Gotowe bibliografie tematyczne / VHF Scintillations

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Gotowa bibliografia na temat „VHF Scintillations”

Autor: Grafiati

Data publikacji: 6 września 2023

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Artykuły w czasopismach na temat "VHF Scintillations"

Pathak, K. N., R. D. Jivrajani, H. P. Joshi i K. N. Iyer. "Characteristics of VHF scintillations in the equatorial anomaly crest region in India". Annales Geophysicae 13, nr 7 (31.07.1995): 730–39. http://dx.doi.org/10.1007/s00585-995-0730-7.

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Abstract. The characteristics of ionospheric scintillations at Rajkot in the equatorial anomaly crest region in India are described for the years 1987–1991 by monitoring the 244-MHz transmission from the satellite FLEETSAT. This period covers the ascending phase of solar cycle 22. Scintillations occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer season. During equinoxes and winter, scintillation occurrence increases with solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by magnetic activity. The characteristics observed during winter and equinoxes are similar to those seen at the equatorial station, Trivandrum. This, coupled with the nature of the post-sunset equatorial F-region drift and h'F variations, supports the view that at the anomaly crest station, scintillations are of equatorial origin during equinox and winter, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.

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Rama Rao, P. V. S., P. T. Jayachandran, P. Sri Ram, B. V. Ramana Rao, D. S. V. V. D. Prasad i K. K. Bose. "Characteristics of VHF radiowave scintillations over a solar cycle (1983−1993) at a low-latitude station: Waltair (17.7°N, 83.3°E)". Annales Geophysicae 15, nr 6 (30.06.1997): 729–33. http://dx.doi.org/10.1007/s00585-997-0729-3.

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Abstract. The characteristics of VHF radiowave scintillations at 244 MHz (FLEETSAT) during a complete solar cycle (1983–93) at a low-latitude station, Waltair (17.7°N, 83.3°E), are presented. The occurrence of night-time scintillations shows equinoctial maxima and summer minima in all the epochs of solar activity, and follows the solar activity. The daytime scintillation occurrence is negatively correlated with the solar activity and shows maximum occurrence during the summer months in a period of low solar activity. The occurrence of night-time scintillations is inhibited during disturbed days of high solar activity and enhanced during low solar activity.

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Singh, R. P., R. P. Patel i A. K. Singh. "Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest". Annales Geophysicae 22, nr 8 (7.09.2004): 2849–60. http://dx.doi.org/10.5194/angeo-22-2849-2004.

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Abstract. The VHF amplitude scintillation recorded during the period January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3°, long.=83.0°, dip=37°N) have been analyzed to study the behavior of ionospheric irregularities during active solar periods and magnetic storms. It is shown that irregularities occur at arbitrary times and may last for <30min. A rise in solar activity increases scintillations during winter (November-February) and near equinoxes (March-April; September-October), whereas it depresses the scintillations during the summer (May-July). In general, the role of magnetic activity is to suppress scintillations in the pre-midnight period and to increase it in the post-midnight period during equinox and winter seasons, whilst during summer months the effect is reversed. The pre-midnight scintillation is sometimes observed when the main phase of Dst corresponds to the pre-midnight period. The annual variation shows suppression of scintillations on disturbed days, both during pre-midnight and post-midnight period, which becomes more effective during years of high solar activity. It is observed that for magnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time. If the magnetic storm occurred during daytime, then the probability of occurrence of scintillations during the night hours is decreased. The penetration of magnetospheric electric fields to the magnetic equator affects the evolution of low-latitude irregularities. A delayed disturbance dynamo electric field also affects the development of irregularities.

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Koparkar, P. V., i R. G. Rastogi. "VHF radio scintillations at Bombay". Journal of Atmospheric and Terrestrial Physics 47, nr 8-10 (sierpień 1985): 907–10. http://dx.doi.org/10.1016/0021-9169(85)90066-2.

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Vijayakumar, P. N., i P. K. Pasricha. "Parametrization of spectra of plasma bubble induced VHF satellite scintillations and its geophysical significance". Annales Geophysicae 15, nr 3 (31.03.1997): 345–54. http://dx.doi.org/10.1007/s00585-997-0345-2.

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Abstract. An important component of ionospheric plasma irregularity studies in the Indian low latitudes involves the study of the plasma bubbles which produce intense scintillations of the transionospheric satellite signals. Many such plasma bubble induced (PBI) scintillation events were identified while recording 244 MHz signal from the geostationary satellite Fleetsat (73°E) at Delhi (28.6°N, 77.2°E) during March-April 1991. This type of scintillations represents changes in plasma processes. These scintillations are spectrally analyzed using an autoregressive (AR) scheme, which is equivalent to maximum entropy method of spectrum analysis, amenable to extracting optimum spectral content from short data lengths (20 – 40 s). Each spectrum is assigned a level of detectability using the final prediction error (FPE) derived from the optimum filter order required to resolve the spectrum. Lower detectability together with a higher order filter indicate a higher level of coherence for the plasma irregularities (discrete structures). Consistent patterns for these scintillations emerge from the present analysis as follows: (1) the initial and final phases of a scintillation patch display quasiperiodic oscillations. Their corresponding spectra show dominant (Gaussian shaped) spectral features with detectability levels of –6 dB to –12 dB and requiring a higher order (>6) AR filter for their spectral resolution. These are most likely associated with discrete "filament-like" or "sheet-like" plasma structures that exist near the bubble walls. (2) Two main features of the scintillation spectra could be positively associated with the well-developed plasma bubble stage: (a) spectra displaying a power-law process with a single component spectral slope between 1.6 to 3.0. Generally such spectra are resolved with a 2nd order filter and have a 1 dB to 6 dB of detectability. (b) Spectra displaying a double slope, indicating an inner and an outer scale regime for the power-law irregularities. These spectra are resolved with higher order filters (>3 but <7) and possess detectability levels of –1 dB to 3 dB. These spectra display finer spectral changes, perhaps indicative of the nature of continuously evolving plasma irregularities. As an example, an analysis of a single scintillation patch is presented to highlight the geophysical significance of the present approach. Some important parameters used in the AR scheme of spectral analysis are given in the Appendix.

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Sripathi, S., S. Bose, A. K. Patra, T. K. Pant, B. Kakad i A. Bhattacharyya. "Simultaneous observations of ESF irregularities over Indian region using radar and GPS". Annales Geophysicae 26, nr 11 (21.10.2008): 3197–213. http://dx.doi.org/10.5194/angeo-26-3197-2008.

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Abstract. In this paper, we present simultaneous observations of temporal and spatial variability of total electron content (TEC) and GPS amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.5° N, 79.2° E, Dip latitude 6.3° N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar during the low solar activity period of 2004 and 2005. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. During magnetically quiet periods, we have recorded plume type radar echoes during a post-midnight period that is devoid of L-band scintillations. Using spectral slopes and cross-correlation index of the VHF scintillation observations, we suggest that these irregularities could be "dead" or "fossil" bubbles which are just drifting in from west. This scenario is consistent with the observations where suppression of pre-reversal enhancement (PRE) in the eastward electric field is indicated by ionosonde observations of the height of equatorial F layer and also occurrence of low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight event, when radar observed plume like structures and scintillations were recorded on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that whereas small scale (~3 m) irregularities are generated through secondary waves that grow on the walls of km scale size irregularities, in this case evolution of the Rayleigh-Taylor instability itself did not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal.

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Rama Rao, P. V. S., S. Tulasi Ram, K. Niranjan, D. S. V. V. D. Prasad, S. Gopi Krishna i N. K. M. Lakshmi. "VHF and L-band scintillation characteristics over an Indian low latitude station, Waltair (17.7° N, 83.3° E)". Annales Geophysicae 23, nr 7 (14.10.2005): 2457–64. http://dx.doi.org/10.5194/angeo-23-2457-2005.

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Abstract. Characteristics of simultaneous VHF (244 MHz) and L-band (1.5 GHz) scintillations recorded at a low-latitude station, Waltair (17.7° N, 83.3° E), during the low sunspot activity year of March 2004 to March 2005, suggest that the occurrence of scintillations is mainly due to two types, namely the Plasma Bubble Induced (PBI), which maximizes during the post sunset hours of winter and equinoctial months, and the Bottom Side Sinusoidal (BSS) type, which maximizes during the post-midnight hours of the summer solstice months. A detailed study on the spectral characteristics of the scintillations at both the frequencies show that the post-sunset scintillations are strong with fast fading (≈40 fad/min) and are multiple in nature in scattering, giving rise to steep spectral slopes, whereas the post-midnight scintillations, which occur mostly on the VHF signal with low fading rate (≈4 fad/min), are of the BSS type, often showing typical Fresnel oscillations with reduced roll off spectral slopes, indicating that the type of irregularity resembles a thin screen structure giving rise to weak scattering. Using the onset times of several similar scintillation patches across the two satellite (FLEETSAT 73° E, INMARSAT 65° E) ray paths (sub-ionospheric points are separated by 82 km), the East ward movement of the irregularity patches is found to vary from 150 to 250 m/s during the post sunset hours and decrease slowly during the post midnight hours. Further, the east-west extent of the PBI type of irregularities is found to vary from 100 to 500 km, while that of the BSS type extend up to a few thousand kilometers. Keywords. Ionosphere (Ionospheric irregularities; Auroral ionosphere; Electric fields and currents)

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Chatterjee, S., i S. K. Chakraborty. "Variability of ionospheric scintillation near the equatorial anomaly crest of the Indian zone". Annales Geophysicae 31, nr 4 (19.04.2013): 697–711. http://dx.doi.org/10.5194/angeo-31-697-2013.

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Abstract. Multistation observations of ionosphere scintillation at VHF (250 MHz) and GNSS L1 frequency from three locations – (i) Bokkhali (BOK) (geographic 21.6° N, 88.2° E, dip 31.48°, (ii) Raja Peary Mohan College Centre (RPMC) (geographic 22.66° N, 88.4° E, dip 33.5°) and (iii) Krishnath College Centre (KNC), Berhampore (geographic 24.1° N, 88.3° E, dip 35.9°) – at ~ 1° latitudinal separations near the northern crest of the equatorial ionization anomaly (EIA) of the Indian longitude sector are investigated in conjunction with total electron content (TEC) data and available ionosonde data near the magnetic equator to study fine structure in spatial and temporal variability patterns of scintillation occurrences. The observations are carried out in the autumnal equinoctial months of a high solar activity year (2011). In spite of smaller latitudinal/spatial separation among the observing stations, conspicuous differences are reflected in the onset time, duration, fade rate and fade depth of VHF scintillations as well as in spectral features. Scintillations are mostly associated with depletion in TEC around the anomaly crest and occurrence of ESF near the magnetic equator at an earlier time. Not only the strength of EIA, but also the locations of observing stations with respect to the post-sunset resurgence peak of EIA seem to play dominant role in dictating the severity of scintillation activity. A secondary enhancement in diurnal TEC in the post-sunset period seems to accentuate the irregularity activities near the anomaly crest, and a threshold value of the same may fruitfully be utilized for the prediction of scintillation around the locations. An idea regarding latitudinal extent of scintillation is developed by considering observations at L1 frequency from the GPS and GLONASS constellation of satellites. A critical value of h'F near the magnetic equator for the occurrence of simultaneous scintillation at the three centres is suggested. The observations are discussed considering electrodynamical aspect of equatorial irregularities.

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Gupta, J. K., Lakha Singh i R. S. Dabas. "Faraday polarization fluctuations and their dependence on post sunset secondary maximum and amplitude scintillations at Delhi". Annales Geophysicae 20, nr 2 (28.02.2002): 185–90. http://dx.doi.org/10.5194/angeo-20-185-2002.

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Abstract. VHF Faraday rotation (FR) and amplitude scintillation data recorded simultaneously during May 1978–December 1980 at Delhi (28.63° N, 77.22° E; Dip 42.44° N) is analyzed in order to study the Faraday polarization fluctuations (FPFs) and their dependence on the occurrence of post sunset secondary maximum (PSSM) and amplitude scintillations. It is noted that FPFs are observed only when both PSSM and scintillations also occur simultaneously. FPFs are observed only during winter and the equinoctial months of high sunspot years. FPFs events are associated with intense scintillation activity, which is characterized by sudden onsets and abrupt endings, and are observed one to three hours after the local sunset. When FPFs and scintillation data from Delhi is compared with the corresponding data from a still lower latitude station, Hyderabad (17.35° N, 78.45° E), it is found that the occurrence of FPFs and scintillations at Delhi is conditional to their prior occurrence at Hyderabad, which indicates their production by a plasma bubble and the as-sociated irregularities generated initially over the magnetic equator. In addition, FPFs and scintillation data for October 1979, when their occurrence was maximum, is also examined in relation to daytime (11:00 LT) electrojet strength (EEj) values and evening hour h’F from an equatorial location, Kodaikanal (10.3° N, 77.5° E). It is interesting to note that FPFs and scintillations are most likely observed when the EEj was 100 nT or more and h’F reaches around 500 km. These results show that EEj and evening hours h’F values over the magnetic equator are important parameters for predicting FPFs and scintillation activity at locations such as Delhi, where scintillation activity is much more intense as compared to the equatorial region due to the enhanced back-ground ionization due to the occurrence of PSSM.Key words. Ionosphere (equatorial ionosphere; ionospheric irregularities) – Radio science (ionospheric physics)

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RASTOGI, R. G., P. V. KOPARKAR, A. PATIL i B. M. PATHAN. "Daytime VHF Radio Wave Scintillations at Equatorial Latitudes." Journal of geomagnetism and geoelectricity 43, nr 7 (1991): 549–61. http://dx.doi.org/10.5636/jgg.43.549.

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Rozprawy doktorskie na temat "VHF Scintillations"

Norén, Magnus. "Measuring the vertical muon intensity with the ALTO prototype at Linnaeus University". Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-107133.

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ALTO is a project, currently in the research and development phase, with the goal of constructing a Very High Energy (VHE) gamma-ray observatory in the southern hemisphere. It will detect the particle content reaching the ground from the interactions of either VHE gamma rays or cosmic rays in the atmosphere known as extensive air showers. In this thesis, we use an ALTO prototype built at Linneaus University to estimate the vertical muon intensity in Växjö. The atmospheric muons we detect at ground level come from hadronic showers caused by a cosmic ray entering the atmosphere. Such showers are considered background noise in the context of VHE gamma-ray astronomy, and the presence of muons is an important indicator of the nature of the shower, and thus of the primary particle. The measurement is done by isolating events that produce signals in two small scintillation detectors that are part of the ALTO prototype, and are placed almost directly above each other. This gives us a data set that we assume represents muons travelling along a narrow set of trajectories, and by measuring the rate of such events, we estimate the muon intensity. We estimate the corresponding momentum threshold using two different methods; Monte Carlo simulation and calculation of the mean energy loss. The vertical muon intensity found through this method is about 21% higher than commonly accepted values. We discuss some possible explanations for this discrepancy, and conclude that the most likely explanation is that the isolated data set contains a significant number of “false positives”, i.e., events that do not represent a single muon following the desired trajectory.

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Części książek na temat "VHF Scintillations"

Chatterjee, S., D. Jana, S. Pal i S. K. Chakraborty. "VHF to L band scintillation around the EIA crest of Indian longitude zone". W Computational Science and Engineering, 215–20. CRC Press/Balkema, P.O. Box 11320, 2301 EH Leiden, The Netherlands, e-mail: Pub.NL@taylorandfrancis.com, www.crcpress.com – www.taylorandfrancis.com: CRC Press, 2016. http://dx.doi.org/10.1201/9781315375021-42.

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Streszczenia konferencji na temat "VHF Scintillations"

Eranna, U., B. Rama Murthy, K. Bhanu Prasad i R. Manjula. "Study of ionospheric irregularities over near-equatorial station Anantapur using VHF scintillations". W IET-UK International Conference on Information and Communication Technology in Electrical Sciences (ICTES 2007). IEE, 2007. http://dx.doi.org/10.1049/ic:20070752.

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Globa, Maria V., Roman V. Vasilyev i Yury V. Yasyukevich. "Simultaneous observation of UHV and VHF radio signal ionospheric scintillations in the magnetic zenith". W 2017 Progress In Electromagnetics Research Symposium - Spring (PIERS). IEEE, 2017. http://dx.doi.org/10.1109/piers.2017.8262399.

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Swamy, K. C. T., A. D. Sarma, A. Supraja Reddy i Tarun Kumar Pant. "Analysis of ionospheric scintillations of GPS and VHF/UHF signals over low latitude Indian region". W 2012 World Congress on Information and Communication Technologies (WICT). IEEE, 2012. http://dx.doi.org/10.1109/wict.2012.6409110.

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Groves, K. M., F. H. Ruggiero, M. J. Starks, T. L. Beach i P. Strauss. "Comparisons of Space-Based GPS Occultation Ionospheric Scintillation Measurements With Ground-Based VHF Measurements". W 11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009. Society of Exploration Geophysicists and Brazilian Geophysical Society, 2009. http://dx.doi.org/10.1190/sbgf2009-035.

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Groves, K. M., F. H. Ruggiero, M. J. Starks, T. L. Beach i P. Strauss. "Comparisons Of Space-Based Gps Occultation Ionospheric Scintillation Measurements With Ground-Based Vhf Measurements". W 11th International Congress of the Brazilian Geophysical Society. European Association of Geoscientists & Engineers, 2009. http://dx.doi.org/10.3997/2214-4609-pdb.195.2079_evt_6year_2009.

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Sharma, Ashok Kumar, i Omkar B. Gurav. "VHF scintillation associated with equatorial plasma bubbles over low latitude Indian region: a case study". W 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC). IEEE, 2019. http://dx.doi.org/10.23919/ursiap-rasc.2019.8738294.

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Olwendo, O. J., P. Baki i P. Doherty. "Low latitude ionospheric scintillation and zonal plasma bubble drifts observation from a GPS scintillation monitoring system and closely spaced VHF receivers in Kenya". W 2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC). IEEE, 2015. http://dx.doi.org/10.1109/ursi-at-rasc.2015.7303124.

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Poddelsky, Igor N., i Aleksey I. Poddelsky. "Effect of geomagnetic disturbances on the spectral and spatial characteristics of VHF scintillation in the northeast of Russia". W SPIE Proceedings, redaktorzy Gelii A. Zherebtsov i Gennadii G. Matvienko. SPIE, 2006. http://dx.doi.org/10.1117/12.675913.

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Bhattacharyya, A., i B. Kakad. "Seasonal and solar flux dependence of the growth and decay of intermediate scale ESF irregularities from VHF scintillation measurements". W 2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS). IEEE, 2014. http://dx.doi.org/10.1109/ursigass.2014.6929722.

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