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1
Pandit, D., N. P. Chapagain, and B. Adhikari. "Study of Ionospheric Variability During Super Substorms." Journal of Nepal Physical Society 6, no. 2 (December 31, 2020): 74–84. http://dx.doi.org/10.3126/jnphyssoc.v6i2.34862.
Повний текст джерелаАнотація:
This paper study variability of three ionospheric parameters foF2, h′F and hmF2 to investigate the middle latitude ionospheric effect at Boulder, Colorado, USA (40°N, l105.0° W) during super substorms (SSSs) of 24 August 2005, and 7 September 2017 and 8 September 2017 respectively. Continuous wavelet transform (cwt) implemented to identify the low and high frequency and longer and shorter duration present in the signal. The result shows decrease in foF2 during SSSs of 24 August 2005 and 8 September 2017 and increase in foF2 during 7 September 2017. The highest fluctuation in h′F is noticed during SSS of 24 August 2005. The cwt shows that the coupling between solar wind and magnetosphere occurs between ~ 16 to 32 minutes for SSS of 24 August 2005 and between 27.9 to 64 minutes during super substorm of 7 and 8 September 2017 for all the ionospheric parameters respectively. This study leads to understand the impact of SSSs on communication signals due to energy injected in ionosphere during the coupling mechanism between magnetosphere-ionosphere.
2
Schmölter, Erik, Jens Berdermann, Norbert Jakowski, Christoph Jacobi, and Rajesh Vaishnav. "Delayed response of the ionosphere to solar EUV variability." Advances in Radio Science 16 (September 4, 2018): 149–55. http://dx.doi.org/10.5194/ars-16-149-2018.
Повний текст джерелаАнотація:
Abstract. Physical and chemical processes in the ionosphere are driven by complex interactions with the solar radiation. The ionospheric plasma is in particular sensitive to solar EUV and UV variations with a time delay between one and two days. This delay is assumed to be related to thermospheric transport processes from the lower ionosphere to the F region. In previous analyses, the delay has been investigated using the F10.7 index. Here we present preliminary results of the ionospheric delay based on a comprehensive and reliable database consisting of GNSS TEC Maps and EUV spectral flux data. We plan to specify the various dependencies from geographic/geomagnetic location, altitude, season, local time, geophysical and solar radiation conditions such as the solar activity level. The first results for dependencies from seasons and wavelengths regions of the EUV are presented in this paper. These results can provide more insight into ionospheric processes and are of interest for applications dependent on reliable ionospheric weather forecasts, e.g. GNSS error analyses, prediction and mitigation.
3
Wilkinson, P. J. "Ionospheric variability and the international reference ionosphere." Advances in Space Research 34, no. 9 (2004): 1853–59. http://dx.doi.org/10.1016/j.asr.2004.08.007.
Повний текст джерела
4
Danzer, J., S. B. Healy, and I. D. Culverwell. "A simulation study with a new residual ionospheric error model for GPS radio occultation climatologies." Atmospheric Measurement Techniques 8, no. 8 (August 21, 2015): 3395–404. http://dx.doi.org/10.5194/amt-8-3395-2015.
Повний текст джерелаАнотація:
Abstract. In this study, a new model was explored which corrects for higher order ionospheric residuals in Global Positioning System (GPS) radio occultation (RO) data. Recently, the theoretical basis of this new "residual ionospheric error model" has been outlined (Healy and Culverwell, 2015). The method was tested in simulations with a one-dimensional model ionosphere. The proposed new model for computing the residual ionospheric error is the product of two factors, one of which expresses its variation from profile to profile and from time to time in terms of measurable quantities (the L1 and L2 bending angles), while the other describes the weak variation with altitude. A simple integral expression for the residual error (Vorob’ev and Krasil’nikova, 1994) has been shown to be in excellent numerical agreement with the exact value, for a simple Chapman layer ionosphere. In this case, the "altitudinal" element of the residual error varies (decreases) by no more than about 25 % between ~10 and ~100 km for physically reasonable Chapman layer parameters. For other simple model ionospheres the integral can be evaluated exactly, and results are in reasonable agreement with those of an equivalent Chapman layer. In this follow-up study the overall objective was to explore the validity of the new residual ionospheric error model for more detailed simulations, based on modeling through a complex three-dimensional ionosphere. The simulation study was set up, simulating day and night GPS RO profiles for the period of a solar cycle with and without an ionosphere. The residual ionospheric error was studied, the new error model was tested, and temporal and spatial variations of the model were investigated. The model performed well in the simulation study, capturing the temporal variability of the ionospheric residual. Although it was not possible, due to high noise of the simulated bending-angle profiles at mid- to high latitudes, to perform a thorough latitudinal investigation of the performance of the model, first positive and encouraging results were found at low latitudes. Furthermore, first application tests of the model on the data showed a reduction in temperature level of the ionospheric residual at 40 km from about −2.2 to −0.2 K.
5
Danzer, J., S. B. Healy, and I. D. Culverwell. "A simulation study with a new residual ionospheric error model for GPS radio occultation climatologies." Atmospheric Measurement Techniques Discussions 8, no. 1 (January 27, 2015): 1151–76. http://dx.doi.org/10.5194/amtd-8-1151-2015.
Повний текст джерелаАнотація:
Abstract. In this study, a new model was explored, which corrects for higher order ionospheric residuals in global positioning system (GPS) radio occultation (RO) data. Recently, the theoretical basis of this new "residual ionospheric error model" has been outlined (Healy and Culverwell, 2015). The method was tested in simulations with a one-dimensional model ionosphere. The proposed new model for computing the residual ionospheric error is the product of two factors, one of which expresses its variation from profile-to-profile and from time-to-time in terms of measurable quantities (the L1 and L2 bending angles), the other of which describes the weak variation with altitude. A simple integral expression for the residual error (Vorob’ev and Krasil’nikova, 1994) has been shown to be in excellent numerical agreement with the exact value, for a simple Chapman layer ionosphere. In this case, the "altitudinal" element of the residual error varies (decreases) by no more than about 25% between ~10 and ~100 km for physically reasonable Chapman layer parameters. For other simple model ionospheres the integral can be evaluated exactly, and results are in reasonable agreement with those of an equivalent Chapman layer. In this follow-up study the overall objective was to explore the validity of the new residual ionospheric error model for more detailed simulations, based on modelling through a complex three-dimensional ionosphere. The simulation study was set up, simulating day and night GPS RO profiles for the period of a solar cycle with and without an ionosphere. The residual ionospheric error was studied, the new error model was tested, and temporal and spatial variations of the model were investigated. The model performed well in the simulation study, capturing the temporal variability of the ionospheric residual. Although, it was not possible, due to high noise of the simulated bending angle profiles at mid to high latitudes, to perform a thorough latitudinal investigation of the performance of the model, first positive and encouraging results were found at low latitudes. Furthermore, first application tests of the model on the data showed a reduction on temperature level of the ionospheric residual at 40 km from about −2.2 to −0.2 K.
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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.
Повний текст джерелаАнотація:
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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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.
Повний текст джерелаАнотація:
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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Zhang, S. R., and J. M. Holt. "Ionospheric climatology and variability from long-term and multiple incoherent scatter radar observations: variability." Annales Geophysicae 26, no. 6 (June 11, 2008): 1525–37. http://dx.doi.org/10.5194/angeo-26-1525-2008.
Повний текст джерелаАнотація:
Abstract. Long-term incoherent scatter radar (ISR) observations are used to study ionospheric variability for two midlatitude sites, Millstone Hill and St. Santin. This work is based on our prior efforts which resulted in an empirical model system, ISR Ionospheric Model (ISRIM), of climatology (and now variability) of the ionosphere. We assume that the variability can be expressed in three terms, the background, solar activity and geomagnetic activity components, each of which is a function of local time, season and height. So the background variability is ascribed mostly to the day-to-day variability arising from non solar and geomagnetic activity sources. (1) The background variability shows clear differences between the bottomside and the topside and changes with season. The Ne variability is low in the bottomside in summer, and high in the topside in winter and spring. The plasma temperature variability increases with height, and reaches a minimum in summer. Ti variability has a marked maximum in spring; at Millstone Hill it is twice as high as at St. Santin. (2) For enhanced solar activity conditions, the overall variability in Ne is reduced in the bottomside of the ionosphere and increases in the topside. For Te, the solar activity enhancement reduces the variability in seasons of high electron density (winter and equinox) at altitudes of high electron density (near the F2-peak). For Ti, however, while the variability tends to decrease at Millstone Hill (except for altitudes near 200 km), it increases at St. Santin for altitudes up to 350 km; the solar flux influence on the variability tends to be stronger at St. Santin than at Millstone Hill.
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Mielich, J., and J. Bremer. "A modified index for the description of the ionospheric short- and long-term activity." Annales Geophysicae 28, no. 12 (December 21, 2010): 2227–36. http://dx.doi.org/10.5194/angeo-28-2227-2010.
Повний текст джерелаАнотація:
Abstract. A modified ionospheric activity index AI has been developed on the basis of ionospheric foF2 observations. Such index can be helpful for an interested user to get information about the current state of the ionosphere. Using ionosonde data of the station Juliusruh (54.6° N; 13.4° E) this index has been tested for the time interval from January 1996 until December 2008. This index has no diurnal and seasonal variations, only a small positive dependence on the solar activity could be found. The variability of this index has, however, a marked seasonal variability with maxima during the equinoxes, a clear minimum in summer, and enhanced values in winter. The observed variability of AI is strongly correlated with the geomagnetic activity, most markedly during the equinoxes, whereas the influence of the solar activity is markedly smaller and mostly insignificant. Strong geomagnetic disturbances cause in middle latitudes in general negative disturbances in AI, mostly pronounced during equinoxes and summer and only partly during winter, thus in agreement with the current physical knowledge about ionospheric storms.
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Amabayo, Emirant Bertillas, Simon Katrini Anguma, and Edward Jurua. "Tracking the Ionospheric Response to the Solar Eclipse of November 03, 2013." International Journal of Atmospheric Sciences 2014 (October 23, 2014): 1–10. http://dx.doi.org/10.1155/2014/127859.
Повний текст джерелаАнотація:
The ionospheric dynamics is highly influenced by the solar radiation. During a solar eclipse, the moon occults the solar radiation from reaching the ionosphere, which may drastically affect the variability of the ionosphere. The variability of total electron content (TEC) observed by dual frequency Global Positioning System (GPS) receivers has made it possible to study effects of solar eclipse on the ionosphere. Total eclipse occurred on November 03, 2013, and the maximum amplitude was visible at Owiny in northern Uganda. Ionospheric behavior during this eclipse was analysed by using TEC data archived at Mbarara (MBAR), Malindi (MAL2), Eldoret (MOIU), and Kigali University (NURK) International GPS Satellite (IGS) stations. TEC variations of four consecutive days were used to study instantaneous changes of TEC during the eclipse event. The results generally show TEC decrease at the four stations. However, a maximum perturbation amplitude of ≥20 TECU was observed at MAL2 (18:00–20:00 UT) which is further south of the equator than the other stations. TEC enhancement and depletion were observed during the totality of the eclipse at MOIU, MBAR, NURK, and MAL2 (13:00–15:00 UT). This study found out that the ionospheric TEC over East Africa was modified by wave-like energy and momentum transport and obscuration of the solar disc due to the total solar eclipse.
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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.
Повний текст джерела
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Scott, Christopher J., and Patrick Major. "The ionospheric response over the UK to major bombing raids during World War II." Annales Geophysicae 36, no. 5 (September 26, 2018): 1243–54. http://dx.doi.org/10.5194/angeo-36-1243-2018.
Повний текст джерелаАнотація:
Abstract. The Earth's ionosphere is subject to disturbance from above (via solar variability and space-weather effects) and from below (such as tectonic activity, thunderstorms and sudden stratospheric warmings). Identifying the relative contribution of these effects remains challenging, despite recent advances in spacecraft monitoring near-Earth space. Man-made explosions provide a quantifiable proxy for natural terrestrial sources, enabling their impact on ionospheric variability to be studied. In this paper, the contribution of ground-based disturbances to ionospheric variability is investigated by considering the response of the ionospheric F2 layer over Slough, UK, to 152 major bombing raids over Europe during World War II, using a superposed epoch analysis. The median response of the F2 layer is a significant decrease in peak electron concentration (∼0.3 MHz decrease in foF2). This response is consistent with wave energy heating the thermosphere, enhancing the (temperature-dependent) loss rate of O+ ions. The analysis was repeated for a range of thresholds in both time of bombing before the (noon) ionospheric measurement and tonnage of bombs dropped per raid. It was found that significant (∼2–3σ) deviations from the mean occurred for events occurring between approximately 3 and 7 h ahead of the noon ionospheric measurements and for raids using a minimum of between 100 and 800 t of high explosives. The most significant ionospheric response (2.99σ) occurred for 20 raids up to 5 h before the ionospheric measurement, each with a minimum of 300 t of explosives. To ensure that the observed ionospheric response cannot be attributable to space-weather sources, the analysis was restricted to those events for which the geomagnetic Ap index was less than 48 (Kp<5). Digitisation of the early ionospheric data would enable the investigation into the response of additional ionospheric parameters (sporadic E, E and F1 layer heights and peak concentrations). One metric ton of TNT has an explosive energy of 4.184×109 J, which is of the same order of energy as a cloud to ground lightning stroke. Since the occurrence of lightning has distinctive diurnal and seasonal cycles, it is feasible that a similar mechanism could contribute to the observed seasonal anomaly in ionospheric F-region electron concentrations. Further investigation, using less extreme examples, is required to determine the minimum explosive energy required to generate a detectable ionospheric response.
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Chernigovskaya, Marina, Boris Shpynev, Denis Khabituev, Konstantin Ratovsky, Anastasiya Belinskaya, Aleksandr Stepanov, Vasily Bychkov, Svetlana Grigor'eva, Valery Panchenko, and Jens Mielich. "Studying the response of the mid-latitude ionosphere of the Northern Hemisphere to magnetic storms in March 2012." Solnechno-Zemnaya Fizika 8, no. 4 (December 24, 2022): 46–56. http://dx.doi.org/10.12737/szf-84202204.
Повний текст джерелаАнотація:
We have studied variations in ionospheric and geomagnetic parameters in the Northern Hemisphere during a series of magnetic storms in March 2012 by analyzing data from the Eurasian mid-latitude ionosonde chain, mid- and high-latitude chains of magnetometers of the global network INTERMAGNET. We have confirmed manifestations of the longitude inhomogeneity of ionospheric effects, which is associated with the irregular structure of the longitudinal variability of geomagnetic field components. The complex physics of the long magnetically disturbed period in March 2012 with switching between positive and negative phases of the ionospheric storm in the same period of the magnetic storm for different spatial regions is emphasized. The change in the effects of the ionospheric storm during this period might have been associated with the superposition in the mid-latitude region of the competing processes affecting the ionospheric ionization whose sources were in the auroral and equatorial ionosphere. We have compared the scenarios for the development of ionospheric disturbances under equinox conditions during magnetic storms in March 2012, October 2016, and March 2015.
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Chernigovskaya, Marina, Boris Shpynev, Denis Khabituev, Konstantin Ratovsky, Anastasiya Belinskaya, Aleksandr Stepanov, Vasily Bychkov, Svetlana Grigor'eva, Valery Panchenko, and Jens Mielich. "Studying the response of the mid-latitude ionosphere of the Northern Hemisphere to magnetic storms in March 2012." Solar-Terrestrial Physics 8, no. 4 (December 24, 2022): 44–54. http://dx.doi.org/10.12737/stp-84202204.
Повний текст джерелаАнотація:
We have studied variations in ionospheric and geomagnetic parameters in the Northern Hemisphere during a series of magnetic storms in March 2012 by analyzing data from the Eurasian mid-latitude ionosonde chain, mid- and high-latitude chains of magnetometers of the global network INTERMAGNET. We have confirmed manifestations of the longitude inhomogeneity of ionospheric effects, which is associated with the irregular structure of the longitudinal variability of geomagnetic field components. The complex physics of the long magnetically disturbed period in March 2012 with switching between positive and negative phases of the ionospheric storm in the same period of the magnetic storm for different spatial regions is emphasized. The change in the effects of the ionospheric storm during this period might have been associated with the superposition in the mid-latitude region of the competing processes affecting the ionospheric ionization whose sources were in the auroral and equatorial ionosphere. We have compared the scenarios for the development of ionospheric disturbances under equinox conditions during magnetic storms in March 2012, October 2016, and March 2015.
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Zhong, Jiahao, Jiuhou Lei, and Xinan Yue. "Comment on Choi et al. Correlation between Ionospheric TEC and the DCB Stability of GNSS Receivers from 2014 to 2016. Remote Sens. 2019, 11, 2657." Remote Sensing 12, no. 21 (October 24, 2020): 3496. http://dx.doi.org/10.3390/rs12213496.
Повний текст джерелаАнотація:
Choi et al. (2019) analyzed the correlation between the ionospheric total electron content (TEC) and the Global Navigation Satellite System (GNSS) receiver differential code bias (DCB) and concluded that the long-term variations of the receiver DCB are caused by the corresponding variations in the ionosphere. Unfortunately, their method is problematic, resulting in conclusions that are not useful. The long-term variations of the Global Positioning System (GPS) DCBs are primarily attributed to the GPS satellite replacement with different satellite block series under the zero-mean constraint condition, rather than the ionospheric variability.
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Silva, Weverton da Costa, та João Francisco Galera Monico. "GBAS: fundamentals and availability analysis according to σ vig". Journal of Geodetic Science 12, № 1 (1 січня 2022): 22–37. http://dx.doi.org/10.1515/jogs-2022-0132.
Повний текст джерелаАнотація:
Abstract Ground-based augmentation system (GBAS) was developed to guide aircraft precision approach and landing, aiming to replace the instrument landing system (ILS), which is currently used in most airports worldwide. GBAS based on differential positioning with reference stations that provide differential corrections to the aircraft to improve its positioning accuracy and ensure other performance parameters such as integrity, continuity, and availability. However, using GBAS in low latitude regions such as Brazil, the occurrence of ionospheric irregularities can affect global navigation satellite system (GNSS) performance so that it does not meet the requirements for aviation. This article evaluates five vertical ionospheric gradient variability scenarios for a GNSS data set of four reference stations, one station simulating an aircraft with GBAS in a static model based on performance requirements for Category Approach Type – CAT I. The results showed that the increase in the variability of the ionosphere and the geometry of satellites used in positioning could affect the integrity and availability of GBAS. In the scenario of more significant variability of the ionosphere evaluated, there was a loss of 38.4% of the availability of GBAS for the CAT I approach.
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Ogwala, Aghogho, Oluwole Johnson Oyedokun, Olugbenga Ogunmodimu, Andrew Ovie Akala, Masood Ashraf Ali, Punyawi Jamjareegulgarn, and Sampad Kumar Panda. "Longitudinal Variations in Equatorial Ionospheric TEC from GPS, Global Ionosphere Map and International Reference Ionosphere-2016 during the Descending and Minimum Phases of Solar Cycle 24." Universe 8, no. 11 (November 1, 2022): 575. http://dx.doi.org/10.3390/universe8110575.
Повний текст джерелаАнотація:
Research on longitudinal discrepancies in local ionospheric variability, especially in equatorial and low-latitude regions, is a focal point of interest for the space weather modeling community. The ionosphere over these regions is influenced by complex electrodynamics, wind, and temperature dynamics that can seriously impact dynamic technological systems such as satellite tracking and positioning, satellite radio communication, and navigation control systems. Here, we researched the longitudinal variability in the ionospheric total electron content (TEC) by analyzing observed global positioning system (GPS)-derived TEC values along with those extracted from the most reliable global ionospheric maps (GIMs) and the International Reference Ionosphere (IRI-2016) model at selected stations in the vicinity of the magnetic equator along the American, African, and Asian longitude sectors. The period of study covered the descending (2016–2017) and deep solar minimum (2018–2019) years in the 24th solar cycle. Apart from the decreasing trend of the TEC from the descending to deep solar minimum period irrespective of season and longitude sector, the results showed a relatively higher magnitude of TEC in the African longitude than the other two longitude sectors. Despite evident overestimation and underestimations of TEC in both models, GIM predictions generally looked better in terms of observed variation patterns, especially in the African longitude. The study also highlights the seasonal and semiannual effects of longitudinal variations in TEC, manifesting in local time offsets and some peculiar anomalies, which seemed to be different from previously reported results, especially during the solar minimum years at the three longitude sectors. The insignificant effects of longitudinal variations on the equinoctial asymmetry are attributed to the diverse electron density distribution and ionospheric morphology at the three longitude sectors that will prompt further investigations in the future. The outcomes from this study may augment the past efforts of scientists to understand the seasonal effects of the longitudinal variations in TEC, thereby complementing the improvements of ionospheric representations in global ionosphere models and maps.
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Bi, Cheng, Peng Ren, Ting Yin, Zheng Xiang, and Yang Zhang. "Modeling and Forecasting Ionospheric foF2 Variation in the Low Latitude Region during Low and High Solar Activity Years." Remote Sensing 14, no. 21 (October 28, 2022): 5418. http://dx.doi.org/10.3390/rs14215418.
Повний текст джерелаАнотація:
Prediction of ionospheric parameters, such as ionospheric F2 layer critical frequency (foF2) at low latitude regions is of significant interest in understanding ionospheric variation effects on high-frequency communication and global navigation satellite system. Currently, deep learning algorithms have made a striking accomplishment in capturing ionospheric variability. In this paper, we use the state-of-the-art hybrid neural network combined with a quantile mechanism to predict foF2 parameter variations under low and high solar activity years (solar cycle-24) and space weather events. The hybrid neural network is composed of a convolutional neural network (CNN) and bidirectional long short-term memory (BiLSTM), in which CNN and BiLSTM networks extracted spatial and temporal features of ionospheric variation, respectively. The proposed method was trained and tested on 5 years (2009–2014) of ionospheric foF2 observation data from Advanced Digital Ionosonde located in Brisbane, Australia (27°53′S, 152°92′E). It is evident from the results that the proposed model performs better than International Reference Ionosphere 2016 (IRI-2016), long short-term memory (LSTM), and BiLSTM ionospheric prediction models. The proposed model extensively captured the variation in ionospheric foF2 feature, and better predicted it under two significant space weather events (29 September 2011 and 22 July 2012).
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Shimhanda, S., S. Francis, and P. J. Cilliers. "Analysis of ionospheric Total Electron Content variability determined from Global Navigation Satellite System data." Namibian Journal for Research, Science and Technology 1, no. 1 (October 16, 2020): 3–9. http://dx.doi.org/10.54421/njrst.v1i1.4.
Повний текст джерелаАнотація:
Free electrons refract signals transmitted from satellites mainly during their trans-ionospheric propagation. The side-effect is the measured path length travelled by a signal is about five to fifteen meters longer than the actual path covered. Moreover, magnitudes of signal delays are directly proportional to the Total Electron Content (TEC). TEC is an ionospheric parameter indicating the total amount of electrons along a signal path between satellites and ground based receivers. This study was conducted because the TEC-induced ionospheric delay is themain error source in single frequency receivers. Hence, this study involved the extraction of TEC values from GNSS data with the Global Positioning System (GPS) TEC software to observe diurnal and seasonal variations of GNSS-TEC. Additionally, the study compared TEC plots of Windhoek(22.5741⁰S; 17.0894⁰E), Hermanus(South Africa, -34.42463056⁰S; 19.22306111⁰E), and Dakar(Senegal, 14.720903⁰N; -17.439503⁰W) to validate whether the ionospheric delay varies in accordance with the geographic location or not.Comparisons of observational GNSS-TEC and IRI-TEC derived from the IRI model were made to determine the accuracy of the IRI-model in the southern hemisphere. GNSS data were derived from a dual-frequency receiver installed at Windhoek (22.5741⁰S; 17.0894⁰E), Namibia. Results show that maximum TEC was prevalent in spring while minimum TEC generally occurred throughout winter. Moreover, results revealed that the International Reference Ionosphere (IRI) model overestimated GNSS-TEC in winter but underestimatedduring summer, autumn and spring.
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Bhattacharyya, Archana. "Equatorial Plasma Bubbles: A Review." Atmosphere 13, no. 10 (October 8, 2022): 1637. http://dx.doi.org/10.3390/atmos13101637.
Повний текст джерелаАнотація:
The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.
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Pulinets, S. A., T. B. Gaivoronska, A. Leyva Contreras, and L. Ciraolo. "Correlation analysis technique revealing ionospheric precursors of earthquakes." Natural Hazards and Earth System Sciences 4, no. 5/6 (November 15, 2004): 697–702. http://dx.doi.org/10.5194/nhess-4-697-2004.
Повний текст джерелаАнотація:
Abstract. In this paper we focus on the variability of electron concentration in the ionosphere measured by ground based ionosondes and GPS receivers around the time of strong earthquakes. It has been detected and statistically proven that several days before the seismic shock the level of this variability increases at the station closest to the epicenter, a fact which can be regarded as precursory phenomenon. More precisely the localness of this specific kind of ionospheric variability is used for the correlation analysis of data of several observation points. The similarity of geographical location of the observation points leads to the similarity of ionospheric variations registered at these sites during both quiet and disturbed geomagnetic conditions, except in the case of those located at the seismoactive zone. As a rule, the local anomalies in the F2 layer and TEC accompanying the preparation of strong earthquakes show themselves in the breaking of the mutual correlation of the critical frequencies foF2 or TEC between stations situated in and outside the seismic zone. The precursory phenomenon appears 1 to 7 days before the time of the seismic shock.
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Semenova, N. V., and A. G. Yahnin. "Diurnal behaviour of the ionospheric Alfvén resonator signatures as observed at high latitude observatory Barentsburg (<I>L</I>=15)." Annales Geophysicae 26, no. 8 (August 5, 2008): 2245–51. http://dx.doi.org/10.5194/angeo-26-2245-2008.
Повний текст джерелаАнотація:
Abstract. The signature of the ionospheric Alfvén resonator (IAR), so called spectral resonant structures (SRS) in the spectra of the electromagnetic noise in the range of 0.1–10 Hz is rather frequently observed with the search coil magnetometer at observatory Barentsburg on Svalbard (L=15). In this report we discuss some peculiarities of diurnal occurrence of SRS at this high latitude station. We show that the pronounced minimum of the SRS occurrence around noon can not be explained by the diurnal variations of the solar zenith angle (illumination of ionosphere). We conclude that the SRS occurrence minimum is the result of the enhanced variability of ionospheric parameters when the observing point enters (during the Earth's rotation) the region of the ionospheric projection of the dayside cusp and its vicinity.
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Klobuchar, John A., and Joseph M. Kunches. "Eye on the Ionosphere: The Spatial Variability of Ionospheric Range Delay." GPS Solutions 3, no. 3 (January 2000): 70–74. http://dx.doi.org/10.1007/pl00012808.
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Yasyukevich, Anna, and Artem Vesnin. "Comparative analysis of variability in the mid-latitude stratosphere and ionosphere in winter periods." Solar-Terrestrial Physics 8, no. 2 (June 30, 2022): 61–68. http://dx.doi.org/10.12737/stp-82202209.
Повний текст джерелаАнотація:
In this work, we perform a joint analysis of the spatial-temporal dynamics of ionospheric and stratospheric variability (with scales characteristic of internal gravity waves) at different longitudes of midlatitudes of the Northern Hemisphere. We analyze the winter periods of 2012–2013 and 2018–2019 when strong midwinter sudden stratospheric warmings (SSWs) occurred. An increase in the variability in the stratosphere is shown to occur in a limited latitude interval 40°–60° N in the region of existence of a winter circumpolar vortex. Under SSW conditions, the generation of wave disturbances in the stratosphere ceases manifesting itself in a significant decrease in the stratospheric variability index. Similar behavior is noted in the spatial-temporal dynamics of the index of the total electron content variability. The level of ionospheric variability at midlatitudes decreases significantly after SSW peaks. The decrease in the ionospheric variability can be explained by a reduction in wave generation in the stratosphere, associated with the destruction of the circumpolar vortex during SSWs
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Liu, Tong, Zhibin Yu, Zonghua Ding, Wenfeng Nie, and Guochang Xu. "Observation of Ionospheric Gravity Waves Introduced by Thunderstorms in Low Latitudes China by GNSS." Remote Sensing 13, no. 20 (October 15, 2021): 4131. http://dx.doi.org/10.3390/rs13204131.
Повний текст джерелаАнотація:
The disturbances of the ionosphere caused by thunderstorms or lightning events in the troposphere have an impact on global navigation satellite system (GNSS) signals. Gravity waves (GWs) triggered by thunderstorms are one of the main factors that drive short-period Travelling Ionospheric Disturbances (TIDs). At mid-latitudes, ionospheric GWs can be detected by GNSS signals. However, at low latitudes, the multi-variability of the ionosphere leads to difficulties in identifying GWs induced by thunderstorms through GNSS data. Though disturbances of the ionosphere during low-latitude thunderstorms have been investigated, the explicit GW observation by GNSS and its propagation pattern are still unclear. In this paper, GWs with periods from 6 to 20 min are extracted from band-pass filtered GNSS carrier phase observations without cycle-slips, and 0.2–0.8 Total Electron Content Unit (TECU) magnitude perturbations are observed when the trajectories of ionospheric pierce points fall into the perturbed region. The propagation speed of 102.6–141.3 m/s and the direction of the propagation indicate that the GWs are propagating upward from a certain thunderstorm at lower atmosphere. The composite results of disturbance magnitude, period, and propagation velocity indicate that GWs initiated by thunderstorms and propagated from the troposphere to the ionosphere are observed by GNSS for the first time in the low-latitude region.
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Ning, Yafei, and Jun Tang. "Study of ionospheric disturbances over the China mid- and low-latitude region with GPS observations." Annales Geophysicae 36, no. 1 (January 22, 2018): 81–89. http://dx.doi.org/10.5194/angeo-36-81-2018.
Повний текст джерелаАнотація:
Abstract. Ionospheric disturbances constitute the main restriction factor for precise positioning techniques based on global positioning system (GPS) measurements. Simultaneously, GPS observations are widely used to determine ionospheric disturbances with total electron content (TEC). In this paper, we present an analysis of ionospheric disturbances over China mid- and low-latitude area before and during the magnetic storm on 17 March 2015. The work analyses the variation of magnetic indices, the amplitude of ionospheric irregularities observed with four arrays of GPS stations and the influence of geomagnetic storm on GPS positioning. The results show that significant ionospheric TEC disturbances occurred between 10:30 and 12:00 UT during the main phase of the large storm, and the static position reliability for this period are little affected by these disturbances. It is observed that the positive and negative disturbances propagate southward along the meridian from mid-latitude to low-latitude regions. The propagation velocity is from about 200 to 700 m s−1 and the amplitude of ionospheric disturbances is from about 0.2 to 0.9 TECU min−1. Moreover, the position dilution of precession (PDOP) with static precise point positioning (PPP) on storm and quiet days is 1.8 and 0.9 cm, respectively. This study is based on the analysis of ionospheric variability with differential rate of vertical TEC (DROVT) and impact of ionospheric storm on positioning with technique of GPS PPP. Keywords. Ionosphere (ionospheric disturbances)
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Kouris, S. S., and D. N. Fotiadis. "Ionospheric variability: a comparative statistical study." Advances in Space Research 29, no. 6 (March 2002): 977–85. http://dx.doi.org/10.1016/s0273-1177(02)00045-5.
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Mendillo, Michael, Clara Narvaez, Marissa F. Vogt, Majd Mayyasi, Jeffrey Forbes, Marina Galand, Edward Thiemann, et al. "Sources of Ionospheric Variability at Mars." Journal of Geophysical Research: Space Physics 122, no. 9 (September 2017): 9670–84. http://dx.doi.org/10.1002/2017ja024366.
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Butcher, N. "Daily ionospheric forecasting service (DIFS) III." Annales Geophysicae 23, no. 12 (December 23, 2005): 3591–98. http://dx.doi.org/10.5194/angeo-23-3591-2005.
Повний текст джерелаАнотація:
Abstract. The daily variability of the ionosphere can greatly affect HF or SATCOM communications. HF skywave operators plan frequency schedules months in advance, however, they also require daily knowledge of the ionospheric conditions in order to modify assignments. SATCOM operators also require daily information about the levels of scintillation, which are variations in phase, amplitude, polarisation and angle of arrival that can cause severe degradation of the received signal. Using a number of ionosonde measurements and geomagnetic and solar values, a Daily Ionospheric Forecasting Service (DIFS) has been developed, which provides HF and SATCOM operators with daily forecasts of predicted ionospheric conditions. The system uses in-house algorithms and an externally developed Global Ionospheric Scintillation Model (GISM) to generate HF and SATCOM forecasts. HF forecasts consist of a past summary and a forecast section, primarily displaying observed values and predicted categories for the Maximum Usable Frequency (MUF), as well as an Ionospheric Correction factor (ICF) that can be fed into the ionospheric propagation prediction tool, WinHF. SATCOM forecasts give predictions of global scintillation levels, for the polar, mid and equatorial latitude regions. Thorough analysis was carried out on DIFS and the results conclude that the service gives good accuracy, with user feedback also confirming this, as well.
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Li, Haimeng, Jing-Song Wang, Zhou Chen, Lianqi Xie, Fan Li, and Tongji Zheng. "The Contribution of Geomagnetic Activity to Ionospheric foF2 Trends at Different Phases of the Solar Cycle by SWM." Atmosphere 11, no. 6 (June 11, 2020): 616. http://dx.doi.org/10.3390/atmos11060616.
Повний текст джерелаАнотація:
Solar activity dominates the temporal variability of ionospheric properties, which makes it difficult to identify and isolate the effects of geomagnetic activity on the ionosphere. Therefore, the latter effects on the ionosphere are still unclear. Here, we use the spectral whitening method (SWM)—a proven approach to extract ionospheric perturbations caused by geomagnetic activity—to directly obtain, in isolation, the effects of geomagnetic activity. We study its contribution to the ionosphere for different phases of the solar cycle. The time lag between the solar and geomagnetic activities provides an opportunity to understand the contribution of geomagnetic activity to the perturbation of the ionosphere. The results suggest that this contribution to the ionosphere is significant when geomagnetic activity is at its maximum level, which usually happens in the declining phase of the solar cycle, but the contribution is very weak at the solar minimum and during the ascending phase. Then, by analyzing the contributions in different months, we find that the role of geomagnetic activity is larger around winter but smaller around summer.
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Choi, Byung-Kyu, Dong-Hyo Sohn, and Sang Jeong Lee. "Reply to Comment on Choi et al. Correlation between Ionospheric TEC and the DCB Stability of GNSS Receivers from 2014 to 2016. Remote Sens. 2019, 11, 2657." Remote Sensing 12, no. 21 (October 26, 2020): 3510. http://dx.doi.org/10.3390/rs12213510.
Повний текст джерелаАнотація:
Choi et al. (2019) suggested that ionospheric total electron content (TEC) and receiver differential code bias (rDCB) stability have a strong correlation during a period of two years from 2014 to 2016. This article is a response to Zhong et al. (2020), who pointed out that the long-term variations of the GPS DCBs are mainly attributed to the satellite replacement rather than the ionospheric variability. In this issue, we investigated the center for orbit determination in Europe (CODE) Global Ionosphere Maps (GIM) products from 2000 to 2020. In this study, changes in TEC and receiver DCB (rDCB) root mean squares (RMS) at Bogota (BOGT) station still have a clear correlation. In addition, there was a moderate correlation between satellite DCB RMS and rDCB RMS. As a result, we suggest that rDCB can be affected simultaneously by GPS sDCB as well as ionospheric activity.
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Scott, C. J., and R. Stamper. "Global variation in the long-term seasonal changes observed in ionospheric F region data." Annales Geophysicae 33, no. 4 (April 8, 2015): 449–55. http://dx.doi.org/10.5194/angeo-33-449-2015.
Повний текст джерелаАнотація:
Abstract. Long-term variability has previously been observed in the relative magnitude of annual and semi-annual variations in the critical frequency (related to the peak electron concentration) of the ionospheric F2 layer (foF2). In this paper we investigate the global patterns in such variability by calculating the time varying power ratio of semi-annual to annual components seen in ionospheric foF2 data sequences from 77 ionospheric monitoring stations around the world. The temporal variation in power ratios observed at each station was then correlated with the same parameter calculated from similar epochs for the Slough/Chilton data set (for which there exists the longest continuous sequence of ionospheric data). This technique reveals strong regional variation in the data, which bears a striking similarity to the regional variation observed in long-term changes to the height of the ionospheric F2 layer. We argue that since both the height and peak density of the ionospheric F2 region are influenced by changes to thermospheric circulation and composition, the observed long-term and regional variability can be explained by such changes. In the absence of long-term measurements of thermospheric composition, detailed modelling work is required to investigate these processes.
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Yasyukevich, Anna, Irina Medvedeva, Vera Sivtseva, Marina Chernigovskaya, Petr Ammosov, and Galina Gavrilyeva. "Strong Interrelation between the Short-Term Variability in the Ionosphere, Upper Mesosphere, and Winter Polar Stratosphere." Remote Sensing 12, no. 10 (May 16, 2020): 1588. http://dx.doi.org/10.3390/rs12101588.
Повний текст джерелаАнотація:
We perform a joint analysis of short-period (up to several hours) variability in parameters of the ionosphere, the mesosphere, and the stratosphere at mid-latitude, subauroral, and high-latitude points for a long time interval. The study is based on the ionospheric total electron content (TEC) measurements and data on the OH rotational temperature at the mesopause height. We reveal similar seasonal variations in the dynamics of the short-term variability level, both in the ionosphere and the mesosphere. Maximum variability is observed during winter months and it exceeds the values in summer period up to 5–6 times. The revealed dynamics has no explicit relation to the levels of geomagnetic and solar activities. We suggest that the instabilities in the high-velocity stratospheric subauroral winter jet stream may be a source of the recorded variability seasonal variations in the ionosphere and the mesosphere. We propose a new index to estimate a short-term variability in the stratosphere. The index is shown to experience similar regular seasonal variations with a maximum during winter months. We show a clear correlation between the mesosphere/ionosphere variability indices values and the stratosphere disturbance index. The correlation is shown to be higher for the mesosphere variability index as compared with that in the ionosphere, and at the high-latitude point located closer to the jet stream. The obtained results indicate a strong interrelation between the short-period variability in the ionosphere, in the upper mesosphere, and in the subauroral stratosphere. The results contribute to elucidating the basic mechanisms for a vertical coupling between different atmospheric layers.
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Fagundes, P. R., Y. Sahai, I. S. Batista, M. A. Abdu, J. A. Bittencourt, and H. Takahashi. "Observations of day-to-day variability in precursor signatures to equatorial F-region plasma depletions." Annales Geophysicae 17, no. 8 (August 31, 1999): 1053–63. http://dx.doi.org/10.1007/s00585-999-1053-x.
Повний текст джерелаАнотація:
Abstract. In December 1995, a campaign was carried out to study the day-to-day variability in precursor signatures to large-scale ionospheric F-region plasma irregularities, using optical diagnostic techniques, near the magnetic equator in the Brazilian sector. Three instruments were operated simultaneously: (a) an all-sky (180° field of view) imaging system for observing the OI 630 nm nightglow emission at Alcântara (2.5°S, 44.4°W); (b) a digisonde (256-Lowell) at São Luis (2.6°S, 44.2°W); and (c) a multi-channel tilting filter-type zenith photometer for observing the OI 630 nm and mesospheric nightglow emissions at Fortaleza (3.9°S, 38.4°W). During the period December 14-18, 1995 (summer in the southern hemisphere), a good sequence of the OI 630 nm imaging observations on five consecutive nights were obtained, which are presented and discussed in this study. The observing period was geomagnetically quiet to moderate (Kp = 0+ to 5+; Dst = 18 nT to -37 nT). On four nights, out of the five observation nights, the OI 630 nm imaging pictures showed formations of transequatorial north-south aligned intensity depletions, which are the optical signatures of large-scale ionospheric F-region plasma bubbles. However, considerable day-to-day variability in the onset and development of the plasma depleted bands was observed. On one of the nights it appears that the rapid uplifting of the F-layer in the post-sunset period, in conjunction with gravity wave activity at mesospheric heights, resulted in generation of very strong plasma bubble irregularities. One of the nights showed an unusual formation of north-south depleted band in the western sector of the imaging system field of view, but the structure did not show any eastward movement, which is a normal characteristic of plasma bubbles. This type of irregularity structure, which probably can be observed only by wide-angle imaging system, needs more investigations for a better understanding of its behaviour.Key words. Atmospheric composition and structure (airglow and aurora) · Ionosphere (equatorial ionosphere; ionospheric irregularities)
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Taoufiq, Jouan, Bouziani Mourad, Azzouzi Rachid, and Christine Amory-Mazaudier. "Study of Ionospheric Variability Using GNSS Observations." Positioning 09, no. 04 (2018): 79–96. http://dx.doi.org/10.4236/pos.2018.94006.
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Forbes, J. M., X. Zhang, S. Palo, J. Russell, C. J. Mertens, and M. Mlynczak. "Tidal variability in the ionospheric dynamo region." Journal of Geophysical Research: Space Physics 113, A2 (February 2008): n/a. http://dx.doi.org/10.1029/2007ja012737.
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Anderson, Phillip C., and Jessica M. Hawkins. "Topside ionospheric response to solar EUV variability." Journal of Geophysical Research: Space Physics 121, no. 2 (February 2016): 1518–29. http://dx.doi.org/10.1002/2015ja021202.
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Opgenoorth, H. J., D. J. Andrews, M. Fränz, M. Lester, N. J. T. Edberg, D. Morgan, F. Duru, O. Witasse, and A. O. Williams. "Mars ionospheric response to solar wind variability." Journal of Geophysical Research: Space Physics 118, no. 10 (October 2013): 6558–87. http://dx.doi.org/10.1002/jgra.50537.
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Araujo-Pradere, E. A., T. J. Fuller-Rowell, and D. Bilitza. "Ionospheric variability for quiet and perturbed conditions." Advances in Space Research 34, no. 9 (2004): 1914–21. http://dx.doi.org/10.1016/j.asr.2004.06.007.
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Calabia, Andres, Chukwuma Anoruo, Munawar Shah, Christine Amory-Mazaudier, Yury Yasyukevich, Charles Owolabi, and Shuanggen Jin. "Low-Latitude Ionospheric Responses and Coupling to the February 2014 Multiphase Geomagnetic Storm from GNSS, Magnetometers, and Space Weather Data." Atmosphere 13, no. 4 (March 24, 2022): 518. http://dx.doi.org/10.3390/atmos13040518.
Повний текст джерелаАнотація:
The ionospheric response and the associated mechanisms to geomagnetic storms are very complex, particularly during the February 2014 multiphase geomagnetic storm. In this paper, the low-latitude ionosphere responses and their coupling mechanisms, during the February 2014 multiphase geomagnetic storm, are investigated from ground-based magnetometers and global navigation satellite system (GNSS), and space weather data. The residual disturbances between the total electron content (TEC) of the International GNSS Service (IGS) global ionospheric maps (GIMs) and empirical models are used to investigate the storm-time ionospheric responses. Three clear sudden storm commencements (SSCs) on 15, 20, and 23 February are detected, and one high speed solar wind (HSSW) event on 19 February is found with the absence of classical SSC features due to a prevalent magnetospheric convection. The IRI-2012 shows insufficient performance, with no distinction between the events and overestimating approximately 20 TEC units (TECU) with respect to the actual quiet-time TEC. Furthermore, the median average of the IGS GIMs TEC during February 2014 shows enhanced values in the southern hemisphere, whereas the IRI-2012 lacks this asymmetry. Three low-latitude profiles extracted from the IGS GIM data revealed up to 20 TECU enhancements in the differential TEC. From these profiles, longer-lasting TEC enhancements are observed at the dip equator profiles than in the profiles of the equatorial ionospheric anomaly (EIA) crests. Moreover, a gradual increase in the global electron content (GEC) shows approximately 1 GEC unit of differential intensification starting from the HSSW event, while the IGS GIM profiles lack this increasing gradient, probably located at higher latitudes. The prompt penetration electric field (PPEF) and equatorial electrojet (EEJ) indices estimated from magnetometer data show strong variability after all four events, except the EEJ’s Asian sector. The low-latitude ionosphere coupling is mainly driven by the variable PPEF, DDEF (disturbance dynamo electric fields), and Joule heating. The auroral electrojet causing eastward PPEF may control the EIA expansion in the Asian sector through the dynamo mechanism, which is also reflected in the solar-quiet current intensity variability.
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Fuller-Rowell, T. J., M. C. Codrescu, and P. Wilkinson. "Quantitative modeling of the ionospheric response to geomagnetic activity." Annales Geophysicae 18, no. 7 (July 31, 2000): 766–81. http://dx.doi.org/10.1007/s00585-000-0766-7.
Повний текст джерелаАнотація:
Abstract. A physical model of the coupled thermosphere and ionosphere has been used to determine the accuracy of model predictions of the ionospheric response to geomagnetic activity, and assess our understanding of the physical processes. The physical model is driven by empirical descriptions of the high-latitude electric field and auroral precipitation, as measures of the strength of the magnetospheric sources of energy and momentum to the upper atmosphere. Both sources are keyed to the time-dependent TIROS/NOAA auroral power index. The output of the model is the departure of the ionospheric F region from the normal climatological mean. A 50-day interval towards the end of 1997 has been simulated with the model for two cases. The first simulation uses only the electric fields and auroral forcing from the empirical models, and the second has an additional source of random electric field variability. In both cases, output from the physical model is compared with F-region data from ionosonde stations. Quantitative model/data comparisons have been performed to move beyond the conventional "visual" scientific assessment, in order to determine the value of the predictions for operational use. For this study, the ionosphere at two ionosonde stations has been studied in depth, one each from the northern and southern mid-latitudes. The model clearly captures the seasonal dependence in the ionospheric response to geomagnetic activity at mid-latitude, reproducing the tendency for decreased ion density in the summer hemisphere and increased densities in winter. In contrast to the "visual" success of the model, the detailed quantitative comparisons, which are necessary for space weather applications, are less impressive. The accuracy, or value, of the model has been quantified by evaluating the daily standard deviation, the root-mean-square error, and the correlation coefficient between the data and model predictions. The modeled quiet-time variability, or standard deviation, and the increases during geomagnetic activity, agree well with the data in winter, but is low in summer. The RMS error of the physical model is about the same as the IRI empirical model during quiet times. During the storm events the RMS error of the model improves on IRI, but there are occasionally false-alarms. Using unsmoothed data over the full interval, the correlation coefficients between the model and data are low, between 0.3 and 0.4. Isolating the storm intervals increases the correlation to between 0.43 and 0.56, and by smoothing the data the values increases up to 0.65. The study illustrates the substantial difference between scientific success and a demonstration of value for space weather applications.Key words: Ionosphere (ionospheric disturbances; mid-latitude ionosphere; modeling and forecasting)
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Chen, Yiding, Libo Liu, Huijun Le, Hui Zhang, and Ruilong Zhang. "Responding trends of ionospheric F2-layer to weaker geomagnetic activities." Journal of Space Weather and Space Climate 12 (2022): 6. http://dx.doi.org/10.1051/swsc/2022005.
Повний текст джерелаАнотація:
Geomagnetic activities frequently occur in varying degrees. Strong geomagnetic activities, which have been widely investigated, occur occasionally; they can cause distinguishable and significant disturbances in the ionosphere. Weaker geomagnetic activities frequently appear, whereas their effects are generally difficult to be distinguished from complex ionospheric variations. Weaker geomagnetic activities play important roles in ionospheric day-to-day variability thus should deserve further attention. In this study, long-term (longer than one solar cycle) measurements of the F2-layer critical frequency (foF2) were collected to statistically investigate ionospheric responses to weaker geomagnetic activities (Ap < 60). The responding trends of low- to high-latitude foF2 to increasing geomagnetic activity are presented for the first time; they are statistically evident. Both increasing and decreasing trends can occur, depending on latitudes and seasons. The trend gradually transits from high-latitude decreasing trends to equatorial increasing trends with decreasing latitude, and this transition is seasonally dependent. As a result, the trend has a seasonal difference at mid-latitudes. The responding trend is generally more distinct at higher latitudes and in the equatorial region than at mid-latitudes, and the responding intensity is largest at higher latitudes. Although theoretically, geomagnetic activities can disturb the ionosphere through multiple mechanisms, the morphology of the trend suggests that the frequent weaker geomagnetic activities modulate the high- to low-latitude ionosphere mainly through disturbing high-latitude thermospheric composition and further altering the thermospheric background circulation.
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Gulyaeva, T. L., I. Stanislwska, and M. Tomasik. "Ionospheric weather: cloning missed foF2 observations for derivation of variability index." Annales Geophysicae 26, no. 2 (February 26, 2008): 315–21. http://dx.doi.org/10.5194/angeo-26-315-2008.
Повний текст джерелаАнотація:
Abstract. A techique for filling the gaps of the missing F2-layer critical frequency is proposed and applied for the derivation of the ionospheric weather index, characterizing the degree of disturbance at each particular station. A daily-hourly analysis of ionosonde observations of foF2 for 16 stations at latitude range 37° to 70° N, longitudes of 10° W to 150° E, is performed during the solar minimum, 2006. Missed ionosonde observations are reconstructed by cloning data of another station. The process of gap filling considers hourly values of the F peak density NmF2 (deduced from foF2), normalized to the respective median, and assumes that this ratio remains the same for the parent and cloned data. It is shown that the correlation coefficient between cloned fcF2 and observed foF2 is greater than 0.75 for the positive and negative ionospheric disturbed days during a year at solar minimum, independent of the distance between the stations in high and middle latitudes. The quiet reference is determined as a running daily-hourly median for 27 days, preceding the day of observation calibrated for a seasonal trend with ITU-R foF2 predictions. The hourly deviation DNmF2 is defined as the logarithm of ratio of NmF2/NmF2med. A segmented logarithmic scale of the ionospheric weather index, W, is introduced, so that W=±1 refers to the quiet state, W=±2 to a moderate disturbance, W=±3 to the ionospheric storm, and W=±4 to the extreme or anomalous conditions. The catalog of the ionospheric disturbances for W exceeding ±2 at least during 3 consecutive hours is produced and presented online at the SRC and IZMIRAN web pages. It is found that the moderate disturbance is a prevailing state of the ionospheric weather for all stations. The stormy conditions comprise 1 to 20% of the times which occur more frequently at high latitudes, by night, during equinox and winter.
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Koucká Knížová, Petra, Kateřina Podolská, Kateřina Potužníková, Daniel Kouba, Zbyšek Mošna, Josef Boška, and Michal Kozubek. "Evidence of vertical coupling: meteorological storm Fabienne on 23 September 2018 and its related effects observed up to the ionosphere." Annales Geophysicae 38, no. 1 (January 17, 2020): 73–93. http://dx.doi.org/10.5194/angeo-38-73-2020.
Повний текст джерелаАнотація:
Abstract. A severe meteorological storm system on the frontal border of cyclone Fabienne passing above central Europe was observed on 23–24 September 2018. Large meteorological systems are considered to be important sources of the wave-like variability visible/detectable through the atmosphere and even up to ionospheric heights. Significant departures from regular courses of atmospheric and ionospheric parameters were detected in all analyzed datasets through atmospheric heights. Above Europe, stratospheric temperature and wind significantly changed in coincidence with fast frontal transition (100–110 km h−1). Zonal wind at 1 and 0.1 hPa changes from the usual westward before the storm to eastward after the storm. With this change are connected changes in temperature where at 1 hPa the analyzed area is colder and at 0.1 hPa warmer. Within ionospheric parameters, we have detected significant wave-like activity occurring shortly after the cold front crossed the observational point. During the storm event, both by Digisonde DPS-4D and continuous Doppler sounding equipment, we have observed strong horizontal plasma flow shears and time-limited increase plasma flow in both the northern and western components of ionospheric drift. The vertical component of plasma flow during the storm event is smaller with respect to the corresponding values on preceding days. The analyzed event of an exceptionally fast cold front of cyclone Fabienne fell into the recovery phase of a minor–moderate geomagnetic storm observed as a negative ionospheric storm at European mid-latitudes. Hence, ionospheric observations consist both of disturbances induced by moderate geomagnetic storms and effects originating in convective activity in the troposphere. Nevertheless, taking into account a significant change in the global circulation pattern in the stratosphere, we conclude that most of the observed wave-like oscillations in the ionosphere during the night of 23–24 September can be directly attributed to the propagation of atmospheric waves launched on the frontal border (cold front) of cyclone Fabienne. The frontal system acted as an effective source of atmospheric waves propagating upward up to the ionosphere.
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Verkhoglyadova, O. P., B. T. Tsurutani, A. J. Mannucci, M. G. Mlynczak, L. A. Hunt, and T. Runge. "Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers." Annales Geophysicae 31, no. 2 (February 19, 2013): 263–76. http://dx.doi.org/10.5194/angeo-31-263-2013.
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Abstract. We study solar wind–ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) – 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and mid-latitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10–22 October 2003, was analyzed for comparative purposes, with daytime low-latitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008–2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008–2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind–ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind–ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals.
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Marchand, R., and J. J. Berthelier. "Simple model for post seismic ionospheric disturbances above an earthquake epicentre and along connecting magnetic field lines." Natural Hazards and Earth System Sciences 8, no. 6 (December 8, 2008): 1341–47. http://dx.doi.org/10.5194/nhess-8-1341-2008.
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Abstract. The detection of ionospheric disturbances associated with seismic activity is one of the main objectives of the DEMETER micro-satellite. Its scientific payload provides a comprehensive set of electron and ion measurements. The present work describes a simple model of post-seismic disturbances in the ionosphere above the epicentre. Following a major seism, the neutral atmosphere is assumed to be subject to an acoustic pulse propagating upward, to high altitudes. By coupling this perturbation to the two-dimensional ionospheric model SAMI2 it is then possible to calculate the variations in a number of plasma parameters in the plume region and along connecting magnetic field lines, for an event of representative magnitude. The feasibility of identifying the signature of seismic events from satellite observations is then assessed in view of representative DEMETER measurements and of their natural variability.
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Béniguel, Yannick, Iurii Cherniak, Alberto Garcia-Rigo, Pierrick Hamel, Manuel Hernández-Pajares, Roland Kameni, Anton Kashcheyev, et al. "MONITOR Ionospheric Network: two case studies on scintillation and electron content variability." Annales Geophysicae 35, no. 3 (March 13, 2017): 377–91. http://dx.doi.org/10.5194/angeo-35-377-2017.
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Abstract. The ESA MONITOR network is composed of high-frequency-sampling global navigation satellite systems (GNSS) receivers deployed mainly at low and high latitudes to study ionosphere variability and jointly with global GNSS data and ionospheric processing software in support of the GNSS and its satellite-based augmentation systems (SBAS) like the European EGNOS. In a recent phase of the project, the network was merged with the CNES/ASECNA network and new receivers were added to complement the latter in the western African sector. This paper summarizes MONITOR, presenting two case studies on scintillations (using almost 2 years of data measurements). The first case occurred during the major St. Patrick's Day geomagnetic storm in 2015. The second case study was performed in the last phase of the project, which was supported by ESA EGNOS Project Office, when we paid special attention to extreme events that might degrade the system performance of the European EGNOS.
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Scott, C. J., R. Stamper, and H. Rishbeth. "Long-term changes in thermospheric composition inferred from a spectral analysis of ionospheric F-region data." Annales Geophysicae 32, no. 2 (February 17, 2014): 113–19. http://dx.doi.org/10.5194/angeo-32-113-2014.
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Abstract. A study of ionospheric data recorded at Slough/Chilton, UK, from 1935 to 2012, has revealed long-term changes in the relative strength of the annual and semi-annual variability in the ionospheric F2 layer critical frequencies. Comparing these results with data from the southern hemisphere station at Stanley in the Falkland Islands between 1945 and 2012 reveals a trend that appears to be anti-correlated with that at Chilton. The behaviour of foF2 is a function of thermospheric composition and so we argue that the observed long-term changes are driven by composition change. The ionospheric trends share some of their larger features with the trend in the variability of the aa geomagnetic index. Changes to the semi-annual/annual ratio in the Slough/Chilton and Stanley data may therefore be attributable to the variability in geomagnetic activity which controls the average latitudinal extent of the auroral ovals and subsequent thermospheric circulation patterns. Changes in ionospheric composition or thermospheric wind patterns are known to influence the height of the F2 layer at a given location. Long-term changes to the height of the F2 layer have been used to infer an ionospheric response to greenhouse warming. We suggest that our observations may influence such measurements and since the results appear to be dependent on geomagnetic longitude, this could explain why the long-term drifts observed in F2 layer height differ between locations.
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Akala, A. O., A. B. Adeloye, and E. O. Somoye. "Ionospheric foF2 variability over the Southeast Asian sector." Journal of Geophysical Research: Space Physics 115, A9 (September 2010): n/a. http://dx.doi.org/10.1029/2010ja015250.
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Mendillo, Michael, Clara Narvaez, Paul Withers, Majd Matta, Wlodek Kofman, and Jeremie Mouginot. "Variability in ionospheric total electron content at Mars." Planetary and Space Science 86 (September 2013): 117–29. http://dx.doi.org/10.1016/j.pss.2013.08.010.
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