scholarly journals Low Ionosphere under Influence of Strong Solar Radiation: Diagnostics and Modeling

2021 ◽  
Vol 11 (16) ◽  
pp. 7194
Author(s):  
Vladimir A. Srećković ◽  
Desanka M. Šulić ◽  
Ljubinko Ignjatović ◽  
Veljko Vujčić
Keyword(s):  
Solar Radiation ◽  
Solar Flares ◽  
Low Frequency ◽  
Ionospheric Disturbances ◽  
D Region ◽  
Radio Signals ◽  
The Impact ◽  
First Time ◽  
Region Plasma ◽  
Intense Radiation

Solar flares (SFs) and intense radiation can generate additional ionization in the Earth’s atmosphere and affect its structure. These types of solar radiation and activity create sudden ionospheric disturbances (SIDs), affect electronic equipment on the ground along with signals from space, and potentially induce various natural disasters. Focus of this work is on the study of SIDs induced by X-ray SFs using very low frequency (VLF) radio signals in order to predict the impact of SFs on Earth and analyze ionosphere plasmas and its parameters. All data are recorded by VLF BEL stations and the model computation is used to obtain the daytime atmosphere parameters induced by this extreme radiation. The obtained ionospheric parameters are compared with results of other authors. For the first time we analyzed physics of the D-region—during consecutive huge SFs which continuously perturbed this layer for a few hours—in detail. We have developed an empirical model of the D-region plasma density and gave a simple approximative formula for electron density.

scholarly journals A comparative study of measured amplitude and phase perturbations of VLF and LF radio signals induced by solar flares

2014 ◽  
pp. 45-54 ◽  
Author(s):  
D.M. Sulic ◽  
V.A. Sreckovic
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Geographic Location ◽  
Electron Density Profile ◽  
Great Circle ◽  
Direct Result ◽  
Ionospheric Disturbances ◽  
X Ray ◽  
Radio Signals ◽  
Middle Europe

Very Low Frequency (VLF) and Low Frequency (LF) signal perturbations were examined to study ionospheric disturbances induced by solar X-ray flares in order to understand processes involved in propagation of VLF/LF radio signals over short paths and to estimate specific characteristics of each short path. The receiver at the Belgrade station is constantly monitoring the amplitude and phase of a coherent and subionospherically propagating LF signal operated in Sicily NSC at 45.90 kHz, and a VLF signal operated in Isola di Tavolara ICV at 20.27 kHz, with the great circle distances of 953 km and 976 km, respectively. A significant number of similarities between these short paths is a direct result of both transmitters and the receiver?s geographic location. The main difference is in transmitter frequencies. From July 2008 to February 2014 there were about 200 events that were chosen for further examination. All selected examples showed that the amplitude and phase of VLF and LF signals were perturbed by solar X-ray flares occurrence. This six-year period covers both minimum and maximum of solar activity. Simultaneous measurement of amplitude and phase of the VLF/LF signals during a solar flare occurrence was applied to evaluate the electron density profile versus altitude, to carry out the function of time over the middle Europe.

scholarly journals X-Ray Solar Flares Observed and Detected by The New Very-Low-Frequency Receiver in Nasiriyah City, South of Iraq

2021 ◽  
Vol 32 (2) ◽  
pp. 58
Author(s):  
Habeeb Allawi ◽  
Moataz Jasim ◽  
Kareem Abdulameer Difar
Keyword(s):  
Solar Flares ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
Ionospheric Disturbances ◽  
Very Low Frequency ◽  
Radio Signals ◽  
South Of Iraq ◽  
Set Up ◽  
June July ◽  
To Receive

A receiver station was installed at Nasiriyah (Dhi Qar University - Faculty of Sciences) to receive very low frequency (VLF) radio signals from transmitters around the world. VLF waves are excellent probes of the sudden ionospheric disturbance (SID); they detect varying properties of the D layer presented as a lower region of the ionosphere when these waves propagate through the Earth-Ionosphere Waveguide. This study describes the set-up of our station system and it demonstrates its ability to detect sudden ionospheric disturbances caused by solar flares in May, June, July, August, and September 2017. We found out that the monitoring station is working successfully to receive FLV signals, and to detect sudden ionospheric disturbances. We detected 17 events resulting from solar flare C-class, 8 events from M-class, and 3 events from X-class that caused an increase in the received FLV amplitude.

scholarly journals Survey of electron density changes in the daytime ionosphere over the Arecibo observatory due to lightning and solar flares

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caitano L. da Silva ◽  
Sophia D. Salazar ◽  
Christiano G. M. Brum ◽  
Pedrina Terra
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Weather Conditions ◽  
Optical Observations ◽  
Radio Waves ◽  
D Region ◽  
E Region ◽  
Arecibo Observatory

AbstractOptical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

scholarly journals Characterization of gravity waves in the lower ionosphere using very low frequency observations at Comandante Ferraz Brazilian Antarctic Station

2020 ◽  
Vol 38 (2) ◽  
pp. 385-394
Author(s):  
Emilia Correia ◽  
Luis Tiago Medeiros Raunheitte ◽  
José Valentin Bageston ◽  
Dino Enrico D'Amico
Keyword(s):  
Low Frequency ◽  
Lower Ionosphere ◽  
Drake Passage ◽  
Wave Period ◽  
Very Low Frequency ◽  
Reflection Height ◽  
D Region ◽  
Radio Signals ◽  
Sky Conditions ◽  
The Waves

Abstract. The goal of this work is to investigate the gravity wave (GW) characteristics in the low ionosphere using very low frequency (VLF) radio signals. The spatial modulations produced by the GWs affect the conditions of the electron density at reflection height of the VLF signals, which produce fluctuations of the electrical conductivity in the D region that can be detected as variations in the amplitude and phase of VLF narrowband signals. The analysis considered the VLF signal transmitted from the US Cutler, Maine (NAA) station that was received at Comandante Ferraz Brazilian Antarctic Station (EACF, 62.1∘ S, 58.4∘ W), with its great circle path crossing the Drake Passage longitudinally. The wave periods of the GWs detected in the low ionosphere are obtained using the wavelet analysis applied to the VLF amplitude. Here the VLF technique was used as a new aspect for monitoring GW activity. It was validated comparing the wave period and duration properties of one GW event observed simultaneously with a co-located airglow all-sky imager both operating at EACF. The statistical analysis of the seasonal variation of the wave periods detected using VLF technique for 2007 showed that the GW events occurred all observed days, with the waves with a period between 5 and 10 min dominating during night hours from May to September, while during daytime hours the waves with a period between 0 and 5 min are predominant the whole year and dominate all days from November to April. These results show that VLF technique is a powerful tool to obtain the wave period and duration of GW events in the low ionosphere, with the advantage of being independent of sky conditions, and it can be used during the whole day and year-round.

scholarly journals The Impact of Sound Exposure on Heart Rate Variability in Adolescent Students

2018 ◽  
pp. 695-702 ◽  
Author(s):  
M. VETERNIK ◽  
I. TONHAJZEROVA ◽  
J. MISEK ◽  
V. JAKUSOVA ◽  
H. HUDECKOVA ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Low Frequency ◽  
Sound Intensity ◽  
Sine Wave ◽  
Adolescent Students ◽  
Sound Exposure ◽  
Cardiac Autonomic Regulation ◽  
The Impact ◽  
First Time

Previous studies of physiological responses to music and noise showed the effect on the autonomic nervous system. The heart rate variability (HRV) has been used to assess the activation of the sympathetic and the parasympathetic nervous systems. The present study was aimed to examine HRV with exposure to four sine-wave pure tones (20 Hz, 50 Hz, 2 kHz and 15 kHz) in an environment where the sound intensity exceeded level 65 dB (A-weighted). The participants (20 adolescent girls) were lying in supine position during exposure protocol divided into 6 periods, the first time with generated sounds and the second time without sounds. In the protocol without sound exposure, the low frequency band of the HRV spectrum was increased compared to the basal state before examination (period_1: 6.05±0.29 ms2 compared to period_5: 6.56±0.20 ms2, p<0.05). The significant increase of root Mean Square of the Successive Differences (rMSSD, period_1: 4.09±0.16 s compared to period_6: 4.33±0.12 s, p<0.05) and prolongation of R to R peak (RR) interval (period_1: 889±30 ms compared to period_5: 973±30 ms, p<0.001) were observed in the protocol without sound exposure comparing to the protocol with sound exposure where only bradycardia was observed. Contrary to rather polemical data in literature our pilot study suggests that sounds (under given frequencies) have no impact on the heart rate variability and cardiac autonomic regulation.

Observation and Analysis of Solar Flares that Cause Large-area Short-wave Communication Interruption

2021 ◽  
Author(s):  
Zhou Kangpo ◽  
Niu youtian ◽  
Liu weina ◽  
Wang zhaodi ◽  
Guo songhao ◽  
...  
Keyword(s):  
Solar Flares ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
High Energy ◽  
Short Wave ◽  
Absorption Capacity ◽  
X Rays ◽  
Large Area ◽  
Radio Signals ◽  
Shortwave Communication

Abstract When a solar flare erupts, the sun emits a flood of X-rays and high-energy particles that reach Earth at the speed of light, causing a sudden ionospheric disturbance event (SID event). The D layer of the ionosphere absorbs high-frequency radio signals. With the increase of flare intensity, the D layer's absorption capacity becomes stronger, which leads to the decline of shortwave communication quality and even the interruption of shortwave communication. In this paper, solar flares, which caused large area short-wave communication interruption in recent years, are observed and analyzed by very low frequency (VLF) method, and the influence of solar flares on short-wave communication is summarized. Finally, several methods to deal with the short-wave communication interruption caused by solar flares are proposed.

Detection of Sudden Ionospheric Disturbances due to Solar flares by monitoring the Very Low Frequency signal at Malda

2010 ◽  
Author(s):  
Nilmadhab Nandy ◽  
Achintya K. Chatterjee ◽  
Md. Washimul Bari ◽  
Asit K. Choudhury ◽  
Sandip K. Chakrabarti
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Ionospheric Disturbances ◽  
Frequency Signal ◽  
Very Low Frequency

scholarly journals Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry

2013 ◽  
Vol 13 (18) ◽  
pp. 9159-9168 ◽  
Author(s):  
S. Palit ◽  
T. Basak ◽  
S. K. Mondal ◽  
S. Pal ◽  
S. K. Chakrabarti
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Radio Wave ◽  
Solar Flares ◽  
Time Variation ◽  
Low Frequency ◽  
Very Low Frequency ◽  
D Region ◽  
Geant4 Monte Carlo Simulation ◽  
Class Flare

Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

scholarly journals Performance of a New Fine Particle Impact Damper

2008 ◽  
Vol 2008 ◽  
pp. 1-6 ◽  
Author(s):  
Yanchen Du ◽  
Shulin Wang ◽  
Yan Zhu ◽  
Laiqiang Li ◽  
Guangqiang Han
Keyword(s):  
Fine Particle ◽  
Mechanical Vibration ◽  
Low Frequency ◽  
Particle Impact ◽  
Momentum Exchange ◽  
Impact Damper ◽  
Low Frequency Vibration ◽  
Cantilevered Beam ◽  
The Impact ◽  
First Time

The energy dissipation mechanisms of conventional impact damper (CID) are mainly momentum exchange and friction. During the impact process, a lot of vibration energy cannot be exhausted but reverberated among the vibration partners. Besides, the CID may produce the additional vibration to the system or even amplify the response in the low-frequency vibration. To overcome these shortcomings, this paper proposes a new fine particle impact damper (FPID) which for the first time introduces the fine particle plastic deformation as an irreversible energy sink. Then, the experiments of the cantilevered beam with the CID and that with the FPID are, respectively, carried out to investigate the behavior of FPID. The experimental results indicate that the FPID has a better performance in vibration damping than in the CID and the FPID works well in control of the vibration with frequency lower than 50 Hz, which is absent to the non-obstructive particle damper. Thus, the FPID has a bright and significant application future because most of the mechanical vibration falls in the range of low freqency.

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