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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.
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   

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.
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   

5.
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   

6.
IMS data from Ottawa, Canada are analyzed to study the propagation characteristics of Pc1 pulsations. The majority of pulsations observed possessed periods of 1 second and lasted less than an hour. Shorter-period Pc1s are observed during the summer than during the winter. Periods of pulsations are also shorter during the noon hours than in the morning, and shorter during intervals of high magnetic activity. The diurnal variation of period at Ottawa is different from that at high-latitude stations. For Pc1s the calculated ratio of the spacing period to the pulse period at Ottawa is 86, in good agreement with values found for both higher- and lower-latitude stations. An IPDP (intervals of pulsations of diminishing periods) event occurred on April 19, 1977. The analysis supports the view that the energy dispersion of storm time protons, as well as the earthward movement of the instability region due to increasing magnetic activity, are involved in the production of such events. Earth Physics Branch Contribution No. 1087.  相似文献   

7.
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   

8.
This paper is devoted to the beautiful and mysterious Pc1 geoelectromagnetic waves that attract the attention of many researchers all over the world as an essential element of the space physics. It is concluded that in spite of the recent progress in the investigation of Pc1 waves, it is still necessary to make a careful study of some unsettled problems posed in the past. Relevant problems and disputable issues of the physics of Pc1 waves are discussed in this paper. The discussion is started with the paradoxical dependence of the Pc1 wave activity on the solar wind plasma density, which is considered as the key problem. It is argued that the solution of this paradox is of paramount importance to understand the 11-year solar cycle variation of the Pc1 occurrence rate, interplay between Pc1 and oxygen ions in the magnetosphere, impact of interplanetary magnetic field sector boundaries on the Pc1 wave activity, and other similar problems. A schematic picture showing the place of Pc1 waves in the system of solar–terrestrial relations is presented.  相似文献   

9.
The analysis of 85,800 events (1979–1981) of Moscow ambulance calls, related to the myocardial infarction (MI), demonstrates a seasonal variation with the profound summer minima and winter maxima. Similar results were obtained by analyzing the 25-year (1970–1995) statistical monthly data on the death from infarction in Bulgaria. The estimated high correlation coefficient (0.84) between Moscow and Bulgarian data suggests a common reason. There is a great number of clinical and statistical studies confirming that the MI number rises during geomagnetic disturbances, which have a maximum of occurrence near equinox, not in winter. In order to explain this contradiction we suggest that one of the critical additional factors, which affect a human cardiovascular system, could be geomagnetic Pc1 pulsations at frequencies comparable with the human heart beat rate. The MI variations as well as the Pc1 pulsations exhibit a summer minimum. The comparative analysis of the Moscow ambulance MI data and Pc1 pulsations recorded at the geophysical observatory in Borok is presented. It is shown that in about 70% of the days when an anomalously great number of ambulance calls (AMI) has been registered Pc1 pulsations have been recorded. In the winter season the probability of the simultaneous AMI and Pc1 occurrence was 1.5 times larger than their accidental coincidence. Moreover, it was found that the effects of magnetic storms and Pc1 in AMI were much higher in winter than in summer. We suggest that the seasonal variation of the production of the pineal hormone melatonin leads to a winter instability in the human organisms and increases the sensitivity of the patient to the “negative” influence of Pc1 geomagnetic pulsations in winter.  相似文献   

10.
Eyvind Sucksdorff (1899–1955) was an enthusiastic scientist who was the director of Sodankylä Geophysical Observatory (SGO) from 1927 to 1945. He continued magnetic measurements, which were started in 1913 when SGO was established. Sucksdorff observed events with periodically modulated amplitude in the registration of the new La Cour quick-run magnetometers in 1932–35. He interpreted these events to be due to short-period oscillations and called them “rapid micropulsations” or “pearl necklace” due to the shape of the signal in the registration. From the “pearl necklaces” he estimated the upper bound of the oscillation to be 2–3 s. Sucksdorff did not know the accurate values of the eigenperiods of the systems (H, D and Z components of the magnetometer). Later measurements have shown that they were 2–3 s. Nowadays, the pearl pulsations discovered by Sucksdorff 70 years ago are known as a subgroup of Pc1 magnetic pulsations. Sucksdorff published his observations in 1936. He studied both the annual and diurnal distributions of the new pulsations. Comparisons of the records made in Stockholm, Copenhagen and Sodankylä revealed for the first time the global features of Pc1 pulsations. Sucksdorff did not present any explanation for the pearl pulsations he had observed. Leiv Harang from the Auroral Observatory at Tromsø, Norway, published his analysis of rapid registrations made in Tromsø in 1932–36 in the same issue of the Terrestrial Magnetism and Atmospheric Electricity. He used the name “vibrations” for his short-period oscillations.  相似文献   

11.
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   

12.
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   

13.
The interrelation between sudden increases in the solar wind dynamic pressure, auroral proton flashes on the dayside equatorward of the oval, and geomagnetic pulsations in the Pc1 range is considered on the basis of simultaneous observations of the solar wind plasma parameters, proton auroras on the IMAGE satellite, and geomagnetic pulsations at the Lovozero Observatory. It is indicated that proton luminosity flashes were observed in 70% of cases equatorward of the auroral oval during sudden changes in the solar wind pressure. In this case, flashes of proton auroras were observed in 85% of cases during sudden changes in the pressure, which were related to interplanetary shocks. Increases in pressure during tangential discontinuities were accompanied by flashes of proton auroras only in 45% of cases. When the ground station was conjugate to the region occupied by a proton aurora flash, the appearance or intensification of existent pulsations in the Pc1 range was observed in 96% of cases. When the ground station was not conjugate to the region of a proton luminosity flash, the response in geomagnetic pulsations was observed in 32% of events. When a sudden change in the solar wind pressure was not accompanied by a proton luminosity flash, the response in pulsations in the Pc1 range was hardly observed.  相似文献   

14.
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   

15.
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   

16.
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   

17.
Relatively little is known about the effects of geomagnetism on plants. Such fundamental questions as (1) whether or not plants perceive the Earth's magnetic field, (2) the physical nature of the magnetic receptor(s) and (3) whether or not the geomagnetic field has any bearing on the physiology and survival of plants remain largely unanswered. The present review examines the possibility that three classes of unexplained biological rhythms in plants may relate to the sensitivity of plants to variations in the geomagnetic field. The first section examines the possibility that a class of plant rhythms, here termed 0.2–5 Hz rhythms, may be reflections of the sensitivity of plants to Pc1 geomagnetic pulsations. The second section reviews recent evidence that plants are affected by geomagnetic storms. The third section examines the possibility that circa-weekly, circa-fortnightly and circa-monthly rhythms in plants may be reflections of the solar rotation cycle and its sub-harmonics.  相似文献   

18.
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   

19.
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   

20.
Geomagnetism and Aeronomy - The results of analysis an unusual event in the frequency range of Pc1 geomagnetic pulsations discovered at the end of solar cycle 24 are presented. This event was...  相似文献   

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