The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jannyenq Liu - One of the best experts on this subject based on the ideXlab platform.
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the source detection of 28 september 2018 sulawesi tsunami by using ionospheric gnss Total Electron Content disturbance
Geoscience Letters, 2020Co-Authors: Jannyenq Liu, Yuhing Chen, Chiyen Lin, Mengju Chung, Tienchi Liu, Yulin Tsai, Loren C Chang, Chikuang Chao, D Ouzounov, Katsumi HattoriAbstract:The 28 September 2018 magnitude Mw7.8 Palu, Indonesia earthquake (0.178° S, 119.840° E, depth 13 km) occurred at 10:02 UTC. The major earthquake triggered catastrophic liquefaction, landslides, and a near-field tsunami. The ionospheric Total Electron Content (TEC) derived from records of 5 ground-based global navigation satellite system (GNSS) receivers is employed to detect tsunami traveling ionospheric disturbances (TTIDs). In Total, 15 TTIDs have been detected. The ray-tracing and beamforming techniques are then used to find the TTID source location. The bootstrap method is applied in order to further explore the possible location of the tsunami source based on results of the two techniques, which show the beamforming technique has a slightly better performance on finding possible locations of the tsunami source. Meanwhile, the circle method is employed to examine tsunami signatures of the sea-surface height and video records, and find possible tsunami origin locations. The coincidence of the TTID source location and the tsunami location shows that the ionospheric TEC recorded by local ground-based GNSS receivers can be used to confirm the tsunami occurrence, find the tsunami location, and support the tsunami early warning.
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observations and simulations of seismoionospheric gps Total Electron Content anomalies before the 12 january 2010 m7 haiti earthquake
Journal of Geophysical Research, 2011Co-Authors: Jannyenq Liu, Weixing Wan, C H Lin, Yuhing Chen, Chiahung Chen, Libo Liu, Y Y Sun, M Q ChenAbstract:[1] In this paper, the Total Electron Content (TEC) of the global ionosphere map (GIM) is used to detect seismoionospheric anomalies associated with the 12 January 2010 M7 Haiti earthquake, and an ionospheric model is applied to simulate the detected anomalies. The GIM temporal variation shows that the TEC over the epicenter significantly enhances on 11 January 2010, 1 day before the earthquake. The latitude-time-TEC (LTT) plots reveal three anomalies: (1) the northern crest of equatorial ionization anomaly (EIA) moves poleward, (2) the TECs at the epicenter and its conjugate increase, and (3) the TECs at two dense bands in the midlatitude ionosphere of 35°N and 60°S further enhance. The spatial analysis demonstrates that the TEC enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area. The simulation well reproduces the three GIM TEC anomalies, which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period.
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seismoionospheric gps Total Electron Content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake
Journal of Geophysical Research, 2009Co-Authors: Jannyenq Liu, Yuhing Chen, Chiahung Chen, Katsumi Hattori, Chengyan Liu, Chowson Chen, Masahide Nishihashi, Yaqin Xia, K I Oyama, C H LinAbstract:[1] The global ionospheric map (GIM) is used to observe variations in the Total Electron Content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and Electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak Electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.
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equatorial ionization anomaly of the Total Electron Content and equatorial electrojet of ground based geomagnetic field strength
Journal of Atmospheric and Solar-Terrestrial Physics, 2008Co-Authors: Chiahung Chen, Jannyenq Liu, C H Lin, Tzuwei Fang, K YumotoAbstract:Abstract Measurements from ground-based receiver chains of the global positioning system (GPS) and magnetometers of the Circum-pan Pacific Magnetometer Network (CPMN) in the west Pacific region during 1999–2003 are examined. The ionospheric Total Electron Content (TEC) derived from the GPS receivers is used to observe the strength, location, and occurrence time of the equatorial ionization anomaly (EIA) crests, which resulted from the equatorial plasma E×B drift fountain. The magnetic field strength of CPMN is employed to monitor the equatorial electrojet (EEJ), and to further estimate the effectiveness of the E×B drift to the EIA crests. Results show that the strength and location of the EIA crests are proportional to the EEJ strength.
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solar flare signatures of the ionospheric gps Total Electron Content
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, C H Lin, Yuhing Chen, Y C Lin, Tzuwei Fang, Chiahung Chen, Yicheng Chen, J J HwangAbstract:[1] In this study, ionospheric solar flare effects on the Total Electron Content (TEC) and associated time rate of change (rTEC) derived from ground-based global positioning system (GPS) receivers in the midday region are examined. The occurrence times and locations of 11 solar flares are isolated from the 1–8 A X-ray radiations of the geosynchronous operational environmental satellite (GOES) and the SOHO Extreme Ultraviolet Imaging Telescope (EIT) images, respectively, while the TEC and rTEC are obtained from the international GPS services (IGS). Results show that the maximum value of the TEC increase solely depends on the flare class, while the maximum value of the rTEC increase is related to not only the flare class but also the time rate of change in flare radiations. A statistical analysis further demonstrates that the two maximum values are inversely proportional to the cosine of the great circle angle between the center and flare locations on the solar disc.
C H Lin - One of the best experts on this subject based on the ideXlab platform.
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observations and simulations of seismoionospheric gps Total Electron Content anomalies before the 12 january 2010 m7 haiti earthquake
Journal of Geophysical Research, 2011Co-Authors: Jannyenq Liu, Weixing Wan, C H Lin, Yuhing Chen, Chiahung Chen, Libo Liu, Y Y Sun, M Q ChenAbstract:[1] In this paper, the Total Electron Content (TEC) of the global ionosphere map (GIM) is used to detect seismoionospheric anomalies associated with the 12 January 2010 M7 Haiti earthquake, and an ionospheric model is applied to simulate the detected anomalies. The GIM temporal variation shows that the TEC over the epicenter significantly enhances on 11 January 2010, 1 day before the earthquake. The latitude-time-TEC (LTT) plots reveal three anomalies: (1) the northern crest of equatorial ionization anomaly (EIA) moves poleward, (2) the TECs at the epicenter and its conjugate increase, and (3) the TECs at two dense bands in the midlatitude ionosphere of 35°N and 60°S further enhance. The spatial analysis demonstrates that the TEC enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area. The simulation well reproduces the three GIM TEC anomalies, which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period.
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seismoionospheric gps Total Electron Content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake
Journal of Geophysical Research, 2009Co-Authors: Jannyenq Liu, Yuhing Chen, Chiahung Chen, Katsumi Hattori, Chengyan Liu, Chowson Chen, Masahide Nishihashi, Yaqin Xia, K I Oyama, C H LinAbstract:[1] The global ionospheric map (GIM) is used to observe variations in the Total Electron Content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and Electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak Electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.
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equatorial ionization anomaly of the Total Electron Content and equatorial electrojet of ground based geomagnetic field strength
Journal of Atmospheric and Solar-Terrestrial Physics, 2008Co-Authors: Chiahung Chen, Jannyenq Liu, C H Lin, Tzuwei Fang, K YumotoAbstract:Abstract Measurements from ground-based receiver chains of the global positioning system (GPS) and magnetometers of the Circum-pan Pacific Magnetometer Network (CPMN) in the west Pacific region during 1999–2003 are examined. The ionospheric Total Electron Content (TEC) derived from the GPS receivers is used to observe the strength, location, and occurrence time of the equatorial ionization anomaly (EIA) crests, which resulted from the equatorial plasma E×B drift fountain. The magnetic field strength of CPMN is employed to monitor the equatorial electrojet (EEJ), and to further estimate the effectiveness of the E×B drift to the EIA crests. Results show that the strength and location of the EIA crests are proportional to the EEJ strength.
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solar flare signatures of the ionospheric gps Total Electron Content
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, C H Lin, Yuhing Chen, Y C Lin, Tzuwei Fang, Chiahung Chen, Yicheng Chen, J J HwangAbstract:[1] In this study, ionospheric solar flare effects on the Total Electron Content (TEC) and associated time rate of change (rTEC) derived from ground-based global positioning system (GPS) receivers in the midday region are examined. The occurrence times and locations of 11 solar flares are isolated from the 1–8 A X-ray radiations of the geosynchronous operational environmental satellite (GOES) and the SOHO Extreme Ultraviolet Imaging Telescope (EIT) images, respectively, while the TEC and rTEC are obtained from the international GPS services (IGS). Results show that the maximum value of the TEC increase solely depends on the flare class, while the maximum value of the rTEC increase is related to not only the flare class but also the time rate of change in flare radiations. A statistical analysis further demonstrates that the two maximum values are inversely proportional to the cosine of the great circle angle between the center and flare locations on the solar disc.
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ionospheric gps Total Electron Content tec disturbances triggered by the 26 december 2004 indian ocean tsunami
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, Ho Fang Tsai, C H Lin, Yuhing Chen, Yiben Tsai, Masashi Kamogawa, Chienping LeeAbstract:[1] Tsunami ionospheric disturbances (TIDs) of the 26 December 2004 Mw 9.3 Sumatra earthquake are detected by the Total Electron Content (TEC) of ground-based receivers of the global positioning system (GPS) in the Indian Ocean area. It is found that the tsunami waves triggered atmospheric disturbances near the sea surface, which then traveled upward with an average velocity of about 730 m/s (2700 km/hr) into the ionosphere and significantly disturbed the Electron density within it. Results further show that the TIDs, which have maximum height of about 8.6–17.2 km, periods of 10–20 min, and horizontal wavelengths of 120–240 km, travel away from the epicenter with an average horizontal speed of about 700 km/hr (190 m/s) in the ionosphere.
Yuhing Chen - One of the best experts on this subject based on the ideXlab platform.
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the source detection of 28 september 2018 sulawesi tsunami by using ionospheric gnss Total Electron Content disturbance
Geoscience Letters, 2020Co-Authors: Jannyenq Liu, Yuhing Chen, Chiyen Lin, Mengju Chung, Tienchi Liu, Yulin Tsai, Loren C Chang, Chikuang Chao, D Ouzounov, Katsumi HattoriAbstract:The 28 September 2018 magnitude Mw7.8 Palu, Indonesia earthquake (0.178° S, 119.840° E, depth 13 km) occurred at 10:02 UTC. The major earthquake triggered catastrophic liquefaction, landslides, and a near-field tsunami. The ionospheric Total Electron Content (TEC) derived from records of 5 ground-based global navigation satellite system (GNSS) receivers is employed to detect tsunami traveling ionospheric disturbances (TTIDs). In Total, 15 TTIDs have been detected. The ray-tracing and beamforming techniques are then used to find the TTID source location. The bootstrap method is applied in order to further explore the possible location of the tsunami source based on results of the two techniques, which show the beamforming technique has a slightly better performance on finding possible locations of the tsunami source. Meanwhile, the circle method is employed to examine tsunami signatures of the sea-surface height and video records, and find possible tsunami origin locations. The coincidence of the TTID source location and the tsunami location shows that the ionospheric TEC recorded by local ground-based GNSS receivers can be used to confirm the tsunami occurrence, find the tsunami location, and support the tsunami early warning.
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observations and simulations of seismoionospheric gps Total Electron Content anomalies before the 12 january 2010 m7 haiti earthquake
Journal of Geophysical Research, 2011Co-Authors: Jannyenq Liu, Weixing Wan, C H Lin, Yuhing Chen, Chiahung Chen, Libo Liu, Y Y Sun, M Q ChenAbstract:[1] In this paper, the Total Electron Content (TEC) of the global ionosphere map (GIM) is used to detect seismoionospheric anomalies associated with the 12 January 2010 M7 Haiti earthquake, and an ionospheric model is applied to simulate the detected anomalies. The GIM temporal variation shows that the TEC over the epicenter significantly enhances on 11 January 2010, 1 day before the earthquake. The latitude-time-TEC (LTT) plots reveal three anomalies: (1) the northern crest of equatorial ionization anomaly (EIA) moves poleward, (2) the TECs at the epicenter and its conjugate increase, and (3) the TECs at two dense bands in the midlatitude ionosphere of 35°N and 60°S further enhance. The spatial analysis demonstrates that the TEC enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area. The simulation well reproduces the three GIM TEC anomalies, which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period.
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seismoionospheric gps Total Electron Content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake
Journal of Geophysical Research, 2009Co-Authors: Jannyenq Liu, Yuhing Chen, Chiahung Chen, Katsumi Hattori, Chengyan Liu, Chowson Chen, Masahide Nishihashi, Yaqin Xia, K I Oyama, C H LinAbstract:[1] The global ionospheric map (GIM) is used to observe variations in the Total Electron Content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and Electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak Electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.
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solar flare signatures of the ionospheric gps Total Electron Content
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, C H Lin, Yuhing Chen, Y C Lin, Tzuwei Fang, Chiahung Chen, Yicheng Chen, J J HwangAbstract:[1] In this study, ionospheric solar flare effects on the Total Electron Content (TEC) and associated time rate of change (rTEC) derived from ground-based global positioning system (GPS) receivers in the midday region are examined. The occurrence times and locations of 11 solar flares are isolated from the 1–8 A X-ray radiations of the geosynchronous operational environmental satellite (GOES) and the SOHO Extreme Ultraviolet Imaging Telescope (EIT) images, respectively, while the TEC and rTEC are obtained from the international GPS services (IGS). Results show that the maximum value of the TEC increase solely depends on the flare class, while the maximum value of the rTEC increase is related to not only the flare class but also the time rate of change in flare radiations. A statistical analysis further demonstrates that the two maximum values are inversely proportional to the cosine of the great circle angle between the center and flare locations on the solar disc.
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ionospheric gps Total Electron Content tec disturbances triggered by the 26 december 2004 indian ocean tsunami
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, Ho Fang Tsai, C H Lin, Yuhing Chen, Yiben Tsai, Masashi Kamogawa, Chienping LeeAbstract:[1] Tsunami ionospheric disturbances (TIDs) of the 26 December 2004 Mw 9.3 Sumatra earthquake are detected by the Total Electron Content (TEC) of ground-based receivers of the global positioning system (GPS) in the Indian Ocean area. It is found that the tsunami waves triggered atmospheric disturbances near the sea surface, which then traveled upward with an average velocity of about 730 m/s (2700 km/hr) into the ionosphere and significantly disturbed the Electron density within it. Results further show that the TIDs, which have maximum height of about 8.6–17.2 km, periods of 10–20 min, and horizontal wavelengths of 120–240 km, travel away from the epicenter with an average horizontal speed of about 700 km/hr (190 m/s) in the ionosphere.
Chiahung Chen - One of the best experts on this subject based on the ideXlab platform.
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observations and simulations of seismoionospheric gps Total Electron Content anomalies before the 12 january 2010 m7 haiti earthquake
Journal of Geophysical Research, 2011Co-Authors: Jannyenq Liu, Weixing Wan, C H Lin, Yuhing Chen, Chiahung Chen, Libo Liu, Y Y Sun, M Q ChenAbstract:[1] In this paper, the Total Electron Content (TEC) of the global ionosphere map (GIM) is used to detect seismoionospheric anomalies associated with the 12 January 2010 M7 Haiti earthquake, and an ionospheric model is applied to simulate the detected anomalies. The GIM temporal variation shows that the TEC over the epicenter significantly enhances on 11 January 2010, 1 day before the earthquake. The latitude-time-TEC (LTT) plots reveal three anomalies: (1) the northern crest of equatorial ionization anomaly (EIA) moves poleward, (2) the TECs at the epicenter and its conjugate increase, and (3) the TECs at two dense bands in the midlatitude ionosphere of 35°N and 60°S further enhance. The spatial analysis demonstrates that the TEC enhancement anomaly appears specifically and persistently in a small region of the northern epicenter area. The simulation well reproduces the three GIM TEC anomalies, which indicate that the dynamoelectric field of the ionospheric plasma fountain might have been perturbed by seismoelectric signals generated around the epicenter during the earthquake preparation period.
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seismoionospheric gps Total Electron Content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake
Journal of Geophysical Research, 2009Co-Authors: Jannyenq Liu, Yuhing Chen, Chiahung Chen, Katsumi Hattori, Chengyan Liu, Chowson Chen, Masahide Nishihashi, Yaqin Xia, K I Oyama, C H LinAbstract:[1] The global ionospheric map (GIM) is used to observe variations in the Total Electron Content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and Electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak Electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.
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equatorial ionization anomaly of the Total Electron Content and equatorial electrojet of ground based geomagnetic field strength
Journal of Atmospheric and Solar-Terrestrial Physics, 2008Co-Authors: Chiahung Chen, Jannyenq Liu, C H Lin, Tzuwei Fang, K YumotoAbstract:Abstract Measurements from ground-based receiver chains of the global positioning system (GPS) and magnetometers of the Circum-pan Pacific Magnetometer Network (CPMN) in the west Pacific region during 1999–2003 are examined. The ionospheric Total Electron Content (TEC) derived from the GPS receivers is used to observe the strength, location, and occurrence time of the equatorial ionization anomaly (EIA) crests, which resulted from the equatorial plasma E×B drift fountain. The magnetic field strength of CPMN is employed to monitor the equatorial electrojet (EEJ), and to further estimate the effectiveness of the E×B drift to the EIA crests. Results show that the strength and location of the EIA crests are proportional to the EEJ strength.
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solar flare signatures of the ionospheric gps Total Electron Content
Journal of Geophysical Research, 2006Co-Authors: Jannyenq Liu, C H Lin, Yuhing Chen, Y C Lin, Tzuwei Fang, Chiahung Chen, Yicheng Chen, J J HwangAbstract:[1] In this study, ionospheric solar flare effects on the Total Electron Content (TEC) and associated time rate of change (rTEC) derived from ground-based global positioning system (GPS) receivers in the midday region are examined. The occurrence times and locations of 11 solar flares are isolated from the 1–8 A X-ray radiations of the geosynchronous operational environmental satellite (GOES) and the SOHO Extreme Ultraviolet Imaging Telescope (EIT) images, respectively, while the TEC and rTEC are obtained from the international GPS services (IGS). Results show that the maximum value of the TEC increase solely depends on the flare class, while the maximum value of the rTEC increase is related to not only the flare class but also the time rate of change in flare radiations. A statistical analysis further demonstrates that the two maximum values are inversely proportional to the cosine of the great circle angle between the center and flare locations on the solar disc.
S M Radicella - One of the best experts on this subject based on the ideXlab platform.
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Total Electron Content in the martian atmosphere a critical assessment of the mars express marsis data sets
Journal of Geophysical Research, 2015Co-Authors: S M Radicella, Beatriz Sanchezcano, D D Morgan, Olivier Witasse, M Herraiz, R Orosei, Marco Cartacci, A CicchettiAbstract:The Total Electron Content (TEC) is one of the most useful parameters to evaluate the behavior of the Martian ionosphere because it contains information on the Total amount of free Electrons, the m ...
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Calibration errors on experimental slant Total Electron Content (TEC) determined with GPS
Journal of Geodesy, 2007Co-Authors: L. Ciraolo, F. Azpilicueta, C. Brunini, A. Meza, S M RadicellaAbstract:The Global Positioning System (GPS) has become a powerful tool for ionospheric studies. In addition, ionospheric corrections are necessary for the augmentation systems required for Global Navigation Satellite Systems (GNSS) use. Dual-frequency carrier-phase and code-delay GPS observations are combined to obtain ionospheric observables related to the slant Total Electron Content (sTEC) along the satellite-receiver line-of-sight (LoS). This observable is affected by inter-frequency biases [IFB; often called differential code biases (DCB)] due to the transmitting and the receiving hardware. These biases must be estimated and eliminated from the data in order to calibrate the experimental sTEC obtained from GPS observations. Based on the analysis of single differences of the ionospheric observations obtained from pairs of co-located dual-frequency GPS receivers, this research addresses two major issues: (1) assessing the errors translated from the code-delay to the carrier-phase ionospheric observable by the so-called levelling process, applied to reduce carrier-phase ambiguities from the data; and (2) assessing the short-term stability of receiver IFB. The conclusions achieved are: (1) the levelled carrier-phase ionospheric observable is affected by a systematic error, produced by code-delay multi-path through the levelling procedure; and (2) receiver IFB may experience significant changes during 1 day. The magnitude of both effects depends on the receiver/antenna configuration. Levelling errors found in this research vary from 1.4 Total Electron Content units (TECU) to 5.3 TECU. In addition, intra-day vaiations of code-delay receiver IFB ranging from 1.4 to 8.8 TECU were detected.
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forecasting Total Electron Content maps by neural network technique
Radio Science, 2006Co-Authors: E Tulunay, E T Senalp, S M Radicella, Yurdanur TulunayAbstract:[1] Near-Earth space processes are highly nonlinear. Since the 1990s, a small group at the Middle East Technical University in Ankara has been working on a data-driven generic model of such processes, that is, forecasting and nowcasting of a near-Earth space parameter of interest. The model developed is called the Middle East Technical University Neural Network (METU-NN) model. The METU-NN is a data-driven neural network model of one hidden layer and several neurons. In order to understand more about the complex response of the magnetosphere and ionosphere to extreme solar events, we chose this time the series of space weather events in November 2003. Total Electron Content (TEC) values of the ionosphere are forecast during these space weather events. In order to facilitate an easier interpretation of the forecast TEC values, maps of TEC are produced by using the Bezier surface-fitting technique.
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use of Total Electron Content data to analyze ionosphere Electron density gradients
cosp, 2006Co-Authors: B Nava, S M Radicella, R Leitinger, P CoissonAbstract:Abstract In the presence of Electron density gradients the thin shell approximation for the ionosphere, used together with a simple mapping function to convert slant Total Electron Content (TEC) to vertical TEC, could lead to TEC conversion errors. These “mapping function errors” can therefore be used to detect the Electron density gradients in the ionosphere. In the present work GPS derived slant TEC data have been used to investigate the effects of the Electron density gradients in the middle and low latitude ionosphere under geomagnetic quiet and disturbed conditions. In particular the data corresponding to the geographic area of the American Sector for the days 5–7 April 2000 have been used to perform a complete analysis of mapping function errors based on the “coinciding pierce point technique”. The results clearly illustrate the Electron density gradient effects according to the locations considered and to the actual levels of disturbance of the ionosphere. In addition, the possibility to assess an ionospheric shell height able to minimize the mapping function errors has been verified.
