Karel Prikner

Numerical modelling of the ionospheric filtration of an ulf micropulsation signal

РезюмеПре¶rt;сmaвлен эффекmuвныŭ aлгорumм, учumывaющuŭ влuянuе uоносферы нa nрохож¶rt;енuе УНЧ сuгнaлов. Ионосферa мо¶rt;елuруеmся в вu¶rt;е многослоŭноŭ сре¶rt;ы. Алгорumм uсnользовaн ¶rt;ля мо¶rt;елеŭ ¶rt;невноŭ u ночноŭ uоносферы сре¶rt;нuхгеомaгнumных щuроm. В зaвuсuмосmu оm углa na¶rt;енuя u чaсmоmы волны nокaзaны сnецuфuческuе особенносmu uоносферного фuльmрa (верmuкaльнaя оmрaжaемосmь нa высоmе 1000 км u uзмененuе nолноŭ aмnлumу¶rt;ы волны nрu nрохож¶rt;енuu с высоmы 1000 км нa nоверхносmь Землu) в ¶rt;невных u ночных условuях nрu na¶rt;енuu элкmронноŭ uлu uонноŭ мо¶rt;ы. Покaзaно, чmо вы¶rt;елгннымu нanрaвленuямu рaсnросmрaненuя являюmся нanрaвленuе в¶rt;оль внещнего мaгнumного nоля u в¶rt;оль nерnен¶rt;uкулярa к верхнеŭгрaнuце uоносферы. Вы¶rt;елгнносmь нanрaвленuŭ обусловленa aнuзоmроnuеŭ оmносumельно нanрaвленuя мaгнumного nоля u верmuкaльноŭ нео¶rt;нос¶rt;носmыо uоносферы.

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

РезюмеНa основе ря¶rt;a mеореmuческuх рaбоm u рaзных эмnuрuческuх меmо¶rt;ов был с¶rt;елaн сuнmез восьмu мо¶rt;елеŭ uоносферы (в МГД nрuблuженuu) в nолном рaнге высоm (50–3000 км), mребуемых ¶rt;ля целеŭ мо¶rt;елuровaнuя uоносферноŭ фuльmрaцuu есmесmвенного мuкроnульсaцuонного (Рс1) сuгнaлa. Мо¶rt;елu nре¶rt;сmaвляюm высоmно-нео¶rt;н оро¶rt;ную, волны nоглощaющую ¶rt;невную u ночную леmнюю uоносферу высщuх щuроm ¶rt;вух облaсmеŭ (L=3 u L=5) северноŭ nолусферы, uлu nрu нuзкоŭ, (F10,7=70),или при высокой (F10,7=200) солнечноŭ aкmuвносmu. Высщaя uоносферa (h>200 км) nре¶rt;сmaвленa в nрuблuженuu квaзuнеуmрaльноŭ кuслоро¶rt;но-во¶rt; оро¶rt;ноŭ(O+,H+) nлaзмоŭ, во внuмaнuе nрuнuмaеmся nоглощенuе uз-зa неуmрaльноŭ сосmaвляQuщеŭ(O, He). Покaзaн меmо¶rt; вычuсленuя фuзuческuх naрaмеmров, месmно хaрaкmерuзующuх uоносферную сре¶rt;у.SummaryEight 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 (F10.7=70) and high (F10.7=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.

Numerical solution to the problem of ionoshperic filtration of ULF waves in thePc1 range. the total wave field inside the ionospheric transition layer

SummaryThis article is a continuation of the methodological series of the authors papers[2–4] related to the problem of numerical modelling of ionospheric filtration of signals in the Pc1 range of micropulation frequencies. A matrix method of treating the total wave field within the ionospheric transition layer is presented in connection with the total wave fields determined at both boundaries of the ionospheric transition layer. The computation is based on the method of thin layers (homogeneous) in a finely stratified, inhomogeneous and anisotropic (magneto-active) ionosphere. The results can be used in constructing automated computation algorithms which add considerably to the applications of the method in question[2–4].

The ionosphere as an Alfven resonator in the Pc1 micropulsation range

SummaryA 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 Earths 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 Earths 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.

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

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.

Resonance of a planeHM-wave in the lower magnetosphere andPc pulsations with periods of 5 to 40 seconds occurring during geomagnetic storms

РезюмеБыла сконструирована моделвь механизма непрерывных пульсаций низких геомагнитных широт для диапазона периодов 5–40сек. Здесь исходяг из резонансаНМ-волны в системе четырех однородных плоских слоев. Было выведено выражение для т.н. фактора связи, аналогичного коэффициенту передачи амплиыуды и определено условие для оптнмального размера резонотора, в котором могут создаваться пульсации заданной частоты. Размер области резонанса для пульсаций приведенного диапазона периодов, по-видимому,—порядка нескольких радиусов Земли и зависит от расаоложения плазмапауэы в земной магнитофере.

Polarization characteristics of ionospheric filtration of ULF waves

РезюмеПре¶rt;сmaвлен меmо¶rt; nолученuя nолярuэaцuонных хaрaкmерuсmuк (nолуосu nолярuзaцuонных эллunсов, nовором uхлaвноŭ nолуосu в сuсmеме коор¶rt;uнam, эллunmuчносmь u нanрaвленuе врaщенuя), коmорыŭ ¶rt;оnолняеm меmо¶rt;uку [1] мо¶rt;елuровaнuя uоносферноŭ фuльmрaцuu УНЧ-сuнaлa. Для nрuмерa nокaэaно nрuмененuе меmо¶rt;uкu в условuях мо¶rt;елu ¶rt;невноŭ uоносферы сре¶rt;нuхеомaнumных щuроm. Укaзывaюmся сnецuфuческuе явленuя в nолярuзaцuu мaнumноŭ u элекmрuческоŭ сосmaвляющuх волненерuровaнных нa¶rt; верmuкaльно нео¶rt;норо¶rt;ноŭ (слоuсmоŭ) u aнuзоmроnноŭ uоносфероŭ u волн nроще¶rt;щuх к земноŭ nоверхносmu в зaвuсuмосmu оm uзмененuя мерu¶rt;uонaльноо улa na¶rt;енuя волны с чaсmоmоŭ 0,3 Гц. Оmлuчumельнымu нanрaвленuямu рaсnросmрaненuя волн являюmся нanрaвленuе в¶rt;оль сuловых лuнuŭ внещнео мaнumноо nоля u нanрaвленuе верmuкaльное.

Frequency analysis of geomagnetic beating-type pulsations in thepc3 range

SummaryThe 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 mHz<f<100 mHz. The average limits of the pulsation frequency range are roughly20 mHz<f<60 mHz. The centre of the occurrence frequency graphs for both components is at the frequency fg ≈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.

Filtration of Pc1 wave packets in the ionosphere. Conjugated experiment GEOS-1 — husafell and results of numerical modelling

SummaryThe spectral analysis of an hourly section of a synchronized conjugated record of an ULF signal made on the GEOS-1 satellite and the Husafell Observatory (Iceland) on July 13, 1977, has been carried out. The time variations of the spectral frequency-amplitude characteristics of the Pc1 wave packet in the neighbourhood of f ≈ 0.5 s−1 at both measurement sites were examined. The transmissibility of the amplitude of the total magnetic component of the wave through the ionosphere towards the Earths surface, found in the frequency range of the packets, varies from 0.03 to 0.07. Moreover, its time behaviour with the development of the micropulsation disturbance was studied. The frequency shift of the packet spectrum centre towards higher frequencies ≈ 0.04 s−1) was determined at the Earths surface as compared with the satellite conditions. Experimental results served to test the developed automated methods of numerical modelling of ionospheric filtration in the ULF range of Pc1 micropulsations. Good agreement between the experimental and numerical results of the two constructed limiting models of the daytime ionosphere at higher latitudes (low and high solar activity) was achieved. The values of the transmissibility calculated for the Pc1 packet frequencies vary from 0.075 to 0.3 and from 0.025 to 0.06.

Characteristics of the mid-latitude ionosphere suitable for modelling ionospheric filtration of ULF waves

РезюмеПокaзaн nрuб лuзumельныŭ меmо¶rt; о¶rt;норaзмерного мо¶rt;елuровaнuя nлaзменноŭ сре¶rt;ы земноŭ uоносферы ¶rt;ля nоmребносmеŭ uзученuя uоносферноŭ фuльmрaцuu УНЧ волн (мuкроnульсaцuŭ). Ря¶rt;ом с основнымu месmнымu naрaмеmрaмu nлaзмы оnре¶rt;елены вmорuчные месmные хaрaкmерuсmuкu — мaссa m. нaз. эффекmuвного uонa,