Temporal variations of the ion-neutral collision frequency from EISCAT observations in the polar lower ionosphere during periods of geomagnetic disturbances

2012 ◽  
Vol 117 (A5) ◽  
pp. n/a-n/a ◽  
Author(s):  
S. Oyama ◽  
J. Kurihara ◽  
B. J. Watkins ◽  
T. T. Tsuda ◽  
T. Takahashi
Keyword(s):  
Collision Frequency ◽  
Lower Ionosphere ◽  
Temporal Variations ◽  
Geomagnetic Disturbances

scholarly journals Comparison of simultaneous variations of the ionospheric total electron content and geomagnetic field associated with strong earthquakes

2001 ◽  
Vol 1 (1/2) ◽  
pp. 53-59 ◽  
Author(s):  
Sh. Naaman ◽  
L. S. Alperovich ◽  
Sh. Wdowinski ◽  
M. Hayakawa ◽  
E. Calais
Keyword(s):  
Total Electron Content ◽  
Vertical Displacement ◽  
Temporal Variations ◽  
Electron Content ◽  
Geomagnetic Disturbances ◽  
Total Electron ◽  
Strong Earthquakes ◽  
Ionospheric Total Electron Content ◽  
Geomagnetic Observations ◽  
Gps Observations

Abstract. In this paper, perturbations of the ionospheric Total Electron Content (TEC) are compared with geomagnetic oscillations. Comparison is made for a few selected periods, some during earthquakes in California and Japan and others at quiet periods in Israel and California. Anomalies in TEC were extracted using Global Positioning System (GPS) observations collected by GIL (GPS in Israel) and the California permanent GPS networks. Geomagnetic data were collected in some regions where geomagnetic observatories and the GPS network overlaps. Sensitivity of the GPS method and basic wave characteristics of the ionospheric TEC perturbations are discussed. We study temporal variations of ionospheric TEC structures with highest reasonable spatial resolution around 50 km. Our results show no detectable TEC disturbances caused by right-lateral strike-slip earthquakes with minor vertical displacement. However, geomagnetic observations obtained at two observatories located in the epicenter zone of a strong dip-slip earthquake (Kyuchu, M = 6.2, 26 March 1997) revealed geomagnetic disturbances occurred 6–7 h before the earthquake.

Theory of energy flux and polarization changes of a radio wave with two magnetoionic components undergoing self demodulation in the ionosphere

1974 ◽  
Vol 341 (1626) ◽  
pp. 361-381 ◽  
Keyword(s):  
Electron Temperature ◽  
Radio Wave ◽  
Phase Difference ◽  
Incident Wave ◽  
Unit Volume ◽  
Collision Frequency ◽  
Lower Ionosphere ◽  
Effective Collision Frequency ◽  
Composite Wave ◽  
Effective Collision

The absorption of a powerful plane radio wave vertically incident on the lower ionosphere is studied. If it contains the two magnetoionic components with roughly equal amplitudes, the power absorbed per unit volume can be either greater or less than the sum of the powers for the separate components, depending on their phase difference. This is determined by the polarization of the incident wave, and the heights where the absorption is a maximum can be changed by changing this polarization. The power absorbed causes an increase in the electron temperature and thence in the effective collision frequency. This is studied first for an unmodulated wave. If the wave is amplitude modulated, the increase of collision frequency varies periodically in the modulation cycle. This results in self demodulation which is different for the two magnetoionic components because of their different rates of absorption. The result is that the polarization of the composite wave varies periodically over the modulation cycle.

On the characterization of VLF radio signal propagation in atmosphere in quite solar conditions

2020 ◽  
Author(s):  
Giovanni Nico ◽  
Aleksandra Nina ◽  
Anita Ermini ◽  
Pierfrancesco Biagi
Keyword(s):  
Radio Signal ◽  
Technological Development ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Signal Propagation ◽  
Temporal Variations ◽  
Seasonal Effects ◽  
Propagation Mode ◽  
Theory Approach ◽  
Radio Signals

<p>In this work we use Very Low Frequency (VLF) radio signals, having a frequency in the bands 20-80 kHz, to study the VLF signal propagation in the atmosphere quite undisturbed conditions by selecting the signals recorded during night. As a good approximation, we can model the propagation of VLF radio signals as characterized by a ground-wave and a sky-wave propagation mode. The first one generates a radio signal that propagates in the channel ground-troposphere, while the second one generates a signal which propagates using the lower ionosphere as a reflector. The VLF receivers of the INFREP (European Network of Electromagnetic Radiation) network are used. These receivers have been installed since 2009 mainly in southern and central Europe and currently the INFREP network consists of 9 receivers. A 1-minute sampling interval is used to record the amplitude of VLF signals. Long time-series of VLF signals propagating during night are extracted from recorded signals to study possible seasonal effects due to temporal variations in the physical properties of troposphere. A graph theory approach is used to investigate the spatial correlation of the aforementioned effects at different receivers. A multivariate analysis is also applied to identify common temporal changes observed at VLF receivers.</p><p>This work was supported by the Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR), Italy, under the project OT4CLIMA. This research is supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, under the projects 176002 and III44002.</p>

scholarly journals GEOMAGNETIC EFFECT OF TURKISH EARTHQUAKE OF JANUARY 24, 2020

2020 ◽  
Vol 25 (4) ◽  
pp. 276-289
Author(s):  
Y. Luo ◽  
◽  
L. F. Chernogor ◽  
K. P. Garmash ◽  
◽  
...  
Keyword(s):  
Fourier Transform ◽  
Flash Memory ◽  
Geomagnetic Field ◽  
Temporal Variations ◽  
Fixed Number ◽  
Mhd Waves ◽  
Geomagnetic Disturbances ◽  
Period Range ◽  
Geomagnetic Effect ◽  
S Period

Purpose:The main cause of geomagnetic disturbances are cosmic sources, processes acting in the solar wind and in the interplanetary medium, as well as large celestial bodies entering the terrestrial atmosphere. Earthquakes (EQs) also act to produce geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS) constitute a unified system, where positive and negative couplings among the subsystems, as well as feedbacks and precondition among the system components take place. The mechanisms for the action of EQs and processes acting in the lithosphere on the geomagnetic field are poorly understood. It is considered that the EQ action is caused by cracking of rocks, fluctuating motion in the pore fluid, static electricity discharges, etc. In the course of EQs, the seismic, acoustic, atmospheric gravity waves (AGWs), and magnetohydrodynamic (MHD) waves are generated. The purpose of this paper is to describe the magnetic effects of the EQ, which took place in Turkey on 24 January 2020. Design/methodology/approach: The measurements are taken with the fluxmeter magnetometer delivering 0.5-500 pT sensitivity in the 1-1000 s period range, respectively, and in a wide enough studied frequency band within 0.001 to 1 Hz. The EM-II magnetometer with the embedded microcontroller digitizes the magnetometer signals and performs preliminary filtering over 0.5 s time intervals, while the external flash memory is used to store the filtered out magnetometer signals and the times of their acquisition. To investigate quasi-periodic processes in detail, the temporal variations in the level of the H and D components of the geomagnetic field were applied to the systems spectral analysis, which makes use of the short-time Fourier transform, the wavelet transform using the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Findings: The train of oscillations in the level of the D component observed 25.5 h before the EQ on 23 January 2020 is supposed to be associated with the magnetic precursor. The bidirectional pulse in the H component observed on 24 January 2020 could be due to the piston action of the EQ, which had generated an MHD pulse. The quasi-periodic variations in the level of the H and D components of the geomagnetic field, which followed 75 min after the EQ, were caused by a magnetic disturbance produced by the traveling ionospheric disturbances due to the AGWs launched by the EQ. The magnetic effect amplitude was estimated to be close to 0.3 nT, and the quasi-period to be 700-900 s. The amplitude of the disturbances in the electron density in the AGW field was estimated to be about 8 % and the period of 700-900 s. Damping oscillations in both components of the magnetic field were detected to occur with a period of approximately 120 s. This effect is supposed to be due to the shock wave generated in the atmosphere in the course of the EQ. Conclusions: The magnetic variations associated with the EQ and occurring before and during the EQ have been studied in the 1-1000 s period range. Key words: earthquake, fluxmeter magnetometer, quasi-periodic disturbance, seismic wave, acoustic-gravity wave, MHD pulse

Theory of the modulation imposed on an obliquely incident radio wave reflected in a disturbed region of the lower ionosphere

1976 ◽  
Vol 349 (1659) ◽  
pp. 555-570 ◽  
Keyword(s):  
Integral Method ◽  
Collision Frequency ◽  
Lower Ionosphere ◽  
Electron Collision ◽  
Disturbed Region ◽  
Quartic Equation ◽  
Obliquely Incident ◽  
Electron Collision Frequency ◽  
Reflexion Coefficient ◽  
Phase Integral

A powerful disturbing wave enters the lower ionosphere and causes a periodic modulation of the electron collision frequency. A simple model is adopted for this disturbed region. The modulation transferred to an obliquely incident wanted wave that is reflected in or near it is investigated. The reflexion coefficient of the wanted wave is found by applying the phase integral method. The complex reflexion height of the wanted wave is a function of time in the modulation cycle. Results are discussed first for an isotropic ionosphere and are then extended to include the effect of the Earth’s magnetic field, and the calculation uses the Booker quartic equation. It is shown that the phase integral method is admirably suited to solve this kind of problem. Some examples are given to illustrate that the greatest amount of modulation is transferred when the wanted wave is reflected near the most disturbed part of the ionosphere. The relation of this to some observed effects near sunrise is discussed.

scholarly journals Monitoring of geomagnetic disturbances using the global survey method in real time

2019 ◽  
Vol 5 (3) ◽  
pp. 93-97 ◽  
Author(s):  
Владислав Григорьев ◽  
Vladislav Grigoryev ◽  
Сергей Стародубцев ◽  
Sergei Starodubtsev ◽  
Петр Гололобов ◽  
...  
Keyword(s):  
Real Time ◽  
Geomagnetic Storms ◽  
Interplanetary Medium ◽  
Three Dimensional ◽  
Cosmic Ray ◽  
Temporal Variations ◽  
Survey Method ◽  
Geomagnetic Disturbances ◽  
Global Survey ◽  
Worldwide Network

A method for forecasting geomagnetic storms using the realization of the global survey method in real time is presented. The method is based on data from the worldwide network of neutron monitors NMDB. Using this method, we analyze the behavior of components of three-dimensional angular distribution of cosmic rays in the interplanetary medium, which were due to the first two spherical harmonics, over the period from 2013 to 2018. We have established that the main parameters that respond to the arrival of geoeffective disturbances of the interplanetary medium at Earth are changes in amplitudes of zonal (north-south) components of cosmic ray distribution. In order to select effective criteria for identifying predictors of geomagnetic disturbances and their possible temporal variations, we have made a retrospective analysis of the relationship between behaviors of the above components and geomagnetic disturbances occurring during the period of interest.

scholarly journals Reduction of the VLF Signal Phase Noise Before Earthquakes

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 444
Author(s):  
Aleksandra Nina ◽  
Pier Francesco Biagi ◽  
Srđan T. Mitrović ◽  
Sergey Pulinets ◽  
Giovanni Nico ◽  
...  
Keyword(s):  
Phase Noise ◽  
Wave Attenuation ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Temporal Variations ◽  
Frequency Domains ◽  
Precursors Of Earthquakes ◽  
Hydrodynamic Wave ◽  
Attenuation Characteristics ◽  
Analyse Time

In this paper we analyse temporal variations of the phase of a very low frequency (VLF) signal, used for the lower ionosphere monitoring, in periods around four earthquakes (EQs) with magnitude greater than 4. We provide two analyses in time and frequency domains. First, we analyse time evolution of the phase noise. And second, we examine variations of the frequency spectrum using Fast Fourier Transform (FFT) in order to detect hydrodynamic wave excitations and attenuations. This study follows a previous investigation which indicated the noise amplitude reduction, and excitations and attenuations of the hydrodynamic waves less than one hour before the considered EQ events as a new potential ionospheric precursors of earthquakes. We analyse the phase of the ICV VLF transmitter signal emitted in Italy recorded in Serbia in time periods around four earthquakes occurred on 3, 4 and 9 November 2010 which are the most intensive earthquakes analysed in the previous study. The obtained results indicate very similar changes in the noise of phase and amplitude, and show an agreement in recorded acoustic wave excitations. However, properties in the obtained wave attenuation characteristics are different for these two signal parameters.

The effect of a time varying collision frequency on a radio wave obliquely incident on the lower ionosphere

1976 ◽  
Vol 348 (1653) ◽  
pp. 245-263 ◽  
Keyword(s):  
Radio Wave ◽  
Collision Frequency ◽  
Modulation Frequency ◽  
Average Power ◽  
Lower Ionosphere ◽  
Angle Of Incidence ◽  
Disturbed Region ◽  
Quartic Equation ◽  
Obliquely Incident ◽  
Cross Modulation

The phenomenon of ionospheric cross-modulation occurs when a ‘wanted’ radio wave passes through a region of the ionospheric plasma where a powerful modulated ‘disturbing’ radio wave is strongly absorbed. Many previous studies have assumed that the wanted wave is vertically incident and, in some cases, that the ionosphere is isotropic. The theory is studied here for an obliquely incident wanted wave propagating through an anisotropic ionosphere. The Booker quartic equation is used to find the modulation transferred to the wanted wave, and how it depends on height, angle of incidence, azimuth and radio frequency. It is assumed that the disturbing wave has a sinusoidal amplitude modulation so that the collision frequency in the disturbed region varies periodically with the modulation frequency. The physical processes that occur in various situations are reviewed. It is found that many of the results from the simpler theories still apply, but some new effects are found. For example, there can be a marked difference in the modulation transferred to two ordinary (or two extraordinary) wanted waves with the same angle of incidence, one travelling obliquely upwards, and the other downwards through the disturbed region. It is found that an increase in the average power of the disturbing wave does not necessarily imply a corresponding increase in the modulation transferred to the wanted wave. The radio engineer who requires an accurate assessment of cross-modulation as a possible source of interference in communications could apply some methods of this paper with the aid of modern computers.

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