Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Ionospheric variations.
Artykuły w czasopismach na temat „Ionospheric variations”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych artykułów w czasopismach naukowych na temat „Ionospheric variations”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj artykuły w czasopismach z różnych dziedzin i twórz odpowiednie bibliografie.
1
Trigunait, A., M. Parrot, S. Pulinets i F. Li. "Variations of the ionospheric electron density during the Bhuj seismic event". Annales Geophysicae 22, nr 12 (22.12.2004): 4123–31. http://dx.doi.org/10.5194/angeo-22-4123-2004.
Pełny tekst źródłaStreszczenie:
Abstract. Ionospheric perturbations by natural geophysical activity, such as volcanic eruptions and earthquakes, have been studied since the great Alaskan earthquake in 1964. Measurements made from the ground show a variation of the critical frequency of the ionosphere layers before and after the shock. In this paper, we present an experimental investigation of the electron density variations around the time of the Bhuj earthquake in Gujarat, India. Several experiments have been used to survey the ionosphere. Measurements of fluctuations in the integrated electron density or TEC (Total Electron Content) between three satellites (TOPEX-POSEIDON, SPOT2, SPOT4) and the ground have been done using the DORIS beacons. TEC has been also evaluated from a ground-based station using GPS satellites, and finally, ionospheric data from a classical ionospheric sounder located close to the earthquake epicenter are utilized. Anomalous electron density variations are detected both in day and night times before the quake. The generation mechanism of these perturbations is explained by a modification of the electric field in the global electric circuit induced during the earthquake preparation. Key words. Ionosphere (ionospheric disturbances) – Radio Science (ionospheric physics) – History of geophysics (seismology)
2
Altadill, D. "On the 18-day quasi-periodic oscillation in the ionosphere". Annales Geophysicae 14, nr 7 (31.07.1996): 716–24. http://dx.doi.org/10.1007/s00585-996-0716-0.
Pełny tekst źródłaStreszczenie:
Abstract. The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.
3
Danzer, J., S. B. Healy i I. D. Culverwell. "A simulation study with a new residual ionospheric error model for GPS radio occultation climatologies". Atmospheric Measurement Techniques 8, nr 8 (21.08.2015): 3395–404. http://dx.doi.org/10.5194/amt-8-3395-2015.
Pełny tekst źródłaStreszczenie:
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.
4
Danzer, J., S. B. Healy i I. D. Culverwell. "A simulation study with a new residual ionospheric error model for GPS radio occultation climatologies". Atmospheric Measurement Techniques Discussions 8, nr 1 (27.01.2015): 1151–76. http://dx.doi.org/10.5194/amtd-8-1151-2015.
Pełny tekst źródłaStreszczenie:
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.
5
Håkansson, Martin. "Nadir-Dependent GNSS Code Biases and Their Effect on 2D and 3D Ionosphere Modeling". Remote Sensing 12, nr 6 (19.03.2020): 995. http://dx.doi.org/10.3390/rs12060995.
Pełny tekst źródłaStreszczenie:
Recent publications have shown that group delay variations are present in the code observables of the BeiDou system, as well as to a lesser degree in the code observables of the global positioning system (GPS). These variations could potentially affect precise point positioning, integer ambiguity resolution by the Hatch–Melbourne–Wübbena linear combination, and total electron content estimation for ionosphere modeling from global navigation satellite system (GNSS) observations. The latter is an important characteristic of the ionosphere and a prerequisite in some applications of precise positioning. By analyzing the residuals from total electron content estimation, the existence of group delay variations was confirmed by a method independent of the methods previously used. It also provides knowledge of the effects of group delay variations on ionosphere modeling. These biases were confirmed both for two-dimensional ionosphere modeling by the thin shell model, as well as for three-dimensional ionosphere modeling using tomographic inversion. BeiDou group delay variations were prominent and consistent in the residuals for both the two-dimensional and three-dimensional case of ionosphere modeling, while GPS group delay variations were smaller and could not be confirmed due to the accuracy limitations of the ionospheric models. Group delay variations were, to a larger extent, absorbed by the ionospheric model when three-dimensional ionospheric tomography was performed in comparison with two-dimensional modeling.
6
Pushin, V. F., i L. F. Chernogor. "A SYNTHESIS OF TEMPORAL VARIATIONS IN DOPPLER SPECTRA RECORDED AT A QUASI-VERTICAL INCIDENCE BY THE HF DOPPLER RADAR WITH SPACED RECEIVERS". Radio physics and radio astronomy 26, nr 3 (14.09.2021): 211–23. http://dx.doi.org/10.15407/rpra26.03.211.
Pełny tekst źródłaStreszczenie:
Purpose: The ionospheric channel is widely used for the communication, radio navigation, radar, direction finding, radio astronomy, and remote radio probing systems. The radio channel parameters are characterized by nonstationarity due to the dynamic processes in the ionosphere, and therefore their study is one of the topical problems of space radio physics and earth-space radio physics of geospace. This work aims at presenting the results of synthesis of temporal variations in the Doppler spectra obtained by the Doppler probing of the ionosphere at vertical and quasi-vertical incidence. Design/methotology/approach: One of the most effective methods of ionosphere research is the Doppler sounding technique. It has a high time resolution (about 10 s), a Doppler shift resolution (0.01–0.1 Hz), and the accuracy of Doppler shift measurements (~0.01 Hz) that permits monitoring the variations in the ionospheric electron density (10–4–10–3) or the study of the ionospheric plasma motion with the speed of 0.1-1 m/s and greater. The solution of the inverse radio physical problem, consisting in determination of the ionosphere parameters, often means solving the direct radio physical problem. In the Doppler sounding technique, it belongs with the construction of variations in Doppler spectra and comparing them with the Doppler spectra measurements. Findings: For the radio wave ordinary component, three echoes being produced by three rays are observed. Influence of the geomagnetic fi eld and large horizontal gradients in the electron density of δ≥10 % give rise to complex ray structures with caustic surfaces. The ionospheric disturbances traveling along the magnetic meridian form the skip zones. The longitudinal and transverse displacement of the ray reflection point attains a few tens of kilometers along the vil. Haidary to vil. Hrakove quasi-vertical radiowave propagation path, for which the great circle range is 50 km. For the vertical incidence, the signal azimuth at the receiver coincides with the traveling ionospheric disturbance azimuth. The synthesis of temporal variations in the HF Doppler spectra has been made and compared with the temporal variations in the Doppler spectra recorded with the V. N. Karazin Kharkiv National University radar. The estimate of δ=15 % obtained confirms the existence of large horizontal gradients in electron density. Conclusions: Temporal variations in Doppler spectra and in azimuth have been calculated for the vertical and quasi-vertical incidence with allowance for large horizontal gradients of the electron density caused by traveling ionospheric disturbances. Key words: ionosphere, Doppler sounding at oblique incidence, synthesis of temporal variations in HF Doppler spectra, traveling ionospheric disturbances, electron density
7
J. E., Thomas,, George, N. J., Ekanem, A.M i Akpan, A. E. "IONOSPHERIC PLASMA VARIATIONS AFORE THE EAST OF KURIL ISLANDS EARTHQUAKE OF 13th JANUARY, 2007". Geological Behavior 4, nr 1 (4.08.2020): 42–46. http://dx.doi.org/10.26480/gbr.01.2020.42.46.
Pełny tekst źródłaStreszczenie:
Plasma Analyzer (IAP) and Langmuir Probe (ISL) experiments of the DEMETER microsatellite were used to check the state of the ionosphere in the region of the M8.1 East of Kuril Islands earthquake of 13th January, 2007,30 days afore and 10 days after the event using statistical approach. The study strongly revealed that all three investigated ionospheric parameters of electron density, total ion density and electron temperature displayed unfamiliar ionospheric variations eight days before the earthquake in the daytime time half orbit measurement. To this, the electron density, total ion density and electron temperature recorded a variation of 4.09, 5.73 and -2.03 respectively. These irregularities were vetted for untrue signals using the geomagnetic indices of Kp and Dst. It was however realized that the state of the ionosphere was geomagnetically quiet during this day, hence the observed variations were seismogenic.
8
Bi, Cheng, Peng Ren, Ting Yin, Zheng Xiang i Yang Zhang. "Modeling and Forecasting Ionospheric foF2 Variation in the Low Latitude Region during Low and High Solar Activity Years". Remote Sensing 14, nr 21 (28.10.2022): 5418. http://dx.doi.org/10.3390/rs14215418.
Pełny tekst źródłaStreszczenie:
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).
9
Xi, Hui, Hu Jiang, Jiachun An, Zemin Wang, Xueyong Xu, Houxuan Yan i Can Feng. "Spatial and Temporal Variations of Polar Ionospheric Total Electron Content over Nearly Thirteen Years". Sensors 20, nr 2 (19.01.2020): 540. http://dx.doi.org/10.3390/s20020540.
Pełny tekst źródłaStreszczenie:
It is of great significance for the global navigation satellite system (GNSS) service to detect the polar ionospheric total electron content (TEC) and its variations, particularly under disturbed ionosphere conditions, including different phases of solar activity, the polar day and night alternation, the Weddell Sea anomaly (WSA) as well as geomagnetic storms. In this paper, four different models are utilized to map the ionospheric TEC over the Arctic and Antarctic for about one solar cycle: the polynomial (POLY) model, the generalized trigonometric series function (GTSF) model, the spherical harmonic (SH) model, and the spherical cap harmonic (SCH) model. Compared to other models, the SCH model has the best performance with ±0.8 TECU of residual mean value and 1.5–3.5 TECU of root mean square error. The spatiotemporal distributions and variations of the polar ionospheric TEC are investigated and compared under different ionosphere conditions in the Arctic and Antarctic. The results show that the solar activity significantly affects the TEC variations. During polar days, the ionospheric TEC is more active than it is during polar nights. In polar days over the Antarctic, the maximum value of TEC always appears at night in the Antarctic Peninsula and Weddell Sea area affected by the WSA. In the same year, the ionospheric TEC of the Antarctic has a larger amplitude of annual variation than that of the TEC in the Arctic. In addition, the evolution of the ionization patch during a geomagnetic storm over the Antarctic can be clearly tracked employing the SCH model, which appears to be adequate for mapping the polar TEC, and provides a sound basis for further automatic identification of ionization patches.
10
Vaishnav, Rajesh, Christoph Jacobi, Jens Berdermann, Erik Schmölter i Mihail Codrescu. "Ionospheric response to solar EUV variations: Preliminary results". Advances in Radio Science 16 (4.09.2018): 157–65. http://dx.doi.org/10.5194/ars-16-157-2018.
Pełny tekst źródłaStreszczenie:
Abstract. We investigate the ionospheric response to solar Extreme Ultraviolet (EUV) variations using different proxies, based on solar EUV spectra observed from the Solar Extreme Ultraviolet Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, the F10.7 index (solar irradiance at 10.7 cm), and the Bremen composite Mg-II index during January 2003 to December 2016. The daily mean solar proxies are compared with global mean Total Electron Content (GTEC) values calculated from global IGS TEC maps. The preliminary analysis shows a significant correlation between GTEC and both the integrated flux from SEE and the Mg II index, while F10.7 correlates less strongly with GTEC. The correlations of EUV proxies and GTEC at different time periods are presented. An ionospheric delay in GTEC is observed at the 27 days solar rotation period with the time scale of about ∼1–2 days. An experiment with the physics based global 3-D Coupled Thermosphere/Ionosphere Plasmasphere electrodynamics (CTIPe) numerical model was performed to reproduce the ionospheric delay. Model simulations were performed for different values of the F10.7 index while keeping all the other model inputs constant. Preliminary results qualitatively reproduce the observed ∼1–2 days delay in GTEC, which is might be due to vertical transport processes.
11
Pimenta, A. A., P. R. Fagundes, Y. Sahai, J. A. Bittencourt i J. R. Abalde. "Equatorial F-region plasma depletion drifts: latitudinal and seasonal variations". Annales Geophysicae 21, nr 12 (31.12.2003): 2315–22. http://dx.doi.org/10.5194/angeo-21-2315-2003.
Pełny tekst źródłaStreszczenie:
Abstract. The equatorial ionospheric irregularities have been observed in the past few years by different techniques (e.g. ground-based radar, digisonde, GPS, optical instruments, in situ satellite and rocket instrumentation), and its time evolution and propagation characteristics can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. At present, one of the most powerful optical techniques to study the large-scale ionospheric irregularities is the all-sky imaging photometer system, which normally measures the strong F-region nightglow 630 nm emission from atomic oxygen. The monochromatic OI 630 nm emission images usually show quasi-north-south magnetic field-aligned intensity depletion bands, which are the bottomside optical signatures of large-scale F-region plasma irregularities (also called plasma bubbles). The zonal drift velocities of the plasma bubbles can be inferred from the space-time displacement of the dark structures (low intensity regions) seen on the images. In this study, images obtained with an all-sky imaging photometer, using the OI 630 nm nightglow emission, from Cachoeira Paulista (22.7° S, 45° W, 15.8° S dip latitude), Brazil, have been used to determine the nocturnal monthly and latitudinal variation characteristics of the zonal plasma bubble drift velocities in the low latitude (16.7° S to 28.7° S) region. The east and west walls of the plasma bubble show a different evolution with time. The method used here is based on the western wall of the bubble, which presents a more stable behavior. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-90 model (Hedin et al., 1991) to investigate the thermosphere-ionosphere coupling. Salient features from this study are presented and discussed.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric irregularities; instruments and techniques)
12
Gupta, J. K., i L. Singh. "Long term ionospheric electron content variations over Delhi". Annales Geophysicae 18, nr 12 (31.12.2000): 1635–44. http://dx.doi.org/10.1007/s00585-001-1635-8.
Pełny tekst źródłaStreszczenie:
Abstract. Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91°E; dip Latitude 24.8°N), India, for the period 1975–80 and 1986–89 belonging to an ascending phase of solar activity during first halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IECmax (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IECmax shows positive correlation with F10.7 up to about 200 flux units at equinox and 240 units both in winter and summer; for greater F10.7 values, IECmax is substantially constant in all the seasons. IECmax and magnetic activity (Ap) are found to be positively correlated in summer in high solar activity. Winter IECmax shows positive correlation with Ap in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IECmax is independent of Ap in both solar cycles in low solar activity. A study of day-to-day variations in IECmax shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.Key words: Ionosphere (equatorial ionosphere) · Magnetospheric physics (magnetosphere · ionosphere interactions) · Radio science (ionospheric physics)
13
Freeshah, Mohamed, Xiaohong Zhang, Erman Şentürk, Muhammad Arqim Adil, B. G. Mousa, Aqil Tariq, Xiaodong Ren i Mervat Refaat. "Analysis of Atmospheric and Ionospheric Variations Due to Impacts of Super Typhoon Mangkhut (1822) in the Northwest Pacific Ocean". Remote Sensing 13, nr 4 (11.02.2021): 661. http://dx.doi.org/10.3390/rs13040661.
Pełny tekst źródłaStreszczenie:
The Northwest Pacific Ocean (NWP) is one of the most vulnerable regions that has been hit by typhoons. In September 2018, Mangkhut was the 22nd Tropical Cyclone (TC) over the NWP regions (so, the event was numbered as 1822). In this paper, we investigated the highest amplitude ionospheric variations, along with the atmospheric anomalies, such as the sea-level pressure, Mangkhut’s cloud system, and the meridional and zonal wind during the typhoon. Regional Ionosphere Maps (RIMs) were created through the Hong Kong Continuously Operating Reference Stations (HKCORS) and International GNSS Service (IGS) data around the area of Mangkhut typhoon. RIMs were utilized to analyze the ionospheric Total Electron Content (TEC) response over the maximum wind speed points (maximum spots) under the meticulous observations of the solar-terrestrial environment and geomagnetic storm indices. Ionospheric vertical TEC (VTEC) time sequences over the maximum spots are detected by three methods: interquartile range method (IQR), enhanced average difference (EAD), and range of ten days (RTD) during the super typhoon Mangkhut. The research findings indicated significant ionospheric variations over the maximum spots during this powerful tropical cyclone within a few hours before the extreme wind speed. Moreover, the ionosphere showed a positive response where the maximum VTEC amplitude variations coincided with the cyclone rainbands or typhoon edges rather than the center of the storm. The sea-level pressure tends to decrease around the typhoon periphery, and the highest ionospheric VTEC amplitude was observed when the low-pressure cell covers the largest area. The possible mechanism of the ionospheric response is based on strong convective cells that create the gravity waves over tropical cyclones. Moreover, the critical change state in the meridional wind happened on the same day of maximum ionospheric variations on the 256th day of the year (DOY 256). This comprehensive analysis suggests that the meridional winds and their resulting waves may contribute in one way or another to upper atmosphere-ionosphere coupling.
14
Inyurt, Samed, Omer Yildirim i Cetin Mekik. "Comparison between IRI-2012 and GPS-TEC observations over the western Black Sea". Annales Geophysicae 35, nr 4 (14.07.2017): 817–24. http://dx.doi.org/10.5194/angeo-35-817-2017.
Pełny tekst źródłaStreszczenie:
Abstract. The ionosphere is a dynamic layer which generally changes according to radiation emitted by the sun, the movement of the earth around the sun, and sunspot activity. Variations can generally be categorized as regular or irregular variations. Both types of variation have a huge effect on radio wave propagation. In this study, we have focused on the seasonal variation effect, which is one of the regular forms of variation in terms of the ionosphere. We examined the seasonal variation over the ZONG station in Turkey for the year 2014. Our analysis results and IRI-2012 present different ideas about ionospheric activity. According to our analysed results, the standard deviation reached a maximum value in April 2014. However, the maximum standard deviation obtained from IRI-2012 was seen in February 2014. Furthermore, it is clear that IRI-2012 underestimated the VTEC values when compared to our results for all the months analysed. The main source of difference between the two models is the IRI-2012 topside ionospheric representation. IRI-2012 VTEC has been produced as a result of the integration of an electron density profile within altitudinal limits of 60–2000 km. In other words, the main problem with regard to the IRI-2012 VTEC representation is not being situated in the plasmaspheric part of the ionosphere. Therefore we propose that the plasmaspheric part should be taken into account to calculate the correct TEC values in mid-latitude regions, and we note that IRI-2012 does not supply precise TEC values for use in ionospheric studies.
15
Ogwala, Aghogho, Oluwole Johnson Oyedokun, Olugbenga Ogunmodimu, Andrew Ovie Akala, Masood Ashraf Ali, Punyawi Jamjareegulgarn i 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, nr 11 (1.11.2022): 575. http://dx.doi.org/10.3390/universe8110575.
Pełny tekst źródłaStreszczenie:
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.
16
Yanchukovsky, Valery, i Anastasiya Belinskaya. "Topside ionosphere during solar cosmic ray bursts and Forbush decreases in galactic cosmic rays". Solar-Terrestrial Physics 8, nr 3 (30.09.2022): 32–37. http://dx.doi.org/10.12737/stp-83202205.
Pełny tekst źródłaStreszczenie:
The paper considers the behavior of the upper ionosphere at heights of the F2 layer during Forbush decreases in galactic cosmic rays (GCR FDs) and solar cosmic ray (SCR) bursts. We use the results of long-term continuous observations of cosmic rays and the ionosphere in Novosibirsk for the period from 1968 to 2021. The ionospheric disturbances in the F2 layer during GCR FDs, which were accompanied by a magnetic storm, took the form of an ionospheric storm negative phase. The scale of the negative phase of the ionospheric F-layer disturbance increases with increasing Dst index of the geomagnetic storm. This increase in the amplitude of the ionospheric disturbance becomes more and more significant depending on the magnitude of Forbush decreases. A burst of the amplitude of the daily variation in the F2-layer critical frequency occurred eight days after SCR bursts and GCR FD front. We assume that this burst might have been caused by disturbances in the lower atmosphere due to significant variations in the intensity of SCR and GCR fluxes.
17
Yanchukovsky, Valery, i Anastasiya Belinskaya. "Topside ionosphere during solar cosmic ray bursts and Forbush decreases in galactic cosmic rays". Solnechno-Zemnaya Fizika 8, nr 3 (30.09.2022): 35–40. http://dx.doi.org/10.12737/szf-83202205.
Pełny tekst źródłaStreszczenie:
The paper considers the behavior of the upper ionosphere at heights of the F2 layer during Forbush decreases in galactic cosmic rays (GCR FDs) and solar cosmic ray (SCR) bursts. We use the results of long-term continuous observations of cosmic rays and the ionosphere in Novosibirsk for the period from 1968 to 2021. The ionospheric disturbances in the F2 layer during GCR FDs, which were accompanied by a magnetic storm, took the form of an ionospheric storm negative phase. The scale of the negative phase of the ionospheric F-layer disturbance increases with increasing Dst index of the geomagnetic storm. This increase in the amplitude of the ionospheric disturbance becomes more and more significant depending on the magnitude of Forbush decreases. A burst of the amplitude of the daily variation in the F2-layer critical frequency occurred eight days after SCR bursts and GCR FD front. We assume that this burst might have been caused by disturbances in the lower atmosphere due to significant variations in the intensity of SCR and GCR fluxes.
18
Zhong, Jiahao, Jiuhou Lei i 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, nr 21 (24.10.2020): 3496. http://dx.doi.org/10.3390/rs12213496.
Pełny tekst źródłaStreszczenie:
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.
19
Elias, Ana G., Blas F. de Haro Barbas, Bruno S. Zossi, Franco D. Medina, Mariano Fagre i 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, nr 1 (28.12.2021): 40. http://dx.doi.org/10.3390/atmos13010040.
Pełny tekst źródłaStreszczenie:
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.
20
DABBAKUTI, J. R. K. Kumar, D. Venkata RATNAM i Surendra SUNDA. "MODELLING OF IONOSPHERIC TIME DELAYS BASED ON ADJUSTED SPHERICAL HARMONIC ANALYSIS". Aviation 20, nr 1 (11.04.2016): 1–7. http://dx.doi.org/10.3846/16487788.2016.1162197.
Pełny tekst źródłaStreszczenie:
The ionosphere is the region of the upper atmosphere and the study of the upper atmosphere has a significant role in monitoring, modeling and forecasting for satellite based navigation services. As India lies in a low latitude region, a more careful approach has to be taken to characterize the ionosphere due to the irregularities and equatorial anomaly conditions. In order to study the ionospheric temporal variations, a regional ionospheric model based on the Adjusted Spherical Harmonic Analysis (ASHA) is implemented. The results indicate that the ASHA model is one of the contenders for estimating ionospheric delays well for GNSS augmentation systems.
21
Edwards, Danielle, i Manuel Cervera. "Seasonal Variation in Land and Sea Surface Backscatter Coefficients at High Frequencies". Remote Sensing 14, nr 21 (2.11.2022): 5514. http://dx.doi.org/10.3390/rs14215514.
Pełny tekst źródłaStreszczenie:
Over the horizon radars (OTHR) rely on the propagation of high frequency (HF) radio waves via the ionosphere to successfully achieve their designated missions. Backscatter sounders (BSS) are environmental over-the-horizon radars which may be used to assess the ionospheric propagation conditions. However, high power observed by a BSS may be due to either good ionospheric propagation, a high surface backscatter coefficient, or a combination of both. Hence, an understanding of the surface backscatter coefficients and their temporal variation is essential to fully understand the ionospheric propagation conditions. A database of surface backscatter coefficients over a decade was created using backscatter ionogram data from four backscatter sounders in Australia. The temporal variations in the backscatter coefficients were investigated and it was found that the land backscatter coefficients were relatively constant over time, while the sea backscatter coefficients showed significant seasonal variation.
22
Yagova, Nadezhda, Eugeny Fedorov, Vyacheslav Pilipenko, Nikolay Mazur i Valeriy Martines-Bedenko. "Geomagnetic variations in the frequency range 2.5–12 Hz in the ionospheric F layer as measured by SWARM satellites". Solnechno-Zemnaya Fizika 9, nr 1 (28.03.2023): 37–50. http://dx.doi.org/10.12737/szf-91202305.
Pełny tekst źródłaStreszczenie:
We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].
23
Yagova, Nadezhda, Eugeny Fedorov, Vyacheslav Pilipenko, Nikolay Mazur i Valeriy Martines-Bedenko. "Geomagnetic variations in the frequency range 2.5–12 Hz in the ionospheric F layer as measured by SWARM satellites". Solar-Terrestrial Physics 9, nr 1 (28.03.2023): 34–46. http://dx.doi.org/10.12737/stp-91202305.
Pełny tekst źródłaStreszczenie:
We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018].
24
Palmroth, M., P. Janhunen, T. I. Pulkkinen i H. E. J. Koskinen. "Ionospheric energy input as a function of solar wind parameters: global MHD simulation results". Annales Geophysicae 22, nr 2 (1.01.2004): 549–66. http://dx.doi.org/10.5194/angeo-22-549-2004.
Pełny tekst źródłaStreszczenie:
Abstract. We examine the global energetics of the solar wind magnetosphere-ionosphere system by using the global MHD simulation code GUMICS-4. We show simulation results for a major magnetospheric storm (6 April 2000) and a moderate substorm (15 August 2001). The ionospheric dissipation is investigated by determining the Joule heating and precipitation powers in the simulation during the two events. The ionospheric dissipation is concentrated largely on the dayside cusp region during the main phase of the storm period, whereas the nightside oval dominates the ionospheric dissipation during the substorm event. The temporal variations of the precipitation power during the two events are shown to correlate well with the commonly used AE-based proxy of the precipitation power. The temporal variation of the Joule heating power during the substorm event is well-correlated with a commonly used AE-based empirical proxy, whereas during the storm period the simulated Joule heating is different from the empirical proxy. Finally, we derive a power law formula, which gives the total ionospheric dissipation from the solar wind density, velocity and magnetic field z-component and which agrees with the simulation result with more than 80% correlation. Key words. Ionosphere (modeling and forecasting) – Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms)
25
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 (18.10.2019): 45–49. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w18-45-2019.
Pełny tekst źródłaStreszczenie:
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.
26
Afraimovich, E. L., E. I. Astafieva i S. V. Voyeikov. "Isolated ionospheric disturbances as deduced from global GPS network". Annales Geophysicae 22, nr 1 (1.01.2004): 47–62. http://dx.doi.org/10.5194/angeo-22-47-2004.
Pełny tekst źródłaStreszczenie:
Abstract. We investigate an unusual class of medium-scale traveling ionospheric disturbances of the nonwave type, isolated ionospheric disturbances (IIDs) that manifest themselves in total electron content (TEC) variations in the form of single aperiodic negative TEC disturbances of a duration of about 10min (the total electron content spikes, TECS). The data were obtained using the technology of global detection of ionospheric disturbances using measurements of TEC variations from a global network of receivers of the GPS. For the first time, we present the TECS morphology for 170 days in 1998–2001. The total number of TEC series, with a duration of each series of about 2.3h (2h18m), exceeded 850000. It was found that TECS are observed in no more than 1–2% of the total number of TEC series mainly in the nighttime in the spring and autumn periods. The TECS amplitude exceeds the mean value of the "background" TEC variation amplitude by a factor of 5–10 as a minimum. TECS represent a local phenomenon with a typical radius of spatial correlation not larger than 500km. The IID-induced TEC variations are similar in their amplitude, form and duration to the TEC response to shock-acoustic waves (SAW) generated during rocket launchings and earthquakes. However, the IID propagation velocity is less than the SAW velocity (800–1000m/s) and are most likely to correspond to the velocity of background medium-scale acoustic-gravity waves, on the order of 100–200m/s. Key words. Ionosphere (ionospheric irregularities, instruments and techniques) - Radio science (ionospheric propagation)
27
Zhu, Huizhong, Jun Li, Longjiang Tang, Maorong Ge i Aigong Xu. "Improving the Stochastic Model of Ionospheric Delays for BDS Long-Range Real-Time Kinematic Positioning". Remote Sensing 13, nr 14 (12.07.2021): 2739. http://dx.doi.org/10.3390/rs13142739.
Pełny tekst źródłaStreszczenie:
Although ionosphere-free (IF) combination is usually employed in long-range precise positioning, in order to employ the knowledge of the spatiotemporal ionospheric delays variations and avoid the difficulty in choosing the IF combinations in case of triple-frequency data processing, using uncombined observations with proper ionospheric constraints is more beneficial. Yet, determining the appropriate power spectral density (PSD) of ionospheric delays is one of the most important issues in the uncombined processing, as the empirical methods cannot consider the actual ionosphere activities. The ionospheric delays derived from actual dual-frequency phase observations contain not only the real-time ionospheric delays variations, but also the observation noise which could be much larger than ionospheric delays changes over a very short time interval, so that the statistics of the ionospheric delays cannot be retrieved properly. Fortunately, the ionospheric delays variations and the observation noise behave in different ways, i.e., can be represented by random-walk and white noise process, respectively, so that they can be separated statistically. In this paper, we proposed an approach to determine the PSD of ionospheric delays for each satellite in real-time by denoising the ionospheric delay observations. Based on the relationship between the PSD, observation noise and the ionospheric observations, several aspects impacting the PSD calculation are investigated numerically and the optimal values are suggested. The proposed approach with the suggested optimal parameters is applied to the processing of three long-range baselines of 103 km, 175 km and 200 km with triple-frequency BDS data in both static and kinematic mode. The improvement in the first ambiguity fixing time (FAFT), the positioning accuracy and the estimated ionospheric delays are analysed and compared with that using empirical PSD. The results show that the FAFT can be shortened by at least 8% compared with using a unique empirical PSD for all satellites although it is even fine-tuned according to the actual observations and improved by 34% compared with that using PSD derived from ionospheric delay observations without denoising. Finally, the positioning performance of BDS three-frequency observations shows that the averaged FAFT is 226 s and 270 s, and the positioning accuracies after ambiguity fixing are 1 cm, 1 cm and 3 cm in the East, North and Up directions for static and 3 cm, 3 cm and 6 cm for kinematic mode, respectively.
28
Zhai, Changzhi, Yutian Chen, Xiaoyun Cheng i Xunzhe Yin. "Spatiotemporal Evolution and Drivers of the Four Ionospheric Storms over the American Sector during the August 2018 Geomagnetic Storm". Atmosphere 14, nr 2 (7.02.2023): 335. http://dx.doi.org/10.3390/atmos14020335.
Pełny tekst źródłaStreszczenie:
The spatiotemporal variations and mechanisms of the ionospheric storms over the American sector during the August 2018 geomagnetic storm are investigated. One positive and one negative ionospheric storm occurred in North America and two positive storms were observed in South America. The ionosphere showed prominent hemispheric asymmetries during the four storms. The maximum VTEC (vertical total electron content) variation was more than 15 TECU during the positive storms and about −10 during the negative storm. The GUVI (Global Ultraviolet Imager) oxygen (O) to nitrogen (N2) column density ratio (∑O/N2) and SuperDARN (Super Dual Auroral Radar Network) polar cap potential results showed that the electric field variations played a decisive role in generating the North American negative storm while the thermspheric composition changes were responsible for the North American positive storm and the two South America positive storms.
29
Parkinson, M. L., R. Polglase, B. G. Fejer, L. Scherliess, P. L. Dyson i S. M. Ujmaia. "Seasonal and magnetic activity variations of ionospheric electric fields above the southern mid-latitude station, Bundoora, Australia". Annales Geophysicae 19, nr 5 (31.05.2001): 521–32. http://dx.doi.org/10.5194/angeo-19-521-2001.
Pełny tekst źródłaStreszczenie:
Abstract. We investigate the seasonal, local solar time, and geomagnetic activity variations of the average Doppler velocity measured by an HF digital ionosonde deployed at Bundoora, Australia (145.1° E, 37.7° S, geographic; 49° S magnetic). The Doppler velocities were heavily averaged to suppress the short-term effects (<3 hours) of atmospheric gravity waves, and thereby obtain the diurnal variations attributed to the tidally-driven ionospheric dynamo and electric fields generated by magnetic disturbances. The observed seasonal variations in Doppler velocity were probably controlled by variations in the lower thermospheric winds and ionospheric conductivity above Bundoora and in the magnetically conjugate location. The diurnal variations of the meridional (field-perpendicular) drifts and their perturbations exhibited a complex structure, and were generally smaller than the variations in the zonal drifts. The latter were basically strongly west-ward during the evening to early morning, and weakly east-ward during the late morning to just past noon. The zonal perturbations were strongly enhanced by increasing geomagnetic activity, and closely resembled the perturbation drifts measured by the incoherent scatter radar (ISR) at Millstone Hill (71.5° W, 42.6° N; 57° N). There was also some resemblance between the diurnal variations in the meridional drifts. Overall, the comparisons suggest that with sufficient averaging, Doppler velocities measured with digital ionosondes at mid-latitudes correspond to true ion motions driven by ionospheric electric fields. This is a useful result because apart from the ISRs located in the American-European sector, there are no ground-based instruments capable of measuring electric fields in the mid-latitude ionosphere.Key words. Ionosphere (electric fields and currents; ionosphere atmosphere interactions; mid-latitude ionosphere)
30
Mukasheva, Saule, Vitaliy Kapytin i Andrey Malimbaev. "VARIATIONS OF IONOSPHERIC PARAMETERS OVER ALMATY (KAZAKHSTAN) IN 1999–2013". Solar-Terrestrial Physics 5, nr 4 (17.12.2019): 91–96. http://dx.doi.org/10.12737/stp-54201912.
Pełny tekst źródłaStreszczenie:
The paper presents the results of a study of the behavior of ionospheric parameters of the total electron content, I(t), and electron density in the maximum F2 layer, Nm, over Almaty (Kazakhstan) [43.25° N; 76.92° E] in 1999–2013. The time interval under study covers different solar activity levels. We have shown that at F10.7>175 in summer and at F10.7>225 in winter there is a saturation effect, i.e. with increasing solar activity level values of I(t) do not increase. The observed nonlinear relationship between the total electron content of the ionosphere and the solar radiation flux F10.7 results from the nonlinear relationship between the solar ultraviolet radiation and the solar radiation flux.
The study of the variability of the mid-latitude ionosphere parameters during different solar and geomagnetic activity levels has shown that the standard deviation ç(x) and average shift Xave of I(t) and Nm fluctuations relative to the quiet level weakly depend on solar activity, but greatly depend on geomagnetic activity when F10.7<100.
31
Ясюкевич, Юрий, Yury Yasyukevich, Илья Живетьев i Ilya Zhivetiev. "Using network technology for studying the ionosphere". Solnechno-Zemnaya Fizika 1, nr 3 (27.09.2015): 21–27. http://dx.doi.org/10.12737/10545.
Pełny tekst źródłaStreszczenie:
One of the key problems of ionosphere physics is the coupling between different ionospheric regions. We apply networks technology for studying the coupling of changing ionospheric dynamics in different regions. We used data from global ionosphere maps (GIM) of total electron content (TEC) produced by CODE for 2005–2010. Distribution of cross-correlation function maxima of TEC variations is not simple. This distribution allows us to reveal two levels of ionosphere coupling: «strong» (r>0.9) and «weak» (r>0.72). The ionosphere of the Arctic region upper 50° magnetic latitude is characterized by a «strong» coupling. In the Southern hemisphere, a similar region is bigger. «Weak» coupling is typical for the whole Southern hemisphere. In North America there is an area where TEC dynamics is «strongly» correlated inside and is not correlated with other ionospheric regions.
32
Mikhailov, A. V. "Ionospheric F1 layer long-term trends and the geomagnetic control concept". Annales Geophysicae 26, nr 12 (28.11.2008): 3793–803. http://dx.doi.org/10.5194/angeo-26-3793-2008.
Pełny tekst źródłaStreszczenie:
Abstract. A previous approach to the ionospheric long-term trend analysis has been applied to the foF1 observations from Slough and Rome in order to investigate a possible relationship between the foF1 and the long-term variation of geomagnetic activity. A 40-year period, starting in 1962, has been used for the analysis. According to the results obtained earlier for F2 and E-region trends, geomagnetic control of the long-term variation has also been revealed for the foF1. Thus, it is now possible to speak about the geomagnetic control of the ionospheric trends in the whole ionosphere. This is not surprising as the Earth's ionosphere is a single entity that is strongly controlled, either directly or indirectly, by the magnetic field. As with the F2-region, this geomagnetic control is provided via neutral composition and temperature changes. A very long-term (centennial) increase in geomagnetic activity in the 20th century is seen in the long-term foF1 variations as well. After its removal, the residual foF1 trends are very small and insignificant. In principal, this means that the observed foF1 long-term variations have a natural origin and can be attributed to solar and geomagnetic activity long-term variations. However, the situation in the thermosphere has been changing since 1997 and available foF2 observations at the two stations reveal information about the "break down" of the geomagnetic control in the F2-region. Possible reasons of these changes are discussed.
33
Rishbeth, H. "The equatorial F-layer: progress and puzzles". Annales Geophysicae 18, nr 7 (31.07.2000): 730–39. http://dx.doi.org/10.1007/s00585-000-0730-6.
Pełny tekst źródłaStreszczenie:
Abstract. This work reviews some aspects of the ionospheric F-layer in the vicinity of the geomagnetic equator. Starting with a historical introduction, brief summaries are given of the physics that makes the equatorial ionosphere so interesting, concentrating on the large-scale structure rather than the smaller-scale instability phenomena. Several individual topics are then discussed, including eclipse effects, the asymmetries of the `equatorial trough', variations with longitude, the semiannual variation, the effects of the global thermospheric circulation, and finally the equatorial neutral thermosphere, including `superrotation' and possible topographic influences.Keyword: Ionosphere (equatorial ionosphere)
34
Namgaladze, A. A., A. N. Namgaladze i M. A. Volkov. "Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region". Annales Geophysicae 16, nr 10 (31.10.1998): 1283–98. http://dx.doi.org/10.1007/s00585-998-1283-3.
Pełny tekst źródłaStreszczenie:
Abstract. The seasonal effects in the thermosphere and ionosphere responses to the precipitating electron flux and field-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF By < 0. In the first variant, the model input data for the summer and winter precipitating fluxes and field-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric field variations leading to the larger Joule heating effects in the ion and neutral gas temperature, ion drag effects in the thermospheric winds and ion drift effects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28–29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the first variant. Geomagnetically asymmetric input data for the summer and winter precipitating fluxes and field-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer) Hemisphere obtained from DE-2 data for IMF By < 0 but for the Northern (winter) Hemisphere there is a disagreement at high latitudes in the afternoon sector of the cusp region. At the same time, the model results for this sector agree with other DE-2 data and with the ground-based FPI data. All ionospheric and thermospheric disturbances in the second variant of the calculations are more intensive in the winter cusp region in comparison with the summer one and this seasonal difference is larger than in the first variant of the calculations, especially in the electron density and all temperature variations. The means that the seasonal effects in the cusp region are stronger in the thermospheric and ionospheric responses to the FAC variations than to the precipitation disturbances.Key words. Ionosphere (ionosphere · atmosphere interactions; ionosphere · magnetosphere interactions; ionospheric disturbances).
35
Biktash, L. Z. "Role of the magnetospheric and ionospheric currents in the generation of the equatorial scintillations during geomagnetic storms". Annales Geophysicae 22, nr 9 (23.09.2004): 3195–202. http://dx.doi.org/10.5194/angeo-22-3195-2004.
Pełny tekst źródłaStreszczenie:
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.
36
Shulha, Maryna, Oleksandr Bogomaz, Taras Zhivolup, Oleksander Koloskov, Andrey Zalizovski i Volodymyr Lisachenko. "Investigation of the ionosphere over Antarctica under quiet space weather conditions: results of vertical sounding of the ionosphere September 14–24, 2020". PHYSICS OF ATMOSPHERE AND GEOSPACE 1, nr 1 (31.12.2020): 45–55. http://dx.doi.org/10.47774/phag.01.01.2020-4.
Pełny tekst źródłaStreszczenie:
We present observational results of variations in the ionospheric parameters hmF2 and NmF2 over the Ukrainian Antarctic station “Akademik Vernadsky” for magnetically quiet conditions. The results of comparative analysis of observational data and the International Reference Ionosphere-2016 model predictions are presented. The main objective of this study is to investigate the temporal variations of two key ionospheric parameters – the F2 layer peak height and electron density – during very quiet space weather conditions using data of vertical sounding of the ionosphere obtained over the Ukrainian Antarctic station “Akademik Vernadsky” and comparison the observation results with model values. Methods: The temporal variations of the F2 layer peak height and electron density were calculated from ionograms obtained with ionosonde installed at the Ukrainian Antarctic station “Akademik Vernadsky” with subsequent electron density profile inversion. Diurnal variations of hmF2 and NmF2 were calculated using a set of sub-models of the IRI-2016 model for comparison with results of observational studies. Results: We found that for the Antarctic region option of IRI-2016 model for the F2 layer peak height SHU-2015 provides a better fit for hmF2 through the investigated period compare to the AMTB-2013 model predictions. Electron density models (URSI, CCIR) generally well reproduce the observed variations of NmF2 during periods of absence non-standard manifestations of space weather, which are possible for quiet conditions too. Hypotheses regarding the possible reasons for experimental and model differences in variations of NmF2 are discussed. The analysis of effect of geomagnetic storm on September 24, 2020 on NmF2 variations was carried out. Conclusions: The obtained results demonstrate peculiarities of the state of the ionosphere-plasmasphere system over Antarctica under very quiet space weather conditions and provide evaluation of predictive capabilities of modern international reference ionosphere models. New knowledge about the features of electron density variations in the ionosphere for magnetically quiet conditions over the Antarctic region has practical value for specialists which are engaged in the study of the near-Earth space environment, in particular, at high latitudes, and also work on correction of global ionospheric models. Keywords: electron density, F2 layer peak height, ionosonde, quiet space weather, models of the ionosphere, downward plasma flux
37
Coco, Igino, Ermanno Amata, Maria Federica Marcucci, Danila Ambrosino i Simon G. Shepherd. "Effects of Abrupt Variations of Solar Wind Dynamic Pressure on the High-Latitude Ionosphere". International Journal of Geophysics 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/207514.
Pełny tekst źródłaStreszczenie:
We show the results of a statistical study on the effects in the high-latitude ionosphere of abrupt variations of solar wind dynamic pressure, using Super Dual Auroral Radar Network (SuperDARN) data in both hemispheres. We find that, during periods of quiet ionospheric conditions, the amount of radar backscatter increases when a variation in the dynamic pressure occurs, both positive (increase of the pressure) and negative (decrease of the pressure). We also investigate the behaviour of the Cross-Polar Cap Potential (CPCP) during pressure variations and show preliminary results.
38
Jin, Rui, i Shuanggen Jin. "Secular variation and fluctuation of GPS Total Electron Content over Antarctica". Proceedings of the International Astronomical Union 8, S288 (sierpień 2012): 322–25. http://dx.doi.org/10.1017/s1743921312017139.
Pełny tekst źródłaStreszczenie:
AbstractThe total electron content (TEC) is an important parameters in the Earth's ionosphere, related to various space weather and solar activities. However, understanding of the complex ionospheric environments is still a challenge due to the lack of direct observations, particularly in the polar areas, e.g., Antarctica. Now the Global Positioning System (GPS) can be used to retrieve total electron content (TEC) from dual-frequency observations. The continuous GPS observations in Antarctica provide a good opportunity to investigate ionospheric climatology. In this paper, the long-term variations and fluctuations of TEC over Antarctica are investigated from CODE global ionospheric maps (GIM) with a resolution of 2.5°×5° every two hours since 1998. The analysis shows significant seasonal and secular variations in the GPS TEC. Furthermore, the effects of TEC fluctuations are discussed.
39
Sethi, N. K., M. K. Goel i K. K. Mahajan. "Solar Cycle variations of ƒ<i>o</i>F2 from IGY to 1990". Annales Geophysicae 20, nr 10 (31.10.2002): 1677–85. http://dx.doi.org/10.5194/angeo-20-1677-2002.
Pełny tekst źródłaStreszczenie:
Abstract. Noontime monthly median values of F2-layer critical frequency foF2 (m) for some ionospheric stations representing low- and mid-latitudes are examined for their dependence on solar activity for the years 1957 (IGY) to 1990. This is the period for which ionospheric data in digital form is available in two CD-ROMs at the World Data Center, Boulder. It is observed that at mid-latitudes, foF2 (m) shows nearly a linear relationship with R12 (the 12-month running average of the Zurich sunspot number), though this relation is nonlinear for low-latitudes. These results indicate some departures from the existing information often used in theoretical and applied areas of space research.Key words. Ionosphere (equatorial ionosphere; mid-latitude ionosphere; modelling and forecasting)
40
Xu, T., J. Wu, Z. Zhao, Y. Liu, S. He, J. Li, Z. Wu i Y. Hu. "<i>Brief communication</i> "Monitoring ionospheric variations before earthquakes using the vertical and oblique sounding network over China"". Natural Hazards and Earth System Sciences 11, nr 4 (11.04.2011): 1083–89. http://dx.doi.org/10.5194/nhess-11-1083-2011.
Pełny tekst źródłaStreszczenie:
Abstract. The problem of earthquake prediction has stimulated the research for correlation between seismic activity and ionospheric anomaly. Many observations have shown the existence of anomaly of critical frequency of ionospheric F-region, foF2, before earthquake onset. Ionospheric sounding has been conducted routinely for more than 60 years in China by the China Research Institute of Radiowave Propagation (CRIRP), and deveoloped a very powerful ability to observe the ionosphere. In this paper, we briefly describe the anomalous variation of the foF2 before Ms8.0 Wenchuan earthquake (occurred on 12 May 2008 at 14:28 LT; 31.00° N, 103.40° E), which is a sign of the great interest arising in the seismo-ionospheric investigation of Chinese researchers. Furthermore, we introduce the routine work on seismo-ionospheric anomaly by the ground based high-resolution ionospheric observation (GBHIO) network comprising 5 vertical and 20 oblique sounding stations.
41
Perrone, Loredana, Angelo De Santis, Cristoforo Abbattista, Lucilla Alfonsi, Leonardo Amoruso, Marianna Carbone, Claudio Cesaroni i in. "Ionospheric anomalies detected by ionosonde and possibly related to crustal earthquakes in Greece". Annales Geophysicae 36, nr 2 (14.03.2018): 361–71. http://dx.doi.org/10.5194/angeo-36-361-2018.
Pełny tekst źródłaStreszczenie:
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)
42
Fujiwara, H., S. Nozawa, Y. Ogawa, R. Kataoka, Y. Miyoshi, H. Jin i H. Shinagawa. "Extreme ion heating in the dayside ionosphere in response to the arrival of a coronal mass ejection on 12 March 2012". Annales Geophysicae 32, nr 7 (23.07.2014): 831–39. http://dx.doi.org/10.5194/angeo-32-831-2014.
Pełny tekst źródłaStreszczenie:
Abstract. Simultaneous measurements of the polar ionosphere with the European Incoherent Scatter (EISCAT) ultra high frequency (UHF) radar at Tromsø and the EISCAT Svalbard radar (ESR) at Longyearbyen were made during 07:00–12:00 UT on 12 March 2012. During the period, the Advanced Composition Explorer (ACE) spacecraft observed changes in the solar wind which were due to the arrival of coronal mass ejection (CME) effects associated with the 10 March M8.4 X-ray event. The solar wind showed two-step variations which caused strong ionospheric heating. First, the arrival of shock structures in the solar wind with enhancements of density and velocity, and a negative interplanetary magnetic field (IMF)-Bz component caused strong ionospheric heating around Longyearbyen; the ion temperature at about 300 km increased from about 1100 to 3400 K over Longyearbyen while that over Tromsø increased from about 1050 to 1200 K. After the passage of the shock structures, the IMF-Bz component showed positive values and the solar wind speed and density also decreased. The second strong ionospheric heating occurred after the IMF-Bz component showed negative values again; the negative values lasted for more than 1.5 h. This solar wind variation caused stronger heating of the ionosphere in the lower latitudes than higher latitudes, suggesting expansion of the auroral oval/heating region to the lower latitude region. This study shows an example of the CME-induced dayside ionospheric heating: a short-duration and very large rise in the ion temperature which was closely related to the polar cap size and polar cap potential variations as a result of interaction between the solar wind and the magnetosphere.
43
Tsugawa, Takuya. "Message from the Winner". Journal of Disaster Research 18, nr 2 (1.02.2023): 83. http://dx.doi.org/10.20965/jdr.2023.p0083.
Pełny tekst źródłaStreszczenie:
I am very honored to receive the JDR Award for the Most Cited Paper 2022, and I am very grateful to the editorial board and staff of the Journal of Disaster Research. The paper, “Total Electron Content Observations by Dense Regional and Worldwide International Networks of GNSS,” reviews our research related to ionospheric observations using GNSS receiver networks. Since the late 1990s, the rapid development of GNSS receiver networks has made it possible to observe the ionosphere in two dimensions with high temporal and spatial resolution, revealing new features of various ionospheric phenomena. Ionospheric observation using GNSS receiver networks has become an indispensable method of observation in the space weather field. After the 2011 Tohoku Earthquake, it was revealed that various atmospheric waves excited by earthquakes and tsunamis propagated up to the ionosphere and caused ionospheric variations, suggesting the possibility of tsunami monitoring using ionospheric observations. We are also working on the standardization of ionospheric data formatting to achieve even higher spatial resolution and wider coverage of ionospheric observation using GNSS receiver networks through international cooperation. Encouraged by this award, we will continue our research and development efforts with a view to applying this technology not only to space weather but also to natural disasters such as earthquakes and tsunamis.
44
Kamal, Sumon, Norbert Jakowski, Mohammed M. Hoque i Jens Wickert. "Evaluation of E Layer Dominated Ionosphere Events Using COSMIC/FORMOSAT-3 and CHAMP Ionospheric Radio Occultation Data". Remote Sensing 12, nr 2 (20.01.2020): 333. http://dx.doi.org/10.3390/rs12020333.
Pełny tekst źródłaStreszczenie:
At certain geographic locations, especially in the polar regions, the ionization of the ionospheric E layer can dominate over that of the F2 layer. The associated electron density profiles show their ionization maximum at E layer heights between 80 and 150 km above the Earth’s surface. This phenomenon is called the “E layer dominated ionosphere” (ELDI). In this paper we systematically investigate the characteristics of ELDI occurrences at high latitudes, focusing on their spatial and temporal variations. In our study, we use ionospheric GPS radio occultation data obtained from the COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3) and CHAMP (Challenging Minisatellite Payload) satellite missions. The entire dataset comprises the long period from 2001 to 2018, covering the previous and present solar cycles. This allows us to study the variation of the ELDI in different ways. In addition to the geospatial distribution, we also examine the temporal variation of ELDI events, focusing on the diurnal, the seasonal, and the solar cycle dependent variation. Furthermore, we investigate the spatiotemporal dependency of the ELDI on geomagnetic storms.
45
Vesnin, Artem, Yury Yasyukevich, Natalia Perevalova i Erman Şentürk. "Ionospheric Response to the 6 February 2023 Turkey–Syria Earthquake". Remote Sensing 15, nr 9 (28.04.2023): 2336. http://dx.doi.org/10.3390/rs15092336.
Pełny tekst źródłaStreszczenie:
Two strong earthquakes occurred in Turkey on 6 February 2023, at 01:17:34 (nighttime, Mw = 7.8) and at 10:24:50 UT (daytime, Mw = 7.5). The seismo-ionospheric impact is an important part of the near-Earth environment state. This paper provides the first results on the ionospheric effects associated with the aforementioned earthquakes. We used data from global navigation satellite system (GNSS) receivers and ionosondes. We found that both earthquakes generated circle disturbance in the ionosphere, detected by GNSS data. The amplitude of the ionospheric response caused by daytime M7.5 earthquake exceeded by five times that caused by nighttime M7.8 earthquake: 0.5 TECU/min and 0.1 TECU/min, respectively, according to the ROTI data. The velocities of the earthquake-related ionospheric waves were ~2000 m/s, as measured by ROTI, for the M7.5 earthquake. TEC variations with 2–10 min periods showed velocities from 1500 to 900 m/s as disturbances evolved. Ionospheric disturbances occurred around epicenters and propagated to the south by means of 2–10 min TEC variations. ROTI data showed a more symmetric distribution with irregularities observed both to the South and to the North from 10:24:50 UT epicenter. The ionospheric effects were recorded over 750 km from the epicenters. Ionosonde located 420/490 km from the epicenters did not catch ionospheric effects. The results show significant asymmetry in the propagation of coseismic ionospheric disturbances. We observed coseismic ionospheric disturbances associated with Rayleigh mode and acoustic modes, but we did not observe disturbances associated with acoustic gravity mode.
46
Le, H., L. Liu, X. Yue i W. Wan. "The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling". Annales Geophysicae 26, nr 1 (4.02.2008): 107–16. http://dx.doi.org/10.5194/angeo-26-107-2008.
Pełny tekst źródłaStreszczenie:
Abstract. A total eclipse occurred on 11 August 1999 with its path of totality passing over central Europe in the latitude range 40°–50° N. The ionospheric responses to this eclipse were measured by a wide ionosonde network. On the basis of the measurements of foE, foF1, and foF2 at sixteen ionosonde stations in Europe, we statistically analyze the variations of these parameters with a function of eclipse magnitude. To model the eclipse effects more accurately, a revised eclipse factor, FR, is constructed to describe the variations of solar radiation during the solar eclipse. Then we simulate the effect of this eclipse on the ionosphere with a mid- and low-latitude ionosphere theoretical model by using the revised eclipse factor during this eclipse. Simulations are highly consistent with the observations for the response in the E-region and F1-region. Both of them show that the maximum response of the mid-latitude ionosphere to the eclipse is found in the F1-region. Except the obvious ionospheric response at low altitudes below 500 km, calculations show that there is also a small response at high altitudes up to about 2000 km. In addition, calculations show that when the eclipse takes place in the Northern Hemisphere, a small ionospheric disturbance also appeared in the conjugate hemisphere.
47
Xu, Xin, Ling Huang, Shun Wang, Yicai Ji, Xiaojun Liu i Guangyou Fang. "VLF/LF Lightning Location Based on LWPC and IRI Models: A Quantitative Study". Remote Sensing 14, nr 22 (16.11.2022): 5784. http://dx.doi.org/10.3390/rs14225784.
Pełny tekst źródłaStreszczenie:
The group velocity of lightning electromagnetic signals plays an important role in lightning location systems using the time difference of arrival (TDOA) method. Accurate estimation of group velocity is difficult due to the space- and time-varying properties of the Earth’s ionospheric waveguide. Besides, the analytical solution of the group velocity is difficult to obtain from the classic mode theory, especially when higher-order modes, anisotropic geomagnetic background, diffuse ionosphere profile, and propagation path segmentation are all taken into consideration. To overcome these challenges, a novel numerical method is proposed in this paper to estimate the group velocity of the lightning signal during ionospheric quiet periods. The well-known Long Wavelength Propagation Capability (LWPC) code is used to model the propagation of VLF/LF radio waves. Since LWPC uses a simplified ionospheric model which is unable to describe the subtle variations of ionospheric parameters over time and space, the IRI-2016 model is incorporated into the numerical modeling process to provide more accurate ionosphere parameters. Experimental results of a VLF/LF lightning location network are demonstrated and analyzed to show the effectiveness of our method. The proposed method is also applicable when there is a sudden ionospheric disturbance as long as the parameters of the ionosphere are obtained in real time by remote sensing methods.
48
Cheng, Na, Shuli Song i Wei Li. "Multi-Scale Ionospheric Anomalies Monitoring and Spatio-Temporal Analysis during Intense Storm". Atmosphere 12, nr 2 (4.02.2021): 215. http://dx.doi.org/10.3390/atmos12020215.
Pełny tekst źródłaStreszczenie:
The ionosphere is a significant component of the geospace environment. Storm-induced ionospheric anomalies severely affect the performance of Global Navigation Satellite System (GNSS) Positioning, Navigation, and Timing (PNT) and human space activities, e.g., the Earth observation, deep space exploration, and space weather monitoring and prediction. In this study, we present and discuss the multi-scale ionospheric anomalies monitoring over China using the GNSS observations from the Crustal Movement Observation Network of China (CMONOC) during the 2015 St. Patrick’s Day storm. Total Electron Content (TEC), Ionospheric Electron Density (IED), and the ionospheric disturbance index are used to monitor the storm-induced ionospheric anomalies. This study finally reveals the occurrence of the large-scale ionospheric storms and small-scale ionospheric scintillation during the storm. The results show that this magnetic storm was accompanied by a positive phase and a negative phase ionospheric storm. At the beginning of the main phase of the magnetic storm, both TEC and IED were significantly enhanced. There was long-duration depletion in the topside ionospheric TEC during the recovery phase of the storm. This study also reveals the response and variations in regional ionosphere scintillation. The Rate of the TEC Index (ROTI) was exploited to investigate the ionospheric scintillation and compared with the temporal dynamics of vertical TEC. The analysis of the ROTI proved these storm-induced TEC depletions, which suppressed the occurrence of the ionospheric scintillation. To improve the spatial resolution for ionospheric anomalies monitoring, the regional Three-Dimensional (3D) ionospheric model is reconstructed by the Computerized Ionospheric Tomography (CIT) technique. The spatial-temporal dynamics of ionospheric anomalies during the severe geomagnetic storm was reflected in detail. The IED varied with latitude and altitude dramatically; the maximum IED decreased, and the area where IEDs were maximum moved southward.
49
Rodger, A. S., i M. Pinnock. "The ionospheric response to flux transfer events: the first few minutes". Annales Geophysicae 15, nr 6 (30.06.1997): 685–91. http://dx.doi.org/10.1007/s00585-997-0685-y.
Pełny tekst źródłaStreszczenie:
Abstract. We utilise high-time resolution measurements from the PACE HF radar at Halley, Antarctica to explore the evolution of the ionospheric response during the first few minutes after enhanced reconnection occurs at the magnetopause. We show that the plasma velocity increases associated with flux transfer events (FTEs) occur first ~100–200 km equatorward of the region to which magnetosheath (cusp) precipitation maps to the ionosphere. We suggest that these velocity variations start near the ionospheric footprint of the boundary between open and closed magnetic field lines. We show that these velocity variations have rise times ~100 s and fall times of ~10 s. When these velocity transients reach the latitude of the cusp precipitation, sometimes the equatorward boundary of the precipitation begins to move equatorward, the expected and previously reported ionospheric signature of enhanced reconnection. A hypothesis is proposed to explain the velocity variations. It involves the rapid outflow of magnetospheric electrons into the magnetosheath along the most recently reconnected field lines. Several predictions are made arising from the proposed explanation which could be tested with ground-based and space-based observations.
50
Mingaleva, G. I., i V. S. Mingalev. "Response of the convecting high-latitude F layer to a powerful HF wave". Annales Geophysicae 15, nr 10 (31.10.1997): 1291–300. http://dx.doi.org/10.1007/s00585-997-1291-8.
Pełny tekst źródłaStreszczenie:
Abstract. A numerical model of the high-latitude ionosphere, which takes into account the convection of the ionospheric plasma, has been developed and utilized to simulate the F-layer response at auroral latitudes to high-power radio waves. The model produces the time variations of the electron density, positive ion velocity, and ion and electron temperature profiles within a magnetic field tube carried over an ionospheric heater by the convection electric field. The simulations have been performed for the point with the geographic coordinates of the ionospheric HF heating facility near Tromso, Norway, when it is located near the midnight magnetic meridian. The calculations have been made for equinox, at high-solar-activity, and low-geomagnetic-activity conditions. The results indicate that significant variations of the electron temperature, positive ion velocity, and electron density profiles can be produced by HF heating in the convecting high-latitude F layer.