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1
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.
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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)
2
Hamza, A. M., i W. Lyatsky. "The Alfvén resonator revisited". Annales Geophysicae 28, nr 2 (2.02.2010): 359–66. http://dx.doi.org/10.5194/angeo-28-359-2010.
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Abstract. Two models for a magnetosphere-ionosphere coupling feedback instability in the lower magnetosphere are studied. In both models the instability arises because of the generation of an Alfvén wave from growing arc-like structures in the ionospheric conductivity. The first model is based on the modulation of precipitating electrons by field-aligned currents of the upward moving Alfvén wave (Modulation Model). The second model takes into consideration the reflection of the Alfvén wave from a maximum of the Alfvén velocity at about 3000 km altitude (Reflection Model). The growth of structures in both models takes place when the ionization function associated with upward field aligned current is shifted from the edges of enhanced conductivity structures to their centers. Such a shift arises because the structures move along the ionosphere at a velocity different from the E×B drift velocity. As a result, field-aligned currents of upward propagating Alfvén wave at some altitude appear shifted with respect to the edges of the structures. Although both models may work, the growth rate for the first model, as based on the modulation of the precipitating accelerated electrons, for typical conditions, may be tens or more times larger than that for the second model based on the Alfvén wave reflection. The proposed models can provide the growth of both single and periodic structures. When applied to auroral arc generation the studied instability leads to high growth rates and narrow arcs. The physical mechanism is mostly suitable for the generation of auroral arcs with widths of the order of 1 km and less. The growth rate of the instability for such structures can be as large as 0.3 s−1. In the case of periodic structures, their motion must lead to the generation of magnetic pulsations with periods of about 1–6 s, which is close to the expected period of Alfvén resonant oscillations in the lower magnetosphere. However, these oscillations (for the first and most effective model MM) are not exactly Alfvén resonant oscillations. These oscillations are modulations in the ionospheric density, which propagate along the ionospheric currents and not along the magnetic field lines.
3
Menk, F. W., T. K. Yeoman, D. M. Wright, M. Lester i F. Honary. "High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground". Annales Geophysicae 21, nr 2 (28.02.2003): 559–76. http://dx.doi.org/10.5194/angeo-21-559-2003.
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Abstract. We report the simultaneous observation of 1.6–1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20° in latitude, coupling to a field line resonance near 72° magnetic latitude. The magnetic pulsations had azimuthal m numbers ~ -2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6–1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ± 10 ms-1. A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66° magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to track features in the ionosphere.Key words. Ionosphere (Ionosphere-magnetosphere interactions; ionospheric disturbances) – Magnetospheric physics (MHD waves and instabilities)
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Пилипенко, Вячеслав, Vyacheslav Pilipenko, Ольга Козырева, Olga Kozyreva, Лиза Бэддели, Liza Baddeley, Дэг Лорентцен, Dag Lorentzen, Владимир Белаховский i Vladimir Belakhovsky. "Suppression of the dayside magnetopause surface modes". Solnechno-Zemnaya Fizika 3, nr 4 (27.12.2017): 17–26. http://dx.doi.org/10.12737/szf-34201702.
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Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of background fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.
5
Nakashima, Yuki, Kosuke Heki, Akiko Takeo, Mokhamad N. Cahyadi, Arif Aditiya i Kazunori Yoshizawa. "Atmospheric resonant oscillations by the 2014 eruption of the Kelud volcano, Indonesia, observed with the ionospheric total electron contents and seismic signals". Earth and Planetary Science Letters 434 (styczeń 2016): 112–16. http://dx.doi.org/10.1016/j.epsl.2015.11.029.
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Yeoman, T. K., D. M. Wright, T. R. Robinson, J. A. Davies i M. Rietveld. "High spatial and temporal resolution observations of an impulse-driven field line resonance in radar backscatter artificially generated with the Tromsø heater". Annales Geophysicae 15, nr 6 (30.06.1997): 634–44. http://dx.doi.org/10.1007/s00585-997-0634-9.
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Abstract. The CUTLASS Finland HF radar has been operated in conjunction with the EISCAT Tromsø RF ionospheric heater facility to examine a ULF wave characteristic of the development of a field line resonance (FLR) driven by a cavity mode caused by a magnetospheric impulse. When the heater is on, striating the ionosphere with field-aligned ionospheric electron density irregularities, a large enough radar target is generated to allow post-integration over only 1 second. When combined with 15 km range gates, this gives radar measurements of a naturally occurring ULF wave at a far better temporal and spatial resolution than has been achieved previously. The time-dependent signature of the ULF wave has been examined as it evolves from a large-scale cavity resonance, through a transient where the wave period was latitude-dependent and the oscillation had the characteristics of freely ringing field lines, and finally to a very narrow, small-scale local field line resonance. The resonance width of the FLR is only 60 km and this is compared with previous observations and theory. The FLR wave signature is strongly attenuated in the ground magnetometer data. The characterisation of the impulse driven FLR was only achieved very crudely with the ground magnetometer data and, in fact, an accurate determination of the properties of the cavity and field line resonant systems challenges the currently available limitations of ionospheric radar techniques. The combination of the latest ionospheric radars and facilities such as the Tromsø ionospheric heater can result in a powerful new tool for geophysical research.
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Pitout, F., P. Eglitis i P. L. Blelly. "High-latitude dayside ionosphere response to Pc5 field line resonance". Annales Geophysicae 21, nr 7 (31.07.2003): 1509–20. http://dx.doi.org/10.5194/angeo-21-1509-2003.
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Abstract. We report observations of pulsations due to Field Line Resonance (FLR) in the morning sector of the high-latitude dayside ionosphere on 1 February 1998. The Geotail spacecraft, ideally skimming the dayside magnetopause, monitored the magnetopause motion, which is seen to induce a modulated response of the ionosphere by means of ULF waves. Pulsations in the Pc5 frequency range were observed in the ground magnetic field measured by the IMAGE array, as well as in the electron and ion temperatures measured by the EISCAT Svalbard Radar. The ion temperature oscillations are an indicator of a modulated convection electric field while field-aligned currents (FAC) associated with the FLR control the electron temperature. We have performed a simulation of the ionosphere experiencing sinusoidal FAC and electric field in order to confirm our hypothesis. In addition to the ionospheric response, the possible cause of the FLR and processes involved are also discussed.Key words. Magnetospheric physics (MHD waves and instabilities; magnetosphere-ionosphere interactions) – Ionosphere (polar ionosphere)
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Reddy, C. A., Sudha Ravindran, K. S. Viswanathan, B. V. Krishna Murthy, D. R. K. Rao i T. Araki. "Observations of Pc5 micropulsation-related electric field oscillations in the equatorial ionosphere". Annales Geophysicae 12, nr 6 (31.05.1994): 565–73. http://dx.doi.org/10.1007/s00585-994-0565-7.
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Abstract. A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5°N, 77°E, 0.5°N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (Ap=161). Simultaneous 100-nT-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6°N gm) and at Narsarsuaq, Greenland (70.6°N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730-1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV m-1 and it increases with height, while it is about 1.0 mV m-1 in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brorfelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the associated ionospheric electric field penetrating from high latitudes to the magnetic equator.
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Nickolaenko, A. P., M. Hayakawa, M. Sekiguchi, Y. Ando i K. Ohta. "Model modifications in Schumann resonance intensity caused by a localized ionosphere disturbance over the earthquake epicenter". Annales Geophysicae 24, nr 2 (23.03.2006): 567–75. http://dx.doi.org/10.5194/angeo-24-567-2006.
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Abstract. This paper is a further extension of our latest observations and modeling by Hayakawa et al. (2005a), in which we discovered the anomalous behavior of Schumann resonance observed in Japan, in possible association with the Chi-chi earthquake in Taiwan. Schumann resonance intensity changes associated with a localized decrease in the lower ionospheric height over the earthquake epicenter are modeled. The knee model of the vertical conductivity profile of the ionosphere describes the regular Earth-ionosphere cavity, and the modified knee model is introduced for the disturbance. The localized ionosphere modification is of a Gaussian radial dependence; it has a 1-Mm radius, and the decrease reaches 20 km in the lower ionosphere height over the epicenter of the earthquake (Taiwan). The diffraction problem in the Earth-ionosphere cavity with a localized disturbance is resolved by using the Stratton-Chu integral equation. This solution is constructed for the case of natural resonance oscillations driven by independent random sources distributed worldwide. The data of the Optical Transient Detector (OTD) are used to introduce the source distribution. A pronounced increase in the intensity of the Schumann resonance is obtained around the fourth mode frequency (up to 20%) when thunderstorms are concentrated in Central America. The worldwide distribution of lightning strokes blurs and slightly reduces the effect (15% increase in intensity) for the observer in Japan and the localized nonuniformity positioned over Taiwan. A clear qualitative similarity is obtained in relation to the experimental data, indicating that records collected in Japan may be explained by the impact of a localized decrease in the lower ionosphere over the epicenter of the earthquake. It is admitted that the assumed conductivity decrease could only be caused by a severe change in the ionization in the middle atmosphere. It is not in the scope of this paper to discuss the possible mechanism, but rather to show that a closer and quantitative agreement with the experiment yields information about the form and size of the ionospheric modification and about the distribution of global thunderstorm activity during measurements.
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Potapov, Alexander, Tatyana Polyushkina i B. Tsegmed. "Morphology and diagnostic potential of the ionospheric Alfvén resonator". Solar-Terrestrial Physics 7, nr 3 (28.09.2021): 36–52. http://dx.doi.org/10.12737/stp-73202104.
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The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.
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Potapov, Alexander, Tatyana Polyushkina i B. Tsegmed. "Morphology and diagnostic potential of the ionospheric Alfvén resonator". Solnechno-Zemnaya Fizika 7, nr 3 (28.09.2021): 39–56. http://dx.doi.org/10.12737/szf-73202104.
Pełny tekst źródłaStreszczenie:
The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.
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Leonovich, A. S., D. A. Kozlov i V. A. Pilipenko. "Magnetosonic resonance in a dipole-like magnetosphere". Annales Geophysicae 24, nr 8 (13.09.2006): 2277–89. http://dx.doi.org/10.5194/angeo-24-2277-2006.
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Abstract. A theory of resonant conversion of fast magnetosonic (FMS) waves into slow magnetosonic (SMS) oscillations in a magnetosphere with dipole-like magnetic field has been constructed. Monochromatic FMS waves are shown to drive standing (along magnetic field lines) SMS oscillations, narrowly localized across magnetic shells. The longitudinal and transverse structures, as well as spectrum of resonant SMS waves are determined. Frequencies of fundamental harmonics of standing SMS waves lie in the range of 0.1–1 mHz, and are about two orders of magnitude lower than frequencies of similar Alfvén field line resonance harmonics. This difference makes an effective interaction between these MHD modes impossible. The amplitude of SMS oscillations rapidly decreases along the field lines from the magnetospheric equator towards the ionosphere. In this context, magnetospheric SMS oscillations cannot be observed on the ground, and the ionosphere does not play any role either in their generation or dissipation. The theory developed can be used to interpret the occurrence of compressional Pc5 waves in a quiet magnetosphere with a weak ring current.
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Ponomarenko, P. V., F. W. F. W. Menk, C. L. Waters i M. D. Sciffer. "Pc3-4 ULF waves observed by the SuperDARN TIGER radar". Annales Geophysicae 23, nr 4 (3.06.2005): 1271–80. http://dx.doi.org/10.5194/angeo-23-1271-2005.
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Abstract. Despite extensive research, the mechanisms for propagation of Pc3-4 energy from the generation region at the bow shock to the high-latitude ionosphere remain unresolved. We used high temporal (6-12s) and spatial (45km) resolution data from the SuperDARN TIGER radar (Tasmania) to examine Pc3-4 wave signatures at the F-region heights. We focus on a case study on 28 September 2000, when large-amplitude band-limited Pc3-4 oscillations were observed across 10-20 range gates in beam #4 (which points towards the CGM pole) for about four hours preceding MLT noon. These waves were detected in sea-scatter echoes reflected from the ionospheric footprint of the plasmatrough. Nearby ground magnetometer data from Macquarie Island showed very similar variations in both the north-south and east-west components. The radar data revealed the occasional presence of quasi-FLR (field-line resonance) spatial structures with frequencies much higher than those of the local fundamental FLR modes. Detailed spectral analysis of the ionospheric and ground data shows that these structures most probably correspond to a 3rd-harmonic, poloidal-mode FLR. Such observations suggest that compressional Pc3-4 waves produced in the upstream solar wind travel earthward from the magnetopause in the magnetic equatorial plane depositing energy into the Alfvenic modes, as either forced or 3rd-harmonic FLR that reach ionospheric heights along magnetic field lines.
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KLIMUSHKIN, DMITRI Yu, i PAVEL N. MAGER. "The structure of low-frequency standing Alfvén waves in the box model of the magnetosphere with magnetic field shear". Journal of Plasma Physics 70, nr 4 (27.07.2004): 379–95. http://dx.doi.org/10.1017/s0022377803002563.
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The paper is concerned with the influence of magnetic field shear on the structure of Alfvén waves standing along field lines in the one-dimensionally inhomogeneous box model of the magnetosphere, enclosed between two parallel, infinitely conducting planes (ionospheres). We consider the transverse small-scale Alfvén waves whose azimuthal component of the wave vector $k_y$ satisfies the condition $k_y l\,{\gg}\,1$, where $l$ is the distance between the ionospheres. For this model, the Alfvén resonance condition has been established. It is shown that resonance can also occur at a constant Alfvén velocity if the field-line inclination to the ionosphere is changed. On resonant magnetic shells there occurs a singularity of the wave field of the same kind as in the absence of shear. Moreover, there are found many resemblances between Alfvén-wave behavior in our one-dimensionally inhomogeneous model and in two-dimensional inhomogeneous models with plasma and magnetic field parallel inhomogeneity taken into account. Thus, the presence of shear leads to a difference of the frequencies of poloidal and toroidal oscillations of field lines, and to the dependence of the wave's frequency on the transversal components of wave vector. Then, in the sheared magnetic field with highly conductive boundaries the source excites multiple standing Alfvén harmonics at different locations. In general, the localization regions of different longitudinal harmonics overlap. However, in the small but finite shear limit, a total wave field represents a set of mutually isolated transparent regions corresponding to different harmonic numbers. In each of these regions the waves are found to be travelling across the magnetic shells, and the transparent region is limited in the coordinate $x$ by two turning points, at one of which the mode is poloidally polarized, and the other point it is toroidally polarized (it is at this latter point where Alfvén resonance occurs). Furthermore, the phase velocity of the wave is directed toward the poloidal point, and the group velocity is directed at the toroidal point.
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Shevtsov, Boris, Andrey Perezhogin i Ilya Seredkin. "Lidar diagnostics of ionosphere precipitations". E3S Web of Conferences 62 (2018): 01010. http://dx.doi.org/10.1051/e3sconf/20186201010.
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Lidar is considered as an electron energy detector of ionosphere precipitations, and the cleaning of radiation belts is like the energy pumping of the ionosphere layer. The excitation efficiency of ionosphere plasma components by precipitations and the features of resonant backscattering of laser radiation in the active ionosphere are discussed. It is shown that in the quantum system in which the lidar plays the role of a master oscillator and the ionosphere layer of the amplifier, different modes of nonlinear oscillations are possible depending on the intensity of the precipitation. Analogies are being made with other natural nonlinear systems.
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Krauklis, I., i D. Orr. "The effects of ionospheric 'phase mixing' on a distributed driven shear Alfvén ulf pulsation'". Annales Geophysicae 12, nr 2/3 (31.01.1994): 188–94. http://dx.doi.org/10.5194/angeo-12-188-1994.
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Abstract. A numerical simulation study of the ultra-low frequency (ULF) H-component magnetic field at the Earth's surface arising from a perturbation ionospheric Hall current has been developed. The Hall current system is driven by field-aligned currents (FACs) associated with shear Alfvén field line resonances (FLRs) driven by fast mode global cavity oscillations. The ionospheric phase mixing of the Hall current manifests itself in a number of ways in the ground field, these are: (i) Smoothing the spectral maxima of the ground signal: (ii) Loss in clarity of the harmonic structure of the spectra: (iii) A small increase in the damping rate of the ULF wave at the resonance latitude and (iv) small localised minimum in the spectra at the resonance latitude.
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Shevtsov, Boris, i Olga Shevtsova. "Fluctuations and nonlinear oscillations in complex natural systems". E3S Web of Conferences 62 (2018): 02006. http://dx.doi.org/10.1051/e3sconf/20186202006.
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Resonance propagation of radiation in the ionosphere, solar activity, magnetic dynamos, lightning discharges, fracture processes, plastic deformations, seismicity, turbulence and hydrochemical variability are considered as examples of complex dynamical systems in which similar fluctuation and nonlinear oscillation regimes arise. Collective effects in the systems behavior and chaotic oscillations in individual subsystems, the ratio of random and deterministic, the analysis of variability factors and the change of dynamic regimes, the scaling relation between the elements of the system and the interaction of scales are discussed. It is shown that consolidation and branching in disruptions or thunderstorm activity is the transfer of disturbances to up and down of cascades as in turbulence, and the alpha-omega effects of the magnetic dynamo are the same cascade processes, but in the presence of an external magnetic field or rotation that removes the degeneracy in the system by directions. Particular attention is paid to natural generators and oscillation amplifiers, in which the Lorentz triplet plays the role of a universal model of a nonlinear oscillator.
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Martines-Bedenko, Valeriy, Vyacheslav Pilipenko, K. Shiokawa i Rinat Akbashev. "Electromagnetic ULF/ELF oscillations caused by the eruption of the Tonga volcano". Solnechno-Zemnaya Fizika 9, nr 1 (28.03.2023): 51–59. http://dx.doi.org/10.12737/szf-91202306.
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The eruption of the Tonga volcano on January 13 and 15, 2022 and related intense lightning activity led to the excitation of a number of specific electromagnetic oscillations in different frequency ranges. We examine properties of these oscillations, using data from magnetometers of various types located in Kamchatka and in the Pacific region. We confirmed that there might have been a geomagnetic response to the formation of an acoustic resonance between the Earth surface and the ionosphere: localized harmonic oscillations with a frequency 3.5–4.0 mHz, which lasted for ~1.5 hr, were detected ~15 min after the beginning of the eruption at distance of ~800 km. An increase was observed in the intensity of the Schumann resonance at stations in the Far East. Broadband emission stimulated by intense volcanic lightning was detected to occur in the Pc1 range (2–5 Hz). The emission presumably results from the excitation of the magnetosonic waveguide in the upper ionosphere by lightning activity.
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Martines-Bedenko, Valeriy, Vyacheslav Pilipenko, K. Shiokawa i Rinat Akbashev. "Electromagnetic ULF/ELF oscillations caused by the eruption of the Tonga volcano". Solar-Terrestrial Physics 9, nr 1 (28.03.2023): 47–55. http://dx.doi.org/10.12737/stp-91202306.
Pełny tekst źródłaStreszczenie:
The eruption of the Tonga volcano on January 13 and 15, 2022 and related intense lightning activity led to the excitation of a number of specific electromagnetic oscillations in different frequency ranges. We examine properties of these oscillations, using data from magnetometers of various types located in Kamchatka and in the Pacific region. We confirmed that there might have been a geomagnetic response to the formation of an acoustic resonance between the Earth surface and the ionosphere: localized harmonic oscillations with a frequency 3.5–4.0 mHz, which lasted for ~1.5 hr, were detected ~15 min after the beginning of the eruption at distance of ~800 km. An increase was observed in the intensity of the Schumann resonance at stations in the Far East. Broadband emission stimulated by intense volcanic lightning was detected to occur in the Pc1 range (2–5 Hz). The emission presumably results from the excitation of the magnetosonic waveguide in the upper ionosphere by lightning activity.
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KUO, S. P. "Cascade of parametric instabilities in ionospheric heating experiments". Journal of Plasma Physics 66, nr 5 (listopad 2001): 315–36. http://dx.doi.org/10.1017/s0022377801001477.
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Two secondary parametric instabilities providing cascade channels for the Langmuir sidebands of the oscillating two-stream instability (OTSI) and parametric decay instability (PDI), which are excited by O-mode high-frequency (HF) heating waves, are studied. The first one decays a Langmuir pump wave into a Langmuir sideband and an ion acoustic decay mode. Both resonant and nonresonant cascade processes are considered. Nonresonant cascade of Langmuir waves proceeds at the same location and is increasingly hampered by the frequency mismatch effect. Resonant cascade takes place in different resonant locations to minimize the frequency mismatch effect, but it has to overcome the severe propagation loss of the mother Langmuir wave in each cascade step. This process produces a narrow spectrum of frequency-downshifted (from the HP wave frequency) plasma waves. The second employs the lower-hybrid wave as the decay mode. Only the nonresonant cascade is of interest, because the propagation loss of the mother Langmuir wave in each resonant cascade step is far too severe. This is a three-dimensional coupling process, because the wavevectors of coupled three waves have to be matched in three-dimensional space, rather than matched in the conventional way on the plane of the pump wavevector and the geomagnetic field. A broad spectrum of frequency-downshifted plasma waves can be produced by this process in a narrow altitude range preferentially located near the matching heights of Langmuir sidebands of the OTSI and PDI.
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Le, G., S. H. Chen, Y. Zheng, C. T. Russell, J. A. Slavin, C. Huang, S. M. Petrinec i in. "Coordinated polar spacecraft, geosynchronous spacecraft, and ground-based observations of magnetopause processes and their coupling to the ionosphere". Annales Geophysicae 22, nr 12 (22.12.2004): 4329–50. http://dx.doi.org/10.5194/angeo-22-4329-2004.
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Abstract. In this paper, we present in-situ observations of processes occurring at the magnetopause and vicinity, including surface waves, oscillatory magnetospheric field lines, and flux transfer events, and coordinated observations at geosynchronous orbit by the GOES spacecraft, and on the ground by CANOPUS and 210° Magnetic Meridian (210MM) magnetometer arrays. On 7 February 2002, during a high-speed solar wind stream, the Polar spacecraft was skimming the magnetopause in a post-noon meridian plane for ~3h. During this interval, it made two short excursions and a few partial crossings into the magnetosheath and observed quasi-periodic cold ion bursts in the region adjacent to the magnetopause current layer. The multiple magnetopause crossings, as well as the velocity of the cold ion bursts, indicate that the magnetopause was oscillating with an ~6-min period. Simultaneous observations of Pc5 waves at geosynchronous orbit by the GOES spacecraft and on the ground by the CANOPUS magnetometer array reveal that these magnetospheric pulsations were forced oscillations of magnetic field lines directly driven by the magnetopause oscillations. The magnetospheric pulsations occurred only in a limited longitudinal region in the post-noon dayside sector, and were not a global phenomenon, as one would expect for global field line resonance. Thus, the magnetopause oscillations at the source were also limited to a localized region spanning ~4h in local time. These observations suggest that it is unlikely that the Kelvin-Helmholz instability and/or fluctuations in the solar wind dynamic pressure were the direct driving mechanisms for the observed boundary oscillations. Instead, the likely mechanism for the localized boundary oscillations was pulsed reconnection at the magnetopause occurring along the X-line extending over the same 4-h region. The Pc5 band pressure fluctuations commonly seen in high-speed solar wind streams may modulate the reconnection rate as an indirect cause of the observed Pc5 pulsations. During the same interval, two flux transfer events were also observed in the magnetosphere near the oscillating magnetopause. Their ground signatures were identified in the CANOPUS data. The time delays of the FTE signatures from the Polar spacecraft to the ground stations enable us to estimate that the longitudinal extent of the reconnection X-line at the magnetopause was ~43° or ~5.2 RE. The coordinated in-situ and ground-based observations suggest that FTEs are produced by transient reconnection taking place along a single extended X-line at the magnetopause, as suggested in the models by Scholer (1988) and Southwood et al. (1988). The observations from this study suggest that the reconnection occurred in two different forms simultaneously in the same general region at the dayside magnetopause: 1) continuous reconnection with a pulsed reconnection rate, and 2) transient reconnection as flux transfer events. Key words. Magnetospheric physics (Magnetopause, cusp and boundary layers; Magnetosphere-ionosphere interactions; MHD waves and instabilities)
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Мазур, Виталий, Vitaliy Mazur, Даниил Чуйко i Daniil Chuiko. "MHD waveguide in the outer magnetosphere and mechanisms of its excitation". Solnechno-Zemnaya Fizika 1, nr 1 (17.03.2015): 36–55. http://dx.doi.org/10.12737/5837.
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The geomagnetic field and plasma inhomogeneities in the outer equatorial part of the magnetosphere are responsible for the existence of the channel with low Alfven speeds, which extends from the nose to the far flanks of the magnetosphere, both in the morning and evening sectors. This channel serves as a waveguide in the fast magnetosonic waves. Travelling along the waveguide (i.e., in the azimuthal direction), an eigenmode undergoes evolution. Parameters of the waveguide vary along the way of the wave propagation and the eigenmode “adapts” to these parameters. Conditions of the Kelvin-Helmholtz instability change due to the variation of the solar wind speed along the magnetopause. Conditions of the penetration of solar wind hydromagnetic waves into the magnetosphere change due to the same variation. The wave penetration process turns to the overreflection regime, which sharply amplifies the pump level of the magnetospheric waveguide. The fast mode propagating along the waveguide is accompanied by the Alfven resonance deep within the magnetosphere. Oscillation energy dissipation takes place in the vicinity of the Alfven resonance. Along the magnetic field lines, the Alfven resonance is a standing Alfven wave; thus it reaches the ionosphere and the Earth’s surface. At the same time, no fast waveguide modes localized in the low Alfven speed channel can be observed on the Earth. Waveguide oscillations evolution is investigated in this paper both analytically and numerically taking into account all of the aforementioned factors as the oscilla-tions propagate from the nose to the tail of the magnetosphere. Spectral composition and spatial structure of the oscillations are found. The theory allows for a description of Pc3 and Pc5 pulsations – the most important magnetospheric pulsations. As such it follows that Pc3 are localized on the dayside of the magnetosphere, whereas Pc 5 are localized in the dawn-dusk sectors – in full agreement with the observations.
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Пархомов, Владимир, Vladimir Parhomov, Наталия Бородкова, Natalia Borodkova, Александр Яхнин, Aleksandr Yahnin, Райта Теро i in. "Magnetospheric response of two types in PSc geomagnetic pulsations to interaction with interplanetary shock waves". Solar-Terrestrial Physics 4, nr 3 (28.09.2018): 52–66. http://dx.doi.org/10.12737/stp-43201808.
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Using the June 22, 2015 event as an example, we present new data confirming the presence of a precursor of the sudden magnetic impulse caused by a powerful interplanetary shock wave (ISW). The precursor in the form of a train of oscillations (broadband pulse) with a falling frequency in the range 0.25÷11 Hz with a duration of ~20 s, which had a spectral resonance structure, was recorded globally by a network of induction magnetometers at 18:33:27 UT. No significant phase delays of the signals were detected in four frequency bands at widely spaced observatories. It is suggested that the impulse can be excited in the Earth – ionosphere waveguide by a pulsed electric field which occurs in the ionosphere due to the short-term impact of ISW on the magnetosphere.
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Пархомов, Владимир, Vladimir Parhomov, Наталия Бородкова, Natalia Borodkova, Александр Яхнин, Aleksandr Yahnin, Райта Теро i in. "Magnetospheric response of two types in PSc geomagnetic pulsations to interaction with interplanetary shock waves". Solnechno-Zemnaya Fizika 4, nr 3 (28.09.2018): 68–83. http://dx.doi.org/10.12737/szf-43201808.
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Using the June 22, 2015 event as an example, we present new data confirming the presence of a precursor of the sudden magnetic impulse caused by a powerful interplanetary shock wave (ISW). The precursor in the form of a train of oscillations (broadband pulse) with a falling frequency in the range 0.25÷11 Hz with a duration of ~20 s, which had a spectral resonance structure, was recorded globally by a network of induc-tion magnetometers at 18:33:27 UT. No significant phase delays of the signals were detected in four fre-quency bands at widely spaced observatories. It is sug-gested that the impulse can be excited in the Earth — ionosphere waveguide by a pulsed electric field which occurs in the ionosphere due to the short-term impact of ISW on the magnetosphere.
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Yagova, Nadezda, Alexander Kozlovsky, Evgeny Fedorov i Olga Kozyreva. "Even moderate geomagnetic pulsations can cause fluctuations of <i>fo</i>F2 frequency of the auroral ionosphere". Annales Geophysicae 39, nr 3 (16.06.2021): 549–62. http://dx.doi.org/10.5194/angeo-39-549-2021.
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Abstract. The ionosonde at the Sodankylä Geophysical Observatory (SOD; 67∘ N, 27∘ E; Finland) routinely performs vertical sounding once per minute which enables the study of fast ionospheric variations at a frequency of the long-period geomagnetic pulsations Pc5–6/Pi3 (1–5 mHz). Using the ionosonde data from April 2014–December 2015 and colocated geomagnetic measurements, we have investigated a correspondence between the magnetic field pulsations and variations of the critical frequency of radio waves reflected from the ionospheric F2 layer (foF2). For this study, we have developed a technique for automated retrieval of the critical frequency of the F2 layer from ionograms. As a rule, the Pc5–6/Pi3 frequency band fluctuations in foF2 were observed at daytime during quiet or moderately disturbed space weather conditions. In most cases (about 80 %), the coherence between the foF2 variations and geomagnetic pulsations was low. However in some cases (specified as “coherent”) the coherence was as large as γ2≥0.5. The following conditions are favorable for the occurrence of coherent cases: enhanced auroral activity (6 h maximal auroral electrojet (AE) ≥800 nT), high solar wind speed (V>600 km/s), fluctuating solar wind pressure and northward interplanetary magnetic field. In the cases when the coherence was higher at shorter periods of oscillations, the magnetic pulsations demonstrated features typical for the Alfvén field line resonance.
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Nickolaenko, A. P., i M. Hayakawa. "Universal and local time components in Schumann resonance intensity". Annales Geophysicae 26, nr 4 (13.05.2008): 813–22. http://dx.doi.org/10.5194/angeo-26-813-2008.
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Abstract. We extend the technique suggested by Sentman and Fraser (1991) and discussed by Pechony and Price (2006), the technique for separating the local and universal time variations in the Schumann resonance intensity. Initially, we simulate the resonance oscillations in a uniform Earth-ionosphere cavity with the distribution of lightning strokes based on the OTD satellite data. Different field components were used in the Dayside source model for the Moshiri (Japan, geographic coordinates: 44.365° N, 142.24° E) and Lehta (Karelia, Russia, 64.427° N, 33.974° E) observatories. We use the extended Fourier series for obtaining the modulating functions. Simulations show that the algorithm evaluates the impact of the source proximity in the resonance intensity. Our major goal was in estimating the universal alteration factors, which reflect changes in the global thunderstorm activity. It was achieved by compensating the local factors present in the initial data. The technique is introduced with the model Schumann resonance data and afterwards we use the long-term experimental records at the above sites for obtaining the diurnal/monthly variations of the global thunderstorms.
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Eriksson, P. T. I., L. G. Blomberg, A. D. M. Walker i K. H. Glassmeier. "Poloidal ULF oscillations in the dayside magnetosphere: a Cluster study". Annales Geophysicae 23, nr 7 (14.10.2005): 2679–86. http://dx.doi.org/10.5194/angeo-23-2679-2005.
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Abstract. Three ULF wave events, all occurring in the dayside magnetopshere during magnetically quiet times, are studied using the Cluster satellites. The multi-point measurements obtained from Cluster are used to determine the azimuthal wave number for the events by means of the phase shift and the azimuthal separation between the satellites. Also, the polarisation of the electric and magnetic fields is examined in a field-aligned coordinate system, which, in turn, gives the mode of the oscillations. The large-inclination orbits of Cluster allow us to examine the phase relationship between the electric and magnetic fields along the field lines. The events studied have large azimuthal wave numbers (m~100), two of them have eastward propagation and all are in the poloidal mode, consistent with the large wave numbers. We also use particle data from geosynchronous satellites to look for signatures of proton injections, but none of the events show any sign of enhanced proton flux. Thus, the drift-bounce resonance instability seems unlikely to have played any part in the excitation of these pulsations. As for the drift-mirror instability we conclude that it would require an unreasonably high plasma pressure for the instability criterion to be satisfied.Keywords. Ionosphere (Wave propagation) – Magnetospheric physics (Plasma waves and instabilities; Instruments and techniques)
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Simões, Fernando, Robert Pfaff, Henry Freudenreich, Jeffrey Klenzing, Douglas Rowland, Kenneth Bromund, Larry Kepko i in. "Equatorial ionosphere semiannual oscillation investigated from Schumann resonance measurements on board the C/NOFS satellite". Journal of Geophysical Research: Atmospheres 118, nr 21 (12.11.2013): 12,045–12,051. http://dx.doi.org/10.1002/jgrd.50797.
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Sarafopoulos, D. V. "Pseudo-field line resonances in ground Pc5 pulsation events". Annales Geophysicae 23, nr 2 (28.02.2005): 593–608. http://dx.doi.org/10.5194/angeo-23-593-2005.
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Abstract. In this work we study four representative cases of Pc5 ground pulsation events with discrete and remarkably stable frequencies extended at least in a high-latitude range of ~20°; a feature that erroneously gives the impression for an oscillation mode with "one resonant field line". Additionally, the presented events show characteristic changes in polarization sense, for a meridian chain of stations from the IMAGE array, and maximize their amplitude at or close to the supposed resonant magnetic field shell, much like the typical FLR. Nevertheless, they are not authentic FLRs, but pseudo-FLRs, as they are called. These structures are produced by repetitive and tilted twin-vortex structures caused by magnetopause surface waves, which are probably imposed by solar wind pressure waves. The latter is confirmed with in-situ measurements obtained by the Cluster satellites, as well as the Geotail, Wind, ACE, and LANL 1994-084 satellites. This research effort is largely based on two recent works: first, Sarafopoulos (2004a) has observationally established that a solar wind pressure pulse (stepwise pressure variation) produces a twin-vortex (single vortex) current system over the ionosphere; second, Sarafopoulos (2004b) has studied ground events with characteristic dispersive latitude-dependent structures and showed that these are associated with twin-vortex ionosphere current systems. In this work, we show that each pseudo-FLR event is associated with successive and tilted large-scale twin-vortex current systems corresponding to a magnetopause surface wave with wavelength 10-20RE. We infer that between an authentic FLR, which is a spatially localized structure with an extent 0.5RE in the magnetospheric equatorial plane, and the magnetopause surface wavelength, there is a scale factor of 20-40. A chief observational finding, in this work, is that there are Pc5 ground pulsation events showing two gradual and latitude dependent phase-shifts of 180°, at the same time.
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Ndiitwani, D. C., i P. R. Sutcliffe. "A study of L-dependent Pc3 pulsations observed by low Earth orbiting CHAMP satellite". Annales Geophysicae 28, nr 2 (3.02.2010): 407–14. http://dx.doi.org/10.5194/angeo-28-407-2010.
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Abstract. Field line resonances (FLR) driven by compressional waves are an important mechanism for the generation of ULF geomagnetic pulsations observed at all latitudes during local daytime. References to observations of toroidal standing Alfvén mode oscillations with clearly L-dependent frequencies from spacecraft in the outer magnetosphere for L>3 are limited in the literature. Such observations in the inner magnetosphere for L<3 have not yet been reported in the literature. This study offers two interesting case studies of observations of ULF waves by the low Earth orbiting CHAMP satellite. The magnetic field measurements from CHAMP, which are of unprecedented accuracy and resolution, are compared to Hermanus magnetometer data for times when CHAMP crosses the ground station L-shell, namely for 13 February 2002 and 18 February 2003. The data were analysed for Pc3 pulsation activity using the Maximum Entropy Spectral Analysis (MESA) method to visualise FLRs in the vector magnetometer data. For the first time observations of Pc3 toroidal oscillations with clearly L-dependent frequencies for lower L-shell values (L<3) observed by an LEO satellite are reported. These observations show FLR frequencies increasing as a function of decreasing latitude down to L=1.6 and then decreasing as a result of the larger plasma density of the upper ionosphere. The L-dependent frequency oscillations were observed in the presence of a broadband compressional wave spectrum. Our observations thus confirm the well-known magnetohydrodynamic (MHD) wave theoretical prediction of a compressional wave being the driver of the field line resonance.
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Borisov, N. D., i T. R. Robinson. "Transformation of an EM pump wave into upper hybrid resonance oscillations in striations in a vertically inhomogeneous ionosphere". Physics Letters A 315, nr 1-2 (sierpień 2003): 126–35. http://dx.doi.org/10.1016/s0375-9601(03)00978-2.
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Klimushkin, D. Yu, i P. N. Mager. "The spatio-temporal structure of impulse-generated azimuthalsmall-scale Alfvén waves interacting with high-energy chargedparticles in the magnetosphere". Annales Geophysicae 22, nr 3 (19.03.2004): 1053–60. http://dx.doi.org/10.5194/angeo-22-1053-2004.
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Abstract. It is assumed to date that the energy source of azimuthal small-scale ULF waves in the magnetosphere (azimuthal wave numbers m≧1) is provided by the energetic particles interacting with the waves through the bounce-drift resonance. In this paper we have solved the problem of the bounce-drift instability influence on the spatio-temporal structure of Alfvén waves excited by a source of the type of sudden impulse in a dipole-like magnetosphere. It is shown that the impulse-generated Alfvén oscillation within a time τ~m∕ΩTN (where ΩTN is the toroidal eigenfrequency) is a poloidal one, and each field line oscillates with its own eigenfrequency that coincides with the poloidal frequency of a given L-shell. As time elapses, the wave becomes toroidally polarized because of the phase difference of the disturbance, and the oscillation frequency of field lines tends to the toroidal frequency. The drift-bounce instability growth rate becomes smaller during the wave temporal evolution, and the instability undergoes stabilization when the wave frequency coincides with the toroidal eigenfrequency. The total amplification of the wave can be estimated as , where is the wave growth rate at the beginning of the process, when it has its maximum value. The wave amplitude can increase only within a time ~τ, when it is poloidally polarized. After this time, when the wave becomes to be toroidally polarized, it goes damped because of the finite ionospheric conductivity. This is in qualitative agreement with the recent radar experimental data.Key words. Magnetospheric physics (MHD waves and instabilities). Space plasma physics (kinetic and MHD theory; wave-particle interactions)
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Heilig, B., H. Lühr i M. Rother. "Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground". Annales Geophysicae 25, nr 3 (29.03.2007): 737–54. http://dx.doi.org/10.5194/angeo-25-737-2007.
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Abstract. Based on magnetic field measurements from the satellite CHAMP, a detailed picture could be obtained of the upstream wave (UW) distribution in the topside ionosphere. The low, near-polar orbit of CHAMP, covering all local times, allows the global distribution of this type of pulsation to be revealed. The observations from space are compared to recordings of the ground-based MM100 meridional array covering the latitude range 66° to 42° in magnetic coordinates. UWs show up very clearly in the compressional component of the satellite magnetic field data, whereas on the ground, their signature is found in the H component, but it is mixed with oscillations from field line resonant pulsations. Here we first introduce a procedure for an automated detection of UW signatures, both in ground and space data. Then a statistical analysis is presented of UW pulsations recorded during a 132-day period, centred on the autumn 2001 equinox. Observations in the top-side ionosphere reveal a clear latitudinal distribution of the amplitudes. Largest signals are observed at the equator. Minima show up at about 40° latitude. The coherence between ground and satellite wave signatures is high over wide latitude and longitude ranges. We make suggestions about the entry mechanism of UWs from the foreshock region into the magnetosphere. The clear UW signature in satellite recordings between −60° and 60° latitude allows for detailed investigations of the dependence on solar wind conditions. We test the control of solar wind speed, interplanetary magnetic field strength and cone angle on UWs. For the first time, it is possible to derive details of the Doppler-shift effect by modifying the UW frequency from direct observations. The results reconcile foreshock wave generation predictions with near-Earth observations.
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Scoffield, H. C., T. K. Yeoman, D. M. Wright, S. E. Milan, A. N. Wright i R. J. Strangeway. "An investigation of the field-aligned currents associated with a large-scale ULF wave using data from CUTLASS and FAST". Annales Geophysicae 23, nr 2 (28.02.2005): 487–98. http://dx.doi.org/10.5194/angeo-23-487-2005.
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Abstract. On 14 December 1999, a large-scale ULF wave event was observed by the Hankasalmi radar of the SuperDARN chain. Simultaneously, the FAST satellite passed through the Hankasalmi field-of-view, measuring the magnetic field oscillations of the wave at around 2000km altitude, along with the precipitating ion and electron populations associated with these fields. A simple field line resonance model of the wave has been created and scaled using the wave's spatial and temporal characteristics inferred from SuperDARN and IMAGE magnetometer data. Here the model calculated field-aligned current is compared with field-aligned currents derived from the FAST energetic particle spectra and magnetic field measurements. This comparison reveals the small-scale structuring and energies of the current carriers in a large-scale Alfvén wave, a topic, which at present, is of considerable theoretical interest. When FAST traverses a region of the wave involving low upward field-aligned current densities, the current appears to be carried by unstructured downgoing electrons of energies less than 30eV. A downward current region appears to be carried partially by upgoing electrons below the FAST energy detection threshold, but also consists of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies <30eV, with the hotter upgoing electrons presumably representing those upgoing electrons which have been accelerated by the wave field above the low energy detection threshold of FAST. A stronger interval of upward current shows that small-scale structuring of scale ~50km has been imposed on the current carriers, which are downgoing magnetospheric electrons of energy 0-500eV.
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Sarafopoulos, D. V. "A case study testing the cavity mode model of the magnetosphere". Annales Geophysicae 23, nr 5 (28.07.2005): 1867–80. http://dx.doi.org/10.5194/angeo-23-1867-2005.
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Abstract. Based on a case study we test the cavity mode model of the magnetosphere, looking for eigenfrequencies via multi-satellite and multi-instrument measurements. Geotail and ACE provide information on the interplanetary medium that dictates the input parameters of the system; the four Cluster satellites monitor the magnetopause surface waves; the POLAR (L=9.4) and LANL 97A (L=6.6) satellites reveal two in-situ monochromatic field line resonances (FLRs) with T=6 and 2.5 min, respectively; and the IMAGE ground magnetometers demonstrate latitude dependent delays in signature arrival times, as inferred by Sarafopoulos (2004b). Similar dispersive structures showing systematic delays are also extensively scrutinized by Sarafopoulos (2005) and interpreted as tightly associated with the so-called pseudo-FLRs, which show almost the same observational characteristics with an authentic FLR. In particular for this episode, successive solar wind pressure pulses produce recurring ionosphere twin vortex Hall currents which are identified on the ground as pseudo-FLRs. The BJN ground magnetometer records the pseudo-FLR (alike with the other IMAGE station responses) associated with an intense power spectral density ranging from 8 to 12 min and, in addition, two discrete resonant lines with T=3.5 and 7 min. In this case study, even though the magnetosphere is evidently affected by a broad-band compressional wave originated upstream of the bow shock, nevertheless, we do not identify any cavity mode oscillation within the magnetosphere. We fail, also, to identify any of the cavity mode frequencies proposed by Samson (1992). Keywords. Magnetospheric physics (Magnetosphereionosphere interactions; Solar wind-magnetosphere interactions; MHD waves and instabilities)
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Mager, P. N., i D. Yu Klimushkin. "Spatial localization and azimuthal wave numbers of Alfvén waves generated by drift-bounce resonance in the magnetosphere". Annales Geophysicae 23, nr 12 (23.12.2005): 3775–84. http://dx.doi.org/10.5194/angeo-23-3775-2005.
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Abstract. Spatial localization and azimuthal wave numbers m of poloidal Alfvén waves generated by energetic particles in the magnetosphere are studied in the paper. There are two factors that cause the wave localization across magnetic shells. First, the instability growth rate is proportional to the distribution function of the energetic particles, hence waves must be predominantly generated on magnetic shells where the particles are located. Second, the frequency of the generated poloidal wave must coincide with the poloidal eigenfrequency, which is a function of the radial coordinate. The combined impact of these two factors also determines the azimuthal wave number of the generated oscillations. The beams with energies about 10 keV and 150 keV are considered. As a result, the waves are shown to be strongly localized across magnetic shells; for the most often observed second longitudinal harmonic of poloidal Alfvén wave (N=2), the localization region is about one Earth radius across the magnetic shells. It is shown that the drift-bounce resonance condition does not select the m value for this harmonic. For 10 keV particles (most often involved in the explanation of poloidal pulsations), the azimuthal wave number was shown to be determined with a rather low accuracy, -100<m<0. The 150 keV particles provide a little better but still a poor determination of this value, -90<m<-70. For the fundamental harmonic (N=1), the azimuthal wave number is determined with a better accuracy, but both of these numbers are too small (if the waves are generated by 150 keV particles), or the waves are generated on magnetic shells (in 10 keV case) which are too far away. The calculated values of γ/ω are not large enough to overcome the damping on the ionosphere. All these have cast some suspicion on the possibility of the drift-bounce instability to generate poloidal pulsations in the magnetosphere.
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Rout, Diptiranjan, Ram Singh, K. Pandey, T. K. Pant, C. Stolle, D. Chakrabarty, S. Thampi i T. Bag. "Evidence for presence of a global quasi-resonant mode of oscillations during high-intensity long-duration continuous AE activity (HILDCAA) events". Earth, Planets and Space 74, nr 1 (13.06.2022). http://dx.doi.org/10.1186/s40623-022-01642-1.
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Abstract The responses of two High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events are investigated using solar wind observations at L1, magnetospheric measurements at geosynchronous orbit, and changes in the global ionosphere. This study provides evidence of the existence of quasi-periodic oscillations (1.5–2 h) in the ionospheric electric field over low latitudes, total electron content at high latitudes, the magnetic field over the globe, energetic electron flux and magnetic field at geosynchronous orbit, geomagnetic indices (SYM-H, AE, and PC) and the Y-component of the interplanetary electric field (IEFy) during the HILDCAA events at all local times. Based on detailed wavelet and cross-spectrum analyses, it is shown that the quasi-periodic oscillation of 1.5–2 h in IEFy is the most effective one that controls the solar wind–magnetosphere–ionosphere coupling process during the HILDCAA events for several days. Therefore, this investigation for the first time, shows that the HILDCAA event affects the global magnetosphere–ionosphere system with a “quasi-resonant” mode of oscillation. Graphical Abstract
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Heki, Kosuke, i Tatsuya Fujimoto. "Atmospheric modes excited by the 2021 August eruption of the Fukutoku-Okanoba volcano, Izu–Bonin Arc, observed as harmonic TEC oscillations by QZSS". Earth, Planets and Space 74, nr 1 (9.02.2022). http://dx.doi.org/10.1186/s40623-022-01587-5.
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AbstractContinuous Plinian eruptions of volcanoes often excite atmospheric resonant oscillations with several distinct periods of a few minutes. We detected such harmonic oscillations by the 2021 August eruption of the Fukutoku-Okanoba volcano, a submarine volcano in the Izu–Bonin arc, in ionospheric total electron content (TEC) observed from Global Navigation Satellite System (GNSS) stations deployed on three nearby islands, Chichijima, Hahajima, and Iwojima. Continuous records with the geostationary satellite of Quasi-Zenith Satellite System (QZSS) presented four frequency peaks of such atmospheric modes. The harmonic TEC oscillations commenced at ~ 5:16 UT with a large amplitude but decayed in a few hours. Graphical Abstract
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Пилипенко, Вячеслав, Vyacheslav Pilipenko, Ольга Козырева, Olga Kozyreva, Лиза Бэддели, Liza Baddeley, Дэг Лорентцен, Dag Lorentzen, Владимир Белаховский i Vladimir Belakhovsky. "Suppression of the dayside magnetopause surface modes". Solar-Terrestrial Physics, 29.12.2017, 17–25. http://dx.doi.org/10.12737/stp-34201702.
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Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of back-ground fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.
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Iyemori, Toshihiko, Michi Nishioka, Yuichi Otsuka i Atsuki Shinbori. "A confirmation of vertical acoustic resonance and field-aligned current generation just after the 2022 Hunga Tonga Hunga Ha’apai volcanic eruption". Earth, Planets and Space 74, nr 1 (30.06.2022). http://dx.doi.org/10.1186/s40623-022-01653-y.
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AbstractA strong volcanic eruption caused a clear vertical acoustic resonance between the sea surface and the thermosphere. Its effects are observed as geomagnetic and GPS-TEC oscillations near the volcano and its geomagnetic conjugate area. The geomagnetic oscillations are observed at Apia and Honolulu geomagnetic observatories with amplitude of about 2 nT and 0.2 nT, respectively. The volcanic eruption started around 04:14 UT on January 15, 2022. The oscillations appeared at 04:21UT at Apia, Samoa, only about 7 min after the start of eruption. Because the distance between the volcano and Apia is about 841 km, it takes about 40 min for a sound wave to propagate from the volcano to Apia. Therefore, it is more plausible to assume that the magnetic oscillation observed at Apia about 7 min after the eruption is caused by the sound waves propagated vertically upward to the ionosphere and generated an electric current. The coherent appearance of geomagnetic oscillation at Honolulu located near the geomagnetic conjugate point of the volcano strongly support the idea that the ionospheric current generated over the volcano diverted as a field-aligned current which flew to the opposite hemisphere and caused the geomagnetic oscillation at Honolulu. The earliest start of GPS-TEC oscillation was around 04:15UT near the volcanic eruption, and it was around 04:20 UT at KOKV station in Hawaii. The time-lag of the TEC variations between Samoa and Hawaii obtained by a cross-correlation analysis is 4.5 min or 8.5 min. These time differences are much smaller than the travel time of the seismic waves from the volcano to Hawaii islands. Therefore, it is suggested that the electric field transmitted along geomagnetic field caused the TEC variation observed over Hawaii Islands. A sawtooth waveform of geomagnetic oscillation observed at Apia and Honolulu is analyzed and a possible generation mechanism is discussed. Graphical Abstract
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"Combinational frequencies of HF doppler radar signals in the PC1 geomagnetic pulsation range". Visnyk of V.N. Karazin Kharkiv National University, series “Radio Physics and Electronics”, nr 33 (2020). http://dx.doi.org/10.26565/2311-0872-2020-33-05.
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Urgency. The urgency of this work is determined by the necessity of studying MHD waves originating from various sources within the Earth–atmosphere–ionosphere– magnetosphere system and arriving at ionospheric heights. The object of research. A matter of this study is ionospheric disturbances that accompanied geomagnetic pulsations during the dawn terminator on 23–24 March 2010. Purpose of Work. The present work was aimed at revealing short-period ionospheric disturbances in the Pc1 micropulsation frequency range (1–5-Hz) and at investigating their spectral content. Techniques and Methotology. The dynamic spectra of the variations under study were obtained with the HF Doppler radar. Results. The ionospheric disturbances have been shown to arise mainly at combinational frequencies. The durations of such disturbances have been estimated to be of the order of one minute, and the disturbance frequencies 0.7 Hz, 1.5 Hz, and 2.5 Hz. The quasi-periodic interference in the 1–5-Hz frequency band has been detected to persist for over one-half hour to a few hours. Based on the model of the signal modulated by ULF waves in the ionosphere, the appearance of constructive interference at combinational frequencies has been validated. The intercomparisons of the variations obtained using the spectrograms and the known models for the phase-modulated signals have been made. A model for the amplitude- and phase-modulated signal reflected from the ionosphere has been developed, and the signal basic parameters have been determined. Conclusions. The HF Doppler sounding can be a means for studying ionospheric disturbances in the Pc1 geomagnetic pulsation range. During the study of time variations of the Doppler frequency shift during the spring equinox, the following results were found. The period of ionospheric perturbations reached 0.2–1 s, their duration varied from 1 min to more than 10 min. A noticeable increase in the amplitude of the beat is detected, which may be a sign of the appearance of lateral maxima in the Doppler spectra. The presence of oscillations in the frequency range of the first harmonic of the spectral resonance system of the ionospheric Alfvén resonator is established. Long-term ionospheric perturbations have a linearly increasing frequency of filling the wave packet. The rate of frequency change is close to 10–3 Hz/s.
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Zhang, Shun-Rong, Juha Vierinen, Ercha Aa, Larisa P. Goncharenko, Philip J. Erickson, William Rideout, Anthea J. Coster i Andres Spicher. "2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves". Frontiers in Astronomy and Space Sciences 9 (23.03.2022). http://dx.doi.org/10.3389/fspas.2022.871275.
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The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric disturbances (TIDs) radially outbound and inbound along entire Great-Circle loci at primary speeds of ∼300–350 m/s (depending on the propagation direction) and 500–1,000 km horizontal wavelength for front shocks, going around the globe for three times, passing six times over the continental US in 100 h since the eruption. TIDs following the shock fronts developed for ∼8 h with 10–30 min predominant periods in near- and far- fields. TID global propagation is consistent with the effect of Lamb waves which travel at the speed of sound. Although these oscillations are often confined to the troposphere, Lamb wave energy is known to leak into the thermosphere through channels such as atmospheric resonance at acoustic and gravity wave frequencies, carrying substantial wave amplitudes at high altitudes. Prevailing Lamb waves have been reported in the literature as atmospheric responses to the gigantic Krakatoa eruption in 1883 and other geohazards. This study provides substantial first evidence of their long-duration imprints up in the global ionosphere. This study was enabled by ionospheric measurements from 5,000+ world-wide Global Navigation Satellite System (GNSS) ground receivers, demonstrating the broad implication of the ionosphere measurement as a sensitive detector for atmospheric waves and geophysical disturbances.
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Iyemori, Toshihiko, Akiyasu Yamada, Tadashi Aoyama, Kornyanat Hozumi, Yoshihiro Yokoyama, Yoko Odagi, Yasuharu Sano i in. "Amplitude enhancement of short period GPS-TEC oscillations over rainfall area". Earth, Planets and Space 74, nr 1 (2.04.2022). http://dx.doi.org/10.1186/s40623-022-01604-7.
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AbstractCorrelation between rainfall and short period GPS-TEC (total electron content) variations are investigated by using the precipitation data obtained on the ground and estimated from satellite observations (JAXA/GSMaP) as a proxy of lower atmospheric wave activity. The GPS-TEC data obtained at a tropical station, PHIM, in Phimai, Thailand, for 2014–2020, and the data obtained at a mid-latitude station, NAKG, in Tokara Nakanoshima Island, Japan, for 2017–2019, are examined. A statistical analysis of MEM (maximum entropy method) power spectral density (PSD) in the period range from 50 to 1200 s over PHIM clearly shows an enhancement in the cases of rainfall from that in no-rainfall cases, in particular, on the dusk side. The enhancement is observed both acoustic wave periods less than 5–6 min and internal gravity wave periods more than 10 min. The enhancement after sunset could be an effect of strong rainfall more frequent on the dusk side than that in other local time, or it could suggest the importance of ionospheric electron density profile change for the TEC variation. On the other hand, the PSD does not show such clear enhancement over NAKG on the dusk side, although it shows a small enhancement on both dayside and night-side. A clear PSD bulge near the main vertical acoustic resonance periods, i.e., around 275 s, appears in the average PSD profile of the TEC at PHIM, which suggests that the resonance effect contribute to some extent the PSD enhancement under rainy condition. An event analysis also suggests the contribution of acoustic resonance to the enhancement of the short period TEC variation. A complicated spatial distribution of TEC oscillation over a rainfall area around PHIM, where the TEC oscillations with various periods co-exist, is presented. Graphical Abstract