Journal articles on the topic 'Ionospheric studies'
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1
Su, Ke, and Shuanggen Jin. "Three Dual-Frequency Precise Point Positioning Models for the Ionospheric Modeling and Satellite Pseudorange Observable-Specific Signal Bias Estimation." Remote Sensing 13, no. 24 (December 15, 2021): 5093. http://dx.doi.org/10.3390/rs13245093.
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Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) enables the estimation the ionospheric vertical total electron content (VTEC) as well as the by-product of the satellite Pseudorange observable-specific signal bias (OSB). The single-frequency PPP models, with the ionosphere-float and ionosphere-free approaches in ionospheric studies, have recently been discussed by the authors. However, the multi-frequency observations can improve the performances of the ionospheric research compared with the single-frequency approaches. This paper presents three dual-frequency PPP approaches using the BeiDou Navigation Satellite System (BDS) B1I/B3I observations to investigate ionospheric activities. Datasets collected from the globally distributed stations are used to evaluate the performance of the ionospheric modeling with the ionospheric single- and multi-layer mapping functions (MFs), respectively. The characteristics of the estimated ionospheric VTEC and BDS satellite pseudorange OSB are both analyzed. The results indicated that the three dual-frequency PPP models could all be applied to the ionospheric studies, among which the dual-frequency ionosphere-float PPP model exhibits the best performance. The three dual-frequency PPP models all possess the capacity for ionospheric applications in the GNSS community.
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Safi’i, A. N., Susilo, D. Ramdani, and B. Muslim. "Utilization of Indonesia’s regional ionosphere model to improve the accuracy of GPS measurements to support disaster mitigation studies." IOP Conference Series: Earth and Environmental Science 950, no. 1 (January 1, 2022): 012097. http://dx.doi.org/10.1088/1755-1315/950/1/012097.
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Abstract Ionospheric can cause severe degradation of GPS (Global Positioning System) functionality and decrease coordinate accuracy. Increasing the precision of GPS station coordinates will improve accuracy in many applications. Many applications can use GPS for deformation studies, such as geodynamic studies, active fault studies, volcanic deformation monitoring, land subsidence studies, and hazard mitigation studies. We can use global ionospheric correction to produce better coordinates by utilizing post-processing GPS data. With the increasing number of GPS stations in Indonesia, it is possible to develop regional ionosphere models. This study computes regional ionospheric models from real-time streaming GPS data and uses them in GPS processing. Regional ionospheric models can increase the accuracy of GPS station coordinates by 5% -10% compared to global ionosphere models (igsg and codg).
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Savastano, Giorgio, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi. "Advantages of Geostationary Satellites for Ionospheric Anomaly Studies: Ionospheric Plasma Depletion Following a Rocket Launch." Remote Sensing 11, no. 14 (July 23, 2019): 1734. http://dx.doi.org/10.3390/rs11141734.
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In this study, we analyzed signals transmitted by the U.S. Wide Area Augmentation System (WAAS) geostationary (GEO) satellites using the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithm in a simulated real-time scenario, to characterize the ionospheric response to the 24 August 2017 Falcon 9 rocket launch from Vandenberg Air Force Base in California. VARION is a real-time Global Navigation Satellites Systems (GNSS)-based algorithm that can be used to detect various ionospheric disturbances associated with natural hazards, such as tsunamis and earthquakes. A noise reduction algorithm was applied to the VARION-GEO solutions to remove the satellite-dependent noise term. Our analysis showed that the interactions of the exhaust plume with the ionospheric plasma depleted the total electron content (TEC) to a level comparable with nighttime TEC values. During this event, the geometry of the satellite-receiver link is such that GEO satellites measured the depleted plasma hole before any GPS satellites. We estimated that the ionosphere relaxed back to a pre-perturbed state after about 3 h, and the hole propagated with a mean speed of about 600 m/s over a region of 700 km in radius. We conclude that the VARION-GEO approach can provide important ionospheric TEC real-time measurements, which are not affected by the motion of the ionospheric pierce points (IPPs). Furthermore, the VARION-GEO measurements experience a steady noise level throughout the entire observation period, making this technique particularly useful to augment and enhance the capabilities of well-established GNSS-based ionosphere remote sensing techniques and future ionospheric-based early warning systems.
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Janhunen, P. "On the possibility of using an electromagnetic ionosphere in global MHD simulations." Annales Geophysicae 16, no. 4 (April 30, 1998): 397–402. http://dx.doi.org/10.1007/s00585-998-0397-y.
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Abstract. Global magnetohydrodynamic (MHD) simulations of the Earth's magnetosphere must be coupled with a dynamical ionospheric module in order to give realistic results. The usual approach is to compute the field-aligned current (FAC) from the magnetospheric MHD variables at the ionospheric boundary. The ionospheric potential is solved from an elliptic equation using the FAC as a source term. The plasma velocity at the boundary is the E × B velocity associated with the ionospheric potential. Contemporary global MHD simulations which include a serious ionospheric model use this method, which we call the electrostatic approach in this paper. We study the possibility of reversing the flow of information through the ionosphere: the magnetosphere gives the electric field to the ionosphere. The field is not necessarily electrostatic, thus we will call this scheme electromagnetic. The electric field determines the horizontal ionospheric current. The divergence of the horizontal current gives the FAC, which is used as a boundary condition for MHD equations. We derive the necessary formulas and discuss the validity of the approximations necessarily involved. It is concluded that the electromagnetic ionosphere-magnetosphere coupling scheme is a serious candidate for future global MHD simulators, although a few problem areas still remain. At minimum, it should be investigated further to discover whether there are any differences in the simulation using the electrostatic or the electromagnetic ionospheric coupling.Key words. Ionosphere · Ionosphere-magnetosphere interaction · Magnetospheric physics · Magnetosphere-ionosphere interaction · Space plasma physics · Numerical simulation studies
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Ratovsky, Konstantin G., Maxim V. Klimenko, Yury V. Yasyukevich, Vladimir V. Klimenko, and Artem M. Vesnin. "Statistical Analysis and Interpretation of High-, Mid- and Low-Latitude Responses in Regional Electron Content to Geomagnetic Storms." Atmosphere 11, no. 12 (December 2, 2020): 1308. http://dx.doi.org/10.3390/atmos11121308.
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Geomagnetic storm is one of the most powerful factors affecting the state of the Earth’s ionosphere. Revealing the significance of formation mechanisms for ionospheric storms is still an unresolved problem. The purpose of the study is to obtain a statistical pattern of the response in regional electron content to geomagnetic storms on a global scale to interpret the results using the upper atmosphere model (the Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere), to make the detailed comparison with the thermospheric storm concept, and to compare the obtained pattern with results from previous statistical studies. The regional electron content is calculated based on the global ionospheric maps data, which allows us to cover the midlatitude and high-latitude zones of both hemispheres, as well as the equatorial zone. Most of the obtained statistical pattern agrees with the thermospheric storm concept and with the previous statistical studies: ionospheric responses at ionospheric storm main phases including their seasonal dependences for the high- and midlatitudes and some features of ionospheric responses at recovery phases. However, some of the statistical patterns are inconsistent with the thermospheric storm concept or contradicts the previous statistical studies: negative midlatitude ionospheric responses at recovery phases in the local winter, the domination of the spring response in the equatorial zone, seasonal features of the positive after-effects, the interhemispheric asymmetry of ionospheric responses, and the prestorm enhancement. We obtained that the contribution of electric field to the interpretation of the zonal and diurnal averaged storm-time regional electron content (REC) disturbances is insignificant. The positive after-storm effects at different latitudes are caused by n(O) disturbances.
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Parker, James A. D., S. Eleri Pryse, Natasha Jackson-Booth, and Rachel A. Buckland. "Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC." Annales Geophysicae 36, no. 1 (January 25, 2018): 125–38. http://dx.doi.org/10.5194/angeo-36-125-2018.
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Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high- and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour. The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere. Keywords. Ionosphere (midlatitude ionosphere; modelling and forecasting) – radio science (ionospheric physics)
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Inyurt, Samed, Selcuk Peker, and Cetin Mekik. "Monitoring potential ionospheric changes caused by the Van earthquake (<i>M</i><sub>w</sub>7.2)." Annales Geophysicae 37, no. 2 (March 15, 2019): 143–51. http://dx.doi.org/10.5194/angeo-37-143-2019.
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Abstract. Many scientists from different disciplines have studied earthquakes for many years. As a result of these studies, it has been proposed that some changes take place in the ionosphere layer before, during or after earthquakes, and that the ionosphere should be monitored in earthquake prediction studies. This study investigates the changes in the ionosphere created by the earthquake with a magnitude of Mw=7.2 in the northwest of Lake Erçek, which is located to the north of the province of Van in Turkey on 23 October 2011 and at 13:41 local time (−3 UT) with the epicenter of 38.75∘ N, 43.36∘ E using the TEC values obtained by the global ionosphere models (GIMs) created by IONOLAB-TEC and CODE. In order to see whether the ionospheric changes obtained by the study in question were caused by the earthquake or not, the ionospheric conditions were studied by utilizing indices providing information on solar and geomagnetic activities (F10.7 cm, Kp, Dst). One of the results of the statistical test of the TEC values obtained from both models is positive and negative anomalies obtained for the times before, on the day of and after the earthquake, and the reasons for these anomalies are discussed in detail in the last section of the study. As the ionospheric conditions on the analyzed days were highly variable, it was thought that the anomalies were caused by geomagnetic effects, solar activity and the earthquake.
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Rahayu, R. W., M. N. Cahyadi, B. Muslim, I. M. Anjasmara, E. Y. Handoko, and I. N. Muafiry. "Three-dimensional Tomography of Coseismic Ionospheric Disturbances from the 2016 West Sumatera Earthquake." IOP Conference Series: Earth and Environmental Science 936, no. 1 (December 1, 2021): 012022. http://dx.doi.org/10.1088/1755-1315/936/1/012022.
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Abstract Global Navigation Satellite System (GNSS) is a navigation system that uses satellite signals to determine its position, which consists of several satellites arranged in a constellation system. GNSS transmits signals to receivers on Earth. The GNSS receiver determines the user’s position, speed, and time by processing the signals transmitted by the satellites. The initial purpose of launching the GNSS was for navigation purposes, but along with its development, GNSS can be used for the purposes of observing deformation of the earth’s crust and in studying the atmosphere. The delayed wave data when passing through the ionosphere can be used to obtain Total Electron Content (TEC) values which then used to study ionospheric disturbances. Ionospheric disturbances are caused by various phenomena, the most common one is the ionospheric disturbances caused by the induction of acoustic and gravitational waves excited by co seismic crustal motions from large earthquakes. Ionospheric disturbances that happened before an earthquake are called Pre-seismic Ionospheric Disturbances and those that occur after an earthquake are called Co-seismic Ionospheric Disturbances (CID). Most studies of ionospheric disturbances still provide information on the timing and value of TEC anomalies in 2D form. Therefore, in this study, a 3D ionosphere profile modelling using computed 3D tomography will be carried out. The 3D information provided is in the form of time, ionosphere altitude and TEC anomaly value by utilizing GNSS data. The TEC anomaly value is obtained from the calculation of linear combination of the ionosphere. This study aims to obtain a spatial and temporal analysis of the CID caused by the West Sumatra Earthquake on March 2, 2016.
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Perrone, Loredana, Angelo De Santis, Cristoforo Abbattista, Lucilla Alfonsi, Leonardo Amoruso, Marianna Carbone, Claudio Cesaroni, et al. "Ionospheric anomalies detected by ionosonde and possibly related to crustal earthquakes in Greece." Annales Geophysicae 36, no. 2 (March 14, 2018): 361–71. http://dx.doi.org/10.5194/angeo-36-361-2018.
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Abstract. Ionosonde data and crustal earthquakes with magnitude M≥6.0 observed in Greece during the 2003–2015 period were examined to check if the relationships obtained earlier between precursory ionospheric anomalies and earthquakes in Japan and central Italy are also valid for Greek earthquakes. The ionospheric anomalies are identified on the observed variations of the sporadic E-layer parameters (h′Es, foEs) and foF2 at the ionospheric station of Athens. The corresponding empirical relationships between the seismo-ionospheric disturbances and the earthquake magnitude and the epicentral distance are obtained and found to be similar to those previously published for other case studies. The large lead times found for the ionospheric anomalies occurrence may confirm a rather long earthquake preparation period. The possibility of using the relationships obtained for earthquake prediction is finally discussed. Keywords. Ionosphere (Ionospheric disturbances)
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Mannucci, A. J., C. O. Ao, X. Pi, and B. A. Iijima. "The impact of large scale ionospheric structure on radio occultation retrievals." Atmospheric Measurement Techniques Discussions 4, no. 3 (May 4, 2011): 2525–65. http://dx.doi.org/10.5194/amtd-4-2525-2011.
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Abstract. We study the impact of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals of atmospheric parameters such as refractivity and temperature. We use a climatological model of the ionosphere as well as an ionospheric data assimilation model to compare quiet and geomagnetically disturbed conditions. The largest contributor to ionospheric bias is physical separation of the two GPS frequencies as the GPS signal traverses the ionosphere and atmosphere. We analyze this effect in detail using ray-tracing and a full geophysical retrieval system. During quiet conditions, our results are similar to previously published studies. The impact of a major ionospheric storm is analyzed using data from the 30 October 2003 "Halloween" superstorm period. The temperature retrieval bias under disturbed conditions varies from 1 K to 2 K between 20 and 32 km altitude, compared to 0.2–0.3 K during quiet conditions. These results suggest the need for ionospheric monitoring as part of an RO-based climate observation strategy. We find that even during quiet conditions, the magnitude of retrieval bias depends critically on ionospheric conditions, which may explain variations in previously published bias estimates that use a variety of assumptions regarding large scale ionospheric structure. We quantify the impact of spacecraft orbit altitude on the magnitude of bending angle error. Satellites in higher altitude orbits (≧700 km) tend to have lower biases due to the tendency of the residual bending to cancel between the top and bottomside ionosphere. We conclude with remarks on the implications of this study for long-term climate monitoring using RO.
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Joshi, Shivani, Suresh Kannaujiya, and Utkarsh Joshi. "Analysis of GNSS Data for Earthquake Precursor Studies Using IONOLAB-TEC in the Himalayan Region." Quaternary 6, no. 2 (April 19, 2023): 27. http://dx.doi.org/10.3390/quat6020027.
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Earthquake precursors are the indicators that appear before an earthquake. The release of radon gas, ionospheric disturbances, anomalous animal behavior, and so on are examples of seismic and aseismic events. Ionospheric perturbations can be proved to be a reliable method in earthquake prediction. The GNSS data detect changes in the ionosphere through the time lag of the transmitted GPS signals recorded at the Earth-based receivers. A negative TEC anomaly is caused by the stress released from the rocks before the earthquake, which elevates positive ions or p-holes in the atmosphere and decreases the ions in the ionosphere. A positive TEC anomaly follows this because of the increase in ions in the ionosphere. The ionospheric disruption in the Himalayan region is examined before five random earthquakes. For this, data from 15 separate GNSS stations are investigated using IONOLAB-TEC. A promising total electron content (TEC) data estimate with a temporal resolution of 30 s was analyzed. The results of the TEC data analysis depict the anomaly a month before the five earthquakes, followed by the later perturbation in the earthquake preparation zone. TEC anomalies are enhanced more by the uniform spatial distribution of GNSS stations in the epicentral region than by randomly distributed stations. The results of IONOLAB-TEC and the widely used GPS-TEC software were compared. Owing to its temporal resolution, IONOLAB-TEC has edge over the GPS-TEC software in that it can identify even the slightest negative anomalies before an earthquake.
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He, L. S., P. L. Dyson, M. L. Parkinson, and W. Wan. "Studies of medium scale travelling ionospheric disturbances using TIGER SuperDARN radar sea echo observations." Annales Geophysicae 22, no. 12 (December 22, 2004): 4077–88. http://dx.doi.org/10.5194/angeo-22-4077-2004.
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Abstract. Seasonal and diurnal variations in the direction of propagation of medium-scale travelling ionospheric disturbances (MSTIDs) have been investigated by analyzing sea echo returns detected by the TIGER SuperDARN radar located in Tasmania (43.4° S, 147.2° E geographic; –54.6°Λ). A strong dependency on local time was found, as well as significant seasonal variations. Generally, the propagation direction has a northward (i.e. equatorward) component. In the early morning hours the direction of propagation is quite variable throughout the year. It then becomes predominantly northwest and changes to northeast around 09:00 LT. In late fall and winter it changes back to north/northwest around 15:00 LT. During the other seasons, northward propagation is very obvious near dawn and dusk, but no significant northward propagation is observed at noon. It is suggested that the variable propagation direction in the morning is related to irregular magnetic disturbances that occur at this local time. The changes in the MSTID propagation directions near dawn and dusk are generally consistent with changes in ionospheric electric fields occurring at these times and is consistent with dayside MSTIDs being generated by the Lorentz force. Key words. Ionosphere (ionospheric disturbances; wave propagation; ionospheric irregularities; signal processing)
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Zhu, Wu, Hyung-Sup Jung, and Jing-Yuan Chen. "Synthetic Aperture Radar Interferometry (InSAR) Ionospheric Correction Based on Faraday Rotation: Two Case Studies." Applied Sciences 9, no. 18 (September 15, 2019): 3871. http://dx.doi.org/10.3390/app9183871.
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Spaceborne synthetic aperture radar (SAR) imagery is affected by the ionosphere, resulting in distortions of the SAR intensity, phase, and polarization. Although several methods have been proposed to mitigate the ionospheric phase delay of SAR interferometry, the application of them with full-polarimetric SAR interferometry is limited. Based on this background, Faraday rotation (FR)-based methods are used in this study to mitigate the ionospheric phase errors on full-polarimetric SAR interferometry. For a performance test of the selected method, L-band Advanced Land Observation Satellite (ALOS) Phase Array L-band SAR (PALSAR) full-polarimetric SAR images over high-latitude and low-latitude regions are processed. The result shows that most long-wavelength ionospheric phase errors are removed from the original phase after using the FR-based method, where standard deviations of the corrected result have decreased by almost a factor of eight times for the high-latitude region and 28 times for low-latitude region, compared to those of the original phase, demonstrating the efficiency of the method. This result proves that the FR-based method not only can mitigate the ionospheric effect on SAR interferometry, but also can map the high-spatial-resolution vertical total electronic content (VTEC) distribution.
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Mannucci, A. J., C. O. Ao, X. Pi, and B. A. Iijima. "The impact of large scale ionospheric structure on radio occultation retrievals." Atmospheric Measurement Techniques 4, no. 12 (December 22, 2011): 2837–50. http://dx.doi.org/10.5194/amt-4-2837-2011.
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Abstract. We study the impact of large-scale ionospheric structure on the accuracy of radio occultation (RO) retrievals. We use a climatological model of the ionosphere as well as an ionospheric data assimilation model to compare quiet and geomagnetically disturbed conditions. The presence of ionospheric electron density gradients during disturbed conditions increases the physical separation of the two GPS frequencies as the GPS signal traverses the ionosphere and atmosphere. We analyze this effect in detail using ray-tracing and a full geophysical retrieval system. During quiet conditions, our results are similar to previously published studies. The impact of a major ionospheric storm is analyzed using data from the 30 October 2003 "Halloween" superstorm period. At 40 km altitude, the refractivity bias under disturbed conditions is approximately three times larger than quiet time. These results suggest the need for ionospheric monitoring as part of an RO-based climate observation strategy. We find that even during quiet conditions, the magnitude of retrieval bias depends critically on assumed ionospheric electron density structure, which may explain variations in previously published bias estimates that use a variety of assumptions regarding large scale ionospheric structure. We quantify the impact of spacecraft orbit altitude on the magnitude of bending angle and retrieval error. Satellites in higher altitude orbits (700+ km) tend to have lower residual biases due to the tendency of the residual bending to cancel between the top and bottomside ionosphere. Another factor affecting accuracy is the commonly-used assumption that refractive index is unity at the receiver. We conclude with remarks on the implications of this study for long-term climate monitoring using RO.
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Yang, Zhenlin, Sheng-Yang Gu, Yusong Qin, Chen-Ke-Min Teng, Yafei Wei, and Xiankang Dou. "Ionospheric Oscillation with Periods of 6–30 Days at Middle Latitudes: A Response to Solar Radiative, Geomagnetic, and Lower Atmospheric Forcing." Remote Sensing 14, no. 22 (November 21, 2022): 5895. http://dx.doi.org/10.3390/rs14225895.
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This research studies the medium timescale (6–30 days) ionospheric response over the Wuhan area to solar radiative, recurrent geomagnetic, and lower atmospheric forcing. The ionospheric response is examined by wavelet analysis of the total electron content (TEC) over the Wuhan area from 2001 to 2020. Ionospheric oscillations with periods centering at the harmonic oscillations of the 27-day solar rotation (e.g., 27 days, 13.5 days, 9 days, and 6.75 days) are focused upon. The results show that the quasi-27-day TEC oscillations at the middle latitude have a better overall correlation with solar radiation than recurrent geomagnetic activity, but the correlation between TEC and recurrent geomagnetic activity has a significant increase at the solar minimum stage. As for ionospheric oscillations with periods shorter than 15 days, these oscillations correlate better with recurrent geomagnetic activity. Moreover, a quasi-27-day TEC oscillation event at the middle latitude caused by convective activity from the lower atmosphere was studied. This suggests that lower atmospheric forcing is also an important factor causing ionospheric oscillations. In addition, the ionospheric oscillations over the Wuhan area also show unique regional characteristics, as the regional ionosphere does not respond well to the Kp oscillation with periods shorter than 20 days, particularly, 13.5 days.
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Lu, Weijun, Guanyi Ma, and Qingtao Wan. "A Review of Voxel-Based Computerized Ionospheric Tomography with GNSS Ground Receivers." Remote Sensing 13, no. 17 (August 29, 2021): 3432. http://dx.doi.org/10.3390/rs13173432.
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Ionized by solar radiation, the ionosphere causes a phase rotation or time delay to trans-ionospheric radio waves. Reconstruction of ionospheric electron density profiles with global navigation satellite system (GNSS) observations has become an indispensable technique for various purposes ranging from space physics studies to radio applications. This paper conducts a comprehensive review on the development of voxel-based computerized ionospheric tomography (CIT) in the last 30 years. A brief introduction is given in chronological order starting from the first report of CIT with simulation to the newly proposed voxel-based algorithms for ionospheric event analysis. The statement of the tomographic geometry and voxel models are outlined with the ill-posed and ill-conditioned nature of CIT addressed. With the additional information from other instrumental observations or initial models supplemented to make the coefficient matrix less ill-conditioned, equation constructions are categorized into constraints, virtual data assimilation and multi-source observation fusion. Then, the paper classifies and assesses the voxel-based CIT algorithms of the algebraic method, statistical approach and artificial neural networks for equation solving or electron density estimation. The advantages and limitations of the algorithms are also pointed out. Moreover, the paper illustrates the representative height profiles and two-dimensional images of ionospheric electron densities from CIT. Ionospheric disturbances studied with CIT are presented. It also demonstrates how the CIT benefits ionospheric correction and ionospheric monitoring. Finally, some suggestions are provided for further research about voxel-based CIT.
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Vanhamäki, H., A. Viljanen, and O. Amm. "Induction effects on ionospheric electric and magnetic fields." Annales Geophysicae 23, no. 5 (July 28, 2005): 1735–46. http://dx.doi.org/10.5194/angeo-23-1735-2005.
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Abstract. Rapid changes in the ionospheric current system give rise to induction currents in the conducting ground that can significantly contribute to magnetic and especially electric fields at the Earth's surface. Previous studies have concentrated on the surface fields, as they are important in, for example, interpreting magnetometer measurements or in the studies of the Earth's conductivity structure. In this paper we investigate the effects of induction fields at the ionospheric altitudes for several realistic ionospheric current models (Westward Travelling Surge, Ω-band, Giant Pulsation). Our main conclusions are: 1) The secondary electric field caused by the Earth's induction is relatively small at the ionospheric altitude, at most 0.4 mV/m or a few percent of the total electric field; 2) The primary induced field due to ionospheric self-induction is locally important, ~ a few mV/m, in some "hot spots", where the ionospheric conductivity is high and the total electric field is low. However, our approximate calculation only gives an upper estimate for the primary induced electric field; 3) The secondary magnetic field caused by the Earth's induction may significantly affect the magnetic measurements of low orbiting satellites. The secondary contribution from the Earth's currents is largest in the vertical component of the magnetic field, where it may be around 50% of the field caused by ionospheric currents. Keywords. Geomagnetism and paleomagnetism (geomagnetic induction) – Ionosphere (electric fields and currents)
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Bakhmetieva, Nataliya V., and Gennadiy I. Grigoriev. "Study of the Mesosphere and Lower Thermosphere by the Method of Creating Artificial Periodic Irregularities of the Ionospheric Plasma." Atmosphere 13, no. 9 (August 24, 2022): 1346. http://dx.doi.org/10.3390/atmos13091346.
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This article presented a brief review of studies of the Earth’s ionosphere at the heights of the mesosphere and lower thermosphere by a method based on the creation of artificial periodic inhomogeneities (APIs) of the ionospheric plasma by high-frequency radiation from powerful thermal installations. APIs are created by a standing wave due to the interference between upward-propagating radio waves and those reflected from the ionosphere. API studies of the ionosphere were based on Bragg scattering of probing impulse signals from an artificial periodic structure. The method makes it possible to measure the parameters of the neutral and ionized components of the Earth’s atmosphere. Note that, despite the fact that the API method assumes an artificial perturbation of the ionospheric plasma, the parameters of the mesosphere and lower thermosphere are determined at the stage of inhomogeneity relaxation and characterize the undisturbed medium. To date, periodic inhomogeneities have been observed at the heating points of Zimenki and Sura ionospheric heating facility (SURA, Vasilsursk, Russia), Gissar (Tajikistan), Arecibo (Puerto Rico, USA), High Power Auroral Stimulation Observatory (HIPAS) and High Frequency Active Auroral Research Program (HAARP, Gakona, AK, USA), and European Incoherent Scatter (EISCAT, Tromso, Norway). Most of the API studies of the ionosphere were carried out at the SURA mid-latitude heating facility (56.1° N; 46.1° E). The review presented the main results of determining the parameters of the ionosphere and neutral atmosphere at altitudes of 60–120 km and studies of the atmosphere during sunrise and sunset events and solar eclipses. In fact, the review is far from a complete illustration of the possibilities of using the API method to study the mesosphere and lower thermosphere.
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Li, Qingfeng, Zeyun Li, and Hanxian Fang. "Using 3D Ray Tracing Technology to Study the Disturbance Effect of Rocket Plume on Ionosphere." Atmosphere 13, no. 7 (July 20, 2022): 1150. http://dx.doi.org/10.3390/atmos13071150.
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In this paper, the initial neutral atmospheric parameters, background ionospheric parameters and geomagnetic field parameters of the ionosphere are obtained by NRLMSISE-00 model, IRI-2016 model and IGRF-13 model, respectively. Considering the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, a three-dimensional dynamic model of chemical substances released by rocket plume disturbing the ionosphere is constructed. The influence of the disturbance on the echo path of high frequency radio waves with different incident frequencies is simulated by using three-dimensional digital ray-tracing technology. Using this model, the process of ionospheric disturbance caused by the main chemical substances H2 and H2O in the rocket plume under three different release conditions: fixed-point release at 300 km, vertical path at 250–350 km and parabolic path at 250–350 km, and the influence of the ionospheric cavity on the radio wave propagation of high frequency radio waves at different frequencies are simulated. The main purpose of the article is to focus on the effect of the cavity generated by the rocket exhaust on the propagation of radio waves. It mainly studies the perturbation effect on the ionosphere under different release conditions, considers the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, and establishes the three-dimensional dynamics of the ionospheric electron density and the spatiotemporal distribution of the plume plasma learning model. Finally, the three-dimensional ray-tracing algorithm is used to simulate the propagation path of the radio wave through the disturbance area. We considered three different release conditions, including fixed-point release, vertical path and parabolic path. The ionospheric disturbances produced by these different releases are compared and analyzed, and their effects on the propagation path of radio waves are studied.
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Горячкин, О. В., and И. В. Маслов. "Определение статистических параметров флуктуаций коэффициента преломления ионосферы по данным радиолинии передачи информации космос-Земля." Письма в журнал технической физики 48, no. 21 (2022): 31. http://dx.doi.org/10.21883/pjtf.2022.21.53710.19303.
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The study considers the problem of restoring the covariance function of fluctuations in the refractive index of the ionosphere based on the analysis of random changes in the frequency of the radio signal. To solve the problem, a trans-ionospheric signal of an information transmission radio line is used, radiated from a low-orbit spacecraft and received at a stationary receiving point. A method for estimating ionospheric parameters based on data from one typical communication session is described. To conduct a full-scale experiment, the signal emitted by the P-band radio transmitter of the on-board monitoring and control system of the Aist-2D spacecraft is used during a typical communication session. To receive the signal, ground-based equipment of a bistatic radar complex with a synthesized aperture of the P frequency band is used
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Dong, Yanfeng, Chengfa Gao, Fengyang Long, and Yuxiang Yan. "Suspected Seismo-Ionospheric Anomalies before Three Major Earthquakes Detected by GIMs and GPS TEC of Permanent Stations." Remote Sensing 14, no. 1 (December 22, 2021): 20. http://dx.doi.org/10.3390/rs14010020.
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Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ). Ionospheric anomalies in the form of abnormal increases and decreases of ionospheric Total Electron Content (TEC) are even regarded as precursors to EQs. In this paper, TEC anomalies associated with three major EQs were investigated by Global Ionospheric Maps (GIMs) and GPS-TEC, including Kumamoto-shi, Japan—EQ occurred on 15 April 2016 with Mw = 7.0; Jinghe, China—EQ occurred on 8 August 2017 with Mw = 6.3; and Lagunas, Peru—EQ occurred on 26 May 2019 with Mw = 8.0. It was found that the negative ionospheric anomalies linger above or near the epicenter for 4–10 h on the day of the EQ. For each EQ, the 10-min sampling interval of TEC was extracted from three permanent GPS stations around the epicenter within 10 days before and after the EQ. Variations of TEC manifest that the negative ionospheric anomalies first appear 10 days before the EQ. From 5 days before to 2 days after the main shock, the negative ionospheric anomalies were more prominent than the other days, with the amplitude of negative ionospheric anomaly reaching −3 TECu and the relative ionospheric anomaly exceeding 20%. In case of Kumamoto-shi EQ, the solar-geomagnetic conditions were not quiet (Dst < −30 nT, Kp > 4, and F10.7 > 100 SFU) on the suspected EQ days. We discussed the differences between ionospheric anomalies caused by active solar-geomagnetic conditions and EQ. Combining the analysis results of Jinghe EQ and Lagunas EQ, under quiet solar-geomagnetic conditions (Dst > −30 nT, Kp < 4, and F10.7 < 100 SFU), it can be found that TEC responds to various solar-geomagnetic conditions and EQ differently. The negative ionospheric anomalies could be considered as significant signals of upcoming EQs. These anomalies under different solar-geomagnetic conditions may be effective to link the lithosphere and ionosphere in severe seismic zones to detect EQ precursors before future EQs.
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Chisham, G., M. P. Freeman, T. Sotirelis, R. A. Greenwald, M. Lester, and J. P. Villain. "A statistical comparison of SuperDARN spectral width boundaries and DMSP particle precipitation boundaries in the morning sector ionosphere." Annales Geophysicae 23, no. 3 (March 30, 2005): 733–43. http://dx.doi.org/10.5194/angeo-23-733-2005.
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Abstract. Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial for making accurate ionospheric measurements of many magnetospheric processes (e.g. magnetic reconnection). This study compares the latitudes of Spectral Width Boundaries (SWBs), identified in the morning sector ionosphere using the Super Dual Auroral Radar Network (SuperDARN), with Particle Precipitation Boundaries (PPBs) determined using the low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the SWB represents a good proxy for the ionospheric projection of the OCB. The latitudes of SWBs and PPBs were identified using automated algorithms applied to 5 years (1997-2001) of data measured in the 00:00-12:00 Magnetic Local Time (MLT) range. A latitudinal difference was measured between each PPB and the nearest SWB within a ±10min Universal Time (UT) window and within a ±1h MLT window. The results show that the SWB represents a good proxy for the OCB close to midnight (~00:00-02:00 MLT) and noon (~08:00-12:00 MLT), but is located some distance (~2°-4°) equatorward of the OCB across much of the morning sector ionosphere (~02:00-08:00 MLT). On the basis of this and other studies we deduce that the SWB is correlated with the poleward boundary of auroral emissions in the Lyman-Birge-Hopfield ``Long" (LBHL) UV emission range and hence, that spectral width is inversely correlated with the energy flux of precipitating electrons. We further conclude that the combination of two factors may explain the spatial distribution of spectral width values in the polar ionospheres. The small-scale structure of the convection electric field leads to an enhancement in spectral width in regions close to the OCB, whereas increases in ionospheric conductivity (relating to the level of incident electron energy flux) lead to a reduction in spectral width in regions just equatorward of the OCB.
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Biktash, L. Z. "Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms." Annales Geophysicae 22, no. 9 (September 23, 2004): 3195–202. http://dx.doi.org/10.5194/angeo-22-3195-2004.
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Abstract. The equatorial ionosphere parameters, Kp, Dst, AU and AL indices characterized contribution of different magnetospheric and ionospheric currents to the H-component of geomagnetic field are examined to test the geomagnetic activity effect on the generation of ionospheric irregularities producing VLF scintillations. According to the results of the current statistical studies, one can predict near 70% of scintillations from Aarons' criteria using the Dst index, which mainly depicts the magnetospheric ring current field. To amplify Aarons' criteria or to propose new criteria for predicting scintillation characteristics is the question. In the present phase of the experimental investigations of electron density irregularities in the ionosphere new ways are opened up because observations in the interaction between the solar wind - magnetosphere - ionosphere during magnetic storms have progressed greatly. According to present view, the intensity of the electric fields and currents at the polar regions, as well as the magnetospheric ring current intensity, are strongly dependent on the variations of the interplanetary magnetic field. The magnetospheric ring current cannot directly penetrate the equatorial ionosphere and because of this difficulties emerge in explaining its relation to scintillation activity. On the other hand, the equatorial scintillations can be observed in the absence of the magnetospheric ring current. It is shown that in addition to Aarons' criteria for the prediction of the ionospheric scintillations, models can be used to explain the relationship between the equatorial ionospheric parameters, h'F, foF2, and the equatorial geomagnetic variations with the polar ionosphere currents and the solar wind.
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Pavelyev, A. G., Y. A. Liou, S. S. Matyugov, A. A. Pavelyev, V. N. Gubenko, K. Zhang, and Y. Kuleshov. "Application of locality principle to radio occultation studies of the Earth's atmosphere and ionosphere." Atmospheric Measurement Techniques Discussions 8, no. 1 (January 20, 2015): 721–58. http://dx.doi.org/10.5194/amtd-8-721-2015.
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Abstract. A new formulation of previously introduced principle of locality is presented. The principle can be applied for modernization of the radio occultation (RO) remote sensing of the atmospheres and ionospheres of the Earth and planets. The principle states that significant contributions to variations of the amplitude and phase of the radio waves passing through a layered medium are connected with influence of the vicinities of tangential points where the refractivity gradient is perpendicular to the radio ray trajectory. The RO method assumes spherical symmetry of the investigated medium. In this case if location of a tangent point relative to the spherical symmetry center is known, the derivatives on time of the RO signal phase and Doppler frequency variations can be recalculated into the refractive attenuation. Several important findings are consequences of the locality principle: (i) if position of the center of symmetry is known, the total absorption along the ray path can be determined at a single frequency, (ii) in the case of low absorption the height, displacement from the radio ray perigee, and tilt of the inclined ionospheric (atmospheric) layers can be evaluated, (iii) the contributions of the layered and irregular structures in the RO signal can be separated and parameters of layers and turbulence can be measured at a single frequency using joint analysis of the amplitude and phase variations. Specially for the Earth's troposphere, the altitude distributions of the weak total absorption (about of 1–4 db) of the radio waves at GPS frequencies corresponding to possible influence of the oxygen and water vapor can be measured with accuracy of about 0.1 db at a single frequency. According with the locality principle, a new index of ionospheric activity is introduced. This index is measured from the phase variations of radio waves passing through the ionosphere. Its high correlation with S4 scintillation index is established. This correlation indicates the significant influence of locally spherical symmetric ionospheric layers on variations of the phase and amplitude of the RO signal passing through transionospheric communication links. Obtained results expand the applicable domain of the RO method as a powerful remote sensing technique for geophysical and meteorological research.
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Pavelyev, A. G., Y. A. Liou, S. S. Matyugov, A. A. Pavelyev, V. N. Gubenko, K. Zhang, and Y. Kuleshov. "Application of the locality principle to radio occultation studies of the Earth's atmosphere and ionosphere." Atmospheric Measurement Techniques 8, no. 7 (July 17, 2015): 2885–99. http://dx.doi.org/10.5194/amt-8-2885-2015.
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Abstract. A new formulation of the previously introduced principle of locality is presented. The principle can be applied for modernization of the radio occultation (RO) remote sensing of the atmospheres and ionospheres of the Earth and other planets. The principle states that significant contributions to variations of the intensity and phase of the radio waves passing through a layered medium are connected with influence of the vicinities of tangential points where the refractivity gradient is perpendicular to the radio ray trajectory. The RO method assumes spherical symmetry of the investigated medium. In this case, if location of a tangent point relative to the spherical symmetry centre is known, the time derivatives of the RO signal phase and Doppler frequency variations can be recalculated into the refractive attenuation. Several important findings are consequences of the locality principle: (i) if position of the centre of symmetry is known, the total absorption along the ray path can be determined at a single frequency; (ii) in the case of low absorption the height, displacement from the radio ray perigee, and tilt of the inclined ionospheric (atmospheric) layers can be evaluated; (iii) the contributions of the layered and irregular structures in the RO signal can be separated and parameters of layers and turbulence can be measured at a single frequency using joint analysis of the intensity and phase variations. Specially for the Earth's troposphere, the altitude distributions of the weak total absorption (about of 1–4 db) of the radio waves at GPS frequencies corresponding to possible influence of the oxygen, water vapour, and hydrometeors can be measured with accuracy of about 0.1 db at a single frequency. In accordance with the locality principle, a new index of ionospheric activity is introduced. This index is measured from the phase variations of radio waves passing through the ionosphere. Its high correlation with the S4 scintillation index is established. This correlation indicates the significant influence of locally spherical symmetric ionospheric layers on variations of the phase and intensity of the RO signal passing through transionospheric communication links. Obtained results expand applicable domain of the RO method as a powerful remote sensing technique for geophysical and meteorological research.
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Bößwetter, A., T. Bagdonat, U. Motschmann, and K. Sauer. "Plasma boundaries at Mars: a 3-D simulation study." Annales Geophysicae 22, no. 12 (December 22, 2004): 4363–79. http://dx.doi.org/10.5194/angeo-22-4363-2004.
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Abstract. The interaction of the solar wind with the ionosphere of planet Mars is studied using a three-dimensional hybrid model. Mars has only a weak intrinsic magnetic field, and consequently its ionosphere is directly affected by the solar wind. The gyroradii of the solar wind protons are in the range of several hundred kilometers and therefore comparable with the characteristic scales of the interaction region. Different boundaries emerge from the interaction of the solar wind with the continuously produced ionospheric heavy-ion plasma, which could be identified as a bow shock (BS), ion composition boundary (ICB) and magnetic pile up boundary (MPB), where the latter both turn out to coincide. The simulation results regarding the shape and position of these boundaries are in good agreement with the measurements made by Phobos-2 and MGS spacecraft. It is shown that the positions of these boundaries depend essentially on the ionospheric production rate, the solar wind ram pressure, and the often unconsidered electron temperature of the ionospheric heavy ion plasma. Other consequences are rays of planetary plasma in the tail and heavy ion plasma clouds, which are stripped off from the dayside ICB region by some instability. Key words. Magnetospheric physics (solar wind interactions with unmagnetized bodies) – Space plasma physics (discontinuities; numerical simulation studies)
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Ezquer, R. G., and M. Mosert. "Ionospheric variability studies in Argentina." Advances in Space Research 39, no. 5 (2007): 949–61. http://dx.doi.org/10.1016/j.asr.2006.05.026.
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Xu, T., Y. L. Hu, F. F. Wang, Z. Chen, and J. Wu. "Is there any difference in local time variation in ionospheric F2-layer disturbances between earthquake-induced and Q-disturbance events?" Annales Geophysicae 33, no. 6 (June 3, 2015): 687–95. http://dx.doi.org/10.5194/angeo-33-687-2015.
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Abstract. Ionospheric anomalies before earthquakes have become the subject of one of the most intensive studies in the area of ionospheric variation. The ionosphere has a large class of disturbances under quiet geomagnetic conditions, i.e., quiet time disturbances (Q disturbances). Hence, the characteristics of seismo-ionospheric anomalies obtained by statistical analysis should be compared with those of Q-disturbance events. Using the data of foF2 (F2-layer critical frequency) during the whole interval of 1978–2008 (~3 solar cycles), the local time (LT) variation in Q disturbances is investigated. The results showed that a well-pronounced nighttime peak took place for positive disturbances induced by Q-disturbance events, while positive disturbances related to earthquakes predominately occurred in the daytime, especially in the afternoon LT sector. This remarkable difference in local time variation in foF2 between the earthquake-triggered and Q-disturbance events is of great significance for the identification of ionospheric precursors.
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LaBelle, J. "High-latitude propagation studies using a meridional chain of LF/MF/HF receivers." Annales Geophysicae 22, no. 5 (April 8, 2004): 1705–18. http://dx.doi.org/10.5194/angeo-22-1705-2004.
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Abstract. For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz) show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.Key words. Magnetospheric physics (annual phenomena) – Radio science (ionosphere propagation; radio-wave propagation)6
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Yizengaw, Endawoke. "Global Longitudinal Dependence Observation of the Neutral Wind and Ionospheric Density Distribution." International Journal of Geophysics 2012 (2012): 1–11. http://dx.doi.org/10.1155/2012/342581.
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The statistical global view of the low-latitude ionospheric density stimulates further interest in studying the strong longitudinal variability of the ionospheric density structures in low-to-equatorial latitudes. However, we are not completely certain how the electrodynamics and ion-neutral coupling proceeds at low latitudes; in particular, the longitudinal difference in the dynamics of plasma structures in the low-to-mid latitude ionosphere is not yet fully understood. Numerical studies of latent heat release in the troposphere have indicated that the lower atmosphere can indeed introduce a longitudinal dependence and variability of the low-latitude ionosphere during quiet conditions. For the first time, we present simultaneous observations of the tidally modulated global wind structure, using TIDI observations, in the E-region and the ionospheric density distribution using ground (global GPS receivers) and space-based (C/NOFS in situ density and GPS TEC on CHAMP) instruments. Our results show that the longitudinally structured zonal wind component could be responsible for the formation of wave number four pattern of the equatorial anomaly.
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Ратовский, Константин, Konstantin Ratovsky, Максим Клименко, Maksim Klimenko, Владимир Клименко, Vladimir Klimenko, Николай Чирик, et al. "After-effects of geomagnetic storms: statistical analysis and theoretical explanation." Solar-Terrestrial Physics 4, no. 4 (December 21, 2018): 26–32. http://dx.doi.org/10.12737/stp-44201804.
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Our previous studies have shown the presence of daytime positive electron density disturb-ances during several days after the start of the recovery phase. The aim of this paper is to study after-effects of geomagnetic storms (after-storm effects), i.e. ionospher-ic effects observed on the 3–5th day after the beginning of the storm recovery phase. From numerical calcula-tions with the GSM TIP model, we have found the main mechanisms for the formation of the after-storm effects. Using Irkutsk (52° N, 104° E) and Kaliningrad (54° N, 20° E) ionosonde data, we have carried out a statistical analysis of daytime ionospheric responses to geomagnetic storms. As a result of the analysis, we obtained averaged ionospheric responses at the beginning of the storm recovery phase and for five consecutive days. The statistical analysis results received near the beginning of the recovery phase are in good agreement with the well-known ionospheric effects of geomagnetic storms obtained in previous studies. For the first time, the obtained statistics of iono-spheric responses observed on the 3–5th day after the beginning of the recovery phase allowed us to reveal the dependence of after-storm ionospheric effects on season, storm intensity, and ionosonde geomagnetic latitude. In addition, we for the first time present the interpretation of after-storm ionospheric effects from numerical simulation results.
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Ратовский, Константин, Konstantin Ratovsky, Максим Клименко, Maksim Klimenko, Владимир Клименко, Vladimir Klimenko, Николай Чирик, et al. "After-effects of geomagnetic storms: statistical analysis and theoretical explanation." Solnechno-Zemnaya Fizika 4, no. 4 (December 20, 2018): 32–42. http://dx.doi.org/10.12737/szf-44201804.
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Our previous studies have shown the presence of daytime positive electron density disturb-ances during several days after the start of the recovery phase. The aim of this paper is to study after-effects of geomagnetic storms (after-storm effects), i.e. ionospher-ic effects observed on the 3–5th day after the beginning of the storm recovery phase. From numerical calcula-tions with the GSM TIP model, we have found the main mechanisms for the formation of the after-storm effects. Using Irkutsk (52° N, 104° E) and Kaliningrad (54° N, 20° E) ionosonde data, we have carried out a statistical analysis of daytime ionospheric responses to geomagnetic storms. As a result of the analysis, we obtained averaged ionospheric responses at the beginning of the storm recovery phase and for five consecutive days. The statistical analysis results received near the beginning of the recovery phase are in good agreement with the well-known ionospheric effects of geomagnetic storms obtained in previous studies. For the first time, the obtained statistics of iono-spheric responses observed on the 3–5th day after the beginning of the recovery phase allowed us to reveal the dependence of after-storm ionospheric effects on season, storm intensity, and ionosonde geomagnetic latitude. In addition, we for the first time present the interpretation of after-storm ionospheric effects from numerical simulation results.
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Mohanty, S., C. Carrano, and G. Singh. "MONITORING OF IONOSPHERIC SCINTILLATION PHENOMENA USING SYNTHETIC APERTURE RADAR (SAR)." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences IV-5 (November 15, 2018): 331–37. http://dx.doi.org/10.5194/isprs-annals-iv-5-331-2018.
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<p><strong>Abstract.</strong> The applications of synthetic aperture radars (SAR) have increased manifold in the past decade, which includes numerous Earth observation applications such as agriculture, forestry, disaster monitoring cryospheric- and atmospheric- studies. Among them, the potential of SAR for ionospheric studies is gaining importance. The susceptibility of SAR to space weather dynamics, and ionosphere in particular, comes at low frequencies of L- and P-bands. This paper discusses one such scintillation event that was observed by L-band Advanced Land Observation Satellite (ALOS)-2 Phased Array L-type SAR (PALSAR) over southern India on March 23, 2015. The sensors also acquired data sets on four other days on which the ionosphere was quiet. Ionospheric parameter measurements of total electron content (TEC) and amplitude scintillation (S<sub>4</sub>) index from ground-based Global Navigation Satellite System (GNSS) receiver at Tirunelveli was used to establish the ionospheric conditions on the days of SAR acquisition as well as to corroborate the S<sub>4</sub> estimated from SAR. Multi-temporal ALOS-2 data sets were utilized to calculate S<sub>4</sub> from two separate methods and the results have a good agreement with GNSS receiver measurements. This highlights the potential of SAR as an alternate technique of monitoring ionospheric scintillations that can be utilized as complementary to the highly accurate and dedicated measurements from the GNSS networks.</p>
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Zhang, Z., R. T. Desai, O. Shebanits, F. L. Johansson, Y. Miyake, and H. Usui. "Simulating Secondary Electron and Ion Emission from the Cassini Spacecraft in Saturn’s Ionosphere." Planetary Science Journal 4, no. 6 (June 1, 2023): 105. http://dx.doi.org/10.3847/psj/acd844.
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Abstract The Cassini spacecraft’s Grand Finale flybys through Saturn’s ionosphere provided unprecedented insight into the composition and dynamics of the gas giant’s upper atmosphere and a novel and complex spacecraft–plasma interaction. In this article, we further study Cassini’s interaction with Saturn’s ionosphere using three-dimensional particle-in-cell simulations. We focus on how electrons and ions, emitted from spacecraft surfaces due to the high-velocity impact of atmospheric water molecules, could have affected the spacecraft potential and low-energy plasma measurements. The simulations show emitted electrons extend upstream along the magnetic field, and for sufficiently high emission rates, charge the spacecraft to positive potentials. The lack of accurate emission rates and characteristics, however, makes differentiation between the prominence of secondary electron emission and ionospheric charged dust populations, which induce similar charging effects, difficult for Cassini. These results provide further context for Cassini’s final measurements and highlight the need for future laboratory studies to support high-velocity flyby missions through planetary and cometary ionospheres.
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Elias, Ana G., Blas F. de Haro Barbas, Bruno S. Zossi, Franco D. Medina, Mariano Fagre, and Jose V. Venchiarutti. "Review of Long-Term Trends in the Equatorial Ionosphere Due the Geomagnetic Field Secular Variations and Its Relevance to Space Weather." Atmosphere 13, no. 1 (December 28, 2021): 40. http://dx.doi.org/10.3390/atmos13010040.
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The Earth’s ionosphere presents long-term trends that have been of interest since a pioneering study in 1989 suggesting that greenhouse gases increasing due to anthropogenic activity will produce not only a troposphere global warming, but a cooling in the upper atmosphere as well. Since then, long-term changes in the upper atmosphere, and particularly in the ionosphere, have become a significant topic in global change studies with many results already published. There are also other ionospheric long-term change forcings of natural origin, such as the Earth’s magnetic field secular variation with very special characteristics at equatorial and low latitudes. The ionosphere, as a part of the space weather environment, plays a crucial role to the point that it could certainly be said that space weather cannot be understood without reference to it. In this work, theoretical and experimental results on equatorial and low-latitude ionospheric trends linked to the geomagnetic field secular variation are reviewed and analyzed. Controversies and gaps in existing knowledge are identified together with important areas for future study. These trends, although weak when compared to other ionospheric variations, are steady and may become significant in the future and important even now for long-term space weather forecasts.
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Neudegg, D. A., S. W. H. Cowley, S. E. Milan, T. K. Yeoman, M. Lester, G. Provan, G. Haerendel, et al. "A survey of magnetopause FTEs and associated flow bursts in the polar ionosphere." Annales Geophysicae 18, no. 4 (April 30, 2000): 416–35. http://dx.doi.org/10.1007/s00585-000-0416-0.
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Abstract. Using the Equator-S spacecraft and SuperDARN HF radars an extensive survey of bursty reconnection at the magnetopause and associated flows in the polar ionosphere has been conducted. Flux transfer event (FTE) signatures were identified in the Equator-S magnetometer data during periods of magnetopause contact in January and February 1998. Assuming the effects of the FTEs propagate to the polar ionosphere as geomagnetic field-aligned-currents and associated Alfvén-waves, appropriate field mappings to the fields-of-view of SuperDARN radars were performed. The radars observed discrete ionospheric flow channel events (FCEs) of the type previously assumed to be related to pulse reconnection. Such FCEs were associated with \\sim80% of the FTEs and the two signatures are shown to be statistically associated with greater than 99% confidence. Exemplary case studies highlight the nature of the ionospheric flows and their relation to the high latitude convection pattern, the association methodology, and the problems caused by instrument limitations.Key words: Ionosphere (polar ionosphere) · Magnetospheric physics (magnetosphere-ionosphere interaction; solar wind-magnetosphere interactions)
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Vybornov, Fedor I., and Olga A. Sheiner. "Influence of helio-geophysical activity on reliability of short-wave communication in transport." Russian Journal of Water Transport, no. 72 (September 20, 2022): 249–59. http://dx.doi.org/10.37890/jwt.vi72.300.
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The results of studies of the influence of coronal mass ejections and high-velocity solar wind streams on the characteristics of the ionosphere are presented. The analysis uses ionospheric data from the CADI vertical sounding station (Vasilsursk, Nizhny Novgorod region) and data from chirp stations for oblique ionospheric sounding on different paths of the Eurasian region of Russia: three subauroral (Lovozero-Vasilsursk, Sodankyulya-Vasilsursk and Salekhard-Vasilsursk) and one mid-latitude (Gorky, Leningrad region-Vasilsursk). A set of space weather parameters (type and speed of coronal mass ejections, high-speed solar wind speed) is considered, which made it possible to reveal the dominant physical relationships between the ionospheric dynamics and these two solar phenomena, which determine the reliability of short-wave radio communication between ships and the coast, especially in the area of the northern sea way.
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Jakowski, N., A. Jungstand, K. Schlegel, H. Kohl, and K. Rinnert. "The ionospheric response to perturbation electric fields during the onset phase of geomagnetic storms." Canadian Journal of Physics 70, no. 7 (July 1, 1992): 575–81. http://dx.doi.org/10.1139/p92-093.
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The generation and propagation of ionospheric storms are studied by analyzing EISCAT radar, and vertical-sounding and total-electron-content data obtained under different geophysical conditions. Both, case studies as well as the average storm pattern of percentage deviations of different ionospheric parameters from their corresponding reference values such as total electron content, F2-layer critical frequency foF2, F2-layer height hmF2, and slab thickness τ indicate the action of a perturbation electric field during the first few hours during the onset phase of geomagnetic storms. Considering the onset phase of the storm on July 28–29, 1987 evidence has been found that high-latitude electric fields may penetrate to lower latitudes before the ring current has developed. In most cases this process is accompanied by a positive phase in the upper ionosphere and F2-layer ionization. Different mechanisms are assumed to be responsible for the daytime and nighttime behaviour, respectively. The negative phase propagates equatorward with velocities in the order of 70–350 m s−1 following a strong heating of the thermosphere and ionosphere due to the auroral electrojet.
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Akhoondzadeh, M. "SEISMO-MAGNETIC FIELD ANOMALIES DETECTION USING SWARM SATELLITES (ALPHA, BRAVO AND CHARLIE)." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4/W18 (October 18, 2019): 45–49. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w18-45-2019.
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Abstract. Among the lithospheric, atmospheric and ionospheric earthquake precursors, it seems that the ionospheric anomalies showing a meaningful association with seismic activities during absence of solar and geomagnetic activities. Unfortunately there are a limited number of satellite sensors to survey the ionosphere and study on seismo-ionospheric anomalies. This paper represents the data analysis results of Swarm satellites including Alpha, Bravo and Charlie data around the Mexico (September 8, 2017) earthquake. The orbital analysis and time series of magnetic field parameters (magnetic scalar and vectors (X, Y, Z) components) inside the Dobrovolsky’s area show anomalous variations close to the time and locations of the Mexico earthquake. There is a concavity or convexity variations in the some of the time-series to the centre of the earthquake day. In other words, from about 90 days before the event a decreasing or increasing trend in variations of parameters is observed and exactly after the earthquake day its trend changes. It should be noted that the variations of the solar and geomagnetic indices must indicate a normal behaviour during the observed seismo-ionospheric anomalies. Therefore this study indicates that the Swarm satellites measurements play an undeniable role in progress the studies of the ionospheric precursors.
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Zhao, Lewen, Jan Douša, and Pavel Václavovic. "Accuracy Evaluation of Ionospheric Delay from Multi-Scale Reference Networks and Its Augmentation to PPP during Low Solar Activity." ISPRS International Journal of Geo-Information 10, no. 8 (July 30, 2021): 516. http://dx.doi.org/10.3390/ijgi10080516.
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The Precise Point Positioning (PPP) with fast integer ambiguity resolution (PPP-RTK) is feasible only if the solution is augmented with precise ionospheric parameters. The vertical ionospheric delays together with the receiver hardware biases, are estimated simultaneously based on the uncombined PPP model. The performance of the ionospheric delays was evaluated and applied in the PPP-RTK demonstration during the low solar activity period. The processing was supported by precise products provided by Deutsches GeoForschungsZentrum Potsdam (GFZ) and also by real-time products provided by the National Centre for Space Studies (CNES). Since GFZ provides only precise orbits and clocks, other products needed for ambiguity resolution, such as phase biases, were estimated at the Geodetic Observatory Pecny (GOP). When ambiguity parameters were resolved as integer values in the GPS-only solution, the initial convergence period was reduced from 30 and 20 min to 24 and 13 min when using CNES and GFZ/GOP products, respectively. The accuracy of ionospheric delays derived from the ambiguity fixed PPP, and the CODE global ionosphere map were then assessed. Comparison of ambiguity fixed ionospheric delay obtained at two collocated stations indicated the accuracy of 0.15 TECU for different scenarios with more than 60% improvement compared to the ambiguity float PPP. However, a daily periodic variation can be observed from the multi-day short-baseline ionospheric residuals. The accuracy of the interpolated ionospheric delay from global maps revealed a dependency on the location of the stations, ranging from 1 to 3 TECU. Precise ionospheric delays derived from the EUREF permanent network with an inter-station distance larger than 73 km were selected for ionospheric modeling at the user location. Results indicated that the PPP ambiguity resolution could be achieved within three minutes. After enlarging the inter-station distance to 209 km, ambiguity resolution could also be achieved within several minutes.
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Moen, J., S. T. Berry, L. Kersley, and B. Lybekk. "Probing discrete auroral arcs by ionospheric tomography." Annales Geophysicae 16, no. 5 (May 31, 1998): 574–82. http://dx.doi.org/10.1007/s00585-998-0574-z.
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Abstract. Optical observations of 557.7 nm and 630.0 nm emissions from discrete auroral arcs in the post-noon sector have been related to localised field-aligned enhancements in the spatial distribution of E- and F-layer electron density respectively seen in images reconstructed by ionospheric tomography. Results from two case studies are presented in which meridian scanning photometer and all-sky camera observations on Svalbard have been compared to electron-density structures found by tomographic inversion of measurements made by reception of radio signals at a chain of four stations at high latitude. The F-layer features are long-lived and show exact correspondence to the red-line emissions. Transient arcs in green-line intensity result in E-region structures that are resolved in one case, but not in another where the dynamic auroral forms are separated by less than one degree of latitude. The signature of an inverted-V precipitation event is clearly evident in one example.Key words. Ionosphere (Auroral ionosphere) · Magnetospheric physics (Auroral phenomena) · Radio science (Ionospheric physics)
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Juan, José Miguel, Jaume Sanz, Adrià Rovira-Garcia, Guillermo González-Casado, D. Ibáñez, and R. Orus Perez. "AATR an ionospheric activity indicator specifically based on GNSS measurements." Journal of Space Weather and Space Climate 8 (2018): A14. http://dx.doi.org/10.1051/swsc/2017044.
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This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.
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Bilitza, Dieter. "IRI the International Standard for the Ionosphere." Advances in Radio Science 16 (September 4, 2018): 1–11. http://dx.doi.org/10.5194/ars-16-1-2018.
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Abstract. This paper gives a brief overview over the International Reference Ionosphere (IRI) project and model. IRI is recognized as the official standard for the ionosphere by the International Standardization Organization (ISO), the International Union of Radio Science (URSI), the Committee on Space Research (COSPAR), and the European Cooperation for Space Standardization (ECCS). Of great importance are the external drivers of the model that help IRI to represent ionospheric conditions as realistically as possible. The paper discusses the drivers currently used presents recent improvements and changes. Besides the standard solar, magnetic, and ionospheric indices the paper also reports on the adjustment of the model with data and equivalent indices and on the progress towards a Real-Time IRI using data assimilation. IRI has been widely validated with many different data sources and has fared very well in community wide assessment studies. We present some of these studies and document the wide usages of the model in the scientific literature. Finally, we present an outlook on things to come in IRI-2018 and thereafter.
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Zakharov, Ivan. "Influence of Lower Atmosphere on Long-Term Total Electron Content Variations of Mid-latitude Ionosphere in Winter Seasons 2012 – 2018." PHYSICS OF ATMOSPHERE AND GEOSPACE 2, no. 2 (December 31, 2021): 15–26. http://dx.doi.org/10.47774/phag.02.02.2021-2.
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Background. In recent decades, new results on the influence of powerful meteorological processes on the ionosphere have been obtained. At the same time, the possibility of tropospheric-ionospheric interaction outside the disturbed periods remains unclear, which is important for assessing the energy of the phenomenon and for modeling the dynamic processes of the lower and upper atmosphere as a single self-organizing system. In this work, for the first time, the possibility of the influence of the lower atmosphere on the median values of ionospheric parameters against the background of processes caused by space weather is considered. Objectives of the work is to search and analyze long-term longitudinal effects of the mid-latitude ionosphere in the winter season and their possible connection with processes in the lower atmosphere. Materials and methods. The studies were carried out using daily data for the winter seasons of 2012 – 2018 at a latitude of 40 °N on the basis of maps of ionospheric total electron content obtained using the global network of navigation satellites and global maps of pressure and temperature of the surface atmosphere. Data on space weather and the magnetosphere (indices of solar and geomagnetic activity) were also used. Statistical analysis methods were used. Results. Significant (up to 40 % of the average level) permanently existing longitudinal extrema of the ionospheric total electron content have been established, which correlate with changes in the pressure and temperature of the surface atmosphere. The relationship is characterized by significant correlation coefficients from +0.34 to +0.48 in the seasons under consideration. The total electron content maxima fall on longitudes with maximum surface atmospheric pressure gradients. The influence of space weather through the mismatch between the geographic and geomagnetic coordinate systems also leads to longitudinal effects in the ionosphere, but without the formation of local extrema. Conclusions. The results obtained indicate the possibility of long-term or continuous interaction of the lower atmosphere with the higher layers of the atmosphere and the ionosphere. Taking into account the constant nature of the longitudinal features of the total electron content, an assumption was made about the important role of stationary planetary waves in the implementation of atmospheric-ionospheric interactions.
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Browne, S., B. Honary, and J. K. Hargreaves. "An imaging riometer for ionospheric studies." Electronics & Communication Engineering Journal 7, no. 5 (October 1, 1995): 209–17. http://dx.doi.org/10.1049/ecej:19950505.
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Santoso, Anwar, Buldan Muslim, and Siti Inayah Fitriyani. "DETEKSI EFEK GEMPABUMI PADA IONOSFER MENGGUNAKAN DATA GNSS." Komunikasi Fisika Indonesia 17, no. 1 (March 26, 2020): 1. http://dx.doi.org/10.31258/jkfi.17.1.1-6.
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Seismic activities such as earthquakes can cause atmospheric and infrared gravitational waves. If the earthquake happens to be strong enough (M> 6 SR), these waves can spread to the ionosphere altitude in the form of atmospheric and infrasonic gravitational waves. The monitoring system of ionospheric wave that associated with earthquakes from network of GNSS data has been much developed in Indonesia by using the sliding Fast Fourier Transform (SFFT) programfor disturbed ionospheric TEC positions. The results of previous studies, differential TEC showed irregular fluctuations in the order of several tens of seconds until to several tens of minutes with average amplitude less than 0.01 TECU. At times the ionospheric is not disturbed (regular), the amplitude can reaching greater than 0.01 TECU. As a case study, in this paper a methodological examination will be conducted on the events of Aceh earthquake on December 26, 2004 (M = 9.2 SR), Tohoku March 11, 2011 (M = 9 SR) and Yogyakarta May 27, 2006 (M = 6.2 SR).
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Grunwald, G., M. Bakuła, and A. Ciećko. "Study of EGNOS accuracy and integrity in eastern Poland." Aeronautical Journal 120, no. 1230 (June 20, 2016): 1275–90. http://dx.doi.org/10.1017/aer.2016.66.
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ABSTRACTThe ionosphere is one of the main factors affecting the accuracy and integrity of satellite-based augmentation system positioning systems. This paper presents the results of a 30-day study of the accuracy and integrity of the European Geostationary Navigation Overlay Service (EGNOS) conducted at the EPOD airport belonging to the Aeroclub of Warmia and Mazury in Olsztyn, in northeastern Poland (the area until recently considered as the edge of EGNOS coverage). Analyses of the parameters characterising the accuracy and integrity of positioning were performed in three calculation variants/modes: with the original EGNOS ionospheric correction, with correction determined by means of Klobuchar algorithm, and finally with modified ionospheric coefficients developed by the CODE. Studies have shown clearly that the original EGNOS ionospheric model gives the best integrity and accuracy results allowing to use EGNOS for approach with vertical guidance procedures, while the Center for Orbit Determination in Europe and Klobuchar models could only be used for non-precision approach operations.
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Amm, O. "Method of characteristics in spherical geometry applied to a Harang-discontinuity situation." Annales Geophysicae 16, no. 4 (April 30, 1998): 413–24. http://dx.doi.org/10.1007/s00585-998-0413-2.
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Abstract. The method of characteristics for obtaining spatial distributions of ionospheric electrodynamic parameters from ground-based spatial observations of the ground magnetic disturbance and the ionospheric electric field is presented in spherical geometry. The method includes tools for separation of the external magnetic disturbance, its continuation to the ionosphere, and calculation of ionospheric equivalent currents. Based on these and the measured electric field distribution, the ionospheric Hall conductance is calculated as the primary output of the method. By estimating the Hall- to-Pedersen conductance ratio distribution, the remaining ionospheric electrodynamic parameters are inferred. The method does not assume ∇×E=0 to allow to study time-dependent situations. The application of this method to a Harang discontinuity (HD) situation on 27 October 1977, 17:39 UT, reveals the following: (1) The conductances at and north of the HD are clearly reduced as compared to the eastern electrojet region. (2) Plasma flow across the HD is observed, but almost all horizontal current is diverted into upward-flowing field-aligned currents (FACs) there. (3) The FACs connected to the Hall currents form a latitudinally aligned sheet with a magnitude peak between the electrically and magnetically defined HD, where break-up arcs are often observed. Their magnitude is larger than that of the more uniformly distributed FACs connected to the Pedersen currents. They also cause the southward shift of the magnetically defined HD with respect to the electrically defined one. (4) A tilt of the HD with respect to geomagnetic latitude as proposed by an earlier study on the same event, which used composite vector plot technique, and by statistical studies, is not observed in our single time-step analysis.Key words. Ionosphere · Electric fields and currents · Instruments and techniques · Magnetospheric physics · Current systems
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Vaishnav, Rajesh, Christoph Jacobi, Jens Berdermann, Mihail Codrescu, and Erik Schmölter. "Role of eddy diffusion in the delayed ionospheric response to solar flux changes." Annales Geophysicae 39, no. 4 (July 12, 2021): 641–55. http://dx.doi.org/10.5194/angeo-39-641-2021.
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Abstract. Simulations of the ionospheric response to solar flux changes driven by the 27 d solar rotation have been performed using the global 3-D Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) physics-based numerical model. Using the F10.7 index as a proxy for solar extreme ultraviolet (EUV) variations in the model, the ionospheric delay at the solar rotation period is well reproduced and amounts to about 1 d, which is consistent with satellite and in situ measurements. From mechanistic CTIPe studies with reduced and increased eddy diffusion, we conclude that the eddy diffusion is an important factor that influences the delay of the ionospheric total electron content (TEC). We observed that the peak response time of the atomic oxygen to molecular nitrogen ratio to the solar EUV flux changes quickly during the increased eddy diffusion compared with weaker eddy diffusion. These results suggest that an increase in the eddy diffusion leads to faster transport processes and an increased loss rate, resulting in a decrease in the ionospheric time delay. Furthermore, we found that an increase in solar activity leads to an enhanced ionospheric delay. At low latitudes, the influence of solar activity is stronger because EUV radiation drives ionization processes that lead to compositional changes. Therefore, the combined effect of eddy diffusion and solar activity leads to a longer delay in the low-latitude and midlatitude region.
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Pulinets, Sergey. "Low-Latitude Atmosphere-Ionosphere Effects Initiated by Strong Earthquakes Preparation Process." International Journal of Geophysics 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/131842.
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Ionospheric and atmospheric anomalies registered around the time of strong earthquakes in low-latitude regions are reported now regularly. Majority of these reports have the character of case studies without clear physical mechanism proposed. Here we try to present the general conception of low-latitude effects using the results of the recent author’s publications, including also rethinking the earlier results interpreted basing on recently established background physical mechanisms of anomalies generation. It should be underlined that only processes initiated by earthquake preparation are considered. Segregation of low-latitude regions for special consideration is connected with the important role of ionospheric equatorial anomaly in the seismoionospheric coupling and specific character of low-latitude earthquake initiated effects. Three main specific features can be marked in low-latitude ionospheric anomalies manifestation: the presence of magnetic conjugacy in majority of cases, local longitudinal asymmetry of effects observed in ionosphere in relation to the vertical projection of epicenter onto ionosphere, and equatorial anomaly reaction even on earthquakes outside equatorial anomaly (i.e., 30–40 LAT). The equality of effects morphology regardless they observed over land or over sea implies only one possible explanation that these anomalies are initiated by gaseous emanations from the Earth crust, and radon plays the major role.