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Xinan Yue - One of the best experts on this subject based on the ideXlab platform.
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an improved inversion for formosat 3 cosmic ionosphere Electron Density Profiles
Journal of Geophysical Research, 2015Co-Authors: N M Pedatella, Xinan Yue, William SchreinerAbstract:An improved method to retrieve Electron Density Profiles from Global Positioning System (GPS) radio occultation (RO) data is presented and applied to Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations. The improved inversion uses a monthly grid of COSMIC F region peak densities (NmF2), which are obtained via the standard Abel inversion, to aid the Abel inversion by providing information on the horizontal gradients in the ionosphere. This lessens the impact of ionospheric gradients on the retrieval of GPS RO Electron Density Profiles, reducing the dominant error source in the standard Abel inversion. Results are presented that demonstrate the NmF2 aided retrieval significantly improves the quality of the COSMIC Electron Density Profiles. Improvements are most notable at E region altitudes, where the improved inversion reduces the artificial plasma cave that is generated by the Abel inversion spherical symmetry assumption at low latitudes during the daytime. Occurrence of unphysical negative Electron densities at E region altitudes is also reduced. Furthermore, the NmF2 aided inversion has a positive impact at F region altitudes, where it results in a more distinct equatorial ionization anomaly. COSMIC Electron Density Profiles inverted using our new approach are currently available through the University Corporation for Atmospheric Research COSMIC Data Analysis and Archive Center. Owing to the significant improvement in the results, COSMIC data users are encouraged to use Electron Density Profiles based on the improved inversion rather than those inverted by the standard Abel inversion.
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evaluating the effect of the global ionospheric map on aiding retrieval of radio occultation Electron Density Profiles
Gps Solutions, 2013Co-Authors: Xinan Yue, William Schreiner, Yinghwa KuoAbstract:Radio occultation (RO) has been proven to be a powerful technique for ionospheric Electron Density profile (EDP) retrieval. The Abel inversion currently used in RO EDP retrieval has degraded performance in regions with large horizontal gradients because of an assumption of spherical symmetry as indicated by many studies. Some alternative methods have been proposed in the past; the global ionospheric map (GIM)-aided Abel inversion is most frequently studied. Since the number of RO observations will likely increase rapidly in the near future, it is worthwhile to continue to improve retrieval method. In this study, both the simulations and the real data test have been done to evaluate the GIM-aided Abel inversion method. It is found that the GIM-aided Abel inversion can significantly improve upon the standard Abel inversion in either the F or the E region if an accurate GIM is available. However, the current IGS GIM does not appear accurate enough to improve retrieval results significantly, because of the spherical symmetry assumption and sparse global navigation satellite system (GNSS) stations used in its creation. Generating accurate GIM based on dense GNSS network to aid the Abel inversion might be an alternative method.
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data assimilation retrieval of Electron Density Profiles from radio occultation measurements
Journal of Geophysical Research, 2011Co-Authors: Xinan Yue, William Schreiner, C Rocken, Yucheng Lin, Biqiang ZhaoAbstract:[1] In this paper, the Kalman filter is used to retrieve the Electron Density profile along the tangent points by assimilating the slant total Electron content data observed during a radio occultation (RO) event into an empirical background model. The RO data observed by COSMIC satellites on day of year 266 in 2009 are selected to do both the simulation work and the real data retrieval test. The results show that the data assimilation technique can improve the Electron Density retrieval in comparison with the Abel inversion. It is less influenced by the ionospheric inhomogeneity than the Abel method. Some pseudo‐large‐scale features made by the Abel retrieval, such as the plasma cave underneath the equatorial ionization anomaly region and the three peaks along the latitude direction in the E layer, disappear in the data assimilation retrieval results. Independent validation by ground‐based ionosonde observations confirms the improvement of data assimilation retrieval below the F2 peak. In addition, some potential research on RO data assimilation is also discussed.
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longitudinal behaviors of the iri b parameters of the equatorial Electron Density Profiles retrieved from formosat 3 cosmic radio occultation measurements
Advances in Space Research, 2010Co-Authors: Libo Liu, Weixing Wan, Baiqi Ning, Manlian Zhang, Xinan YueAbstract:The Electron Density Profiles in the bottomside F2-layer ionosphere are described by the thickness parameter B0 and the shape parameter B1 in the International Reference Ionosphere (IRI) model. We collected the ionospheric Electron Density (Ne) Profiles from the FORMOSAT-3/COSMIC (F3/C) radio occultation measurements from DoY (day number of year) 194, 2006 to DoY 293, 2008 to investigate the daytime behaviors of IRI-B parameters (B0 and B1) in the equatorial regions. Our fittings confirm that the IRI bottomside profile function can well describe the averaged Profiles in the bottomside ionosphere. Analysis of the equatorial Electron Density profile datasets provides unprecedented detail of the behaviors of B0 and B1 parameters in equatorial regions at low solar activity. The longitudinal averaged B1 has values comparable with IRI-2007 while it shows little seasonal variation. In contrast, the observed B0 presents semiannual variation with maxima in solstice months and minima in equinox months, which is not reproduced by IRI-2007. Moreover, there are complicated longitudinal variations of B0 with patterns varying with seasons. Peaks are distinct in the wave-like longitudinal structure of B0 in equinox months. An outstanding feature is that a stable peak appears around 100E in four seasons. The significant longitudinal variation of B0 provides challenges for further improving the presentations of the bottomside ionosphere in IRI. 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.
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error analysis of abel retrieved Electron Density Profiles from radio occultation measurements
Annales Geophysicae, 2010Co-Authors: Xinan Yue, William Schreiner, Jiuhou Lei, C Rocken, Douglas HuntAbstract:Abstract. This letter reports for the first time the simulated error distribution of radio occultation (RO) Electron Density Profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total Electron content (TEC) along the COSMIC occultation paths with the "true" Electron Density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved Electron Density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates Electron Density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime Electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial Electron densities.
William Schreiner - One of the best experts on this subject based on the ideXlab platform.
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an improved inversion for formosat 3 cosmic ionosphere Electron Density Profiles
Journal of Geophysical Research, 2015Co-Authors: N M Pedatella, Xinan Yue, William SchreinerAbstract:An improved method to retrieve Electron Density Profiles from Global Positioning System (GPS) radio occultation (RO) data is presented and applied to Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations. The improved inversion uses a monthly grid of COSMIC F region peak densities (NmF2), which are obtained via the standard Abel inversion, to aid the Abel inversion by providing information on the horizontal gradients in the ionosphere. This lessens the impact of ionospheric gradients on the retrieval of GPS RO Electron Density Profiles, reducing the dominant error source in the standard Abel inversion. Results are presented that demonstrate the NmF2 aided retrieval significantly improves the quality of the COSMIC Electron Density Profiles. Improvements are most notable at E region altitudes, where the improved inversion reduces the artificial plasma cave that is generated by the Abel inversion spherical symmetry assumption at low latitudes during the daytime. Occurrence of unphysical negative Electron densities at E region altitudes is also reduced. Furthermore, the NmF2 aided inversion has a positive impact at F region altitudes, where it results in a more distinct equatorial ionization anomaly. COSMIC Electron Density Profiles inverted using our new approach are currently available through the University Corporation for Atmospheric Research COSMIC Data Analysis and Archive Center. Owing to the significant improvement in the results, COSMIC data users are encouraged to use Electron Density Profiles based on the improved inversion rather than those inverted by the standard Abel inversion.
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evaluating the effect of the global ionospheric map on aiding retrieval of radio occultation Electron Density Profiles
Gps Solutions, 2013Co-Authors: Xinan Yue, William Schreiner, Yinghwa KuoAbstract:Radio occultation (RO) has been proven to be a powerful technique for ionospheric Electron Density profile (EDP) retrieval. The Abel inversion currently used in RO EDP retrieval has degraded performance in regions with large horizontal gradients because of an assumption of spherical symmetry as indicated by many studies. Some alternative methods have been proposed in the past; the global ionospheric map (GIM)-aided Abel inversion is most frequently studied. Since the number of RO observations will likely increase rapidly in the near future, it is worthwhile to continue to improve retrieval method. In this study, both the simulations and the real data test have been done to evaluate the GIM-aided Abel inversion method. It is found that the GIM-aided Abel inversion can significantly improve upon the standard Abel inversion in either the F or the E region if an accurate GIM is available. However, the current IGS GIM does not appear accurate enough to improve retrieval results significantly, because of the spherical symmetry assumption and sparse global navigation satellite system (GNSS) stations used in its creation. Generating accurate GIM based on dense GNSS network to aid the Abel inversion might be an alternative method.
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data assimilation retrieval of Electron Density Profiles from radio occultation measurements
Journal of Geophysical Research, 2011Co-Authors: Xinan Yue, William Schreiner, C Rocken, Yucheng Lin, Biqiang ZhaoAbstract:[1] In this paper, the Kalman filter is used to retrieve the Electron Density profile along the tangent points by assimilating the slant total Electron content data observed during a radio occultation (RO) event into an empirical background model. The RO data observed by COSMIC satellites on day of year 266 in 2009 are selected to do both the simulation work and the real data retrieval test. The results show that the data assimilation technique can improve the Electron Density retrieval in comparison with the Abel inversion. It is less influenced by the ionospheric inhomogeneity than the Abel method. Some pseudo‐large‐scale features made by the Abel retrieval, such as the plasma cave underneath the equatorial ionization anomaly region and the three peaks along the latitude direction in the E layer, disappear in the data assimilation retrieval results. Independent validation by ground‐based ionosonde observations confirms the improvement of data assimilation retrieval below the F2 peak. In addition, some potential research on RO data assimilation is also discussed.
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error analysis of abel retrieved Electron Density Profiles from radio occultation measurements
Annales Geophysicae, 2010Co-Authors: Xinan Yue, William Schreiner, Jiuhou Lei, C Rocken, Douglas HuntAbstract:Abstract. This letter reports for the first time the simulated error distribution of radio occultation (RO) Electron Density Profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total Electron content (TEC) along the COSMIC occultation paths with the "true" Electron Density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved Electron Density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates Electron Density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime Electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial Electron densities.
David P. Hinson - One of the best experts on this subject based on the ideXlab platform.
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characterization of a semidiurnal eastward propagating tide at high northern latitudes with mars global surveyor Electron Density Profiles
Geophysical Research Letters, 2007Co-Authors: Kerri Cahoy, David P. Hinson, G. L. TylerAbstract:[1] Apparent phase velocities of zonal structure, estimated from Mars Global Surveyor (MGS) Electron Density Profiles, are used to identify and characterize SE1, the semidiurnal eastward-propagating tide with zonal wave number one, at high northern latitudes during the summer of Mars Year 26. SE1 shows impressive phase stability with altitude, season, and local time. SE1 maintains a presence at amplitudes between 5 and 15% of the zonal mean at 125 ± 10 km altitude for most of the summer season. Further analyses using MGS Electron Density Profiles will contribute to the identification and characterization of nonmigrating tides in the upper atmosphere of Mars.
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mgs radio science Electron Density Profiles interannual variability and implications for the martian neutral atmosphere
Journal of Geophysical Research, 2004Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J. R. MurphyAbstract:Density of 7.3–8.5 � 10 4 cm � 3 is also measured during solar moderate conditions at Mars. Strong wave number 2–3 oscillations in peak heights are consistently observed as a function of longitude over the 2 Martian years. These observed ionospheric features are remarkably similar during aphelion conditions 1 Martian year apart. This year-to-year repeatability in the thermosphere-ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the Mars lower atmosphere [Clancy et al., 2000; Smith, 2004]. Coupled Mars general circulation model (MGCM) and Mars thermospheric general circulation model (MTGCM) codes are run for Mars aphelion conditions, yielding mean and longitude variable ionospheric peak heights that reasonably match RS observations. A tidal decomposition of MTGCM thermospheric densities shows that observed ionospheric wave number 3 features are linked to a nonmigrating tidal mode with semidiurnal period (s = 2) and zonal wave number 1 (s = � 1) characteristics. The height of this photochemically determined ionospheric peak should be monitored regularly. INDEX TERMS: 5435 Planetology: Solid Surface Planets: Ionospheres (2459); 5409 Planetology: Solid Surface Planets: Atmospheres—structure and dynamics; 6225 Planetology: Solar System Objects: Mars; KEYWORDS: ionosphere, Mars, thermosphere
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Mars Global Surveyor Radio Science Electron Density Profiles: Interannual Variability and Implications for the Neutral Atmosphere
2003Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J. R. MurphyAbstract:The Mars Global Surveyor (MGS) Radio Science (RS) experiment employs an ultrastable oscillator aboard the spacecraft. The signal from the oscillator to Earth is refracted by the Martian ionosphere, allowing retrieval of Electron Density Profiles versus radius and geopotential. The present analysis is carried out on five sets of occultation measurements: (1) four obtained near northern summer solstice (Ls = 74-116, near aphelion) at high northern latitudes (64.7-77.6N), and (2) one set of Profiles approaching equinox conditions (Ls = 135- 146) at high southern latitudes (64.7-69.1S). Electron Density Profiles (95 to 200 km) are examined over a narrow range of solar zenith angles (76.5-86.9 degrees) for local true solar times of (1) 3-4 hours and (2) 12.1 hours. Variations spanning 1-Martian year are specifically examined in the Northern hemisphere.
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mars global surveyor radio science Electron Density Profiles neutral atmosphere implications
Geophysical Research Letters, 2001Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J M ForbesAbstract:The Mars Global Surveyor (MGS) Radio Sci- ence (RS) experiment permits retrieval of Electron Density prof iles versus height (∼90-200 km) from occultation mea- surements. An initial set of Electron Profiles is examined spanning high northern latitudes, early morning solar local times and high solar zenith angles (78 to 81 ◦ ) near aphelion. Sampling for these 32-Profiles is well distributed over longi- tude. The height of the photochemically driven ionospheric peak is observed to respond to the background neutral den- sity structure, with a mean height during this season at this location of ∼134.4 km. Strong wave-3 oscillations about this mean are clearly observed as a function of longitude, and correspond to neutral Density variations measured by the MGS Accelerometer (ACC) experiment. The wave-3 tidal pattern implicated by both the RS and ACC datasets is consistent with a semi-diurnal wave frequency. Clearly, the height of the martian dayside ionospheric peak is a sensitive indicator of the state of the underlying Mars atmosphere. This ionospheric peak height can be used as a proxy of the longitude specific non-migrating tidal variations present in the Mars lower thermosphere.
Stephen W. Bougher - One of the best experts on this subject based on the ideXlab platform.
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mgs radio science Electron Density Profiles interannual variability and implications for the martian neutral atmosphere
Journal of Geophysical Research, 2004Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J. R. MurphyAbstract:Density of 7.3–8.5 � 10 4 cm � 3 is also measured during solar moderate conditions at Mars. Strong wave number 2–3 oscillations in peak heights are consistently observed as a function of longitude over the 2 Martian years. These observed ionospheric features are remarkably similar during aphelion conditions 1 Martian year apart. This year-to-year repeatability in the thermosphere-ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the Mars lower atmosphere [Clancy et al., 2000; Smith, 2004]. Coupled Mars general circulation model (MGCM) and Mars thermospheric general circulation model (MTGCM) codes are run for Mars aphelion conditions, yielding mean and longitude variable ionospheric peak heights that reasonably match RS observations. A tidal decomposition of MTGCM thermospheric densities shows that observed ionospheric wave number 3 features are linked to a nonmigrating tidal mode with semidiurnal period (s = 2) and zonal wave number 1 (s = � 1) characteristics. The height of this photochemically determined ionospheric peak should be monitored regularly. INDEX TERMS: 5435 Planetology: Solid Surface Planets: Ionospheres (2459); 5409 Planetology: Solid Surface Planets: Atmospheres—structure and dynamics; 6225 Planetology: Solar System Objects: Mars; KEYWORDS: ionosphere, Mars, thermosphere
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Mars Global Surveyor Radio Science Electron Density Profiles: Interannual Variability and Implications for the Neutral Atmosphere
2003Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J. R. MurphyAbstract:The Mars Global Surveyor (MGS) Radio Science (RS) experiment employs an ultrastable oscillator aboard the spacecraft. The signal from the oscillator to Earth is refracted by the Martian ionosphere, allowing retrieval of Electron Density Profiles versus radius and geopotential. The present analysis is carried out on five sets of occultation measurements: (1) four obtained near northern summer solstice (Ls = 74-116, near aphelion) at high northern latitudes (64.7-77.6N), and (2) one set of Profiles approaching equinox conditions (Ls = 135- 146) at high southern latitudes (64.7-69.1S). Electron Density Profiles (95 to 200 km) are examined over a narrow range of solar zenith angles (76.5-86.9 degrees) for local true solar times of (1) 3-4 hours and (2) 12.1 hours. Variations spanning 1-Martian year are specifically examined in the Northern hemisphere.
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mars global surveyor radio science Electron Density Profiles neutral atmosphere implications
Geophysical Research Letters, 2001Co-Authors: Stephen W. Bougher, David P. Hinson, S Engel, J M ForbesAbstract:The Mars Global Surveyor (MGS) Radio Sci- ence (RS) experiment permits retrieval of Electron Density prof iles versus height (∼90-200 km) from occultation mea- surements. An initial set of Electron Profiles is examined spanning high northern latitudes, early morning solar local times and high solar zenith angles (78 to 81 ◦ ) near aphelion. Sampling for these 32-Profiles is well distributed over longi- tude. The height of the photochemically driven ionospheric peak is observed to respond to the background neutral den- sity structure, with a mean height during this season at this location of ∼134.4 km. Strong wave-3 oscillations about this mean are clearly observed as a function of longitude, and correspond to neutral Density variations measured by the MGS Accelerometer (ACC) experiment. The wave-3 tidal pattern implicated by both the RS and ACC datasets is consistent with a semi-diurnal wave frequency. Clearly, the height of the martian dayside ionospheric peak is a sensitive indicator of the state of the underlying Mars atmosphere. This ionospheric peak height can be used as a proxy of the longitude specific non-migrating tidal variations present in the Mars lower thermosphere.
A J Kliore - One of the best experts on this subject based on the ideXlab platform.
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unusual Electron Density Profiles observed by cassini radio occultations in titan s ionosphere effects of enhanced magnetospheric Electron precipitation
Journal of Geophysical Research, 2011Co-Authors: A J Kliore, A F Nagy, T E Cravens, M S Richard, A M RymerAbstract:[1] The Cassini radio science facility provided 13 occultation Electron Density Profiles of Titan during the period of 2006 and 2009. This paper presents the results of all of these occultation observations. It shows that ten of the observed Electron Density Profiles are similar, but three are significantly different. The number of observations is relatively small for meaningful statistical conclusions, but it is shown, using the corresponding measured Electron spectra, that the three anomalous Profiles in the ionospheric peak regions are likely to be the result of unusually intense Electron precipitation events.
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midlatitude and high latitude Electron Density Profiles in the ionosphere of saturn obtained by cassini radio occultation observations
Journal of Geophysical Research, 2009Co-Authors: A J Kliore, A F Nagy, Essam A Marouf, Aseel Anabtawi, E Barbinis, D Fleischman, Daniel KahanAbstract:[1] Nineteen new radio occultations of the ionosphere of Saturn have been obtained since 2006. Sixteen of these occultations were from midlatitude and high latitudes and thus provided important, new information of the ionosphere for these regions. A high degree of variability in the Electron densities were observed, but grouping and averaging the observations as low-, middle-, and high-latitude ones clearly showed that the Electron densities increase with latitude. The topside scale heights also indicate small increases with latitude, but these changes are small enough so these increases may not be statistically significant.
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effects of magnetic anomalies discovered at mars on the structure of the martian ionosphere and solar wind interaction as follows from radio occultation experiments
Journal of Geophysical Research, 2000Co-Authors: N F Ness, M H Acuna, J E P Connerney, A J Kliore, T K Breus, A M Krymskii, P A Cloutier, Siegfried BauerAbstract:The slopes of the Electron Density Profiles obtained by radio occultation experiments at Mars revealed different variations with solar zenith angle in comparison with behavior of the Electron Density Profiles in the magnetic field free ionosphere of Venus. The results obtained by the Mars-Global-Surveyor (MGS) spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at Mars. Addressing the difference between the ionosphere at Venus and Mars, the scale heights of Electron Density Profiles obtained by radio occultation methods onboard Mariner 9 and Viking 1 are analyzed at altitudes higher than the topside boundary of the photoequlibrium region in the magnetic field-free ionosphere. The local increase of the mean scale height in the altitude region 180–250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere. The areas where the scale height of Electron Density profile is increased in comparison with average one have been selected. The angle between the magnetic field measured by MGS MAG/ER at altitudes 120–250 km and local zenith direction is investigated throughout these selected areas.