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J H A Sobral - One of the best experts on this subject based on the ideXlab platform.

  • equatorial spread f initiation and growth from satellite traces as revealed from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2014
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J H A Sobral
    Abstract:

    [1] A better understanding of the precursor conditions for the instability growth is very important for identifying the causes of day-to-day variability in the equatorial spread F (ESF)/plasma bubble irregularity development. We investigate here the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic Conjugate sites in Brazil during a 66 day observational campaign (Conjugate Point Equatorial Experiment 2002). The satellite traces first occur at the equatorial site, and sequentially, after a variable delay of approximately 20 to 50 min, they are observed nearly simultaneously over the two Conjugate sites. The evening prereversal enhancement in the zonal electric field/vertical drift is found to control its development. Using a three-dimensional simulation code based on collisional interchange instability mechanism, it is shown that the observed S-trace occurrence sequence is fully consistent with the instability initiation over the equator with the field-aligned plasma depletion vertical growth marked by latitudinal expansion of its extremities to Conjugate locations. The delay in the S-trace occurrence at the Conjugate sites (a measure of the nonlinear growth of the instability for plasma depletion) is controlled also by field line parallel (meridional) neutral wind. The relationship between the S-trace and the large-scale wave structure in the F layer, another widely known characterization of the precursor condition for the ESF development, is also clarified.

  • equatorial ionosphere responses to two magnetic storms of moderate intensity from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2012
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, Fernando C P Bertoni, E A Kherani, J H A Sobral
    Abstract:

    [1] Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by Conjugate Point observations in Brazil. The study focuses on storm-induced changes in the evening prereversal vertical drift, thermospheric trans-equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a Conjugate Point equatorial experiment (COPEX) involving a dip equatorial and two magnetic Conjugate sites at ±12°. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under-shielding (over-shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under-shielding (over-shielding) electric fields, while it can be disrupted by over-shielding (under-shielding) electric field. Trans-equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms.

  • Equatorial spread F echo and irregularity growth processes from Conjugate Point digital ionograms
    2011 XXXth URSI General Assembly and Scientific Symposium, 2011
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J. W. Macdougall, J H A Sobral
    Abstract:

    Spread F irregularity signatures in the form of range spreading F layer traces are examined in Digisonde ionograms from dip equatorial and Conjugate sites in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF echo structures is found to be consistent with them originating from coherent back-scattering at field line perpendicular directions. The spread range of the echoes is found to increase linearly with the top frequency of the echo trace. Further, the irregularity strength is asymmetric at Conjugate sites.

  • Magnetic Conjugate Point observations of kilometer and hundred‐meter scale irregularities and zonal drifts
    Journal of Geophysical Research, 2010
    Co-Authors: E R De Paula, J H A Sobral, I S Batista, Marcio T A H Muella, Mangalathayil Ali Abdu, T L Beach, Keith M. Groves
    Abstract:

    [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.

  • magnetic Conjugate Point observations of kilometer and hundred meter scale irregularities and zonal drifts
    Journal of Geophysical Research, 2010
    Co-Authors: E R De Paula, J H A Sobral, I S Batista, Marcio T A H Muella, Mangalathayil Ali Abdu, T L Beach, K M Groves
    Abstract:

    [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.

M A Abdu - One of the best experts on this subject based on the ideXlab platform.

  • equatorial spread f initiation and growth from satellite traces as revealed from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2014
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J H A Sobral
    Abstract:

    [1] A better understanding of the precursor conditions for the instability growth is very important for identifying the causes of day-to-day variability in the equatorial spread F (ESF)/plasma bubble irregularity development. We investigate here the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic Conjugate sites in Brazil during a 66 day observational campaign (Conjugate Point Equatorial Experiment 2002). The satellite traces first occur at the equatorial site, and sequentially, after a variable delay of approximately 20 to 50 min, they are observed nearly simultaneously over the two Conjugate sites. The evening prereversal enhancement in the zonal electric field/vertical drift is found to control its development. Using a three-dimensional simulation code based on collisional interchange instability mechanism, it is shown that the observed S-trace occurrence sequence is fully consistent with the instability initiation over the equator with the field-aligned plasma depletion vertical growth marked by latitudinal expansion of its extremities to Conjugate locations. The delay in the S-trace occurrence at the Conjugate sites (a measure of the nonlinear growth of the instability for plasma depletion) is controlled also by field line parallel (meridional) neutral wind. The relationship between the S-trace and the large-scale wave structure in the F layer, another widely known characterization of the precursor condition for the ESF development, is also clarified.

  • equatorial ionosphere responses to two magnetic storms of moderate intensity from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2012
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, Fernando C P Bertoni, E A Kherani, J H A Sobral
    Abstract:

    [1] Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by Conjugate Point observations in Brazil. The study focuses on storm-induced changes in the evening prereversal vertical drift, thermospheric trans-equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a Conjugate Point equatorial experiment (COPEX) involving a dip equatorial and two magnetic Conjugate sites at ±12°. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under-shielding (over-shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under-shielding (over-shielding) electric fields, while it can be disrupted by over-shielding (under-shielding) electric field. Trans-equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms.

  • Equatorial spread F echo and irregularity growth processes from Conjugate Point digital ionograms
    2011 XXXth URSI General Assembly and Scientific Symposium, 2011
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J. W. Macdougall, J H A Sobral
    Abstract:

    Spread F irregularity signatures in the form of range spreading F layer traces are examined in Digisonde ionograms from dip equatorial and Conjugate sites in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF echo structures is found to be consistent with them originating from coherent back-scattering at field line perpendicular directions. The spread range of the echoes is found to increase linearly with the top frequency of the echo trace. Further, the irregularity strength is asymmetric at Conjugate sites.

  • Conjugate Point equatorial experiment copex campaign in brazil electrodynamics highlights on spread f development conditions and day to day variability
    Journal of Geophysical Research, 2009
    Co-Authors: M A Abdu, Inez S Batista, B W Reinisch, J R De Souza, J H A Sobral, T R Pedersen, A F Medeiros, N J Schuch, E R De Paula, K M Groves
    Abstract:

    [1] A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October–December 2002 period in Brazil, with the objective to investigate the equatorial spread F/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was deployed at magnetic Conjugate and dip equatorial locations in a geometry that permitted field line mapping of the Conjugate E layers to dip equatorial F layer bottomside. We analyze in this paper the extensive Digisonde data from the COPEX stations, complemented by limited all-sky imager Conjugate Point observations. The Sheffield University Plasmasphere-Ionosphere Model (SUPIM) is used to assess the transequatorial winds (TEW) as inferred from the observed difference of hmF2 at the Conjugate sites. New results and evidence on the ESF development conditions and the related ambient electrodynamic processes from this study can be highlighted as follows: (1) large-scale bottomside wave structures/satellite traces at the equator followed by their simultaneous appearance at Conjugate sites are shown to be indicative of the ESF instability initiation; (2) the evening prereversal electric field enhancement (PRE)/vertical drift presents systematic control on the time delay in SF onset at off-equatorial sites indicative of the vertical bubble growth, under weak transequatorial wind; (3) the PRE presents a large latitude/height gradient in the Brazilian sector; (4) Conjugate Point symmetry/asymmetry of large-scale plasma depletions versus smaller-scale structures is revealed; and (5) while transequatorial winds seem to suppress ESF development in a case study, the medium-term trend in the ESF seems to be controlled more by the variation in the PRE than in the TEW during the COPEX period. Competing influences of the evening vertical plasma drift in favoring the ESF development and that of the TEW in suppressing its growth are discussed, presenting a perspective on the ESF day-to-day and medium-term variabilities.

  • equatorial spread f and sporadic e layer connections during the brazilian Conjugate Point equatorial experiment copex
    Journal of Atmospheric and Solar-Terrestrial Physics, 2008
    Co-Authors: Inez S Batista, M A Abdu, B W Reinisch, N J Schuch, E R De Paula, A J Carrasco, F Bertoni
    Abstract:

    The Conjugate Point Equatorial Experiment (COPEX) was conducted in Brazil from October to December 2002. The observational instruments were placed at three sites nearly along a magnetic meridian, one at the magnetic equator and the other two at magnetically Conjugate Points. We analyzed the spread F (SF) occurrence and sporadic E (Es) layer characteristics in the simultaneous data to look for any possible relation between these two phenomena. The present study does not detect any significant correlation between the SF occurrence/generation at the magnetic equator and the presence of Es layers at the Conjugate E regions along the same field line. The integrated field line conductivity is not significantly affected by the occurrence of Es at the Conjugate E regions and its presence is not sufficient to inhibit the vertical drift and SF generation at the magnetic equator. Model results show that the presence of a vertical equatorial electric field (associated with the eastward electric field pre-reversal enhancement) is too week to affect the Es development at the Conjugate stations.

B W Reinisch - One of the best experts on this subject based on the ideXlab platform.

  • equatorial spread f initiation and growth from satellite traces as revealed from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2014
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J H A Sobral
    Abstract:

    [1] A better understanding of the precursor conditions for the instability growth is very important for identifying the causes of day-to-day variability in the equatorial spread F (ESF)/plasma bubble irregularity development. We investigate here the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic Conjugate sites in Brazil during a 66 day observational campaign (Conjugate Point Equatorial Experiment 2002). The satellite traces first occur at the equatorial site, and sequentially, after a variable delay of approximately 20 to 50 min, they are observed nearly simultaneously over the two Conjugate sites. The evening prereversal enhancement in the zonal electric field/vertical drift is found to control its development. Using a three-dimensional simulation code based on collisional interchange instability mechanism, it is shown that the observed S-trace occurrence sequence is fully consistent with the instability initiation over the equator with the field-aligned plasma depletion vertical growth marked by latitudinal expansion of its extremities to Conjugate locations. The delay in the S-trace occurrence at the Conjugate sites (a measure of the nonlinear growth of the instability for plasma depletion) is controlled also by field line parallel (meridional) neutral wind. The relationship between the S-trace and the large-scale wave structure in the F layer, another widely known characterization of the precursor condition for the ESF development, is also clarified.

  • equatorial ionosphere responses to two magnetic storms of moderate intensity from Conjugate Point observations in brazil
    Journal of Geophysical Research, 2012
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, Fernando C P Bertoni, E A Kherani, J H A Sobral
    Abstract:

    [1] Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by Conjugate Point observations in Brazil. The study focuses on storm-induced changes in the evening prereversal vertical drift, thermospheric trans-equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a Conjugate Point equatorial experiment (COPEX) involving a dip equatorial and two magnetic Conjugate sites at ±12°. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under-shielding (over-shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under-shielding (over-shielding) electric fields, while it can be disrupted by over-shielding (under-shielding) electric field. Trans-equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms.

  • Equatorial spread F echo and irregularity growth processes from Conjugate Point digital ionograms
    2011 XXXth URSI General Assembly and Scientific Symposium, 2011
    Co-Authors: M A Abdu, B W Reinisch, I S Batista, E A Kherani, J. W. Macdougall, J H A Sobral
    Abstract:

    Spread F irregularity signatures in the form of range spreading F layer traces are examined in Digisonde ionograms from dip equatorial and Conjugate sites in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF echo structures is found to be consistent with them originating from coherent back-scattering at field line perpendicular directions. The spread range of the echoes is found to increase linearly with the top frequency of the echo trace. Further, the irregularity strength is asymmetric at Conjugate sites.

  • Conjugate Point equatorial experiment copex campaign in brazil electrodynamics highlights on spread f development conditions and day to day variability
    Journal of Geophysical Research, 2009
    Co-Authors: M A Abdu, Inez S Batista, B W Reinisch, J R De Souza, J H A Sobral, T R Pedersen, A F Medeiros, N J Schuch, E R De Paula, K M Groves
    Abstract:

    [1] A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October–December 2002 period in Brazil, with the objective to investigate the equatorial spread F/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was deployed at magnetic Conjugate and dip equatorial locations in a geometry that permitted field line mapping of the Conjugate E layers to dip equatorial F layer bottomside. We analyze in this paper the extensive Digisonde data from the COPEX stations, complemented by limited all-sky imager Conjugate Point observations. The Sheffield University Plasmasphere-Ionosphere Model (SUPIM) is used to assess the transequatorial winds (TEW) as inferred from the observed difference of hmF2 at the Conjugate sites. New results and evidence on the ESF development conditions and the related ambient electrodynamic processes from this study can be highlighted as follows: (1) large-scale bottomside wave structures/satellite traces at the equator followed by their simultaneous appearance at Conjugate sites are shown to be indicative of the ESF instability initiation; (2) the evening prereversal electric field enhancement (PRE)/vertical drift presents systematic control on the time delay in SF onset at off-equatorial sites indicative of the vertical bubble growth, under weak transequatorial wind; (3) the PRE presents a large latitude/height gradient in the Brazilian sector; (4) Conjugate Point symmetry/asymmetry of large-scale plasma depletions versus smaller-scale structures is revealed; and (5) while transequatorial winds seem to suppress ESF development in a case study, the medium-term trend in the ESF seems to be controlled more by the variation in the PRE than in the TEW during the COPEX period. Competing influences of the evening vertical plasma drift in favoring the ESF development and that of the TEW in suppressing its growth are discussed, presenting a perspective on the ESF day-to-day and medium-term variabilities.

  • equatorial spread f and sporadic e layer connections during the brazilian Conjugate Point equatorial experiment copex
    Journal of Atmospheric and Solar-Terrestrial Physics, 2008
    Co-Authors: Inez S Batista, M A Abdu, B W Reinisch, N J Schuch, E R De Paula, A J Carrasco, F Bertoni
    Abstract:

    The Conjugate Point Equatorial Experiment (COPEX) was conducted in Brazil from October to December 2002. The observational instruments were placed at three sites nearly along a magnetic meridian, one at the magnetic equator and the other two at magnetically Conjugate Points. We analyzed the spread F (SF) occurrence and sporadic E (Es) layer characteristics in the simultaneous data to look for any possible relation between these two phenomena. The present study does not detect any significant correlation between the SF occurrence/generation at the magnetic equator and the presence of Es layers at the Conjugate E regions along the same field line. The integrated field line conductivity is not significantly affected by the occurrence of Es at the Conjugate E regions and its presence is not sufficient to inhibit the vertical drift and SF generation at the magnetic equator. Model results show that the presence of a vertical equatorial electric field (associated with the eastward electric field pre-reversal enhancement) is too week to affect the Es development at the Conjugate stations.

K M Groves - One of the best experts on this subject based on the ideXlab platform.

  • latitudinal and local time variation of ionospheric turbulence parameters during the Conjugate Point equatorial experiment in brazil
    International Journal of Geophysics, 2012
    Co-Authors: Charles S Carrano, C E Valladares, K M Groves
    Abstract:

    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.

  • magnetic Conjugate Point observations of kilometer and hundred meter scale irregularities and zonal drifts
    Journal of Geophysical Research, 2010
    Co-Authors: E R De Paula, J H A Sobral, I S Batista, Marcio T A H Muella, Mangalathayil Ali Abdu, T L Beach, K M Groves
    Abstract:

    [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.

  • Conjugate Point equatorial experiment copex campaign in brazil electrodynamics highlights on spread f development conditions and day to day variability
    Journal of Geophysical Research, 2009
    Co-Authors: M A Abdu, Inez S Batista, B W Reinisch, J R De Souza, J H A Sobral, T R Pedersen, A F Medeiros, N J Schuch, E R De Paula, K M Groves
    Abstract:

    [1] A Conjugate Point Equatorial Experiment (COPEX) campaign was conducted during the October–December 2002 period in Brazil, with the objective to investigate the equatorial spread F/plasma bubble irregularity (ESF) development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur. A network of instruments, including Digisondes, optical imagers, and GPS receivers, was deployed at magnetic Conjugate and dip equatorial locations in a geometry that permitted field line mapping of the Conjugate E layers to dip equatorial F layer bottomside. We analyze in this paper the extensive Digisonde data from the COPEX stations, complemented by limited all-sky imager Conjugate Point observations. The Sheffield University Plasmasphere-Ionosphere Model (SUPIM) is used to assess the transequatorial winds (TEW) as inferred from the observed difference of hmF2 at the Conjugate sites. New results and evidence on the ESF development conditions and the related ambient electrodynamic processes from this study can be highlighted as follows: (1) large-scale bottomside wave structures/satellite traces at the equator followed by their simultaneous appearance at Conjugate sites are shown to be indicative of the ESF instability initiation; (2) the evening prereversal electric field enhancement (PRE)/vertical drift presents systematic control on the time delay in SF onset at off-equatorial sites indicative of the vertical bubble growth, under weak transequatorial wind; (3) the PRE presents a large latitude/height gradient in the Brazilian sector; (4) Conjugate Point symmetry/asymmetry of large-scale plasma depletions versus smaller-scale structures is revealed; and (5) while transequatorial winds seem to suppress ESF development in a case study, the medium-term trend in the ESF seems to be controlled more by the variation in the PRE than in the TEW during the COPEX period. Competing influences of the evening vertical plasma drift in favoring the ESF development and that of the TEW in suppressing its growth are discussed, presenting a perspective on the ESF day-to-day and medium-term variabilities.

V. Zeidan - One of the best experts on this subject based on the ideXlab platform.