The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Qihou Zhou - One of the best experts on this subject based on the ideXlab platform.
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Incoherent Scatter Radar observation of e region vertical electric field at arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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Incoherent Scatter Radar observation of E‐region vertical electric field at Arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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Imaging coherent Scatter Radar, Incoherent Scatter Radar, and optical observations of quasiperiodic structures associated with sporadic E layers
Journal of Geophysical Research: Space Physics, 2007Co-Authors: Miguel F. Larsen, Qihou Zhou, David L. Hysell, Steven M. Smith, Jonathan S. Friedman, Rebecca BishopAbstract:[1] During June and July 2002, a 30-MHz imaging coherent Scatter Radar was installed and operated on the island of St. Croix, to view the E region ionosphere above Arecibo, Puerto Rico. During the observing period, 10 events with discernible quasiperiodic echo structure were observed with the coherent Scatter Radar. In six of those events, simultaneous measurements were made with the Arecibo 430-MHz Incoherent Scatter Radar. The imaging coherent Scatter Radar allows us to locate and track the echo structures within the volume illuminated by the transmitter, which shows structures that are generally aligned along wavefronts. A slight preference for motion of the structures toward the southwest is evident throughout the period, but the propagation directions and speeds vary greatly. The Incoherent Scatter Radar measurements show a close correspondence between the occurrence of the coherent echoes and the location of the enhanced electron density structures. In particular, the coherent echoes occur when the electron density layers show uplifts.
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A case study of mesospheric gravity wave momentum flux and dynamical instability using the Arecibo dual beam Incoherent Scatter Radar
Geophysical Research Letters, 2006Co-Authors: Qihou Zhou, Yu MortonAbstract:We report the first observation of gravity wave momentum flux in the mesosphere using the dual-beam Arecibo Incoherent Scatter Radar (ISR). Quasimonochromatic waves were observed throughout the daytime of July 28, 2001 in the altitude range of 65â 85 km. The largest wave speed was about 100 m/s and the dominant period was about 15 min. Instability, as indicated by the Richardson number, occurred at several altitudes, most dramatically at 77 and 81 kilometers. The zonal momentum flux is found to change sign at altitudes where dynamical instability occurs. No significant gravity waves were observed in the region having an eastward background wind, while they were ubiquitous when the background wind was westward. Citation: Zhou, Q., and Y. T. Morton (2006), A case study of mesospheric gravity wave momentum flux and dynamical instability using the Arecibo dual beam Incoherent Scatter Radar, Geophys. Res. Lett., 33, L10802, doi:10.1029/ 2005GL025608.
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Incoherent Scatter Radar study of photochemistry in the E‐region
Geophysical Research Letters, 2005Co-Authors: Qihou Zhou, Yu MortonAbstract:[1] The ionospheric E-region from 100 km to 150 km is typically regarded as being in photo-chemical equilibrium (PCE) state during daytime. Incoherent Scatter Radar observations at Arecibo show that PCE is not always valid. During July 31–Aug. 5, 1992, the vertical ion drift was observed to increase by 50 m/s over a ten kilometer altitude range. The large divergence resulting from the steep velocity gradient reduced the electron concentration by 30%, invalidating the generally held PCE. Observations of non-PCE allow us to estimate the chemical loss rate. By assuming that the loss rate does not have a day-to-day variability, the dissociative recombination rate derived from the Incoherent Scatter Radar (ISR) observation is about 1.0 × 10−7 cm3s−1, which is significantly lower than the laboratory rate of NO+, or O2+. The most plausible explanation for the discrepancy is that the relative concentration of O2+ and NO+ changed significantly when non-PCE occurred.
Michael P. Sulzer - One of the best experts on this subject based on the ideXlab platform.
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On resolution/error trade‐offs in Incoherent Scatter Radar measurements
Radio Science, 2012Co-Authors: Romina Nikoukar, Farzad Kamalabadi, Erhan Kudeki, Michael P. SulzerAbstract:[1] In this work, we investigate the performance of amplitude modulated coding schemes in Incoherent Scatter Radar (ISR) measurements in terms of statistical estimation error, range resolution, and signal-to-noise ratio. We approach this goal by formulating the inherent trade-off between estimation error and resolution as mathematical measures for model order selection. These trade-offs are examined on numerical experiments with several amplitude modulated waveforms with different duty cycles. We demonstrate that compared with an unmodulated long pulse, reduced statistical estimation error with similar range resolution, or finer range resolution with similar estimation accuracy can be obtained by incorporating coding schemes.
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Incoherent Scatter Radar observation of e region vertical electric field at arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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Incoherent Scatter Radar observation of E‐region vertical electric field at Arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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An efficient near‐optimal approach to Incoherent Scatter Radar parameter estimation
Radio Science, 2008Co-Authors: Romina Nikoukar, Farzad Kamalabadi, Erhan Kudeki, Michael P. SulzerAbstract:[1] We present a computationally efficient, near-optimal approach to the estimation of ionospheric parameters from Incoherent Scatter Radar measurements. The method consists of removing the range smearing of ionospheric autocorrelation function via a set of 1-D deconvolutions and performing nonlinear least squares fitting on the deconvolved autocorrelation functions. To stabilize the solution in the presence of noise, we incorporate regularization techniques. The computational cost is reduced significantly by estimating the ionospheric parameters at individual altitudes, in comparison to full-profile-type analysis, which attempts to estimate ionospheric parameters at all altitudes simultaneously. The performance of the new technique is evaluated in a numerical example and is shown to give estimates of almost equal quality as the full-profile technique but at a 95% reduction in computation.
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An analysis of the scale heights in the lower topside ionosphere based on the Arecibo Incoherent Scatter Radar measurements
Journal of Geophysical Research: Space Physics, 2007Co-Authors: Libo Liu, Michael P. Sulzer, Weixing Wan, Jiuhou Lei, Man-lian ZhangAbstract:[1] We statistically analyze the ionospheric scale heights in the lower topside ionosphere based on the electron density (Ne) and temperature profiles observed from the Incoherent Scatter Radar (ISR) at Arecibo (293.2E, 18.3N), Puerto Rico. In this study, a database containing the Arecibo ISR observations from 1966 to 2002 has been used in order to investigate the diurnal and seasonal variations and solar activity dependences of the vertical scale height (VSH), which is deduced from the electron concentration profiles
Yu Morton - One of the best experts on this subject based on the ideXlab platform.
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a comparative study of ionospheric irregularity drift velocity derived from a gnss receiver array and poker flat Incoherent Scatter Radar measurements during high latitude ionospheric scintillation
Journal of Geophysical Research, 2017Co-Authors: Jun Wang, Yu MortonAbstract:The conventional ionospheric scintillation-based, spaced-receiver technique uses Global Navigation Satellite Systems (GNSS) signal intensity measurements. It is not suitable, however, for high-latitude regions where phase scintillations occur much more often than amplitude scintillations. This paper demonstrates that GNSS signal carrier phase scintillations observed from a spaced-receiver array can be used to infer horizontal ionospheric drift velocities via time domain correlation. Drift velocities measured by the colocated Poker Flat Incoherent Scatter Radar are cross compared against the estimated results from the GNSS receiver array. A comparative study is conducted based on two case studies on 20 and 31 December 2015, both accompanied by intense geomagnetic storms. Overall, the comparison results show statistical agreement between the GNSS receiver array estimation and Incoherent Scatter Radar measurements.
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Incoherent Scatter Radar observation of e region vertical electric field at arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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Incoherent Scatter Radar observation of E‐region vertical electric field at Arecibo
Geophysical Research Letters, 2011Co-Authors: Qihou Zhou, Yu Morton, C. M. Huang, Nestor Aponte, Michael P. Sulzer, Sixto A. GonzálezAbstract:[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo Incoherent Scatter Radar. This is achieved by employing the dual beam Incoherent Scatter Radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.
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A case study of mesospheric gravity wave momentum flux and dynamical instability using the Arecibo dual beam Incoherent Scatter Radar
Geophysical Research Letters, 2006Co-Authors: Qihou Zhou, Yu MortonAbstract:We report the first observation of gravity wave momentum flux in the mesosphere using the dual-beam Arecibo Incoherent Scatter Radar (ISR). Quasimonochromatic waves were observed throughout the daytime of July 28, 2001 in the altitude range of 65â 85 km. The largest wave speed was about 100 m/s and the dominant period was about 15 min. Instability, as indicated by the Richardson number, occurred at several altitudes, most dramatically at 77 and 81 kilometers. The zonal momentum flux is found to change sign at altitudes where dynamical instability occurs. No significant gravity waves were observed in the region having an eastward background wind, while they were ubiquitous when the background wind was westward. Citation: Zhou, Q., and Y. T. Morton (2006), A case study of mesospheric gravity wave momentum flux and dynamical instability using the Arecibo dual beam Incoherent Scatter Radar, Geophys. Res. Lett., 33, L10802, doi:10.1029/ 2005GL025608.
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Incoherent Scatter Radar study of photochemistry in the E‐region
Geophysical Research Letters, 2005Co-Authors: Qihou Zhou, Yu MortonAbstract:[1] The ionospheric E-region from 100 km to 150 km is typically regarded as being in photo-chemical equilibrium (PCE) state during daytime. Incoherent Scatter Radar observations at Arecibo show that PCE is not always valid. During July 31–Aug. 5, 1992, the vertical ion drift was observed to increase by 50 m/s over a ten kilometer altitude range. The large divergence resulting from the steep velocity gradient reduced the electron concentration by 30%, invalidating the generally held PCE. Observations of non-PCE allow us to estimate the chemical loss rate. By assuming that the loss rate does not have a day-to-day variability, the dissociative recombination rate derived from the Incoherent Scatter Radar (ISR) observation is about 1.0 × 10−7 cm3s−1, which is significantly lower than the laboratory rate of NO+, or O2+. The most plausible explanation for the discrepancy is that the relative concentration of O2+ and NO+ changed significantly when non-PCE occurred.
Craig Heinselman - One of the best experts on this subject based on the ideXlab platform.
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Three‐dimensional measurements of traveling ionospheric disturbances with the Poker Flat Incoherent Scatter Radar
Geophysical Research Letters, 2007Co-Authors: Michael J. Nicolls, Craig HeinselmanAbstract:[1] In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three-dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)-TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
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three dimensional measurements of traveling ionospheric disturbances with the poker flat Incoherent Scatter Radar
Geophysical Research Letters, 2007Co-Authors: Michael J. Nicolls, Craig HeinselmanAbstract:[1] In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three-dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)-TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
Michael J. Nicolls - One of the best experts on this subject based on the ideXlab platform.
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First observations from the RISR‐C Incoherent Scatter Radar
Radio Science, 2016Co-Authors: R. G. Gillies, Michael J. Nicolls, David J. Knudsen, J. D. Kelly, A. P. Van Eyken, Emma Spanswick, M. Greffen, Martin Connors, M. Schutzer, Todd ValenticAbstract:First-light measurements from the Canadian face of the Resolute Bay Incoherent Scatter Radar (RISR-C) were taken in August of 2015. Data were taken for roughly 25 hours on both RISR-C and the North face of the Resolute Bay Radar (RISR-N) in an 11-beam World Day mode. Overall, the measurements from the RISR-C Radar are of high quality and consistent with results from the RISR-N Radar. During the 25-hour period analyzed in this study, the ionosphere responded to changes in orientation of the Interplanetary Magnetic Field (IMF). During one particular event, a change from Bz negative to positive and By positive to negative caused the anti-sunward flow to stall, and a strong dawn-to-dusk flow, with decreased electron density and increased ion temperature, replaced it in the RISR-C field-of-view. Overall, it is clear that measurements from the RISR-C Radar will complement and greatly expand the scope of ionospheric polar cap measurements.
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Resolute Bay Incoherent Scatter Radar observations of plasma structures in the vicinity of polar holes
Journal of Geophysical Research: Space Physics, 2015Co-Authors: Roman A. Makarevich, Leslie J. Lamarche, Michael J. NicollsAbstract:The Resolute Bay Incoherent Scatter Radar North (RISR-N) data collected between January 2012 and June 2013 are employed to identify and analyze 14 events with significant plasma density depressions (Ne 150 km), with no apparent differences between structure shapes outside and inside low-density regions. The structure propagation velocity is perpendicular to its elongation direction and consistent with that of the large-scale plasma convection. The observations indicate that large-scale density depressions can form under a variety of convection conditions and that plasma structuring processes outside the depressions may be responsible for their partial filling.
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Direct three‐dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar
Geophysical Research Letters, 2012Co-Authors: Hanna Dahlgren, Michael J. Nicolls, Joshua Semeter, Keisuke Hosokawa, T. W. Butler, Magnar Gullikstad Johnsen, Kazuo Shiokawa, C. J. HeinselmanAbstract:[1] Ionospheric plasma density structures in the dayside F-region of the polar cap are commonly occurring events, but adequate measurements of their formation and evolution have been sparse. With the advent of the advanced modular Incoherent Scatter Radar RISR-N (Resolute Bay Incoherent Scatter Radar) it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions, with a spatial resolution of tens of kilometers, from which the plasma rest frame can be experimentally established. We demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over Resolute Bay in December 2009. A colocated all-sky imager showed faint 630.0 and 557.7 nm emission corresponding to the plasma enhancements, and the structures could be traced back to a formation region in the open/closed field line boundary. This new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere.
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Three‐dimensional measurements of traveling ionospheric disturbances with the Poker Flat Incoherent Scatter Radar
Geophysical Research Letters, 2007Co-Authors: Michael J. Nicolls, Craig HeinselmanAbstract:[1] In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three-dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)-TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
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three dimensional measurements of traveling ionospheric disturbances with the poker flat Incoherent Scatter Radar
Geophysical Research Letters, 2007Co-Authors: Michael J. Nicolls, Craig HeinselmanAbstract:[1] In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three-dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)-TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
