The ionosphere as an Alfven resonator in the Pc1 micropulsation range     

Karel Prikner  Vladimír Vagner 《Studia Geophysica et Geodaetica》1990,34(4):342-361

Summary A local planar approximation of a stratified, inhomogeneous, anisotropic and dissipative ionosphere is presented as an Alfven quarter-wave plate resonator in the Pc1 micropulsation range. The frequency-amplitude structure of the resonance response of an isotropic Alfven wave on the Earth's surface and at a given altitude in the ionosphere is studied in comparison to standing waves in vacuum above an ideal conductor for a particular model of the ionosphere. An asymmetry in the response was found at both boundary of the resonator, at the Earth's surface and at the given altitude z₀. The results are related to the vertical changes of frequency dispersion in the dissipative medium of the ionosphere and to the vertical profile of the inhomogeneities of the resonator being considered.  相似文献   

Numerical modelling of the ionospheric filtration of an ulf micropulsation signal     

Karel Prikner  Vladimír Vagner  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1983,27(2):173-190

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Polarization characteristics of ionospheric filtration of ULF waves     

Vladimír Vagner  Karel Prikner  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1983,27(3):285-297

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Frequency analysis of geomagnetic beating-type pulsations in thepc3 range     

Karel Prikner  Jaroslav Střeštík  Karel Dobeš  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1972,16(3):262-270

Summary The spectral analysis of samples of beating-type pc3 pulsations, recorded at the Budkov Observatory during the summer months of 1968 and 1969 was carried out in the frequency interval10 mHz100 mHz. The average limits of the pulsation frequency range are roughly20 mHz60 mHz. The centre of the occurrence frequency graphs for both components is at the frequency f_g 41 mHz. The analysis of three separated daily intervals showed a very slight tendency to a systematic decrease in the frequency of the centre from the morning to the afternoon. The study of the sense of rotation of the pulsation disturbance vector in the (X, Y)-plane showed an overall predominancy of L over R-types during daytime, particularly during the morning.  相似文献   

Rapid changes in the fourier spectra ofPi1 pulsations during magnetically disturbed periods     

Karel Prikner 《Studia Geophysica et Geodaetica》1969,13(3):276-292

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Geomagnetic Pc3 Pulsations During the Total Solar Eclipse on Aug 11, 1999     

Střeštík  J.  Prikner  K. 《Studia Geophysica et Geodaetica》2003,47(3):565-578

The solar eclipse on August 11, 1999, observed in the region covered by many geomagnetic observatories, has offered a unique opportunity to look for an effect of the eclipse on geomagnetic pulsations. The pulsation activity digital data have been taken from Budkov Observatory in the Czech Republic (in the X component only), from observatories in Germany (Niemegk, Fürstenfeldbruck, Bad Bergzabern), in Hungary (Nagycenk), and for comparison in South Africa (Hermanus, conjugate-point station), and in Finland (Sodankylä, far from the eclipse zone). At all these stations the field in all three component has been recorded. The pulsation amplitudes in the X component exhibit a long-term minimum near the time of the eclipse. Spectral analysis of selected short intervals confirmed this decrease and also revealed a decrease of the average pulsation period during the eclipse. Such a change in the amplitude or in the period was not observed outside of the eclipse interval or in other days. Investigation in some narrower frequency bands showed that the maximal decrease occurred in the 15–20 s band. All these changes can be found in records from all the stations near the eclipse totality belt, also in records at the conjugate-point station, where no eclipse occurred. No signature has been found in records at the station situated far from the eclipse zone.  相似文献   

Nonstationary pearl pulsations as a signature of magnetospheric disturbances     

F. Z. Feygin  N. G. Kleimenova  O. A. Pokhotelov  M. Parrot  K. Prikner  K. Mursula  J. Kangas  T. Pikkarainen 《Annales Geophysicae》2000,18(5):517-522

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   

Simultaneous conjugate ground-satellite ULF pulsation measurements at the middle latitudes     

K. Prikner 《Annales Geophysicae》1997,15(6):645-655

The spectra of three series of simultaneous ground (Budkov Observatory) and satellite (Freja) ULF measurements have been processed. The following features were studied in the FFT spectra, power-spectra and cross-spectra of the six-minute samples, recorded during quasi-conjugate approaches of Freja to the local Budkov magnetic field line: (a) the Doppler frequency shift (about 1 mHz and less) in the predominant and some particular spectral components on Freja; (b) the amplitude relations between the ground and satellite (ratios 0.3 to 0.8); (c) phase shifts between particular signal components on the spacecraft above the ionosphere (in the azimuthal y-direction on Freja) and on the ground (in the meridional x-direction at Budkov) have been estimated (phase lags on the ground 0.9 rad) and (d) also dynamical characteristics of the fundamental wave modes in the (x,y)-plane, perpendicular to the magnetic field line, have been estimated for the predominant spectral components, considering standing oscillation along the field line. Azimuthal wave numbers were about 2.0, propagating northwest at 400km/s.  相似文献   

On the mathematical modelling of the spectral structure of geomagneticPC1 pulsations via the response of Alfvén's ionospheric resonator     

Karel Prikner  Felix Z. Feygin  Dora S. Fligel 《Studia Geophysica et Geodaetica》1995,39(1):19-36

Summary A method of numerical simulation of the coefficient of reflection of the ionospheric transition layer as a function of frequency is applied to the experimental data related to several series of pearl-type pulsations Pc1 (f = 0.2 – 2 Hz) recorded at the observatories of Kerguelen, Sogra and Nurmijarvi. The inverse problem of modelling, i.e. determining the vertical profiles of ionospheric electron concentration corresponding to the actual experimental situations, was solved approximately. The initial assumption for interpreting the specific nature of the series of Pc1 micropulsations parallel in time was their resonance origin under reflection of the signal at magnetically conjugate ionospheres, Alfvén's resonators, in both of the Earth's hemispheres.  相似文献   

Application of the method of numerical simulation of ionospheric filtration of Pc1 signals to solving the inverse problem of ionospheric modelling     

Karel Prikner  Dora S. Fligel 《Studia Geophysica et Geodaetica》1992,36(3):240-256

Summary The numerical method of simulating ionospheric filtration of ULF signals in the range of Pc1 frequencies has been applied to French geomagnetically conjugate observations of ULF signals made by the GEOS-1 satellite and at the observatory of Husafell (Iceland) [2]. The experimentally obtained variable values of the transmissivity of the Pc1 signal through the ionosphere [5] in the course of the micropulsation distrubance of 13.7. 1977 have been compared with the results of the numerical simulation taking into consideration the fundamental physical parameters of the high-latitude external ionosphere. This approximate form of solving the inverse problem of ionospheric modelling yielded quantitative estimates of the rapid variations of the concentration of charged particles in connection with the expected changes of their temperature. It is assumed that nonstationary states of the ionospheric plasma are caused by the very ion-cyclotron waves penetrating the ionosphere at high latitudes ( 70°) along the plasmapause.  相似文献