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1.
An abrupt decrease in the solar wind pressure and its effect on the magnetosphere and ionosphere during the event occurring on April 4, 1971, are studied. This event differs fundamentally from a typical sudden commencement (SC) of a geomagnetic storm or from a positive sudden impulse (SI+) and is determined as a negative sudden impulse (SI–). The geomagnetic variations at different latitudes and the cosmic radio emission in the auroral zone are analyzed. From the data of low-latitude geomagnetic observatories, several subsequent negative impulses observed with a periodicity of ~45 min were found. At the same time, a sudden decrease in the absorption of cosmic radio emission in the auroral zone was revealed. Possible physical explanations of the observed changes are discussed. 相似文献
2.
《Journal of Atmospheric and Solar》2000,62(9):737-749
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
3.
The solar wind–magnetosphere coupled system is characterized by dynamical processes. Recent works have shown that nonlinear couplings and turbulence might play a key role in the study of solar wind–magnetosphere interaction processes.Within this framework, this study presents a statistical analysis aimed to investigate the relationship between solar wind MHD turbulence and geomagnetic activity at high and low latitudes as measured by the AE and SYM-H indices, respectively. This analysis has been performed for different phases of solar cycle 23. The state of turbulence was characterized by means of 2-D histograms of the normalized cross-helicity and the normalized residual energy. The geomagnetic response was then studied in relation to those histograms.The results found clearly show that, from a statistical point of view, solar cycle 23 is somewhat peculiar. Indeed, good Alfvénic correlations are found unexpectedly even during solar activity maximum. This fact has implications on the geomagnetic response as well since a statistical relationship is found between Alfvénic fluctuations and auroral activity. Conversely, solar wind turbulence does not seem to play a relevant role in the geomagnetic response at low latitudes. 相似文献
4.
A. V. Roldugin V. G. Vorobjev V. C. Roldugin S. A. Chernouss 《Geomagnetism and Aeronomy》2010,50(1):34-40
The results of the ground-based optical observations of sunlit auroras, performed at Lovozero and Apatity observatories on
April 10 (event 1) and April 27, 2007(event 2), are presented. The observations were performed in the (OI) 557.7 nm emission,
using a new equipment based on a Fabry-Pérot interferometer connected to a PhotonMAX CCD camera. During event 1, the observations
were performed in the Harang discontinuity region at a low magnetic disturbance. It has been indicated that an auroral arc
was located in the polar part of the eastward electrojet, and the arc position coincides with the equatorward boundary of
structured precipitation (b2e). During event 2, auroras were observed within the average statistical boundaries of the auroral
oval and the region of structured precipitation under the conditions of rather high geomagnetic activity. However, during
the period of low geomagnetic activity, discrete auroras were registered at a geomagnetic latitude of ~64° on that day, which
is 3°—4° equatorward of the structured precipitation region. Such a low latitudinal position of auroras can be explained by
the effect of a high solar wind velocity, which was ~580 km/s during the period of observations. 相似文献
5.
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
6.
In the period of the International Geophysical Year (IGY), almost the entire planet was covered for the first time by ground-based
geophysical observations. Their analysis led to two fundamental results: the existence of the auroral oval and auroral (magnetospheric)
substorm. At the final stage of the IGY, satellite explorations of the near-Earth space began. The auroral luminosity appeared
to be related to the plasma structure of the magnetosphere. That opened new possibilities for parameters diagnostics of the
Earth’s magnetosphere on the basis of ground-based aurora observations. The concepts of auroral oval and magnetospheric substorm
became paradigms of the new science of solar-terrestrial physics. 相似文献
7.
8.
B.T. Tsurutani X.-Y. Zhou V.M. Vasyliunas G. Haerendel J.K. Arballo G.S. Lakhina 《Surveys in Geophysics》2001,22(2):101-130
Dayside near-polar auroral brightenings occur when interplanetary shocks impinge upon the Earth's magnetosphere. The aurora first brightens near local noon and then propagates toward dawn and dusk along the auroral oval. The propagation speed of this wave of auroral light is 10 km s-1 in the ionosphere. This speed is comparable to the solar wind speed along the outer magnetosphere. The fundamental shock-magnetospheric interaction occurs at the magnetopause and its boundary layer. Several physical mechanisms transferring energy from the solar wind directly to the magnetosphere and from the magnetosphere to the ionosphere are reviewed. The same physical processes can occur at other solar system magnetospheres. We use the Haerendel (1994) formulation to estimate the acceleration of energetic electrons to 50 keV in the Jovian magnetosphere/ionosphere. Auroral brightenings by shocks could be used as technique to discover planets in other stellar systems. 相似文献
9.
Based on the DMSP F6 and F7 satellite observations, the characteristics of precipitating particles in different auroral precipitation regions of the dayside sector have been studied depending on the solar wind plasma density. Under quiet geomagnetic conditions (|AL| < 100 nT and B z > 0), a considerable increase in the fluxes of precipitating ions is observed in the zones of structured auroral oval precipitation (AOP) and soft diffuse precipitation (SDP). A decrease in the mean energy of precipitating ions is observed simultaneously with the flux growth in these regions. The global pattern of variations in the fluxes of precipitating ions, which shows the regions of effective penetration of solar wind particles into the magnetosphere at a change in the solar wind density from 2 to 20 cm?3, has been constructed. The maximal flux variation (ΔJ i = 1.8 · 107 cm?2 s?1, i.e., 3.5% of an increase in the solar wind particle flux) is observed in the SDP region on the dayside of the Earth. The dependence of precipitating ion fluxes in the low-latitude boundary layer (LLBL), dayside polar cusp, and mantle on the solar wind density at positive and negative values of the IMF B z component has been studied. In the cusp region, an increase in the precipitating ion flux is approximately 17% of an increase in the solar wind density. The IMF southward turning does not result in an appreciable increase in the ion precipitation fluxes either in the cusp or in the mantle. This fact can indicate that the reconnection of the geomagnetic field with southward IMF is not the most effective mechanism for penetration of solar wind particles into these regions. 相似文献
10.
M. I. Tyasto N. G. Ptitsyna I. S. Veselovsky O. S. Yakovchouk 《Geomagnetism and Aeronomy》2009,49(2):153-162
A retrospective analysis of the Russian magnetic observations of the Carrington event that occurred on September 2–3, 1859, has been performed. The conclusion has been made that this event was caused by the series of three recurrent eruptive solar flares during ～40 h. The characteristics of the geomagnetic crochet, related to a considerable flux of the ionizing electromagnetic radiation during this flare, have been studied. The value and direction of a magnetic field disturbance, registered during the maximum of the geomagnetic storm of September 2, unambiguously indicate that all Russian stations were in the auroral oval zone, which was strongly expanded southward from its average position. The disturbance dependence on the station longitude—the absence of magnetometer pinning in Nerchinsk—is interpreted as the possible manifestation of a strong asymmetry in the effective contour of the current system, which was connected to the heliosphere and covered the disturbed magnetosphere and ionosphere during the short period that lasted only 1–3 h. 相似文献
11.
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
12.
Paleomagnetic studies have shown that, moving backwards in time, the geomagnetic dipole moment increased to a peak nearly 50% greater than at present ca. 2500 years ago. Attempts to model how changes in dipole moment affect solar–terrestrial relations have hitherto invoked a scaling relation for the size of the magnetosphere based on finding where the magnetic pressure of the dipole field balances the ram pressure of the solar wind. This approach predicts that, following a solar storm, the strength of the terrestrial response represented by the electrical potential across the auroral zones in the ionosphere should vary as the 1/3 power of dipole moment. Such a weak dependence suggests that a 50% increase in dipole moment would minimally effect (14%) terrestrial manifestations of solar storms. Recent work, however, based on a feedback mechanism involving electrical currents coupling the magnetosphere and ionosphere has identified a stronger 4/3, power scaling relation applicable to storm conditions. Here we use a global MHD simulation to calculate for a 50% increased dipole moment the correspondingly increased auroral-zone potential and its extension to low latitudes. 相似文献
13.
O. M. Chugunova V. F. Pilipenko M. Engebretson A. S. Rodger 《Geomagnetism and Aeronomy》2006,46(1):64-73
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
14.
As a rule, bright auroral arcs evolve near the poleward boundary of the auroral oval at the growth phase of a substorm, a phenomenon that is known to occur near the poleward edge of the auroral oval. The closeness of these arcs to the projection of the magnetic separatrix on the night side suggests that their generation is related to magnetic reconnection in the magnetospheric tail in a particular way. In this study this suggestion is confirmed by the fact that integral brightness of the auroral oval at the poleward edge correlates with magnetic field structures in the solar wind that are observed by ACE and Wind satellites at distances of 50–300 RE upstream and are shifted towards the magnetospheric tail with time delays of ~ 10–80 min, consistent with measurements of the solar wind velocity. About 50 examples of this correlation have been found. The possible physical mechanisms of the effect observed are discussed. 相似文献
15.
The results of observations of turbulent transport in the Earth’s magnetosphere tail are summarized. The results of recent works on the projection of the auroral oval onto the equatorial plane, according to which the main part of the oval is not projected onto the plasma sheet, are taken into account. Analysis of the eddy diffusion coefficient dependences on the geocentric distance and on the phase of a magnetosphere substorm, both across the sheet and in the azimuthal direction, is carried out. The role of eddy diffusion in the creation of quasi-equilibrium plasma structures and in the plasma transport from the magnetospheric flanks into the plasma sheet is considered. The transport along the sheet is discussed. The problems of turbulent transport that can be solved by analysis the data of multisatellite projects are indicated. 相似文献
16.
I. P. Kirpichev O. I. Yagodkina V. G. Vorobjev E. E. Antonova 《Geomagnetism and Aeronomy》2016,56(4):407-414
The position of the auroral oval poleward and equatorward boundary projections on the equatorial plane in the nightside MLT sector during magnetically quiet periods (|AL| < 200 nT, |Dst| < 10 nT) has been determined. The oval boundary positions were determined according to the precipitation model developed at Polar Geophysical Institute (http://apm.pgia.ru/). The isotropy of the averaged plasma pressure and the experimentally confirmed balance of pressures during the nighttime have been taken into account. The morphological mapping method has been used to map the oval poleward and equatorward edges without the use of any magnetic field model on the assumption that the condition of magnetostatic equilibrium is valid. Ion pressures at ionospheric altitudes and in the equatorial plane have been compared. It has been shown that the auroral oval equatorward boundary in the midnight sector is localized at geocentric distances of ~7 RE, which is in good agreement with the position of the energetic particle injection boundary in the equatorial plane. The oval poleward edge is localized at the ~10 RE geocentric distance, which is in good agreement with the position of the equatorward boundary of the region with a high turbulence level in the Earth’s magnetosphere plasma sheet. 相似文献
17.
The effect of the ponderomotive force on the background plasma modification near magnetic holes, which form at the dayside magnetospheric boundary under the action of the solar wind, has been studied. It was shown that this effect results in a substantial increase in a nonlinear plasma density disturbance. The dependence of the ponderomotive force on the magnetospheric parameters (the magnetic longitude, distance from the Earth’s surface, ratio of the wave frequency to the proton gyrofrequency, and ionospheric ion cyclotron wave amplitude) has been studied. Nonlinear plasma density disturbances will be maximal in the region of magnetic holes, which are located in the dayside magnetosphere at λ ~ 0°?30° geomagnetic longitudes (λ = 0° corresponds to noon), where the effect of the solar wind pressure is maximal. A similar effect is also observed in the dependence of a nonlinear plasma density disturbance on other magnetospheric parameters. 相似文献
18.
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
19.
The works in the alternative direction of magnetospheric studies are reviewed. In contrast to the traditional approach, where the basis process is magnetic field line reconnection, transformation of kinetic energy into electromagnetic one at the bow shock front is the basis process in the proposed approach. It has been indicated that this new paradigm makes it possible to overcome the main difficulties that remained within the scope of the previous paradigm. It has been briefly demonstrated how several following processes and phenomena are explained within the scope of the new approach: (1) transformation of the solar wind kinetic energy into the electromagnetic energy; (2) electromagnetic energy transfer into the magnetosphere; (3) organization of the system of bulk currents, formation of field-aligned currents from the magnetosphere, and compatibility of these currents with the ionospheric current systems; (4) shape, value, and dynamics of the particle precipitation auroral regions; and (5) substorm expansion (auroral breakup). Other possibilities of the new approach and paradigm replacement consequences are briefly considered. 相似文献
20.
Cosmic ray (CR) fluxes, which penetrate into the Earth??s magnetosphere and atmosphere from the interplanetary space, are an important factor of space weather. The geomagnetic field allows or forbids CR particles to enter into a given point in the magnetosphere depending on their energy. The geomagnetic cutoff rigidity regulates the distribution of CR fluxes in the magnetosphere. The geomagnetic cutoff rigidity (geomagnetic threshold) determination accuracy is closely related to the accuracy of the magnetospheric model used in calculations. Using a method for tracing of charged CR particle trajectories in the magnetic field of a model magnetosphere, we obtained geomagnetic thresholds for two magnetosphere empirical models (Ts01 and Ts04), constructed based on the same initial database. The Ts01 model describes the middle magnetosphere for certain conditions in the solar wind and interplanetary field. The Ts04 model pays the main attention to describing the large-scale evolution of magnetospheric currents during a storm. The theoretically obtained geomagnetic thresholds have been compared with experimental thresholds, calculated using the spectrographic global survey method based on data from the global network of CR stations. The study has been performed for the period of a strong geomagnetic storm that occurred in November 2003. 相似文献