首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The structure and dynamics of auroras in the midnight sector during substorms, which develop during the magnetic storm main phase as compared to the characteristics of a typical auroral substorm, have been studied using the ground-based and satellite observations. It has been found out that a difference from the classical substorm is observed in auroras during the magnetic storm main phase. At the beginning of the storm main phase, the series of pseudobreakups with the most pronounced jump-like motion toward the equator shifts to lower latitudes. The substorm expansion phase can be observed not only as arc jumps to higher latitudes but also as an explosive expansion of a bright diffuse luminosity in all directions. During the magnetic storm main phase, auroras are mainly characterized by the presence of stable extensive rayed structures and by the simultaneous existence of different auroral forms, typical of different substorm phases, in the TV camera field of view.  相似文献   

2.
Data from the meridian scanning photometers of the NORSTAR network and all-sky cameras of the THEMIS network were used for a detailed study of the response of night auroras to the sharp decrease of the solar wind dynamic pressure on September 28, 2009. The decrease in dynamic pressure was accompanied by a corresponding depression of the magnetic field in the SYM-H index and the origin of a negative sudden impulse (SI) with a duration of 5–8 min and amplitude of 150–200 nT in the horizontal component of the magnetic field at stations of the night sector of the auroral zone. The magnetic impulse was preceded by a long calm magnetic period, although the IMF Bz-component was negative for ~1.5 hour before the SI –. The commencement of the SI –, which was determined by variations in the magnetic field at ~0650 UT, was accompanied by a sharp increase in the intensity of discrete forms of polar auroras in the midnight sector of the auroral zone and their fast propagation to the pole. Approximately 6–8 min after the SI –, the auroral intensity in the emissions, which were excited by the fluxes of precipitated electrons and protons, quickly began to decrease in the night sector. Analysis of the optical observations showed the two-stage character of the response of the night auroras to the SI – in the considered event: first, fast movement of the discrete aurora forms to the pole with a significant increase in their intensity, and a further fast decrease in auroral intensity with a delay of ~6–8 min relative to the SI –. The possible reasons for such aurora behavior are discussed.  相似文献   

3.
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   

4.
More than one hundred years ago Kristian Birkeland (1867–1917) first addressed the question as to why auroras appear overhead when the Earth's magnetic field is disturbed. He laid foundations for our current understanding of geomagnetism and polar auroras. For the first time cosmic phenomena were scaled and simulated in a laboratory. Birkeland's terrella experiments were ingenious. Even though the famous Lord Kelvin, in 1892, wrote that no matter passes between the Sun and the Earth, Birkeland's first auroral theory from 1896 is based on charged particle of solar origin, illustrated by the following quotation: “the auroras are formed by corpuscular rays drawn in from space, and coming from the sun”. Thus, the year 1896 marks the founding of space plasma physics. His most enduring contribution to auroral physics was his recognition that field-aligned currents are needed to couple auroral phenomena in the upper atmosphere to interplanetary space. The existence of field-aligned currents was controversial and disputed vigorously among scientists for more than 50 years. During The Birkeland Symposium in 1967 it was unanimously proposed that field-aligned currents in space should be called “Birkeland currents”, which was accepted by the International Union for Geomagnetism and Aeronomy. Today, plasma physicists strongly believe that many significant cosmic phenomena result from streams of Birkeland currents.  相似文献   

5.
Based on results of the simultaneous TV observations at Barentsburg high-latitude observatory and Lovozero auroral observatory and using the IMAGE auroral luminosity images, the auroral fine structure and dynamics has been studied during the substorm of December 26, 2000, when the auroral luminosity distribution represented a double oval. It has been indicated that the interaction between the processes proceeding in different magnetospheric regions, the projections of which are the poleward and equatorward edges of the double oval, is observed in auroras in the process of substorm development.  相似文献   

6.
The energy of precipitating particles that cause auroras can be characterized by the ratio of different atom and molecule emissions in the upper atmospheric layers. It is known that the spectrum of precipitating electrons becomes harder when substorms develop. The ratio of the I 6300 red line to the I 5577 green line was used to determine the precipitating-electron spectrum hardness. The I 6300/I 5577 parameter was used to roughly estimate the electron energy in auroral arcs observed in different zones of the auroral bulge at the bulge poleward edge and within this bulge. The variations in the emission red and green lines in auroral arcs during substorms that occurred in the winter season 2007–2008 and in January 2006 were analyzed based on the zenith photometer and all-sky camera data at the Barentsburg and Longyearbyen (LYR) high-latitude observatories. It has been indicated that the average value of the I 6300/I 5577 emission ratio for arcs within the auroral bulge is larger than this value at the bulge poleward edge. This means that the highest-energy electron precipitation is observed in arcs at the poleward edge of the substorm auroral bulge.  相似文献   

7.
Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.  相似文献   

8.
The position of the auroral luminosity equatorward boundary during the interaction between the Earth’s magnetosphere and isolated solar wind streams from different solar sources has been statistically studied based on the ground and satellite observations of auroras. These studies continue the series of the works performed in order to develop the technique for predicting auroras based on the characteristics of the interplanetary medium and auroral disturbances. The dependences of the minimal position of the auroral luminosity equatorward boundary (Φ′) on the values of the azimuthal component of the interplanetary electric field (E y ) and AL indices of magnetic activity, averaged over 6 and 24 h, are presented. The distribution limits for each type of isolated solar wind streams on the Φ′-E y and Φ′-AL planes have been determined.  相似文献   

9.
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   

10.
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   

11.
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   

12.
  相似文献   

13.
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   

14.
为了解极光电集流在sawtooth事件期间的响应情形,本文利用北半球高纬地磁台站的磁场数据,建立了以球元基本电流系反演法求得大尺度电离层水平等效电流系分布的方法,以此研究了2000年9月30日同步轨道LANL卫星观测到的sawtooth事件期间极光电集流的变化.本文将sawtooth注入事件后极区电离层夜侧西向电集流增长的特征,与中低纬地基磁场北向分量正弯扰的特征做比较分析.两者的观测结果都表明在本sawtooth注入事件期间有电流楔的形成,且电流楔约有11 h磁地方时(MLT)的宽度.此外,中低纬磁弯扰达到最大扰动值的时间一般比高纬电集流达到最大扰动值的时间长,说明影响中低纬磁弯扰变化的电流源较丰富.  相似文献   

15.
Large auroral and ionospheric databases, covering a solar cycle (1978–1986), were used to obtain a comprehensive evaluation of the auroral electrojet effect (as inferred from the auroral AE-index) on the ionospheric response in both hemispheres from sub-auroral to equatorial latitudes. The study was limited to the East Asian-Australian longitudinal sector where data are available from a chain of nine latitudinally displaced stations. Enhancement in the standard ionospheric parameter, the virtual height of the F-region (Δh′F) recorded by vertical-incidence ionosondes, was used to trace the ionospheric disturbance.Unlike the previous studies of this type, the total magnetic and ionospheric data, in hourly intervals, were used to derive the correlation coefficient r between two intrinsically different parameters: Δh′F and AE-index for the local nighttime (20–06 LT or 10–20 UT). A suitable averaging and smoothing technique was applied to the data to enhance the correlation trend between these parameters. It is evident that the height fluctuations of sub-auroral ionosphere (for stations: Yakutsk in Siberia and Hobart and Canberra in Australia) closely resemble the auroral electrojet surges, inferred from the AE-index over the solar cycle. The linear coefficient r is highly significant, being close to 0.6 for most of the time; during the years of maximum auroral activity (1981–1983) r approached 0.8. The consistently high correlation r, regardless of the season, applies only to the most poleward station used in this study, Yakutsk. The sub-auroral stations (Hobart and Canberra) positioned further equatorwards show a strong decline in the correlation coefficient r during the local summer but have high r during winter and the equinoxes. There is a general decline in r towards lower latitudes, suggesting that the response to auroral substorms is on the whole diminishing with the distance from the auroral source to the equator. There appears to be an anomalous increase in r as observed around 10° invariant latitude.These findings appear to be the first long-term proof of the symmetry of the ionospheric responses to auroral substorm activity in the northern and southern auroral ovals which is an important contribution to space climatology. It is suggested that the aurorally generated acoustic gravity waves (AGWs), manifested in the global ionosphere as large scale travelling ionospheric disturbances (LSTIDs), may contribute to the observed auroral-ionospheric phenomena.  相似文献   

16.
We have used the global numerical model of the coupled ionosphere-thermosphere-protonosphere system to simulate the electric-field, ion- and electron-temperature and -concentration variations observed by EISCAT during the substorm event of 25 March 1987. In our previous studies we adopted the model input data for field-aligned currents and precipitating electron fluxes to obtain an agreement between observed and modelled ionospheric variations. Now, we have calculated the field-aligned currents needful to simulate the substrom variations of the electric field and other parameters observed by EISCAT. The calculations of the field-aligned currents have been performed by means of numerical integration of the time-dependent continuity equation for the cold mag-netospheric electrons. This equation was added to the system of the modelling equations including the equation for the electric-field potential to be solved jointly. In this case the inputs of the model are the spatial and time variations of the electric-field potential at the polar-cap boundaries and those of the cold magnetospheric electron concentration which have been adopted to obtain the agreement between the observed and modelled ionospheric variations for the substorm event of 25 March 1987. By this means it has been found that during the active phase of the substorm the current wedge is formed. It is connected with the region of the decreased cold magnetospheric electron content travelling westwards with a velocity of about 1 km s–1 at ionospheric levels.  相似文献   

17.
The results of studying the Pc4–5 pulsation parameters based on the method of bistatic backscatter of radio waves, using the EISCAT/Heating HF facility (Tromsø, Norway) and IMAGE ground-based magnetometers (Scandinavia), are presented. The observations were performed during the morning hours on October 3, 2006, when a substorm developed on the nightside. An analysis of the observational data obtained from 1000 to 1020 UT indicated that wave-like disturbances with periods corresponding to Pc4–5 pulsations (80–240 s) existed at that time. The variations in the full vector of the ionospheric irregularity motion and the electric field strength in an artificially disturbed high-latitude ionospheric F region has been reconstructed based on simultaneous Doppler observations on two paths. A general conformity is observed among the time variations in Pc4–5 pulsations in the magnetic and ionospheric data: between the velocity amplitude (|V|) and the X component of the Earth’s magnetic field and between the irregularity motion azimuth and the Y component. Large-scale waves, corresponding to the natural resonances of magnetic field lines (small values of the azimuthal number |m| ～ 2–4), and small-scale waves (large values |m| ～ 17–20) were simultaneously registered during the experiment based on magnetic data. It has been indicated that the periods of wave-like processes registered using the method of bistatic backscatter and ground-based magnetometers were in agreement with one another. The formation of wave-like processes is explained by the nonstationary impact of the solar wind and IMF on the Earth’s magnetosphere. The variations in the IMF, according to the ACE satellite measurements, were characterized by a sharp increase in the solar wind plasma dynamic pressure that occurred at about 09 UT on October 3, 2006, and was accompanied by rapid polarity reversals of the north-ward-southward (B z) and transverse (B y) IMF components.  相似文献   

18.
The sensitive method for detecting and measuring the velocity of a weak luminosity wave, traveling from bottom to top along an arc or isolated auroral beams, has been developed. This wave is caused by dispersion of precipitating electrons over velocities and by a differential atmospheric penetration of different-energy electrons, and the wave velocity gives information about the location of the electron acceleration region in the magnetosphere. The method was tested using different model signals and was used to study pulsating auroras and auroral breakup. A luminosity wave has been detected in pulsating auroras, and it has been estimated that the injection region is located at a distance of 5–6 R e . The application of the method to intensification of auroras during breakup indicated that such a wave is absent; i.e., breakup electrons being accelerated near the ionosphere at altitudes of 2000–8000 km. It has been assumed that the regions of anomalous resistance, generated in the ionosphere by field-aligned currents during the breakup phase, cause intense local field-aligned electric fields. These fields accelerate thermal electrons and form the auroral breakup pattern.  相似文献   

19.
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   

20.
Auroras have been extensively studied using images obtained by space-borne experiments. We use global UVI images obtained from Polar and simultaneous plasma data obtained by the 3D instrument on Wind from the near-earth plasma sheet to study the dynamics of auroras with different size and intensity. Unstable phase space ion distributions are detected in the plasma sheet under diverse geomagnetic and solar wind IMF conditions (positive and negative Bz) and at all phases of a substorm. These results indicate that plasma instability processes with different disturbance levels operate in the plasma sheet and produce a continuum of auroral size and intensity. The criteria for triggering an instability are dependent on the local properties of the plasma distributions. These observations suggest a new framework to integrate previous and current results and a new way to examine the causal relationships of auroral and plasma sheet dynamics.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号