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Yang, Li-Xia, Chao Liu, Qing-Liang Li i Yu-Bo Yan. "Electromagnetic wave propagation characteristics of oblique incidence nonlinear ionospheric Langmuir disturbance". Acta Physica Sinica 71, nr 6 (2022): 064101. http://dx.doi.org/10.7498/aps.71.20211204.
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Based on the generalized Zakharov model, a numerical model of electromagnetic wave propagating in the ionosphere at different angles is established by combining the finite difference time domain (FDTD) method of obliquely incident plasma with the double hydrodynamics equation and through equivalently transforming the two-dimensional Maxwell equation into one-dimensional Maxwell equation and the plasma hydrodynamics equation. In this paper. the dominant equation of Z-wave in obliquely incident nonlinear ionospheric plasma having been analyzed and deduced, the FDTD algorithm suitable for calculating the propagation characteristics of ionospheric electromagnetic wave is deduced. The simulation results prove the accuracy and effectiveness of this method for the Langmuir disturbance caused by electromagnetic wave heating the ionosphere at a small inclination angle. The results show that under small angle incidence, the high-power high-frequency electromagnetic wave excites the Langmuir wave near the O-wave reflection point in the ionospheric plasma. At the same time, the wave particle interaction causes the O-wave to convert into Z-wave and propagate into the higher region of the ionosphere. In this work, the electromagnetic wave propagation characteristics are further studied based on ionospheric plasma, which is helpful in laying the foundation of numerical algorithm for comprehensively and in depth analyzing the influence of ionospheric Langmuir disturbance on ionospheric radio wave propagation characteristics.
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Ueda, H. O., Y. Omura i H. Matsumoto. "Computer simulations for direct conversion of the HF electromagnetic wave into the upper hybrid wave in ionospheric heating experiments". Annales Geophysicae 16, nr 10 (31.10.1998): 1251–58. http://dx.doi.org/10.1007/s00585-998-1251-y.
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Abstract. Excitation of upper hybrid waves associated with the ionospheric heating experiments is assumed to be essential in explaining some of the features of stimulated electromagnetic emissions (SEE). A direct conversion process is proposed as an excitation mechanism of the upper hybrid waves where the energy of an obliquely propagating electromagnetic pump wave is converted into the electrostatic upper hybrid waves due to small-scale density irregularities. We performed electromagnetic particle-in-cell simulations to investigate the energy conversion process in the ionospheric heating experiments. We studied dependence of the amplitude of the excited wave on the propagation angle of the pump wave, scale length of the density irregularity, degree of the irregularity, and thermal velocity of the plasma. The maximum amplitude is found to be 37 of the pump amplitude under an optimum condition.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; wave-particle interactions).
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Mabie, Justin, i Terence Bullett. "Multiple Cusp Signatures in Ionograms Associated with Rocket-Induced Infrasonic Waves". Atmosphere 13, nr 6 (12.06.2022): 958. http://dx.doi.org/10.3390/atmos13060958.
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We are interested in understanding how and when infrasonic waves propagate in the thermosphere, specifying the physical properties of those waves, and understanding how they affect radio wave propagation. We use a combination of traditional ionosonde observations and fixed frequency Doppler soundings to make high quality observations of vertically propagating infrasonic waves in the lower thermosphere/bottom side ionosphere. The presented results are the first simultaneous observations of infrasonic wave-induced deformations in ionograms and high-time-resolution observations of corresponding plasma displacements. Deformations in ionospheric echoes, which manifest as additional cusps and range variations, are shown to be caused by infrasonic wave-induced plasma displacements.
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Leyser, Thomas B., H. Gordon James, Björn Gustavsson i Michael T. Rietveld. "Evidence of <i>L</i>-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith". Annales Geophysicae 36, nr 1 (21.02.2018): 243–51. http://dx.doi.org/10.5194/angeo-36-243-2018.
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Abstract. The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect. Keywords. Space plasma physics (active perturbation experiments)
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Pokhotelov, O. A., M. Parrot, E. N. Fedorov, V. A. Pilipenko, V. V. Surkov i V. A. Gladychev. "Response of the ionosphere to natural and man-made acoustic sources". Annales Geophysicae 13, nr 11 (30.11.1995): 1197–210. http://dx.doi.org/10.1007/s00585-995-1197-2.
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Abstract. A review is presented of the effects influencing the ionosphere which are caused by acoustic emission from different sources (chemical and nuclear explosions, bolides, meteorites, earthquakes, volcanic eruptions, hurricanes, launches of spacecrafts and flights of supersonic jets). A terse statement is given of the basic theoretical principles and simplified theoretical models underlying the physics of propagation of infrasonic pulses and gravity waves in the upper atmosphere. The observations of "quick" response by the ionosphere are pointed out. The problem of magnetic disturbances and magnetohydrodynamic (MHD) wave generation in the ionosphere is investigated. In particular, the supersonic propagation of ionospheric disturbances, and the conversion of the acoustic energy into the so-called gyrotropic waves in the ionospheric E-layer are considered.
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Waters, C. L., T. K. Yeoman, M. D. Sciffer, P. Ponomarenko i D. M. Wright. "Modulation of radio frequency signals by ULF waves". Annales Geophysicae 25, nr 5 (4.06.2007): 1113–24. http://dx.doi.org/10.5194/angeo-25-1113-2007.
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Abstract. The ionospheric plasma is continually perturbed by ultra-low frequency (ULF; 1–100 mHz) plasma waves that are incident from the magnetosphere. In this paper we present a combined experimental and modeling study of the variation in radio frequency of signals propagating in the ionosphere due to the interaction of ULF wave energy with the ionospheric plasma. Modeling the interaction shows that the magnitude of the ULF wave electric field, e, and the geomagnetic field, B0, giving an e×B0 drift, is the dominant mechanism for changing the radio frequency. We also show how data from high frequency (HF) Doppler sounders can be combined with HF radar data to provide details of the spatial structure of ULF wave energy in the ionosphere. Due to spatial averaging effects, the spatial structure of ULF waves measured in the ionosphere may be quite different to that obtained using ground based magnetometer arrays. The ULF wave spatial structure is shown to be a critical parameter that determines how ULF wave effects alter the frequency of HF signals propagating through the ionosphere.
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Husin, Asnawi, i Buldan Muslim. "EFEK GELOMBANG TSUNAMI ACEH 2004 PADA GANGGUAN IONOSFER BERGERAK SKALA MENENGAH DARI PENGAMATAN JARINGAN GPS SUMATRA". Komunikasi Fisika Indonesia 16, nr 2 (31.10.2019): 130. http://dx.doi.org/10.31258/jkfi.16.2.130-137.
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Medium Scale Travelling Ionospheric Disturbance (MSTID), thought to be manifestation of atmospheric gravity wave (AGW) in the ionospheric altitude that propagates horizontally and effects on in the electron density structure of ionosphere. These atmospheric gravity waves sourced from lower atmospheric activities such as typhoons, volcanic eruptions and tsunamis. Wave energy by its coupling induction process can travel to the ionosphere region. It has been understood that the TID's wave structure have an impact on the propagation of radio waves in the ionosphere so that it will affect the performance of navigation satellite-based positioning measurements. Based on Aceh tsunami in December 2004, this study aimed to investigation of the induction of atmospheric gravity waves in the ionosphere using total electron content (TEC) data from the Sumatra GPS network (Sumatra GPS Array, SUGAR). The detection technique of TEC changes due to AGW induction with a filter to separate medium scale disturbance at the ionospheric pierce point at an altitude of 350 km (IPP, Ionospheric Pierce Point). The results show the horizontal wavelength of a medium-scale TID around 180 ± 12 Km with a velocities of around 376 ± 9 ms-1. Based on two-dimensional map, the TID moves to the southeast.
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Li, Qingfeng, Zeyun Li i Hanxian Fang. "Using 3D Ray Tracing Technology to Study the Disturbance Effect of Rocket Plume on Ionosphere". Atmosphere 13, nr 7 (20.07.2022): 1150. http://dx.doi.org/10.3390/atmos13071150.
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In this paper, the initial neutral atmospheric parameters, background ionospheric parameters and geomagnetic field parameters of the ionosphere are obtained by NRLMSISE-00 model, IRI-2016 model and IGRF-13 model, respectively. Considering the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, a three-dimensional dynamic model of chemical substances released by rocket plume disturbing the ionosphere is constructed. The influence of the disturbance on the echo path of high frequency radio waves with different incident frequencies is simulated by using three-dimensional digital ray-tracing technology. Using this model, the process of ionospheric disturbance caused by the main chemical substances H2 and H2O in the rocket plume under three different release conditions: fixed-point release at 300 km, vertical path at 250–350 km and parabolic path at 250–350 km, and the influence of the ionospheric cavity on the radio wave propagation of high frequency radio waves at different frequencies are simulated. The main purpose of the article is to focus on the effect of the cavity generated by the rocket exhaust on the propagation of radio waves. It mainly studies the perturbation effect on the ionosphere under different release conditions, considers the neutral gas diffusion process, ion chemical reaction and plasma diffusion process, and establishes the three-dimensional dynamics of the ionospheric electron density and the spatiotemporal distribution of the plume plasma learning model. Finally, the three-dimensional ray-tracing algorithm is used to simulate the propagation path of the radio wave through the disturbance area. We considered three different release conditions, including fixed-point release, vertical path and parabolic path. The ionospheric disturbances produced by these different releases are compared and analyzed, and their effects on the propagation path of radio waves are studied.
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Hoffmann, P., i Ch Jacobi. "Planetary wave characteristics of gravity wave modulation from 30–130 km". Advances in Radio Science 10 (19.09.2012): 271–77. http://dx.doi.org/10.5194/ars-10-271-2012.
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Abstract. Fast gravity waves (GW) have an important impact on the momentum transfer between the middle and upper atmosphere. Experiments with a circulation model indicate a penetration of high phase speed GW into the thermosphere as well as an indirect propagation of planetary waves by the modulation GW of momentum fluxes into the thermosphere. Planetary wave characteristics derived from middle atmosphere SABER temperatures, GW potential energy and ionospheric GPS-TEC data at midlatitudes reveal a possible correspondence of PW signatures in the middle atmosphere and ionosphere in winter around solar maximum (2002–2005). In the case of the westward propagating 16-day wave with zonal wavenumber 1 a possible connection could be found in data analysis (November–December 2003) and model simulation. Accordingly, GW with high phase speeds might play an essential role in the transfer of PW and other meteorological disturbances up to the ionospheric F-region.
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Liu, Tong, Zhibin Yu, Zonghua Ding, Wenfeng Nie i Guochang Xu. "Observation of Ionospheric Gravity Waves Introduced by Thunderstorms in Low Latitudes China by GNSS". Remote Sensing 13, nr 20 (15.10.2021): 4131. http://dx.doi.org/10.3390/rs13204131.
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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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Robinson, T. R., i K. Schlegel. "The generation of non aspect sensitive plasma density irregularities by field aligned drifts in the lower ionosphere". Annales Geophysicae 18, nr 7 (31.07.2000): 799–806. http://dx.doi.org/10.1007/s00585-000-0799-y.
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Abstract. A theory of the generation of plasma density irregularities with virtually no aspect sensitivity, in the lower ionosphere at high latitudes, by electron drifts aligned with the geomagnetic field, is presented. The theory is developed through fluid equations in which the destabilising mechanism involves positive feedback from electron collisional heating. When field aligned electron drift speeds exceed a few km s-1, this effect destabilises waves with wavelengths in excess of a few tens of metres in the lower E-region, where collisional effects are sufficiently large. Furthermore, the threshold conditions are almost independent of the wave propagation direction and the unstable waves propagate at speeds well below the ion acoustic speed. The role that this new instability may play in recent radar backscatter observations of short scale irregularities propagating in directions close to that of the geomagnetic field, in the lower E-region is also considered.Key words: Ionosphere (auroral ionosphere; ionospheric irregularities; plasma waves and instabilities)
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Xu, Xiang, Chen Zhou, Run Shi, Binbin Ni, Zhengyu Zhao i Yuannong Zhang. "Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes". Annales Geophysicae 34, nr 9 (21.09.2016): 815–29. http://dx.doi.org/10.5194/angeo-34-815-2016.
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Abstract. Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.
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Wang, Jin, Gang Chen, Tao Yu, Zhongxin Deng, Xiangxiang Yan i Na Yang. "Middle-Scale Ionospheric Disturbances Observed by the Oblique-Incidence Ionosonde Detection Network in North China after the 2011 Tohoku Tsunamigenic Earthquake". Sensors 21, nr 3 (2.02.2021): 1000. http://dx.doi.org/10.3390/s21031000.
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The 2011 Tohoku earthquake and the following enormous tsunami caused great disturbances in the ionosphere that were observed in various regions along the Pacific Ocean. In this study, the oblique-incidence ionosonde detection network located in North China was applied to investigate the inland ionospheric disturbances related to the 2011 tsunamigenic earthquake. The ionosonde network consists of five transmitters and 20 receivers and can monitor regional ionosphere disturbances continuously and effectively. Based on the recorded electron density variations along the horizontal plane, the planar middle-scale ionospheric disturbances (MSTIDs) associated with the 2011 Tohoku tsunamigenic earthquake were detected more than 2000 km west of the epicenter about six hours later. The MSTIDs captured by the Digisonde, high-frequency (HF) Doppler measurement, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellite provided more information about the far-field inland propagation characteristics of the westward propagating gravity waves. The results imply that the ionosonde network has the potential for remote sensing of ionospheric disturbances induced by tsunamigenic earthquakes and provide a perspective for investigating the propagation process of associated gravity waves.
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Pavelyev, A. G., Y. A. Liou, K. Zhang, C. S. Wang, J. Wickert, T. Schmidt, V. N. Gubenko, A. A. Pavelyev i Y. Kuleshov. "Identification and localization of layers in the ionosphere using the eikonal and amplitude of radio occultation signals". Atmospheric Measurement Techniques 5, nr 1 (4.01.2012): 1–16. http://dx.doi.org/10.5194/amt-5-1-2012.
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Abstract. By using the CHAllenge Minisatellite Payload (CHAMP) radio occultation (RO) data, a description of different types of the ionospheric impacts on the RO signals at the altitudes 30–90 km of the RO ray perigee is given and compared with the results of measurements obtained earlier in the satellite-to-Earth communication link at frequency 1.5415 GHz. An analytical model is introduced for describing propagation of radio waves in a stratified medium consisting of sectors with spherically symmetric refractivity distribution. This model gives analytical expressions for the phase, bending angle, and refractive attenuation of radio waves and is applied to the analysis of radio wave propagation phenomena along an extended path including the atmosphere and two parts of the ionosphere. The model explains significant amplitude and phase variations at altitudes 30–90 km of the RO ray perigee and attributes them to inclined ionospheric layers. Based on this analytical model, an innovative technique is introduced to locate layers in the atmosphere and ionosphere. A necessary and sufficient criterion is obtained for a layer to be located at the RO ray perigee. This criterion gives both qualitative and quantitative estimation of the displacement of an ionospheric and/or atmospheric layer from the RO ray perigee. This is important, in particular, for determining the location of wind shears and directions of the internal wave propagation in the lower ionosphere, and, possibly, in the atmosphere.
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LaBelle, J. "High-latitude propagation studies using a meridional chain of LF/MF/HF receivers". Annales Geophysicae 22, nr 5 (8.04.2004): 1705–18. http://dx.doi.org/10.5194/angeo-22-1705-2004.
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Abstract. For over a decade, Dartmouth College has operated programmable radio receivers at multiple high-latitude sites covering the frequency range 100-5000kHz with about a 1-s resolution. Besides detecting radio emissions of auroral origin, these receivers record characteristics of the ionospheric propagation of natural and man-made signals, documenting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of distant transmissions on MF/HF frequencies are often enhanced by a few dB just before they fade away at dawn. The polarization and/or direction of the arrival of ionospherically propagating signals in the lower HF range (3-5MHz) show a consistent variation between pre-midnight, post-midnight, and pre-dawn conditions. As is well known, magnetic storms and substorms dramatically affect ionospheric propagation; data from multiple stations spanning the invariant latitude range 67-79° reveal spatial patterns of propagation characteristics associated with magnetic storms and substorms. For example, in the hours preceding many isolated substorms, favorable propagation conditions occur at progressively lower latitudes as a function of time preceding the substorm onset. For some of these effects, explanations follow readily from elementary ionospheric physics, but understanding others requires further investigation.Key words. Magnetospheric physics (annual phenomena) – Radio science (ionosphere propagation; radio-wave propagation)6
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Koucká Knížová, Petra, Kateřina Podolská, Kateřina Potužníková, Daniel Kouba, Zbyšek Mošna, Josef Boška i 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, nr 1 (17.01.2020): 73–93. http://dx.doi.org/10.5194/angeo-38-73-2020.
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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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Altadill, David, Antoni Segarra, Estefania Blanch, José Miguel Juan, Vadym V. Paznukhov, Dalia Buresova, Ivan Galkin, Bodo W. Reinisch i Anna Belehaki. "A method for real-time identification and tracking of traveling ionospheric disturbances using ionosonde data: first results". Journal of Space Weather and Space Climate 10 (2020): 2. http://dx.doi.org/10.1051/swsc/2019042.
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Traveling Ionospheric Disturbances (TIDs) are wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere. A method combining spectral analysis and cross-correlation is applied to time series of ionospheric characteristics (i.e., MUF(3000)F2 or foF2) using data of the networks of ionosondes in Europe and South Africa to estimate the period, amplitude, velocity and direction of propagation of TIDs. The method is verified using synthetic data and is validated through comparison of TID detection results made with independent observational techniques. The method provides near real time capability of detection and tracking of Large-Scale TIDs (LSTIDs), usually associated with auroral activity.
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Danskin, D. W., A. V. Koustov, T. Ogawa, N. Nishitani, S. Nozawa, S. E. Milan, M. Lester i D. Andre. "On the factors controlling occurrence of F-region coherent echoes". Annales Geophysicae 20, nr 9 (30.09.2002): 1385–97. http://dx.doi.org/10.5194/angeo-20-1385-2002.
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Abstract. Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave), D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines) condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere)
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Galushko, V. G., V. V. Paznukhov, Y. M. Yampolski i J. C. Foster. "Incoherent scatter radar observations of AGW/TID events generated by the moving solar terminator". Annales Geophysicae 16, nr 7 (31.07.1998): 821–27. http://dx.doi.org/10.1007/s00585-998-0821-3.
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Abstract. Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300-400 m s-1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation.Key words. Ionosphere (wave propagation) · Meteorology and atmospheric dynamics (waves and tides)
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Prikner, K., K. Mursula, J. Kangas, R. Kerttula i F. Z. Feygin. "An effect of the ionospheric Alfvén resonator on multiband Pc1 pulsations". Annales Geophysicae 22, nr 2 (1.01.2004): 643–51. http://dx.doi.org/10.5194/angeo-22-643-2004.
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Abstract. On 2 December 1999, the magnetometer stations in northern Finland registered structured Pc1 activity simultaneously in three distinct frequency bands. Using simultaneous EISCAT radar measurements of the high-latitude ionosphere, we have studied the ionospheric resonator properties during this multiband Pc1 event. The frequencies of the three structured Pc1 bands were found to closely correspond to the second, third and fourth harmonic of the calculated fundamental frequency of the ionospheric Alfvén resonator (IAR). In addition, those frequencies of the three pearl bands that were closest to the exact IAR harmonics were found to have the strongest intensities. The results demonstrate that the resonator can have an important role on ground-based Pc1 activity over a notably large frequency range, favoring transmission of waves with frequencies close to the resonator's eigenfrequencies. Since the frequencies of all three bands correspond to the maximum rather than the minimum of the transmission coefficient, the traditional bouncing wave packet model needs to be revised. Key words. Ionosphere (auroral ionosphere; ionosphere magnetosphere interactions; wave propagation)
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Kotik, Dmitriy, Ekaterina Orlova i Vladimir Yashnov. "Peculiarities of ULF wave characteristics in a multicomponent ionospheric plasma". Solnechno-Zemnaya Fizika 8, nr 4 (24.12.2022): 57–65. http://dx.doi.org/10.12737/szf-84202205.
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We have examined the properties of low-frequency electromagnetic waves in multicomponent ionospheric plasma in the 1–30 Hz band, using the magnetoionic theory. Complex permittivity tensor components and refractive indices of normal waves (ordinary and extraordinary) were calculated at altitudes from 80 to 750 km. The calculations show that the refractive indices are highly dependent on frequency and height. Polarization of ordinary and extraordinary waves is elliptical over the entire range of the frequencies investigated. The refractive index and the polarization of normal waves are demonstrated to tend to magnetohydrodynamic (MHD) values only at frequencies lower than 1 Hz. The group velocity vector of an extraordinary wave is not directed along the magnetic field, as follows from the MHD approximation, but it lies inside a cone within ±(5–10) degrees, depending on frequency. The group velocity vector of an ordinary wave is practically independent of the angle with the geomagnetic field as in the MHD approximation. The proposed method for calculating the characteristics of normal waves in the ionosphere can be used to study ULF wave propagation from both natural and artificial ionospheric sources, which arise under the action of powerful HF radio waves in the lower and upper ionosphere.
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Kotik, Dmitriy, Ekaterina Orlova i Vladimir Yashnov. "Peculiarities of ULF wave characteristics in a multicomponent ionospheric plasma". Solar-Terrestrial Physics 8, nr 4 (24.12.2022): 55–62. http://dx.doi.org/10.12737/stp-84202205.
Pełny tekst źródłaStreszczenie:
We have examined the properties of low-frequency electromagnetic waves in multicomponent ionospheric plasma in the 1–30 Hz band, using the magnetoionic theory. Complex permittivity tensor components and refractive indices of normal waves (ordinary and extraordinary) were calculated at altitudes from 80 to 750 km. The calculations show that the refractive indices are highly dependent on frequency and height. Polarization of ordinary and extraordinary waves is elliptical over the entire range of the frequencies investigated. The refractive index and the polarization of normal waves are demonstrated to tend to magnetohydrodynamic (MHD) values only at frequencies lower than 1 Hz. The group velocity vector of an extraordinary wave is not directed along the magnetic field, as follows from the MHD approximation, but it lies inside a cone within ±(5–10) degrees, depending on frequency. The group velocity vector of an ordinary wave is practically independent of the angle with the geomagnetic field as in the MHD approximation. The proposed method for calculating the characteristics of normal waves in the ionosphere can be used to study ULF wave propagation from both natural and artificial ionospheric sources, which arise under the action of powerful HF radio waves in the lower and upper ionosphere.
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Takahashi, Hisao, Cosme A. O. B. Figueiredo, Patrick Essien, Cristiano M. Wrasse, Diego Barros, Prosper K. Nyassor, Igo Paulino, Fabio Egito, Geangelo M. Rosa i Antonio H. R. Sampaio. "Signature of gravity wave propagations from the troposphere to ionosphere". Annales Geophysicae 40, nr 6 (1.12.2022): 665–72. http://dx.doi.org/10.5194/angeo-40-665-2022.
Pełny tekst źródłaStreszczenie:
Abstract. We observed a gravity wave (GW) signature in the OH emission layer in the upper mesosphere, and 4 h later, a medium-scale travelling ionospheric disturbance (MSTID) in the OI 630 nm emission layer. Spectral analysis of the two waves showed that both have almost the same wave characteristics: wavelength, period, phase speed and propagation direction, respectively, 200 km, 60 min, 50 m s−1, toward the southeast. From the gravity wave ray-tracing simulation for the mesospheric gravity wave, we found that the wave came from a tropospheric deep convection spot and propagated up to the 140 km altitude. Regarding the same wave characteristics between mesospheric GW and ionospheric MSTID, the two possible cases are investigated: a direct influence of the GW oscillation in the OI 630 nm emission height and the generation of a secondary wave during the GW breaking process. This is the first time to report an observational event of gravity wave propagation from the troposphere, mesosphere to thermosphere–ionosphere in the South American region.
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Yoshida, M., T. Yamauchi, T. Horie i M. Hayakawa. "On the generation mechanism of terminator times in subionospheric VLF/LF propagation and its possible application to seismogenic effects". Natural Hazards and Earth System Sciences 8, nr 1 (25.02.2008): 129–34. http://dx.doi.org/10.5194/nhess-8-129-2008.
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Abstract. The signals from VLF/LF transmitters are known to propagate in the Earth-ionosphere waveguide, so that the subionospheric propagation characteristics are very sensitive to the condition of the lower ionosphere. We know that there appear the terminator times just around the sunrise and sunset in the diurnal variation of subionospheric VLF/LF signal (amplitude and phase). These terminator times are found to shift significantly just around an earthquake, which enables us to infer the change in the ionosphere during the earthquake. In this paper we try to understand the physical mechanism on the generation of those terminator times for relatively short propagation path (less than 2000 km) by means of wave-hop method. It is found that the lowering of the ionosphere boundary during an earthquake decreases the path length of the sky wave and this alters the interference condition of this wave with the ground wave, which lead to an appearance of terminator times as the destructive interference between the ground and sky waves. Finally, we suggest a possible use of terminator time shifts to investigate the lower ionospheric plasma changes during the earthquakes.
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Chen, P., J. J. Chen, W. Q. Yao i B. Zhang. "Study of the 2013 Lushan <i>M</i> = 7.0 earthquake coseismic ionospheric disturbances". Natural Hazards and Earth System Sciences Discussions 1, nr 5 (16.10.2013): 5643–62. http://dx.doi.org/10.5194/nhessd-1-5643-2013.
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Abstract. On 20 April 2013, an earthquake of M =7.0 occurred in Lushan, Sichuan province, China. This paper investigates the coseismic ionospheric anomalies using GPS (Global Positioning System) data from 23 reference stations in Sichuan province that are a part of the Crustal Movement Observation Network of China (CMONOC). The recorded results show that a clear ionospheric anomaly occurred within 15 min after the earthquake near the epicenter, and the occurrence time of the anomalies recorded by various stations is related to the distance from the epicenter. The maximum anomaly is 0.25 TECu, with a 2 min duration and the distance of the recording station to the epicenter is 83 km. Acoustic waves generated by the crustal vertical movement during the earthquake propagate up to the height of the ionosphere lead to the ionospheric anomaly, and the propagation speed of the acoustic wave is calculated as 0.72 ± 0.04 km s-1 based on the propagation time and propagation distance, consistent with the average speed of sound waves within a 0–450 km atmospheric height.
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Liu, Yuhan, i Shuanggen Jin. "Ionospheric Rayleigh Wave Disturbances Following the 2018 Alaska Earthquake from GPS Observations". Remote Sensing 11, nr 8 (13.04.2019): 901. http://dx.doi.org/10.3390/rs11080901.
Pełny tekst źródłaStreszczenie:
Big earthquakes often excite the acoustic resonance between the earth’s surface and the lower atmosphere. The perturbations can propagate upward into the ionosphere and trigger ionospheric anomalies detected by dual-frequency GPS observations, but coseismic ionospheric disturbance (CID) directivity and mechanism are not clear. In this paper, the ionospheric response to the Mw = 7.9 Alaska earthquake on 23 January 2018 is investigated from about 100 continuous GPS stations near the epicenter. The fourth-order zero-phase Butterworth band-pass filter with cutoffs of 2.2 mHz and 8 mHz is applied to obtain the ionospheric disturbances. Results show that the CIDs with an amplitude of up to 0.06 total electron content units (TECU) are detected about 10 min after the Alaska earthquake. The CIDs are as a result of the upward propagation acoustic waves triggered by the Rayleigh wave. The propagation velocities of TEC disturbances are around 2.6 km/s, which agree well with the wave propagation speed of 2.7 km/s detected by the bottom pressure records. Furthermore, the ionospheric disturbances following the 2018 Mw = 7.9 Alaska earthquake are inhomogeneous and directional which is rarely discussed. The magnitude of ionospheric disturbances in the western part of the epicenter is more obvious than in the eastern part. This phenomenon also corresponds to the data obtained from the seismographs and bottom pressure records (BPRs) at the eastern and western side of the epicenter.
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Robinson, T. R. "Effects of multiple scatter on the propagation and absorption of electromagnetic waves in a field-aligned-striated cold magneto-plasma: implications for ionospheric modification experiments". Annales Geophysicae 20, nr 1 (31.01.2002): 41–55. http://dx.doi.org/10.5194/angeo-20-41-2002.
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Abstract. A new theory of the propagation of low power electromagnetic test waves through the upper-hybrid resonance layer in the presence of magnetic field-aligned plasma density striations, which includes the effects of multiple scatter, is presented. The case of sinusoidal striations in a cold magnetoplasma is treated rigorously and then extended, in an approximate manner, to the broad-band striation spectrum and warm plasma cases. In contrast to previous, single scatter theories, it is found that the interaction layer is much broader than the wavelength of the test wave. This is due to the combined electric fields of the scattered waves becoming localised on the contour of a fixed plasma density, which corresponds to a constant value for the local upper-hybrid resonance frequency over the whole interaction region. The results are applied to the calculation of the refractive index of an ordinary mode test wave during modification experiments in the ionospheric F-region. Although strong anomalous absorption arises, no new cutoffs occur at the upper-hybrid resonance, so that in contrast to the predictions of previous single scatter theories, no additional reflections occur there. These results are consistent with observations made during ionospheric modification experiments at Tromsø, Norway.Key words. Ionosphere (active experiments; ionospheric irregularities) Radio science (ionospheric propagation)
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Rapoport, Yuriy G., Oleg K. Cheremnykh, Volodymyr V. Koshovy, Mykola O. Melnik, Oleh L. Ivantyshyn, Roman T. Nogach, Yuriy A. Selivanov i in. "Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment". Annales Geophysicae 35, nr 1 (5.01.2017): 53–70. http://dx.doi.org/10.5194/angeo-35-53-2017.
Pełny tekst źródłaStreszczenie:
Abstract. We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100–420 m s−1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical–numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 − f1 in the altitude ranges 0–0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1–20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere–ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling.
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Onohara, Amelia Naomi, Inez Staciarini Batista i Paulo Prado Batista. "Wavenumber-4 structures observed in the low-latitude ionosphere during low and high solar activity periods using FORMOSAT/COSMIC observations". Annales Geophysicae 36, nr 2 (21.03.2018): 459–71. http://dx.doi.org/10.5194/angeo-36-459-2018.
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Abstract. The main purpose of this study is to investigate the four-peak structure observed in the low-latitude equatorial ionosphere by the FORMOSAT/COSMIC satellites. Longitudinal distributions of NmF2 (the density of the F layer peak) and hmF2 (ionospheric F2-layer peak height) averages, obtained around September equinox periods from 2007 to 2015, were submitted to a bi-spectral Fourier analysis in order to obtain the amplitudes and phases of the main waves. The four-peak structure in the equatorial and low-latitude ionosphere was present in both low and high solar activity periods. This kind of structure possibly has tropospheric origins related to the tidal waves propagating from below that modulate the E-region dynamo, mainly the eastward non-migrating diurnal tide with wavenumber 3 (DE3, E for eastward). This wave when combined with the migrating diurnal tide (DW1, W for westward) presents a wavenumber-4 (wave-4) structure under a synoptic view. Electron densities observed during 2008 and 2013 September equinoxes revealed that the wave-4 structures became more prominent around or above the F-region altitude peak (∼ 300–350 km). The four-peak structure remains up to higher ionosphere altitudes (∼ 800 km). Spectral analysis showed DE3 and SPW4 (stationary planetary wave with wavenumber 4) signatures at these altitudes. We found that a combination of DE3 and SPW4 with migrating tides is able to reproduce the wave-4 pattern in most of the ionospheric parameters. For the first time a study using wave variations in ionospheric observations for different altitude intervals and solar cycle was done. The conclusion is that the wave-4 structure observed at high altitudes in ionosphere is related to effects of the E-region dynamo combined with transport effects in the F region.
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Blagoveshchensky, D. V., i O. A. Maltseva. "Simulation of Medium Wave Propagation in the Magnetosphere". Geomagnetism and Aeronomy 62, nr 1-2 (luty 2022): 58–65. http://dx.doi.org/10.1134/s0016793222020049.
Pełny tekst źródłaStreszczenie:
Abstract A model of the medium of the ionosphere and magnetosphere, including the distributions of the concentrations and temperatures, collision frequencies, and magnetic field parameters, is described. The ray-tracing method was used to simulate the parameters of medium radio waves in this environment. The wave trajectories were calculated in the approximation of geometric optics. When the level of solar and geomagnetic activity and the location of the transmitter and the frequency are set, the parameters of the wave paths can be calculated. Numerical modeling of the characteristics of experimental echo signals has shown that the mechanism of magnetospheric propagation is of paramount importance. In this case, the main ionospheric trough turned out to be an unusual channel. Medium waves propagate inside the trough along the plasmapause. This is possible with sufficiently clear relationships between the positions of the trough, plasmapause, and transmitter. The considered effect of medium wave channeling can be used to diagnose the position of the trough and plasmapause.
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Kouris, S. S., P. A. Bradley i P. Dominici. "<i>Letter to the Editor:</i> Solar-cycle variation of the daily <i>fo</i>F2 and M(3000)F2". Annales Geophysicae 16, nr 8 (31.08.1998): 1039–42. http://dx.doi.org/10.1007/s00585-998-1039-0.
Pełny tekst źródłaStreszczenie:
Abstract. Daily values of the ionospheric characteristics foF2 and M(3000)F2 for a given hour and month are correlated with the corresponding daily values of sunspot number using measured data collected at seven European locations. The significance of applying different-order polynomials is considered and the times are confirmed when the higher-order terms are important. Mean correlation coefficients for combined data sets over all hours, months and stations are determined, together with the standard errors of estimates. Comparisons are made with corresponding figures for monthly median values derived from the same data sets.Key words. Electromagnetics (Guided waves) · Ionosphere (Ionospheric disturbances) · Radio Science (Radio wave propagation)
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Arnold, N. F., T. B. Jones, T. R. Robinson, A. J. Stocker i J. A. Davies. "Validation of the CUTLASS HF radar gravity wave observing capability using EISCAT CP-1 data". Annales Geophysicae 16, nr 10 (31.10.1998): 1392–99. http://dx.doi.org/10.1007/s00585-998-1392-z.
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Abstract. Quasi-periodic fluctuations in the returned ground-scatter power from the SuperDARN HF radars have been linked to the passage of medium-scale gravity waves. We have applied a technique that extracts the first radar range returns from the F-region to study the spatial extent and characteristics of these waves in the CUTLASS field-of-view. Some ray tracing was carried out to test the applicability of this method. The EISCAT radar facility at Tromsø is well within the CUTLASS field-of-view for these waves and provides a unique opportunity to assess independently the ability of the HF radars to derive gravity wave information. Results from 1st March, 1995, where the EISCAT UHF radar was operating in its CP-1 mode, demonstrate that the radars were in good agreement, especially if one selects the electron density variations measured by EISCAT at around 235 km. CUTLASS and EISCAT gravity wave observations complement each other; the former extends the spatial field of view considerably, whilst the latter provides detailed vertical information about a range of ionospheric parameters.Key words. Ionosphere (ionosphere – atmosphere interactions) · Meteorology and atmospheric dynamics (thermospheric dynamics) · Radio science (ionospheric propagations)
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Hocke, K., i K. Schlegel. "A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995". Annales Geophysicae 14, nr 9 (30.09.1996): 917–40. http://dx.doi.org/10.1007/s00585-996-0917-6.
Pełny tekst źródłaStreszczenie:
Abstract. Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth\\'s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.
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Afraimovich, E. L., N. P. Perevalova, A. V. Plotnikov i A. M. Uralov. "The shock-acoustic waves generated by earthquakes". Annales Geophysicae 19, nr 4 (30.04.2001): 395–409. http://dx.doi.org/10.5194/angeo-19-395-2001.
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Abstract. We investigate the form and dynamics of shock-acoustic waves generated by earthquakes. We use the method for detecting and locating the sources of ionospheric impulsive disturbances, based on using data from a global network of receivers of the GPS navigation system, and require no a priori information about the place and time of the associated effects. The practical implementation of the method is illustrated by a case study of earthquake effects in Turkey (17 August and 12 November 1999), in Southern Sumatra (4 June 2000), and off the coast of Central America (13 January 2001). It was found that in all instances the time period of the ionospheric response is 180–390 s, and the amplitude exceeds, by a factor of two as a minimum, the standard deviation of background fluctuations in total electron content in this range of periods under quiet and moderate geomagnetic conditions. The elevation of the wave vector varies through a range of 20–44°, and the phase velocity (1100–1300 m/s) approaches the sound velocity at the heights of the ionospheric F-region maximum. The calculated (by neglecting refraction corrections) location of the source roughly corresponds to the earthquake epicenter. Our data are consistent with the present views that shock-acoustic waves are caused by a piston-like movement of the Earth’s surface in the zone of an earthquake epicenter.Key words. Ionosphere (ionospheric disturbances; wave propagation) – Radio science (ionospheric propagation)
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Marshall, R. A., i F. W. Menk. "Observations of Pc 3-4 and Pi 2 geomagnetic pulsations in the low-latitude ionosphere". Annales Geophysicae 17, nr 11 (30.11.1999): 1397–410. http://dx.doi.org/10.1007/s00585-999-1397-2.
Pełny tekst źródłaStreszczenie:
Abstract. Day-time Pc 3–4 (~5–60 mHz) and night-time Pi 2 (~5–20 mHz) ULF waves propagating down through the ionosphere can cause oscillations in the Doppler shift of HF radio transmissions that are correlated with the magnetic pulsations recorded on the ground. In order to examine properties of these correlated signals, we conducted a joint HF Doppler/magnetometer experiment for two six-month intervals at a location near L = 1.8. The magnetic pulsations were best correlated with ionospheric oscillations from near the F region peak. The Doppler oscillations were in phase at two different altitudes, and their amplitude increased in proportion to the radio sounding frequency. The same results were obtained for the O- and X-mode radio signals. A surprising finding was a constant phase difference between the pulsations in the ionosphere and on the ground for all frequencies below the local field line resonance frequency, independent of season or local time. These observations have been compared with theoretical predictions of the amplitude and phase of ionospheric Doppler oscillations driven by downgoing Alfvén mode waves. Our results agree with these predictions at or very near the field line resonance frequency but not at other frequencies. We conclude that the majority of the observations, which are for pulsations below the resonant frequency, are associated with downgoing fast mode waves, and models of the wave-ionosphere interaction need to be modified accordingly.Key words. Ionosphere (ionosphere irregularities) · Magnetospheric physics (magnetosphere-ionosphere interactions) · Radio science (ionospheric physics)
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Yang, Xuguang, Aijun Liu, Changjun Yu i Linwei Wang. "Ionospheric Clutter Model for HF Sky-Wave Path Propagation with an FMCW Source". International Journal of Antennas and Propagation 2019 (8.05.2019): 1–10. http://dx.doi.org/10.1155/2019/1782942.
Pełny tekst źródłaStreszczenie:
A theoretical model of the sky-wave path propagation with frequency modulated continuous wave (FMCW) source for high frequency (HF) radar is proposed in this paper. Based on the modeling of pulsed source, the expression of the received electric field with an FMCW source is derived for the reflection case from the ionospheric irregularities. Subsequently, the ionospheric reflection coefficient with different phase power spectrums for vertical and oblique backscattering propagation paths is incorporated into the ionospheric clutter model. Simulation results show that the peak power of FMCW in average is lower than that of pulsed waveform. Furthermore, different incident angles and magnetic field in mid-latitude can also influence the power density of the backscattering ionospheric clutter. Finally, the data analysis results from the high frequency surface wave radar (HFSWR) and Ionosonde collected in Yellow Sea preliminarily verify the inversion of the variance of the electron density fluctuation and the vertical drift velocity of the irregularities within ionosphere.
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Pavelyev, A. G., K. Zhang, J. Wickert, T. Schmidt, Y. A. Liou, V. N. Gubenko, A. A. Pavelyev, R. R. Salimzjanov i Y. Kuleshov. "Identification and localization of layers in the ionosphere using the eikonal and amplitude of radio occultation signals". Atmospheric Measurement Techniques Discussions 4, nr 2 (1.03.2011): 1465–92. http://dx.doi.org/10.5194/amtd-4-1465-2011.
Pełny tekst źródłaStreszczenie:
Abstract. Conditions for communication, navigation, and remote sensing in the ionosphere and atmosphere depend strongly on the ionospheric impact on the radio waves propagation. By use of the CHAllenge Minisatellite Payload (CHAMP) radio occultation (RO) data a description of different types of the ionospheric contributions to the RO signals at the altitudes 30–90 km of the RO ray perigee is introduced and compared with results of measurements obtained earlier in the communication link satellite-to-Earth at frequency 1.5415 GHz. An analytical model is introduced for description of the radio waves propagation in a stratified medium consisting of sectors having the spherically symmetric distributions of refractivity. Model presents analytical expressions for the phase path and refractive attenuation of radio waves. Model is applied for analysis of the radio waves propagation effects along a prolonged path including the atmosphere and two parts of the ionosphere. Model explains significant amplitude and phase variations at the altitudes 30–90 km of the RO ray perigee as connected with influence of the inclined ionospheric layers. An innovative eikonal acceleration technique is described and applied for the identification of the inclined ionospheric layers contributions and their location. Possibility to separate the influence of layered structures from contributions of irregularities and turbulence is analyzed.
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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.
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Khantadze, A. G., G. V. Jandieri, A. Ishimaru, T. D. Kaladze i Zh M. Diasamidze. "Electromagnetic oscillations of the Earth's upper atmosphere (review)". Annales Geophysicae 28, nr 7 (1.07.2010): 1387–99. http://dx.doi.org/10.5194/angeo-28-1387-2010.
Pełny tekst źródłaStreszczenie:
Abstract. A complete theory of low-frequency MHD oscillations of the Earth's weakly ionized ionosphere is formulated. Peculiarities of excitation and propagation of electromagnetic acoustic-gravity, MHD and planetary waves are considered in the Earth's ionosphere. The general dispersion equation is derived for the magneto-acoustic, magneto-gravity and electromagnetic planetary waves in the ionospheric E- and F-regions. The action of the geomagnetic field on the propagation of acoustic-gravity waves is elucidated. The nature of the existence of the comparatively new large-scale electromagnetic planetary branches is emphasized.
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Aburjania, G. D., K. Z. Chargazia, G. V. Jandieri, A. G. Khantadze i O. A. Kharshiladze. "On the new modes of planetary-scale electromagnetic waves in the ionosphere". Annales Geophysicae 22, nr 4 (2.04.2004): 1203–11. http://dx.doi.org/10.5194/angeo-22-1203-2004.
Pełny tekst źródłaStreszczenie:
Abstract. Using an analogy method the frequencies of new modes of the electromagnetic planetary-scale waves (with a wavelength of 103 km or more), having a weather forming nature, are found at different ionospheric altitudes. This method gives the possibility to determine spectra of ionospheric electromagnetic perturbations directly from the dynamic equations without solving the general dispersion equation. It is shown that the permanently acting factor-latitude variation of the geomagnetic field generates fast and slow weakly damping planetary electromagnetic waves in both the E- and F-layers of the ionosphere. The waves propagate eastward and westward along the parallels. The fast waves have phase velocities (1–5)km s–1 and frequencies (10–1–10–4), and the slow waves propagate with velocities of the local winds with frequencies (10–4–10–6)s–1 and are generated in the E-region of the ionosphere. Fast waves having phase velocities (10-1500)km s–1 and frequencies (1–10–3)s–1 are generated in the F-region of the ionosphere. The waves generate the geomagnetic pulsations of the order of one hundred nanoTesla by magnitude. The properties and parameters of the theoretically studied electromagnetic waves agree with those of large-scale ultra-low frequency perturbations observed experimentally in the ionosphere. Key words. Ionosphere (ionospheric disturbances; waves propagation; ionosphere atmosphere interactions)
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Wu, Dong L., Nimalan Swarnalingam, Cornelius Csar Jude H. Salinas, Daniel J. Emmons, Tyler C. Summers i Robert Gardiner-Garden. "Optimal Estimation Inversion of Ionospheric Electron Density from GNSS-POD Limb Measurements: Part I-Algorithm and Morphology". Remote Sensing 15, nr 13 (23.06.2023): 3245. http://dx.doi.org/10.3390/rs15133245.
Pełny tekst źródłaStreszczenie:
GNSS-LEO radio links from Precise Orbital Determination (POD) and Radio Occultation (RO) antennas have been used increasingly in characterizing the global 3D distribution and variability of ionospheric electron density (Ne). In this study, we developed an optimal estimation (OE) method to retrieve Ne profiles from the slant total electron content (hTEC) measurements acquired by the GNSS-POD links at negative elevation angles (ε < 0°). Although both OE and onion-peeling (OP) methods use the Abel weighting function in the Ne inversion, they are significantly different in terms of performance in the lower ionosphere. The new OE results can overcome the large Ne oscillations, sometimes negative values, seen in the OP retrievals in the E-region ionosphere. In the companion paper in this Special Issue, the HmF2 and NmF2 from the OE retrieval are validated against ground-based ionosondes and radar observations, showing generally good agreements in NmF2 from all sites. Nighttime hmF2 measurements tend to agree better than the daytime when the ionosonde heights tend to be slightly lower. The OE algorithm has been applied to all GNSS-POD data acquired from the COSMIC-1 (2006–2019), COSMIC-2 (2019–present), and Spire (2019–present) constellations, showing a consistent ionospheric Ne morphology. The unprecedented spatiotemporal sampling of the ionosphere from these constellations now allows a detailed analysis of the frequency–wavenumber spectra for the Ne variability at different heights. In the lower ionosphere (~150 km), we found significant spectral power in DE1, DW6, DW4, SW5, and SE4 wave components, in addition to well-known DW1, SW2, and DE3 waves. In the upper ionosphere (~450 km), additional wave components are still present, including DE4, DW4, DW6, SE4, and SW4. The co-existence of eastward- and westward-propagating wave4 components implies the presence of a stationary wave4 (SPW4), as suggested by other earlier studies. Further improvements to the OE method are proposed, including a tomographic inversion technique that leverages the asymmetric sampling about the tangent point associated with GNSS-LEO links.
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Gan, Q., J. Yue, L. C. Chang, W. B. Wang, S. D. Zhang i J. Du. "Observations of thermosphere and ionosphere changes due to the dissipative 6.5-day wave in the lower thermosphere". Annales Geophysicae 33, nr 7 (24.07.2015): 913–22. http://dx.doi.org/10.5194/angeo-33-913-2015.
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Abstract. In the current work, temperature and wind data from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during the years 2002–2007 were used to describe the seasonal variations of the westward propagating 6.5-day planetary wave in the mesosphere and lower thermosphere (MLT). Thermospheric composition data from the TIMED satellite and ionospheric total electron content (TEC) from the International Global Navigation Satellite System (GNSS) Service were then employed to carry out two case studies on the effect of this dissipating wave on the thermosphere/ionosphere. In both cases, there were westward anomalies of ~ 30–40 m s−1 in zonal wind in the MLT region that were caused by momentum deposition of the 6.5-day wave, which had peak activity during equinoxes. The westward zonal wind anomalies led to extra poleward meridional flows in both hemispheres. Meanwhile, there were evident overall reductions of thermospheric column density O / N2 ratio and ionospheric TEC with magnitudes of up to 16–24 % during these two strong 6.5-day wave events. Based on the temporal correlation between O / N2 and TEC reductions, as well as the extra poleward meridional circulations associated with the 6.5-day waves, we conclude that the dissipative 6.5-day wave in the lower thermosphere can cause changes in the thermosphere/ionosphere via the mixing effect, similar to the quasi-two-day wave (QTDW) as predicted by Yue and Wang (2014).
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Kong, Jian, Lulu Shan, Xiao Yan i Youkun Wang. "Analysis of Ionospheric Disturbance Response to the Heavy Rain Event". Remote Sensing 14, nr 3 (21.01.2022): 510. http://dx.doi.org/10.3390/rs14030510.
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Meteorological activities in the troposphere would affect electron concentrations and distributions in the ionosphere, thereby exciting ionospheric disturbance. To explore the ionospheric anomalies during severe convective weather, the ionospheric phenomenon during the heavy rainfall in Sichuan Province on 9 July 2013 was analyzed based on GNSS data. The Total Electron Content (TEC) are evaluated by carrier phase smoothed pseudoranges. Then, the dTEC (detrend TEC) sequences are obtained by using the cubic smoothing spline. They show obvious N-shaped ionospheric disturbances and have propagation characteristics, with the maximum of 0.4 TECU. Frequency domain analysis using continuous wavelet transform (CWT) also reached similar conclusions—that there are obvious ionospheric disturbances with different frequencies and intensity. Based on the isotropic assumption and feature points method, the horizontal propagation velocity of the disturbances in the ionosphere is estimated to be approximately 150 m/s. Then, Sichuan Province is divided into 1° × 1° grids, and the disturbance trigger source is determined via the grid searching method to be the central of Sichuan Province. Finally, the mechanisms causing ionospheric disturbance are discussed. During the heavy rainfall, the strong convection may excite gravity waves (GWs), which are driven by terrain and background wind fields to propagate upwards to the ionosphere and release energy, causing ionospheric disturbances.
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Sun, L., W. Wan, F. Ding i T. Mao. "Gravity wave propagation in the realistic atmosphere based on a three-dimensional transfer function model". Annales Geophysicae 25, nr 9 (2.10.2007): 1979–86. http://dx.doi.org/10.5194/angeo-25-1979-2007.
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Abstract. In order to study the filter effect of the background winds on the propagation of gravity waves, a three-dimensional transfer function model is developed on the basis of the complex dispersion relation of internal gravity waves in a stratified dissipative atmosphere with background winds. Our model has successfully represented the main results of the ray tracing method, e.g. the trend of the gravity waves to travel in the anti-windward direction. Furthermore, some interesting characteristics are manifest as follows: (1) The method provides the distribution characteristic of whole wave fields which propagate in the way of the distorted concentric circles at the same altitude under the control of the winds. (2) Through analyzing the frequency and wave number response curve of the transfer function, we find that the gravity waves in a wave band of about 15–30 min periods and of about 200–400 km horizontal wave lengths are most likely to propagate to the 300-km ionospheric height. Furthermore, there is an obvious frequency deviation for gravity waves propagating with winds in the frequency domain. The maximum power of the transfer function with background winds is smaller than that without background winds. (3) The atmospheric winds may act as a directional filter that will permit gravity wave packets propagating against the winds to reach the ionospheric height with minimum energy loss.
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Васильев, Павел, Pavel Vasilyev, Иван Карпов, Ivan Karpov, Сергей Кшевецкий i Sergey Kshevetskii. "Modeling of the effect of internal gravity waves on upper atmospheric conditions during sudden stratospheric warming". Solar-Terrestrial Physics 2, nr 3 (27.10.2016): 99–105. http://dx.doi.org/10.12737/22288.
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We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of development of a sudden stratospheric warming (SSW), on upper atmospheric conditions. In the numerical experiment, we use a two-dimensional model of propagation of atmospheric waves, taking into account dissipative and nonlinear processes accompanying wave propagation. As a source of disturbances we consider temperature and density disturbances in the stratosphere during SSWs. Amplitude and frequency characteristics of the source of disturbances are estimated from observations and IGW theory. Numerical calculations showed that waves generated at stratospheric heights during SSW can cause temperature changes in the upper atmosphere. Maximum relative disturbances, caused by such waves, with respect to quiet conditions are observed at 100–200 km. Disturbances of the upper atmosphere in turn have an effect on the dynamics of charged component in the ionosphere and can contribute to observable ionospheric effects of SSW.
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Васильев, Павел, Pavel Vasilyev, Иван Карпов, Ivan Karpov, Сергей Кшевецкий i Sergey Kshevetskii. "Modeling of the effect of internal gravity waves on upper atmospheric conditions during sudden stratospheric warming". Solnechno-Zemnaya Fizika 2, nr 3 (17.09.2016): 69–73. http://dx.doi.org/10.12737/18890.
Pełny tekst źródłaStreszczenie:
We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of development of a sudden stratospheric warming (SSW), on upper atmospheric conditions. In the numerical experiment, we use a two-dimensional model of propagation of atmospheric waves, taking into account dissipative and nonlinear processes accompanying wave propagation. As a source of disturbances we consider temperature and density disturbances in the stratosphere during SSWs. Amplitude and frequency characteristics of the source of disturbances are estimated from observations and IGW theory. Numerical calculations showed that waves generated at stratospheric heights during SSW can cause temperature changes in the upper atmosphere. Maximum relative disturbances, generated by such waves, with respect to quiet conditions are observed at 100–200 km. Disturbances of the upper atmosphere in turn have an effect on dynamics of a charged component in the ionosphere and can contribute to observable ionospheric effects of SSW.
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Li, Mei, Handong Tan i Meng Cao. "Ionospheric influence on the seismo-telluric current related to electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake". Solid Earth 7, nr 5 (19.10.2016): 1405–15. http://dx.doi.org/10.5194/se-7-1405-2016.
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Abstract. A three-layer (Earth–air–ionosphere) physical model, as well as a two-layer (Earth–air) model, is employed in this paper to investigate the ionospheric effect on the wave fields for a finite length dipole current source co-located at a hypocenter depth and along the main fault of an earthquake when the distance between the epicenter and an observing station is up to 1000 km or even more. The results show that all electrical fields are free of ionospheric effects for different frequencies in a relative short range, e.g., ∼ 300 km for f = 1 Hz, implying the ionospheric influence on electromagnetic fields can be neglected within this range, which becomes smaller as the frequency increases. However, the ionosphere can give a constructive interference to the waves passing through and make them decay slowly when an observation is out of this range; moreover, the ionospheric effect can be up to 1–2 orders of magnitude of the electrical fields. For a ground-based observable 1.3 mV m−1 electric signal at f = 1 Hz 1440 km away from the Wenchuan MS 8.0 earthquake, the expected seismo-telluric current magnitude for the Earth–air–ionosphere model is of 5.0 × 107A, 1 magnitude smaller than the current value of 3.7 × 108A obtained by the Earth–air model free of ionospheric effects. This indicates that the ionosphere facilitates the electromagnetic wave propagation, as if the detectability of the system were improved effectively and it is easier to record a signal even for stations located at distances beyond their detectability thresholds. Furthermore, the radiating patterns of the electrical field components |Ex| and |Ey| are complementary to each other, although any two-dimensional (2-D) power distribution of these components shows strong power areas as well as weak ones, which is advantageous to register a signal if the observing system is designed to measure both of them instead of only one.
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Shi, Liu, Guo, Liu, You i Wang. "Pre-Earthquake and Coseismic Ionosphere Disturbances of the Mw 6.6 Lushan Earthquake on 20 April 2013 Monitored by CMONOC". Atmosphere 10, nr 4 (22.04.2019): 216. http://dx.doi.org/10.3390/atmos10040216.
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In order to study the coupling relationship between large earthquakes and the ionosphere, the techniques of ionosphere data acquisition were refined by the Crustal Movement Observation Network of China (CMONOC) to detect the pre-earthquake ionospheric abnormal and coseismic ionospheric disturbances (CID) of the Mw 6.6 Lushan earthquake on 20 April 2013. Based on the regional ionosphere maps (RIMs) derived from the Global Positioning System (GPS) observations of CMONOC, the ionospheric local effects near the epicenter of the Lushan earthquake one month prior to the shock were analyzed. The results show that the total electron content (TEC) anomalies appeared 12–14 (6–8 April), 19 (1 April), and 25–27 (24–26 March) days prior to the Lushan earthquake, which are defined as periods 1, 2, and 3, respectively. Multi-indices including the ring current index (Dst), geomagnetic planetary (Kp) index, wind plasma speed (Vsw) index, F10.7, and solar flares were utilized to represent the solar–terrestrial environment in different scales and eliminate the effects of solar and geomagnetic activities on the ionosphere. After the interference of solar–terrestrial activity and the diurnal variation in the lower thermosphere were excluded, the TEC variations with obvious equatorial ionospheric anomaly (EIA) in period-1 were considered to be related to the Lushan earthquake. We further retrieved precise slant TECs (STECs) near the epicenter to study the coseismic ionospheric disturbance (CID). The results show that there was clear STEC disturbance occurring within half an hour after the Lushan earthquake, and the CID propagation distance was less than the impact radius of the Lushan earthquake (689 km). The shell models with different altitudes were adopted to analyze the propagation speed of the CID. It is found that at the F2-layer with the altitude of 277 km, which had a CID horizontal propagation velocity of 0.84 ± 0.03 km/s, was in accordance with the acoustic wave propagation velocity. The calculated velocity acoustic wave from the epicenter to the ionospheric pierce points of this shell model was about 0.53 ± 0.03km/s, which was also consistent with its actual velocity within the altitude of 0–277 km. Affected by the geomagnetic field, the CID mainly propagated along the southeast direction at the azimuth of 190°, which was almost parallel to the local magnetic line.
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Silva, Graziela B. D., Antonio L. Padilha i Livia R. Alves. "Latitudinal variation of Pc3–Pc5 geomagnetic pulsation amplitude across the dip equator in central South America". Annales Geophysicae 38, nr 1 (7.01.2020): 35–49. http://dx.doi.org/10.5194/angeo-38-35-2020.
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Abstract. In order to clarify the equatorial electrojet effects on ground magnetic pulsations in central South America, we statistically analyzed the amplitude structure of Pc3 and Pc5 pulsations recorded during days considered quiet to moderately disturbed at multiple equatorial stations nearly aligned along the 10∘ magnetic meridian. It was observed that Pc3 amplitudes are attenuated around noon at the dip equator for periods shorter than ∼35 s. It is proposed that daytime Pc3s are related to MHD (magnetohydrodynamic) compressional wave vertically incident on the ionosphere, with the screening effect induced by enhanced conductivity in the dip equator causing wave attenuation. Daytime Pc5s showed amplitude enhancement at all equatorial stations, which can be explained by the model of waves excited at higher latitudes and propagating equatorward in an Earth–ionosphere waveguide. However, a slight depression in Pc5 amplitude compared to neighboring equatorial stations and a phase lag in relation to an off-equatorial station were detected at the dip equator. This wave amplitude depression in the Pc5 frequency band cannot be explained by the ionospheric waveguide model alone, and we propose that an alternative propagation model that allows ULF (ultra-low-frequency) waves to penetrate directly from the magnetosphere to low latitudes could be operating simultaneously to produce these features at the dip equator. Significant effects of the sunrise terminator on Pc3 pulsations were also observed at the stations closest to the dip equator. Contrary to what is reported at other longitudes, in central South America the sunrise effect decreases the D∕H amplitude ratio. We suggest that these differences may arise from the unique characteristics of this sector, with a strong longitudinal variation in the magnetic declination and precipitation of energetic particles due to the presence of the South Atlantic Magnetic Anomaly (SAMA). The H-component amplification can be explained by enhancements of the zonal electric field near the magnetic equator driven by F-region neutral winds and waves in the fast-mode of propagation during sunrise.
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Kryukovsky, Andrew S., Boris G. Kutuza, Vladimir I. Stasevich i Dmitry V. Rastyagaev. "Ionospheric Inhomogeneities and Their Influences on the Earth’s Remote Sensing from Space". Remote Sensing 14, nr 21 (30.10.2022): 5469. http://dx.doi.org/10.3390/rs14215469.
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An important problem that arises when planning experiments on remote sensing from space in the P-band is taking into account the influence of the Earth’s ionosphere. We investigated the influence of ionospheric inhomogeneities on the results of remote sensing of the Earth from space, taking into account the curvature of the propagation medium. One- and two-layer models of the ionosphere, both with and without large-scale inhomogeneities of the cold ionospheric plasma, were considered. To obtain numerical results, a bicharacteristic system was used, which makes it possible to adequately take into account the complex structures of ionospheric plasma layers. The dependence of the rate of phase change on the height and the dependence of the total electron concentration on the horizontal distance and group time were investigated. The case was compared when the vector of the strength of the Earth’s magnetic field is perpendicular to the plane of propagation, and the case when this vector lies in the plane of propagation. The dependence of the difference between the refractive indices on the height along the rays was studied. Estimates of the Faraday rotation angle and phase deviation were obtained for various models. The magnitude of the angle of Faraday rotation depends significantly on the orientation of the trajectory relative to the Earth’s magnetic field. Polarization coefficients are investigated. It is shown that the o- and x-waves are separately circularly polarized, and the contribution of the longitudinal component of the electric field in the electromagnetic wave is insignificant.