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  • 1
    Publication Date: 2021-07-21
    Description: We report on simultaneous observation of artificial plasma density irregularities near the magnetic zenith (MZ) by incoherent scatter radar and GNSS satellite in the high latitude. During an EISCAT (European Incoherent Scatter Scientific Association) HF heating experiment, a GLONASS satellite signal intersected the disturbed ionospheric volume along the local magnetic field lines. The satellite signal amplitude and phase were simultaneously perturbed when the electron temperature increased in the F region through O‐mode HF waves. The field‐aligned irregularities (FAIs) and associated density perturbations are most significantly found in the MZ direction. The growth of FAI reached the saturation level in 30 s while large‐scale electron density perturbation on the order of 0.1 TECU developed in a few minutes. The observed density perturbations agree well with recent numerical studies of FAI generation due to the thermal self‐focusing process.
    Description: Plain Language Summary: Powerful high‐frequency radio waves are used to study electron heating process in the high latitude ionosphere. We observed the development of plasma density structures by analyzing small changes of amplitude and phase of ground‐based satellite signals and incoherent scatter radar measurements. It is concluded that the electron heating causes irregular electron density structures along local magnetic field lines. This experiment shows that coordinated ground‐based satellite and incoherent scatter radar measurements essentially help to better understand the physics of ionospheric plasma dynamics and radio wave propagation.
    Description: Key Points: HF‐induced field‐aligned plasma irregularities are simultaneously observed by GLONASS satellite and incoherent scatter radar. The satellite signal amplitude fluctuation and TEC deviation are generally correlated. Observed positive density deviations suggest that the density perturbations are likely caused by the thermal self‐focusing process.
    Keywords: 538.7 ; Active experiment ; EISCAT ; GNSS ; ionosphere ; irregularities
    Type: article
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  • 2
    Publication Date: 2021-10-26
    Description: Представлены результаты наблюдений изменения температуры, электронной концентрации и полного электронного содержания высокоширотной области ионосферы во время ее модификации мощным коротковолновым радиоизлучением нагревного комплекса EISCAT/Heating (Тромсё, Норвегия) по данным сигналов спутников ГЛОНАСС и радара некогерентного рассеяния УВЧ ЕИСКАТ (Тромсё, Норвегия). Рассмотрена геометрия пролетов спутников ГЛОНАСС и GPS для условий работы нагревного комплекса в Тромсё. Показано, что во время экспериментов на комплексе EISCAT/Heating для изучения модифицированной структуры высокоширотной ионосферы удобнее использовать спутники ГЛОНАСС. Параметры орбит этих спутников позволяют исследовать изменения полного электронного содержания в направлении вдоль геомагнитной силовой линии в месте наблюдения. Показано, что во время нагрева ионосферы мощной коротковолновой радиоволной ее структура приобретает неоднородный характер. Работа нагревного комплекса в режиме "включено – выключено" вызывает появление волнообразных вариаций полного электронного содержания с периодом, близким к периоду нагрева. Основными особенностями поведения полного электронного содержания при непрерывном нагреве ионосферы в направлении магнитного зенита по данным спутника ГЛОНАСС явились уменьшение полного электронного содержания в центральной зоне диаграммы направленности антенны нагревного комплекса, т. е. в направлении магнитного зенита, и присутствие повышенных значений полного электронного содержания на краях зоны нагрева. По данным радара некогерентного рассеяния во время нагрева ионосферы вблизи направления на магнитный зенит формируется область повышенной электронной температуры и электронной концентрации. Поведение полного электронного содержания по данным спутника ГЛОНАСС и радара некогерентного рассеяния во многом соответствует друг другу, кроме этой области. Высказываются предположения о причинах такого несоответствия.
    Description: Results of observations of variations of temperature, electron concentration and total electron content of the high-latitude region of the ionosphere during its modification by powerful short radio waves of the heating complex EISCAT/Heating (Tromsø, Norway) according to signals of the GLONASS satellites and the incoherent scattering UHF EISCAT radar (Tromsø, Norway) have been provided. The geometry of passes of the GLONASS and GPS satellites for operating conditions of the heating complex in Tromsø has been considered. It has been shown that during the experiments on the EISCAT/Heating complex for the study of the modified structure of the high-latitude ionosphere it is more convenient to use the GLONASS satellites. Parameters of orbits of these satellites allow researching changes of total electron content in the direction along the geomagnetic field line at the place of observation. It has been shown that during heating of the ionosphere by powerful short radio waves its structure is becoming an irregular one. Operation of the heating complex in the mode "switched on – switched off" has caused appearance of wavy variations of total electron content with the periods close to the heating period. The main features of behavior of the total electron content in the case of the continuous heating of the ionosphere in the direction of the magnetic zenith according to the GLONASS satellite are: reduction of total electron content in the central zone of the antenna diagram, i. e. in the direction of the magnetic zenith, and presence of the increased values of total electron content at the edges of the heating zone. According to the incoherent scattering radar the heating of the ionosphere by the powerful short radio wave has created the region of the increased electron temperature and electron concentration along the direction of the magnetic zenith. The behavior of total electron content according to the GLONASS satellite and the radar of incoherent scattering in many respects corresponds each other except the central part. Reasons of the mismatches have been considered.
    Description: Published
    Description: Refereed
    Keywords: GLONASS ; ГЛОНАСС ; High-latitude ionopshere ; Full electronic content ; Radio wave installations ; Высокоширотная ионосфера ; Радиоволновые установки ; Полное электронное содержание ; ASFA_2015::A::Atmospheric physics ; ASFA_2015::I::Ionosphere
    Repository Name: AquaDocs
    Type: Journal Contribution
    Format: pp.170-181
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  • 3
    ISSN: 0992-7689
    Keywords: Mesophere ; Lower thermosphere ; EISCAT UHF radar ; EISCAT VHF radar
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Mesospheric observations were obtained by the EISCAT UHF and VHF radars during the solar proton event of March 1990. We present the first comparison of incoherent-scatter spectral measurements from the middle mesosphere using simultaneous, co-located observations by the two radars. VHF spectra observed with a vertical antenna were found to be significantly narrower than model predictions, in agreement with earlier UHF results. For antenna pointing directions that were significantly away from the vertical, the wider VHF radar beam gave rise to broadening of the observed spectra due to vertical shears in the horizontal wind. In this configuration, UHF spectral measurements were found to be more suitable for aeronomical applications. Both radar systems provide consistent and reliable estimates of the neutral wind. Spectral results using both the multipulse and pulse-to-pulse schemes were intercompared and their suitability for application to combined mesosphere - lower thermosphere studies investigated.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0992-7689
    Keywords: Satellite radio-wave probing ; HF radiation ; Electron density irregularities ; Statistical analysis ; Ionospheric heating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We describe an experiment in satellite radio-wave probing of the ionosphere, modified by powerful waves from the HF heating facility at Tromsø (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregularities (several tens of kilometers in size) and small-scale ones (from hundreds of meters to kilometers) can be generated by the HF radiation. Maximum effects caused by small-scale irregularities detected in the satellite signals are observed in the directions sector approximately parallel to the geomagnetic field lines although large-scale structures can be detected within a much larger area. The properties of small-scale irregularities (electron density fluctuations) are investigated by applying a statistical analysis and by studying experimental and model mean values of the logarithm of the relative amplitude of the signal. The results indicate that satellite radio probing can be a supporting diagnostic technique for ionospheric heating and add valuable information to studies of effects produced by HF modification.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Results are presented from an experimental campaign in April 1996, in which the new CUTLASS (Co-operative UK twin-located Auroral Sounding System) coherent scatter radar was employed to observe artificial field aligned irregularities (FAI) generated by the EISCAT (European Incoherent SCATter) heating facility at Tromso, Norway. The distribution of back-scatter intensity from within the heated region has been investigated both in azimuth and range with the Finland component of CUTLASS, and the first observations of artificial irregularities by the Iceland radar are also presented. The heated region has been measured to extend over a horizontal distance of 170 ± 50 km, which by comparison with a model of the heater beam pattern corresponds to a threshold electric field for FAI of between 0.1 and O.OlV/m. Differences between field-aligned and vertical propagation heating are also presented.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0992-7689
    Keywords: Ionosphere (active experiments; ionosphere – magnetosphere interactions) ; Radio science (nonlinear phenomena)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present an analysis of phenomena observed by HF distance-diagnostic tools located in St. Petersburg combined with multi-instrument observation at Tromsø in the HF modified ionosphere during a magnetospheric substorm. The observed phenomena that occurred during the Tromsø heating experiment in the nightside auroral Es region of the ionosphere depend on the phase of substorm. The heating excited small-scale field-aligned irregularities in the E region responsible for field-aligned scattering of diagnostic HF waves. The equipment used in the experiment was sensitive to electron density irregularities with wavelengths 12–15 m across the geomagnetic field lines. Analysis of the Doppler measurement data shows the appearance of quasiperiodic variations with a Doppler frequency shift, fd and periods about 100–120 s during the heating cycle coinciding in time with the first substorm activation and initiation of the upward field-aligned currents. A relationship between wave variations in fd and magnetic pulsations in the Y-component of the geomagnetic field at Tromsø was detected. The analysis of the magnetic field variations from the IMAGE magnetometer stations shows that ULF waves occurred, not only at Tromsø, but in the adjacent area bounded by geographical latitudes from 70.5° to 68° and longitudes from 16° to 27°. It is suggested that the ULF observed can result from superposition of the natural and heater-induced ULF waves. During the substorm expansion a strong stimulated electromagnetic emission (SEE) at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the VLF waves penetrating into magneto-sphere and stimulating the precipitation of the energetic electrons (10–40 keV) of about 1-min duration. This is due to a cyclotron resonant interaction of natural precipitating electrons (1–10 keV) with heater-induced whistler waves in the magnetosphere. It is reasonable to suppose that a new substorm activation, exactly above Tromsø, was closely connected with the heater-induced precipitation of energetic electrons.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 14 (1997), S. 1437-1453 
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Artificial periodic irregularities (API) are produced in the ionospheric plasma by a powerful standing electromagnetic wave reflected off the F region. The resulting electron-density irregularities can scatter other high-frequency waves if the Bragg scattering condition is met. Such measurements have been performed at mid-latitudes for two decades and have been developed into a useful ionospheric diagnostic technique. We report here the first measurements from a high-latitude station, using the EISCAT heating facility near Troms0, Norway. Both F-region and lower-altitude ionospheric echoes have been obtained, but the bulk of the data has been in the E and D regions with echoes extending down to 52-km altitude. Examples of API are shown, mainly from the D region, together with simultaneous VHP incoherent-scatter-radar (ISR) data. Vertical velocities derived from the rate of phase change during the irregularity decay are shown and compared with velocities derived from the ISR. Some of the API-derived velocities in the 75–115-km height range appear consistent with vertical neutral winds as shown by their magnitudes and by evidence of gravity waves, while other data in the 50–70-km range show an unrealistically large bias. For a comparison with ISR data it has proved difficult to get good quality data sets overlapping in height and time. The initial comparisons show some agreement, but discrepancies of several metres per second do not yet allow us to conclude that the two techniques are measuring the same quantity. The irregularity decay time-constants between about 53 and 70 km are compared with the results of an advanced ion-chemistry model, and height profiles of recorded signal power are compared with model estimates in the same altitude range. The calculated amplitude shows good agreement with the data in that the maximum occurs at about the same height as that of the measured amplitude. The calculated time-constant agrees very well with the data below 60 km but is larger above 60 km by a factor of up to 2 at 64 km. The comparisons with the model are considered to be a good basis for more refined comparisons.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0992-7689
    Keywords: Auroral ionosphere ; Plasma convection Instruments and techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these ‘Doppler’ measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of ‘blanketing’ by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0992-7689
    Keywords: Ionosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Since the auroral ionosphere provides an important energy sink for the magnetosphere, ionosphere-thermosphere coupling must be investigated when considering the energy budget of the ionosphere-magnetosphere coupling. We present the first Scandinavian ground-based study of high-latitude F-region ion-neutral frictional heating where ion velocity and temperature are measured by the EISCAT incoherent scatter radar as well as neutral wind and temperature being measured simultaneously by a Fabry-Perot interferometer. A geomagnetically active period (Kp = 7- - 5-) and quiet period (Kp = 0+ - 0) were studied. Neglecting the neutral wind can result in errors of frictonal heating estimates of 60% or more in the F-layer. About 96% of the local ion temperature enhancement over the neutral temperature is accounted for by ion-neutral frictional heating.
    Type of Medium: Electronic Resource
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