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K M Groves - One of the best experts on this subject based on the ideXlab platform.
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Climatology of GPS amplitude Scintillations over equatorial Africa during the minimum and ascending phases of solar cycle 24
Astrophysics and Space Science, 2015Co-Authors: A. O. Akala, Charles S Carrano, K M Groves, Patricia H. Doherty, L. L. N. Amaeshi, E.o. Somoye, Raphael Idolor, Emeka Emmanuel Okoro, C. Bridgwood, P. BakiAbstract:This study characterizes African equatorial Scintillations at L-band frequency during the minimum and ascending phases of solar cycle 24. Three years’ (2009–2011) of amplitude Scintillation data from three African equatorial GPS stations, namely; Lagos (6.48°N, 3.27°E, dip: 4.95°S), Nigeria; Nairobi (1.16°S, 36.80°E, dip: 10.65°S), Kenya; and Kampala (0.30°N, 32.50°E, dip: 11.12°S), Uganda were used for this investigation. We grouped the data into daily, monthly, seasonal, and yearly scales, at elevation angles greater than or equal to 30°. Scintillations exhibit daily trend of occurrences during the hours of 1900 LT–0200 LT, with higher occurrence levels being localized within the hours of 2000–2300 LT. Generally, highest Scintillation occurrences were recorded during equinoxes and the least during June solstice. Intriguingly, over equatorial Africa, January was observed to be a non-Scintillation month, and post-midnight Scintillations were observed during June solstice months, although at weak intensities. Scintillations were also observed to increase with solar and geomagnetic activities. These results would support the development of future African equatorial Scintillation models, which could also be of support to the implementation of global navigation satellite system (GNSS)-based navigation in Africa.
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latitudinal and local time variation of ionospheric turbulence parameters during the conjugate point equatorial experiment in brazil
International Journal of Geophysics, 2012Co-Authors: Charles S Carrano, C E Valladares, K M GrovesAbstract:Previous authors have reported on the morphology of GPS Scintillations and irregularity zonal drift during the 2002 Conjugate Point Equatorial Experiment (COPEX) in Brazil. In this paper, we characterize the turbulent ionospheric medium that produced these Scintillations. Using 10 Hz GPS carrier-to-noise measurements at Boa Vista (2.9°N, 60.7°W), Alta Floresta (9.9°S, 56.1°W), and Campo Grande (20.5°S, 54.7°W), we report on the variation of turbulent intensity, phase spectral index, and irregularity zonal drift as a function of latitude and local time for the evening of 1-2 November 2002. The method of analysis is new and, unlike analytical theories of Scintillation based on the Born or Rytov approximations, it is valid when the Scintillation index saturates due to multiple-scatter effects. Our principal findings are that (1) the strength of turbulence tended to be largest near the crests of the equatorial anomaly and at early postsunset local times, (2) the turbulent intensity was generally stronger and lasted two hours longer at Campo Grande than at Boa Vista, (3) the phase spectral index was similar at the three stations but increased from 2.5 to 4.5 with local time, and (4) our estimates of zonal irregularity drift are consistent with those provided by the spaced-receiver technique.
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Magnetic conjugate point observations of kilometer and hundred‐meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
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magnetic conjugate point observations of kilometer and hundred meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
Marcio T A H Muella - One of the best experts on this subject based on the ideXlab platform.
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GPS L1-Frequency Observations of Equatorial Scintillations and Irregularity Zonal Velocities
Surveys in Geophysics, 2014Co-Authors: Marcio T A H Muella, Eurico R. Paula, Olusegun F. JonahAbstract:In this work, the climatology of ionospheric Scintillations at global positioning system (GPS) L-band frequency and the zonal drift velocities of Scintillation-producing irregularities were depicted for the equatorial observatory of São Luis (2.33°S; 44.21°W; dip latitude 1.3°S), Brazil. This is the first time that the hourly, monthly, and seasonal variations of Scintillations and irregularity zonal drifts at São Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of Scintillations at different sectors of the sky was also investigated, and the results revealed that the Scintillations are more probable to be observed in the west sector of the sky above São Luis, whereas the north–south asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The Scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the Scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial Scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of Scintillations ( S _4 index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the Scintillation occurrence is extremely low), stronger levels of Scintillations ( S _4 > 0.6) may occur at comparable rate with the weak Scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.
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Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients
Surveys in Geophysics, 2010Co-Authors: Marcio T A H Muella, E R De Paula, P. R. Fagundes, J. A. Bittencourt, Y. SahaiAbstract:The possible role, on L-band Scintillation activity, played by the nighttime magnetic meridional component of the thermospheric horizontal neutral winds, the post-sunset F -layer base height, the electrical field pre-reversal enhancement (PRE) and the latitudinal gradients of the F 2-layer peak density is analyzed, considering different cases of Scintillation occurrence (and their latitudinal extent) during August and September 2002. The meridional winds were derived over low-latitudes from a modified form of the nonlinear time-dependent servo-model. A chain of two Scintillation monitors and three digital ionosondes was operational in Brazil and used to collect, respectively, global positioning system signal amplitude Scintillation and ionospheric height ( h ′ F ; hpF 2) and frequency ( foF 2) parameters. From the overall behavior in the 2 months analyzed, the results suggest that high near sunset upward vertical plasma drifts are conducive for the generation of spread- F irregularities, whereas large poleward meridional winds tend to suppress the development of plasma bubble irregularities and the occurrence of their associated Scintillations. Even when generated, a reduced fountain effect, due to weak electric field PRE, acts for the bubbles to be expanded less effectively to higher latitudes. The results also reveal that high F -layer base and peak heights (at equatorial and off-equatorial latitudes), and intense gradients in the F 2-peak density between the dip equator and the equatorial anomaly crests, are favorable conditions for the generation of F -region irregularities and increased Scintillation activity. Other distinct features of the controlling factors in the cases of occurrence and non-occurrence of equatorial Scintillations are presented and discussed.
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Magnetic conjugate point observations of kilometer and hundred‐meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
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magnetic conjugate point observations of kilometer and hundred meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
V I Shishov - One of the best experts on this subject based on the ideXlab platform.
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interstellar Scintillations of psr b1919 21 space ground interferometry
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V I Shishov, T V Smirnova, C. R. Gwinn, A S Andrianov, M V Popov, Alexey Rudnitskiy, V A SoglasnovAbstract:We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radiotelescope together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60000 km. We show that interstellar Scintillation of this pulsar consists of two components: diffractive Scintillations from inhomogeneities in a layer of turbulent plasma at a distance $z_{1} = 440$ pc from the observer or homogeneously distributed scattering material to pulsar; and weak Scintillations from a screen located near the observer at $z_{2} = 0.14 \pm 0.05$ pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift of observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded the scattering angle in the observer plane: $\theta_{scat}$ = 0.7 mas. An analysis of the time-frequency correlation function for weak Scintillations yielded the angle of refraction in the direction to the pulsar: $\theta_{ref, 0}$ = 110 ms and the distance to the prism $z_{prism} \le 2$ pc.
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Interstellar Scintillations of PSR B1919+21: space–ground interferometry
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V I Shishov, T V Smirnova, C. R. Gwinn, A S Andrianov, M V Popov, Alexey Rudnitskiy, V A SoglasnovAbstract:We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radiotelescope together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60000 km. We show that interstellar Scintillation of this pulsar consists of two components: diffractive Scintillations from inhomogeneities in a layer of turbulent plasma at a distance $z_{1} = 440$ pc from the observer or homogeneously distributed scattering material to pulsar; and weak Scintillations from a screen located near the observer at $z_{2} = 0.14 \pm 0.05$ pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift of observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded the scattering angle in the observer plane: $\theta_{scat}$ = 0.7 mas. An analysis of the time-frequency correlation function for weak Scintillations yielded the angle of refraction in the direction to the pulsar: $\theta_{ref, 0}$ = 110 ms and the distance to the prism $z_{prism} \le 2$ pc.
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the turbulence spectrum of the interstellar plasma toward the pulsars psr b0809 74 and b0950 08
Astronomy Reports, 2008Co-Authors: T V Smirnova, V I ShishovAbstract:The interstellar Scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive Scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 (n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the Scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ0 = 107 m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the Scintillations of PSR B0809+74.
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The turbulence spectrum of the interstellar plasma toward the pulsars PSR B0809+74 and B0950+08
Astronomy Reports, 2008Co-Authors: T V Smirnova, V I ShishovAbstract:The interstellar Scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive Scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 ( n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the Scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ _0 = 10^7 m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the Scintillations of PSR B0809+74.
E R De Paula - One of the best experts on this subject based on the ideXlab platform.
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Thermospheric Meridional Wind Control on Equatorial Scintillations and the Role of the Evening F-Region Height Rise, E × B Drift Velocities and F2-Peak Density Gradients
Surveys in Geophysics, 2010Co-Authors: Marcio T A H Muella, E R De Paula, P. R. Fagundes, J. A. Bittencourt, Y. SahaiAbstract:The possible role, on L-band Scintillation activity, played by the nighttime magnetic meridional component of the thermospheric horizontal neutral winds, the post-sunset F -layer base height, the electrical field pre-reversal enhancement (PRE) and the latitudinal gradients of the F 2-layer peak density is analyzed, considering different cases of Scintillation occurrence (and their latitudinal extent) during August and September 2002. The meridional winds were derived over low-latitudes from a modified form of the nonlinear time-dependent servo-model. A chain of two Scintillation monitors and three digital ionosondes was operational in Brazil and used to collect, respectively, global positioning system signal amplitude Scintillation and ionospheric height ( h ′ F ; hpF 2) and frequency ( foF 2) parameters. From the overall behavior in the 2 months analyzed, the results suggest that high near sunset upward vertical plasma drifts are conducive for the generation of spread- F irregularities, whereas large poleward meridional winds tend to suppress the development of plasma bubble irregularities and the occurrence of their associated Scintillations. Even when generated, a reduced fountain effect, due to weak electric field PRE, acts for the bubbles to be expanded less effectively to higher latitudes. The results also reveal that high F -layer base and peak heights (at equatorial and off-equatorial latitudes), and intense gradients in the F 2-peak density between the dip equator and the equatorial anomaly crests, are favorable conditions for the generation of F -region irregularities and increased Scintillation activity. Other distinct features of the controlling factors in the cases of occurrence and non-occurrence of equatorial Scintillations are presented and discussed.
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Magnetic conjugate point observations of kilometer and hundred‐meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
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magnetic conjugate point observations of kilometer and hundred meter scale irregularities and zonal drifts
Journal of Geophysical Research, 2010Co-Authors: E R De Paula, T L Beach, Marcio T A H Muella, Mangalathayil Ali Abdu, Inez S Batista, J H A Sobral, K M GrovesAbstract:[1] The Conjugate Point Equatorial Experiment (COPEX) campaign was carried out in Brazil, between October and December 2002, to study the conjugate nature of plasma bubble irregularities and to investigate their generation mechanisms, development characteristics, spatial-temporal distribution, and dynamics. In this work we will focus mainly on the zonal spaced GPS (1.575 GHz) and VHF (250 MHz) receivers' data collected simultaneously at two magnetic conjugate sites of the COPEX geometry: Boa Vista and Campo Grande. These GPS/VHF receivers were set up to detect the equatorial Scintillations and to measure ionospheric Scintillation pattern velocities. Then, the zonal irregularity drift velocities were estimated by applying a methodology that corrects the effects caused by vertical drifts and geometrical factors. The results reveal the coexistence of kilometer- (VHF) and hundred-meter-scale (GPS L-band) irregularities into the underlying depletion structure. Over the conjugate site of Campo Grande, the average zonal velocity at VHF seems to be consistently larger than the estimated GPS velocities until ∼0200 UT, whereas over Boa Vista the irregularities detected from both techniques are drifting with comparable velocities. The hundred-meter-scale structures causing L-band Scintillations appear to be drifting with comparable velocities over both the conjugate sites, whereas the kilometer-scale structures are drifting over Campo Grande with larger average velocities (before 0300 UT). Complementary data of ionospheric parameters scaled from collocated digital ionosondes are used in the analysis to explain differences/similarities on the Scintillation/zonal drift results.
T V Smirnova - One of the best experts on this subject based on the ideXlab platform.
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interstellar Scintillations of psr b1919 21 space ground interferometry
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V I Shishov, T V Smirnova, C. R. Gwinn, A S Andrianov, M V Popov, Alexey Rudnitskiy, V A SoglasnovAbstract:We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radiotelescope together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60000 km. We show that interstellar Scintillation of this pulsar consists of two components: diffractive Scintillations from inhomogeneities in a layer of turbulent plasma at a distance $z_{1} = 440$ pc from the observer or homogeneously distributed scattering material to pulsar; and weak Scintillations from a screen located near the observer at $z_{2} = 0.14 \pm 0.05$ pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift of observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded the scattering angle in the observer plane: $\theta_{scat}$ = 0.7 mas. An analysis of the time-frequency correlation function for weak Scintillations yielded the angle of refraction in the direction to the pulsar: $\theta_{ref, 0}$ = 110 ms and the distance to the prism $z_{prism} \le 2$ pc.
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Interstellar Scintillations of PSR B1919+21: space–ground interferometry
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V I Shishov, T V Smirnova, C. R. Gwinn, A S Andrianov, M V Popov, Alexey Rudnitskiy, V A SoglasnovAbstract:We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radiotelescope together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60000 km. We show that interstellar Scintillation of this pulsar consists of two components: diffractive Scintillations from inhomogeneities in a layer of turbulent plasma at a distance $z_{1} = 440$ pc from the observer or homogeneously distributed scattering material to pulsar; and weak Scintillations from a screen located near the observer at $z_{2} = 0.14 \pm 0.05$ pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift of observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded the scattering angle in the observer plane: $\theta_{scat}$ = 0.7 mas. An analysis of the time-frequency correlation function for weak Scintillations yielded the angle of refraction in the direction to the pulsar: $\theta_{ref, 0}$ = 110 ms and the distance to the prism $z_{prism} \le 2$ pc.
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the turbulence spectrum of the interstellar plasma toward the pulsars psr b0809 74 and b0950 08
Astronomy Reports, 2008Co-Authors: T V Smirnova, V I ShishovAbstract:The interstellar Scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive Scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 (n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the Scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ0 = 107 m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the Scintillations of PSR B0809+74.
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The turbulence spectrum of the interstellar plasma toward the pulsars PSR B0809+74 and B0950+08
Astronomy Reports, 2008Co-Authors: T V Smirnova, V I ShishovAbstract:The interstellar Scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive Scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 ( n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the Scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ _0 = 10^7 m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the Scintillations of PSR B0809+74.
