Spatial structure of standing wave electromagnetic fields at the lower harmonics of the ionospheric Alfvén resonator     

Karel Prikner  Felix Z. Feygin  Tero Raita 《Studia Geophysica et Geodaetica》2014,58(2):326-337

During the multiband wave Pc1 event on March 7, 2001 the EISCAT UHF and VHF incoherent scatter radars operated simultaneously covering an exceptionally wide altitude range of the ionosphere ～90—2000 km. This made possible to test the ionospheric Alfvén resonator (IAR) model over a large altitude range. The three lowest IAR eigenfrequencies, where the most of the Pc1 pulsation signal bands occur, were selected for the spatial analysis of the standing wave electromagnetic fields, applying the full-wave numerical simulation method. The altitude spread of amplitude maxima and nodes together with polarization characteristics of oscillation maxima in the horizontal plane are presented. The comparison of the standing wave oscillations on the altitude profile with the signal amplitude observed on the ground is also presented.  相似文献   

Coordinated Simultaneous Freja Satellite and Niemegk Observatory ULF Measurements     

Prikner  Karel 《Studia Geophysica et Geodaetica》1997,41(3):247-263

The standard FFT analysis was applied to thirteen pulsation events selected from the March–April 1993 simultaneous measurements in space (Freja satellite) and on the ground (Niemegk Observatory). The spectral processing of the six-minute sections of record in two coordinate components perpendicular to the magnetic field lines had two principal subjects in view: a) Frequency-amplitude satellite-ground relations. The average values of smoothed spectral amplitude transmission coefficients in the total Pc4-3 and, separately, in Pc4 and Pc3 bands were 0.60, 0.48 and 0.70, respectively. The maximum values were observed within the Pc3 band, near f 30 mHz. b) Estimation of frequency bands of field line resonances (FLRs) recorded on Freja. Freja's motion in a broad latitude range (±5° around Niemegk) during the measurements enabled two frequency bands of FLRs with a width of 10's of mHz to be identified on Freja. The weighted frequencies of the FLRs bands on Freja were f _wA 36 mHz and f _wB 18 mHz with fine structure separations of about 5 mHz and 4 mHz, respectively. The second band with f _wB 18 mHz was mostly not observed at Niemegk, and this could be the consequence of the satellite moving partly through regions of L greater than that of Niemegk.  相似文献   

HM-wave filtration in a horizontally stratified earth's magnetosphere     

Karel Prikner  Reviewer G. Siráň 《Studia Geophysica et Geodaetica》1976,20(1):39-51

Summary The model of filtration of a linearly polarized HM-wave in a system of three homogeneous layers, limited by two halfspaces and treated in[1], is generalized. The wave attenuation is considered in all inner layers of the system and the model is applied to the filtration of HM-waves in the lower layers of the magnetosphere, i.e. in the ionosphere. The nature of the changes of the functional dependences is studied, i.e. of the amplitude coupling factor on the frequency under variation of the fundamental parameters, defining the filtering medium. Filtration models are demonstrated and discussed for the periods of maximum and minimum solar activity during daytime and at night. The relation between the properties of filtration and the possibilities of observing geomagnetic pulsations on the Earth's surface is pointed out.  相似文献   

Algorithm of the problem of simulating the total wave field of the geomagnetic pulsation signal within the ionospheric transition layer     

Karel Prikner  Vladimír Vagner 《Studia Geophysica et Geodaetica》1995,39(2):208-212

Summary This supplement to paper by Prikner and Vagner (1991) describes the optimum algorithm for the automated computer program of numerical simulation of the total wave field anywhere within the ionospheric filter. The matrix method of thin layers in an inhomogeneous, anisotropic and dissipative ionosphere has been applied. The application of this method enables in situ measurements of geomagnetic pulsations in the ionosphere to be compared with the results of the numerical simulation.  相似文献   

Polarization characteristics of standing wave electromagnetic fields at the ionospheric Alfvén resonator lower harmonics: altitude profiles     

Karel Prikner  Felix Z. Feygin  Tero Raita 《Studia Geophysica et Geodaetica》2014,58(2):338-341

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A comparative Pc1 case study applying two modes of ionospheric Alfvén resonator modeling     

Karel Prikner  Felix Z. Feygin  Tero Raita 《Studia Geophysica et Geodaetica》2010,54(3):495-511

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   

O<Superscript>+</Superscript>-Reduced Models of the High Latitude Ionosphere and the Ionospheric Alfvén Resonator in Broadband Pc1 Events     

K. Prikner  R. Kerttula 《Studia Geophysica et Geodaetica》2005,49(1):127-139

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   

Ionospheric Alfvén Resonator Control over the Frequency-Variable Pc1 Event in Finland on May 14, 1997     

Prikner  K.  Mursula  K.  Kangas  J.  Feygin  F. Z. 《Studia Geophysica et Geodaetica》2001,45(4):363-381

The ionospheric Alfvén resonator (IAR) control mechanism over the EMIC wave transmission to the ground is demonstrated on a selected long-term frequency-variable subauroral Pcl event. The proper ionospheric plasma data obtained from EISCAT were accessible in a wide altitude range. Applying the numerical method of simulation of a realistic inhomogeneous IAR, the problem of appearance and disappearance of the ground Pc1 signal record was clarified on the basis of coincidence between the EMIC wave frequency spectrum and the IAR fundamental frequency peak (the frequency window). A shift of the signal source field line to lower latitudes during the development of the disturbance was noticed, and the signal frequency variation on the ground was modelled in the nonstationary IAR. Variation of the IAR altitude structure in the fundamental frequency was illustrated on altitude profiles of the normalized wave magnetic field amplitude in the horizontal and vertical components. Particular conditions of L - and R -wave mode incidence were assumed. The electron density vertical profile of IAR determines the effective resonator dimensions. In this way the IAR fundamental frequency window controls the signal within the ionosphere and on the ground.  相似文献   

The ionosphere of higher geomagnetic latitudes (L=3 andL=5) as a ulf wave filter     

Karel Prikner  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1986,30(3):304-319

Summary Eight models of the ionosphere in the MHD approximation over the whole range of required heights(50–3000 km) are synthesized on the basis of other theoretical studies and a number of empirical methods for the purposes of modelling the ionospheric filtration of the natural micropulsation (Pc1) signal. The models represent a vertically inhomogeneous and dissipative daytime and nighttime ionosphere of higher latitudes in two regions (L=3 and L=5) of the Northern Hemisphere in summer under low (F _10.7 =70) and high (F _10.7 =200) solar activity. The higher ionosphere (h>200 km) is approximated by a quasineutral oxygen-hydrogen plasma(O ⁺,H ⁺) taking into account the wave-dissipating effects of the neutral component(O, He). The procedure of computing the physical parameters, locally characterizing the medium of the ionosphere, is demonstrated.

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