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1.
The dynamics of the Pc5 and Pi1 pulsation characteristics and relativistic electron fluxes at geostationary orbit were comparatively analyzed for three nine-day intervals, including quiet periods and periods of geomagnetic storms. It was shown that relativistic electron fluxes increase considerably when the power of global Pc5 pulsations and the index of midlatitude irregular Pi1 pulsations increase simultaneously. The correlation between the characteristics of Pi1 and Pc5 geomagnetic pulsations and the level of the relativistic electron flux at geostationary orbit during the magnetic storm recovery phase were studied. It was shown that the correlation coefficient of the relativistic electron maximal fluxes during the magnetic storm recovery phase with the parameter of midlatitude Pi1 pulsations is slightly higher than such a correlation coefficient with the solar wind velocity.  相似文献   

2.
Using Pc1 data gathered at Ottawa (45.4°N, 75.6°W; L = 3.5) during the International Magnetospheric Study (IMS) period, relationships between ssc, Dst, and the occurrence of Pc1 pulsations are examined. It is found that the sudden compressions of the magnetoshere that took place in the postnoon period (13–22 hLT) frequently produced Pc1 pulsations at Ottawa. This pulsational activity took place about 25 to 125 hours after the occurrence of ssc’s of amplitude 5–25 nT and duration 2–6 min. Pc1’s also occur 20 to 40 hours after maximum Dst deviations in the range 50–110 nT, when the ring current has decayed to a considerable extent (5 nT < Dst < 25 nT). In agreement withHeacock andKivinen (1972), it appears that during the storm recovery phase energetic particles of the ring current with anisotropic pitch angle distribution interact with the surrounding cold plasma of the plasmasphere. When stable trapping limit is reached, proton cyclotron instability is triggered and pulsations in the Pc1 period range are generated.  相似文献   

3.
A new index of wave activity (ULF index) is applied to analyze daytime magnetic pulsations in the Pc5 range (f = 2–7 mHz) during ten successive recurrent magnetic storms (CIR (corotating interaction region) storms) of 2006. The most intense daytime geomagnetic Pc5 pulsations on the Earth’s surface in all phases of CIR storms are predominantly observed in the pre-noon sector at latitudes higher than 70°, while those in CME storms (storms initiated by coronal mass ejection (CME)) are observed at latitudes lower than 70°. A comparison of wave activity during CIR and CME storms has shown that the amplitude of Pc5 pulsations in CIR storms is much smaller than that in CME storms and the spectrum maximum is observed at lower frequencies and higher latitudes. At the same time, the mechanism of ULF wave generation during both types of magnetic storms seems to be similar, namely, resonance of magnetic field lines due to the development of the Kelvin-Helmholtz instability caused by an approach of a high-velocity solar wind stream to the Earth’s magnetosphere. Since resonance oscillations are excited only in the closed magnetosphere, the higher-latitude position of the Pc5 pulsation intensity maximum in CIR storms points to larger dimensions of the daytime magnetosphere during CIR storms as compared to CME storms.  相似文献   

4.
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   

5.
The results of magnetometric observations and radar studies of the lower ionosphere during the superstrong magnetic storm (geospace storm) of November 7–10, 2004, are presented and analyzed. An increase in the electron density and in the amplitudes of its aperiodic and quasi-periodic variations at high level of magnetic activity is detected. In individual time intervals, the relation of Pc5-6 magnetic pulsations to short-period (5–15 min) wave disturbances in the electron density in the lower ionosphere was observed.  相似文献   

6.
The occurrence of pearl-type (Pc 1) micropulsations recorded at the mid-latitude station Nagycenk (Hungary) during a half solar cycle showed a quite regular variation on this long time scale. Around solar activity maximum, the number of days with Pc 1 occurrence was rather low, while it began to increase during medium solar activity rising to a maximum around solar activity minimum. Pc 1 pulsations have been analyzed in relation to further parameters and on a shorter time scale, too. Based on data of 2 years with maximum Pc 1 occurrence (around solar activity minimum in 1985 and 1986), a seasonal variation was also found. Additionally, it was confirmed that pearl-type micropulsations might frequently occur, on and after days, with geomagnetic disturbances. At Nagycenk, the selected geomagnetic disturbances were generally associated with an increased ionospheric absorption of radio waves caused by enhanced ionization due to particle precipitation from the magnetosphere into the lower ionosphere. Whistler observations carried out at Panska Veš (a station in the Czech Republic) showed a significant whistler activity connected with these geomagnetic disturbances, however, no after-effect appeared in whistler activity. One of the main goals of the present study was to find a relationship between Pc 1 pulsations and whistlers. Results revealing an increased whistler activity associated with Pc 1 occurrences confirm our previous findings rather convincingly. The latter ones hinted at the probability that certain magnetospheric configurations, e.g. geomagnetic field line shells and whistler ducts are closely connected, as similar positions of the two structures were found within the magnetosphere when characteristics of Pc 3 pulsations and whistlers were analyzed.  相似文献   

7.
Simultaneous whistler records of one station and geomagnetic pulsation (Pc3) records at three stations were compared. In a previous study correlation was found between occurrence and L value of propagation/excitation for the two phenomena. The recently investigated simultaneous records have shown that the correlation is better on longer time scales (days) than on shorter ones (minutes), but the L values of the propagation of whistlers/excitation of pulsations are correlated, i.e. if whistlers propagate in higher latitude ducts, pulsations have periods longer than in the case when whistlers propagate in lower latitude ducts.  相似文献   

8.
This paper is devoted to the morphology of Pc1 geomagnetic pulsations (frequency range 0.2–5.0 Hz). This study is based on the series of continuous observations of Pc1 pulsations during more than three solar cycles (July 1957–December 1995). The main attention is given to the temporal characteristics of Pc1 activity, i.e. daily, seasonal and cyclic variations, and also the relationship of Pc1 activity with magnetic storms, sector structure of the interplanetary magnetic field and parameters of the solar wind. The results may be used in the studies of medicobiologic aspects of the problem of solar–terrestrial relations.  相似文献   

9.
2007年3月3日位于磁层昏侧THEMIS的5颗卫星、同步轨道晨侧和午前的GOES 3颗卫星和地面地磁台站同时观测到了持续近4 h的Pc5 ULF波.我们用交叉小波相关分析计算脉动的传播速度,用MVA分析求解脉动的传播方向,然后结合两者的计算结果获得了Pc5相速度矢量信息.THEMIS卫星观测到Pc5具有压缩特性,且向阳传播,速度约在6~20 km/s左右,相比于磁层中阿尔芬速度(1000 km/s)较低.这些Pc5 ULF波动可能产生于磁尾或磁层内部不稳定性.GOES 3颗卫星观测到不同情况的Pc5 ULF波,极向模占主要成分,且具有波包结构,具有阿尔芬驻波特性,可能产生于K-H(Kelvin-Helmholtz)不稳定性.地面台站观测到ULF波扰动幅度随纬度升高而增强,Pc5脉动在地理纬度60°附近达到最大值, Dumont durville台站观测到的脉动与THEMIS观测到波形有很好的相似性.  相似文献   

10.
Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.  相似文献   

11.
Examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere, observed by INTERBALL-Auroral satellite during January 11, April 11 and June 28, 1997 are shown. Identification of corresponding magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured simultaneously onboard the spacecraft. The examined Pc5 pulsations reveal a compressional character. A fairly good correlation is demonstrated between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The ULF Pc5 wave occurrence is observed in both upward and downward FACs.  相似文献   

12.
中低纬地区地磁脉动的研究   总被引：1，自引：0，他引：1  
近年来我们对中低纬地区地磁脉动进行了大量的观测和研究。本文不仅介绍了观测仪器的设计、台网设置及数据处理方法。而且还简要地介绍了一些主要科研成果,如低纬Pc3脉动特点,低纬Pi2脉动偏振特性。南极地区的地磁脉动观测结果,以及在磁暴和太阳耀斑期间在低纬地区观测的地磁脉动。这对于进一步认识中低纬地区地磁脉动是十分有益的。  相似文献   

13.
The negative and positive fronts of the IMF B z component arrived at intervals of 3 h during a strong magnetic storm of May 15, 2005. The occurrence of Pc5 pulsations at these three characteristic instants has been considered based on the WIND satellite magnetic data. Pulsations originated not only during sudden compression SC of the magnetosphere but also during the B z sign reversal from positive to negative. The IMF B z sign reversal from negative to positive did not affect the development of pulsations. It is assumed that Pc5 pulsations observed after the negative IMF B z front are related to the development of surface waves at the magnetopause as a result of impulsive reconnection of field lines.  相似文献   

14.
We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations.  相似文献   

15.
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   

16.
Quasi-periodic Pc 5 pulsations have been reported inside and just outside the Earth’s magnetotail during intervals of low geomagnetic activity. In order to further define their characteristics and spatial extent, we present three case studies of simultaneous magnetic field and plasma observations by IMP-8, ISEE-1 (and ISEE-2 in one case) in the Earth’s magnetotail and ISEE-3 far upstream of the bow shock, during intervals in which the spacecraft were widely separated. In the first case study, similar pulsations are observed by IMP-8 at the dawn flank of the plasma sheet and by ISEE-1 near the plasma sheet boundary layer (PSBL) near midnight local time. In the second case study, simultaneous pulsations are observed by IMP-8 in the dusk magnetosheath and by ISEE-1 and 2 in the dawn plasma sheet. In the third case study, simultaneous pulsations are observed in the north plasma sheet boundary layer and the south plasma sheet. We conclude that the pulsations occur simultaneously throughout much of the nightside magnetosphere and the surrounding magnetosheath, i.e. that they have a global character. Some additional findings are the following: (a) the observed pulsations are mixed mode compressional and transverse, where the compressional character is more apparent in the close vicinity of the plane ZGSM=0; (b) the compressional pulsations of the magnetic field in the dusk magnetosheath show peaks that coincide (almost one-to-one) with similar peaks observed inside the dawn plasma sheet; (c) in the second case study the polarization sense of the magnetic field and the recurrent left-hand plasma vortices observed in the dawn plasma sheet are consistent with antisunward moving waves on the magneto-pause; (d) pulsation amplitudes are weaker in the PSBL(or lobe) as compared with those in the magneto-tail’s flanks, suggesting a decay with distance from the magnetopause; (e) the thickness of the plasma sheet (under extremely quiet conditions) is estimated to be \sim22 RE at an average location of (X, Y)GSM=(16, 17) RE, whereas at midnight local time the thickness is \sim14 RE. The detected pulsations are probably due to the pressure variations (recorded by ISEE-3) in the solar wind, and/or the Kelvin Helmholtz instability in the low-latitude boundary layer or the magnetopause due to a strongly northward IMF.  相似文献   

17.
The spatial structure of intensive Pc5 pulsations of the geomagnetic field and riometer absorption during the recovery phase of a strong magnetic storm that occurred on October 31, 2003, have been considered in detail. The global structure of disturbances has been analyzed based on a global network of magnetometers and riometers supplemented by the data of magnotometers and particle detectors on geostationary satellites GOES and LANL. The local spatial structure was studied by the data of a regional network of Finland vertical riometers and the stations at the IMAGE magnetic network. Quasiperiodic variations in the magnetic field and riometer absorption are generally similar and have a close frequency composition; nevertheless, their local spatial structures are different, as a result of which the concept that riometer absorption pulsations represent a purely modulation process is doubtful. It is assumed that the observed variations are oscillations of two related systems: the magnetospheric MHD waveguide/resonator and systems including cyclotron noise and electrons. Geomagnetic Pc5 oscillations during the recovery phase of a strong magnetic storm supposedly result from the generation of the magnetospheric waveguide on magnetospheric flanks. An analysis of azimuthal propagation phase velocities indicates that these oscillations depend on intramagnetospheric parameters rather than on the solar wind velocity. The magnetospheric waveguide is in a metastable state when solar wind velocities are high, and the quasiperiodic fluctuations of the solar wind pressure stimulate the excitation of the waveguide.  相似文献   

18.
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   

19.
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   

20.
Recent work suggests that the quasi-periodic (QP) modulation \sim10-50 s of naturally occurring ELF-VLF radio emissions (\sim0.5-5 kHz) is produced by the compressional action of Pc3 magnetic pulsations on the source of the emissions. Whilst it is generally accepted that these magnetic pulsations have an exogenic source, it is not clear what the mechanism of their generation is. A study of QP emissions observed during 1988 at Halley, Antarctica, in conjunction with IMP-8 satellite solar wind data, shows that the occurrence and modulation frequency of the emissions are strongly dependent upon the direction and strength of the IMF, respectively. The observed relationships are very similar to those previously reported for Pc3 pulsations associated with upstream ion-cyclotron resonance, involving proton beams reflected at the bowshock. In comparing the observed QP modulation frequencies with upstream wave theory, agreement was found by considering wave excitation exclusively associated with a proton beam reflected from a position on the bowshock at which the shock normal is parallel to the ambient IMF direction. Other geometries were found to be either impropitious or uncertain. The work indicates the useful diagnostic role QP emissions could play in the study of compressional ULF waves in the upstream solar wind and in monitoring the IMF conditions responsible for their generation.  相似文献   

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