it has been indicated that classical quasimonochromatic resonance Pc5 pulsations were observed in the first case (on October 12, 1999; Kp = 5); in this case the maximal amplitude of the spectral maximum at a frequency of 2.5 mHz was registered at Φ ～ 65°. Two maximums were observed in the spectrum in the second case (on October 13, 1999; Kp = 4): ～2.5 mHz (the same maximum) and 2.9 mHz; in this case the maximal oscillation amplitude (2.5 mHz) shifted to Φ > 67°. These results were compared with the echo signal intensity simultaneously registered with the STARE Finland radar on a beam oriented along the 105° geomagnetic meridian. The spatial-temporal maps of the Pc5 pulsation amplitude latitudinal distribution (“keograms”), constructed based on the radar measurements in the wide range of geomagnetic latitudes (63°–70°) where the resolution was substantially higher than that of the ground-based observations, made it possible to detect two regions spaced in latitude (Φ ～ 65° and Φ ～ 67°–68°) with the simultaneous excitation of oscillations (double resonance?), between which the plasmapause projection was supposedly located.  相似文献   

19.
A search for Pc3–4 wave activity was performed using data from a trans-Antarctic profile of search-coil magnetometers extending from the auroral zone through cusp latitudes and deep into the polar cap. Pc3–4 pulsations were found to be a ubiquitous element of ULF wave activity in all these regions. The diurnal variations of Pc3 and Pc4 pulsations at different latitudes have been statistically examined using discrimination between wave packets (pulsations) and noise. Daily variations of the Pc3–4 wave power differ for the stations at the polar cap, cusp, and auroral latitudes, which suggests the occurrence of several channels of propagation of upstream wave energy to the ground: via the equatorial magnetosphere, cusp, and lobe/mantle. An additional maximum of Pc3 pulsations during early-morning hours in the polar cap has been detected. This maximum, possibly, is due to the proximity of the geomagnetic field lines at these hours to the exterior cusp. The statistical relation between the occurrence of Pc3–4 pulsations and interplanetary parameters has been examined by analyzing normalized distributions of wave occurrence probability. The dependences of the occurrence probability of Pc3–4 pulsations on the IMF and solar wind parameters are nearly the same at all latitudes, but remarkably different for the Pc3 and Pc4 bands. We conclude that the mechanisms of high-latitude Pc3 and Pc4 pulsations are different: Pc3 waves are generated in the foreshock upstream of the quasi-parallel bow shock, whereas the source of the Pc4 activity is related to magnetospheric activity. Hourly Pc3 power has been found to be strongly dependent on the season: the power ratio between the polar summer and winter seasons is 8. The effect of substantial suppression of the Pc3 amplitudes during the polar night is reasonably well explained by the features of Alfven wave transmission through the ionosphere. Spectral analysis of the daily energy of Pc3 and Pc4 pulsations in the polar cap revealed the occurrence of several periodicities. Periodic modulations with periods 26, 13 and 8–9 days are caused by similar periodicities in the solar wind and IMF parameters, whereas the 18-day periodicity, observed during the polar winter only, is caused, probably, by modulation of the ionospheric conductance by atmospheric planetary waves. The occurrence of the narrow-band Pc3 waves in the polar cap is a challenge to modelers, because so far no band-pass filtering mechanism on open field lines has been identified.  相似文献   

20.
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   

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