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1.
We conducted a statistical analysis of the physical characteristics of the micropulsation activity (Pc3 and Pc4 range) detected, during the austral summer 1994/95, at Terra Nova Bay (Antarctica, corrected latitude 80.0°S), a station which is few degrees poleward of those where most of the Antarctic measurements in these frequency ranges have been performed. The emerging overview suggests that the correspondence between the pulsation power and the external parameters (solar wind speed, interplanetary magnetic field magnitude and orientation) is significantly stronger than at somewhat lower latitudes. The day-to-day power variability was found to be strictly related to the general level of the geomagnetic activity, and the power level sharply maximizes at local magnetic noon. In the Pc4 range peaks of correlation with the SW speed are found in the dawn and dusk sides of the Earths magnetosphere and the daily variation of the polarization pattern is closely consistent with that found at auroral latitudes and at lower frequencies. In the Pc3 range the correlation coefficient between the pulsation power and the SW speed has maximum values in the local morning, and the frequency of selected events reveals a strong IMF control during closed magnetospheric conditions. The local time dependence of the correlation coefficient between the pulsation power and the cone angle reveals an additional control by the IMF orientation, which becomes more explicit around local noon. 相似文献
2.
Based on the data of the ground observations, the global distributions of the Pc5 geomagnetic pulsation amplitudes during the recovery phase of the superstorm of October 31, 2003, have been mapped, and an unusually deep penetration of these pulsations into the inner magnetosphere has been found out. Thus, two more zones with identical dynamic spectra and oscillation amplitudes from the polar to equatorial latitudes have been detected in the postnoon sector simultaneously with morning classical Pc5 pulsations in the narrow (～63°–68° CGM) latitudinal band extended along longitude. The higher-latitude zone as if continues the morning band, and the lower-latitude zone is characterized by the maximal intensity at latitudes of ～50°–57° CGM. The oscillation amplitudes are of the same order of magnitude in both zones. The zones are spatially separated by a very narrow latitudinal amplitude minimum and by a change in the phase and sense of rotation of the wave polarization vector. The pulsation spectra in the morning and daytime sectors are different, which indicates that the nature of the morning and postnoon oscillations is different. 相似文献
3.
A preliminary analysis of Pc5, ULF wave activity observed with the IMAGE magnetometer array and the EISCAT UHF radar in the post midnight sector indicates that such waves can be caused by the modulation of the ionospheric conductivity as well as the wave electric field. An observed Pc5 pulsation is divided into three separate intervals based upon the EISCAT data. In the first and third, the Pc5 waves are observed only in the measured electron density between 90 and 112 km and maxima in the electron density at these altitudes are attributed to pulsed precipitation of electrons with energies up to 40 keV which result in the height integrated Hall conductivity being pulsed between 10 and 50 S. In the second interval, the Pc5 wave is observed in the F-region ion temperature, electron density and electron temperature but not in the D and E region electron densities. The analysis suggests that the wave during this interval is a coupled Alfven and compressional mode. 相似文献
4.
5.
O. M. Chugunova V. A. Pilipenko S. L. Shalimov M. Engebretson 《Geomagnetism and Aeronomy》2008,48(3):307-313
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
6.
Experiments on the generation of artificial electromagnetic pulsations constitute an important part of investigations of the
magnetosphere-ionosphere system with the use of an active action. The investigation of the generation of magnetic pulsations
in the Pc1 frequency range has shown that the response of the ionosphere to heating is detected only in a few experiments.
Although the primary perturbed parameter is the electron temperature, the efficiency of the generation of pulsations is determined
by the perturbations of the ionospheric conductivity. The magnitude of these hertz perturbations depends complexly on the
electron density profile and the parameters of a pump wave. The numerical experiment demonstrates the determining effect of
the electron density in the D region on the magnitude of perturbations of the ionospheric conductivity. Under conditions of a low electron density, it
is impossible to create a large perturbation of the conductivity in the Pc1 frequency range, although perturbations of the
electron temperature can be large in this case. In view of a large number of electrons at altitudes of 70–90 km, which absorb
a considerable fraction of the energy of a high-frequency wave, the electron temperature in the E region of the ionosphere cannot be sharply increased, but the amplitude of the variations of the ionospheric conductivity
in this case is larger than that for the profiles with a low electron density. In the presence of the developed D region, the efficiency of the modification of the conductivity in the indicated frequency range can be increased by choosing
the optimal frequency and polarization of the pump wave. A low efficiency of the experiments on the generation of artificial
magnetic pulsations in the Pc1 frequency range is apparently explained by the fact that they were performed in winter in the
absence of a well-developed D region of the ionosphere. 相似文献
7.
T. D. Borisova N. F. Blagoveshchenskaya V. A. Kornienko M. T. Rietveld 《Geomagnetism and Aeronomy》2011,51(5):620-632
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
8.
The case study of four Pc1 subauroral pulsation events from Finland has been carried out on the basis of the full-wave numerical
method. This method has been applied to simultaneous Scandinavian EISCAT radar measurements of the ionospheric plasma parameters,
and their vertical (altitude) profiles have been utilized. Two alternative plasma profiles with different ion composition
displays have been put to the test. A comparison between both types of the modeled ionospheric Alfvén resonator (IAR) ground
signal frequency response and the frequency range of the Pc1 signal records has been studied. The results of the applied method
can illustrate possible quiescent or disturbance changes in the upper ionosphere above the dense F2 layer. The ionospheric
region up to ∼ 2000 km has been taken into account for this comparative analysis. 相似文献
9.
N. J. Fox M. Lockwood S. W. H. Cowley M. P. Freeman E. Friis-Christensen D. K. Milling M. Pinnock G. D. Reeves 《Annales Geophysicae》1994,12(6):541-553
A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at \sim0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (\sim0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is “pinched off”, and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked “viscous-like” momentum transfer across the magnetopause. 相似文献
10.
《Journal of Atmospheric and Solar》2000,62(4):311-322
A Pc1/IPDP event recorded by the Finnish search coil magnetometers on 15 December 1984 was analyzed in a companion paper (Mursula et al., 2000. Non-stationary Alfvén resonator: new results on Pc1 pearls and IPDP events. J. Atmos. Solar-Terr. Phys. 62(4), 299–309) using numerical simulations of the ionospheric Alfvén resonator (IAR). EISCAT incoherent scatter radar data were used to determine the vertical profiles of ionospheric plasma parameters. In this paper, the detailed altitude profiles of several wave characteristics at the IAR eigenfrequency are computed up to 1000 km height, including, e.g., the real normalized amplitude of the magnetic wave field component, ellipticity and orientation of the polarization ellipse in the horizontal plane. We also calculate the altitude profile of the energy flux density (Poynting vector). These features illustrate in detail the ionospheric effects on the wave spectral structure in a non-stationary IAR, and their significance in the formation of the Pc1/IPDP signal on the ground. 相似文献
11.
Felix Borleanu Mihaela Popa Mircea Radulian Johannes Schweitzer 《Journal of Seismology》2011,15(3):431-442
The BURAR seismic array, located in Northern Romania (Bucovina region), is designed to monitor events located in an area poorly
covered by other existing seismic stations. In order to use the BURAR array for single-station locations, it is crucial to
calibrate the azimuth and slowness parameters, which are currently used in array techniques to locate earthquakes, blasts
or nuclear explosions. The goal of this study is to apply “f–k” and plane wave fit techniques in order to constrain the slowness
and azimuth parameters at BURAR for teleseismic, regional and local events. The analysis was carried out using P and S waves
recorded for events occurred between 2004 and 2008 within a radius of 50° around BURAR. The azimuth values obtained applying
both methods strongly deviated from the theoretical values for regions like Central Turkey, Bulgaria, Dodecanese Islands and
other parts of Greece, while the ray parameter deviations with respect to a 1-D IASP91 reference model are less significant.
For the local events, the anomalies are smaller, except the particular case of Vrancea intermediate-depth earthquakes for
which strong azimuth deviations (33.5°), both positive and negative, are observed. We investigate how these systematic deviations
in azimuth are explained by the structure lateral heterogeneities which characterize the study region. 相似文献
12.
The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals. 相似文献
13.
《Journal of Atmospheric and Solar》1999,61(8):619-628
This paper presents results of an experimental verification of our earlier suggested spectral-polarization method of measuring the interference pattern velocity by analyzing three mutually orthogonal projections of the radio signal field vector using a single receiving antenna. The measurements were made on an HF radio path about 100 km in length, with a simultaneous monitoring of the ionospheric situation using an oblique-incidence sounding chirp–ionosonde. In an effort to eliminate multipath effects, in the analysis we used nighttime intervals, for which a stable one-mode reflected radio signal was observed. It is shown that the proposed method gives the mean values of the azimuth and zenith angle which differ by no more than 2 to 5° from calculated values. Mean values of the velocity of travelling ionospheric disturbances (of order 50 m/s) and propagation directions (north-westward changing to northward by the morning hours) obtained for these time intervals are consistent with existing published data. 相似文献
14.
用1957~2006年间515个主相单步发展的磁暴事件,分析东亚扇区4个中低纬台站的电离层扰动类型及电离层暴开始时间,得到该地区电离层暴随纬度、季节和地方时的分布规律.研究表明,中纬区负暴明显,低纬区正暴明显;夏季负暴比正暴多,冬季正暴比负暴多,春秋季正负暴分布表现出明显的纬度差异.在东亚扇区,中纬区负暴开始时间主要分布在夜间及清晨时段,且在正午至午后时段极少发生.低纬区正暴开始时间主要发生在白天时段,且在夜间18~21 LT时段也易发生正暴.中低纬电离层正相暴平均延迟时间在10 h以内,负相暴平均延迟时间在10 h以上,且中纬区延迟时间明显比低纬区短.电离层暴延迟时间与磁暴主相开始时间对应的地方时很相关,正相暴对白天发生的磁暴比对晚上发生的磁暴响应快些,而负相暴正好相反.但电离层暴延迟时间与磁暴强度之间并没有十分明显的依赖关系. 相似文献
15.
The dawn and dusk electrojet response to substorm onset 总被引：1，自引：0，他引：1
E. Borälv P. Eglitis H. J. Opgenoorth E. Donovan G. Reeves P. Stauning 《Annales Geophysicae》2000,18(9):1097-1107
We have investigated the time delay between substorm onset and related reactions in the dawn and dusk ionospheric electrojets, clearly separated from the nightside located substorm current wedge by several hours in MLT. We looked for substorm onsets occurring over Greenland, where the onset was identified by a LANL satellite and DMI magnetometers located on Greenland. With this setup the MARIA magnetometer network was located at dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the westward jet. In the first few minutes following substorm onset, sudden enhancements of the electrojets were identified by looking for rapid changes in magnetograms. These results show that the speed of information transfer between the region of onset and the dawn and dusk ionosphere is very high. A number of events where the reaction seemed to preceed the onset were explained by either unfavorable instrument locations, preventing proper onset timing, or by the inner magnetospheres reaction to the Earthward fast flows from the near-Earth neutral line model. Case studies with ionospheric coherent (SuperDARN) and incoherent (EISCAT) radars have been performed to see whether a convection-induced electric field or enhanced conductivity is the main agent for the reactions in the electrojets. The results indicate an imposed electric field enhancement. 相似文献
16.
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 significance of the O+-ion density altitude profile of the outer ionosphere for determination of the Ionospheric Alfvén Resonator (IAR) lower harmonic structure has been demonstrated. The O+-reduced and exponentially extrapolated ionosphere models at high altitudes are generally acceptable for the IAR interpretation of subauroral broadband Pc1 events. Instantaneous ionospheric plasma data based on simultaneous EISCAT (CP-1, CP-7) measurements should be most suitable for the interpretation of different pulsation events. The limited applicability of the averaged International Reference Ionosphere (IRI) models has also been demonstrated. 相似文献
19.
利用武汉电离层观象台高频多普勒台阵的覆盖太阳活动高、低年份，长达５年的连续观测数据，采用小波分析等方法估算电离层声重波扰动（ＴＩＤ）的传播参量，通过这些参量对武汉地区电离层扰动形态和变化规律进行了系统分析研究．结果表明，观测到的中尺度电离层声重波扰动（ＭＳＴＩＤ）存在二个显著季变化，在传播速度和周期上有明显差异的优势传播方向：一个指向东北方，传播的方位角主要分布在３０°─７０°之间（０°为正北，以顺时针方向表示传播方位角），它在夏季出现率最大，冬季基本消失；另一个优势方向指向正南，方位角主要分布在１５０°─２２０°范围，主要出现在冬季．文中还给出了ＭＳＴＩＤ的年、日变化，并进一步探讨了其变化特性的可能形成机理． 相似文献