scholarly journals Spectral properties of low-frequency electrostatic waves in the ionospheric E region

2000 ◽  
Vol 105 (A5) ◽  
pp. 10585-10601 ◽  
Author(s):  
B. Krane ◽  
H. L. Pécseli ◽  
J. Trulsen ◽  
F. Primdahl
Keyword(s):  
Spectral Properties ◽  
Low Frequency ◽  
Electrostatic Waves ◽  
E Region

scholarly journals Propagation and dispersion of electrostatic waves in the ionospheric E region

1997 ◽  
Vol 15 (7) ◽  
pp. 878-889 ◽  
Author(s):  
K. Iranpour ◽  
H. L. Pécseli ◽  
J. Trulsen ◽  
A. Bahnsen ◽  
F. Primdahl ◽  
...  
Keyword(s):  
Hall Current ◽  
Low Frequency ◽  
Plasma Waves ◽  
Electrostatic Waves ◽  
Field Fluctuations ◽  
E Region ◽  
Band Pass ◽  
Electrostatic Fluctuations ◽  
The Waves ◽  
The Rose

Abstract. Low-frequency electrostatic fluctuations in the ionospheric E region were detected by instruments on the ROSE rockets. The phase velocity and dispersion of plasma waves in the ionospheric E region are determined by band-pass filtering and cross-correlating data of the electric-field fluctuations detected by the probes on the ROSE F4 rocket. The results were confirmed by a different method of analysis of the same data. The results show that the waves propagate in the Hall-current direction with a velocity somewhat below the ion sound speed obtained for ionospheric conditions during the flight. It is also found that the waves are dispersive, with the longest wavelengths propagating with the lowest velocity.

scholarly journals Low-frequency electrostatic waves in the ionospheric E-region: a comparison of rocket observations and numerical simulations

2006 ◽  
Vol 24 (11) ◽  
pp. 2959-2979 ◽  
Author(s):  
L. Dyrud ◽  
B. Krane ◽  
M. Oppenheim ◽  
H. L. Pécseli ◽  
K. Schlegel ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Low Frequency ◽  
Homogeneous Magnetic Field ◽  
Small Scale ◽  
Electrostatic Waves ◽  
Neutral Gas ◽  
E Region ◽  
Locally Homogeneous ◽  
Secondary Instabilities

Abstract. Low frequency electrostatic waves in the lower parts of the ionosphere are studied by a comparison of observations by instrumented rockets and of results from numerical simulations. Particular attention is given to the spectral properties of the waves. On the basis of a good agreement between the observations and the simulations, it can be argued that the most important nonlinear dynamics can be accounted for in a 2-D numerical model, referring to a plane perpendicular to a locally homogeneous magnetic field. It does not seem necessary to take into account turbulent fluctuations or motions in the neutral gas component. The numerical simulations explain the observed strongly intermittent nature of the fluctuations: secondary instabilities develop on the large scale gradients of the largest amplitude waves, and the small scale dynamics is strongly influenced by these secondary instabilities. We compare potential variations obtained at a single position in the numerical simulations with two point potential-difference signals, where the latter is the adequate representation for the data obtained by instrumented rockets. We can demonstrate a significant reduction in the amount of information concerning the plasma turbulence when the latter signal is used for analysis. In particular we show that the bicoherence estimate is strongly affected. The conclusions have implications for studies of low frequency ionospheric fluctuations in the E and F regions by instrumented rockets, and also for other methods relying on difference measurements, using two probes with large separation. The analysis also resolves a long standing controversy concerning the supersonic phase velocities of these cross-field instabilities being observed in laboratory experiments.

scholarly journals Frequency Selective Auto-Encoder for Smart Meter Data Compression

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1521
Author(s):  
Jihoon Lee ◽  
Seungwook Yoon ◽  
Euiseok Hwang
Keyword(s):  
Data Compression ◽  
High Frequency ◽  
Spectral Properties ◽  
Situational Awareness ◽  
Time Windows ◽  
Low Frequency ◽  
Smart Meters ◽  
Compression Performance ◽  
Reconstruction Performance ◽  
Frequency Selective

With the development of the internet of things (IoT), the power grid has become intelligent using massive IoT sensors, such as smart meters. Generally, installed smart meters can collect large amounts of data to improve grid visibility and situational awareness. However, the limited storage and communication capacities can restrain their infrastructure in the IoT environment. To alleviate these problems, efficient and various compression techniques are required. Deep learning-based compression techniques such as auto-encoders (AEs) have recently been deployed for this purpose. However, the compression performance of the existing models can be limited when the spectral properties of high-frequency sampled power data are widely varying over time. This paper proposes an AE compression model, based on a frequency selection method, which improves the reconstruction quality while maintaining the compression ratio (CR). For efficient data compression, the proposed method selectively applies customized compression models, depending on the spectral properties of the corresponding time windows. The framework of the proposed method involves two primary steps: (i) division of the power data into a series of time windows with specified spectral properties (high-frequency, medium-frequency, and low-frequency dominance) and (ii) separate training and selective application of the AE models, which prepares them for the power data compression that best suits the characteristics of each frequency. In simulations on the Dutch residential energy dataset, the frequency-selective AE model shows significantly higher reconstruction performance than the existing model with the same CR. In addition, the proposed model reduces the computational complexity involved in the analysis of the learning process.

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.

Determine the Physical Mechanism and Source Region of Beat Wave Modulation by Changing the Frequency of HF Waves

2021 ◽  
Author(s):  
Zhe Guo ◽  
Hanxian Fang ◽  
Farideh Honary
Keyword(s):  
Physical Mechanism ◽  
Source Region ◽  
Low Frequency ◽  
Signal Amplitude ◽  
New Approach ◽  
Wave Modulation ◽  
F Region ◽  
Source Regions ◽  
High Modulation ◽  
E Region

Abstract This paper introduces a new approach for the determination of the source region of BW (beat wave) modulation. This type of modulation is achieved by transmitting HF continuous waves with a frequency difference of f, where f is the frequency of modulated ELF/VLF (extremely low frequency/very low frequency) waves from two sub-arrays of a high power HF transmitter. Despite the advantages of BW modulation in terms of generating more stable ELF/VLF signal and high modulation efficiency, there exists a controversy on the physical mechanism of BW and its source region. In this paper, the two controversial theories, i.e. BW based on D-E region thermal nonlinearity and BW based on F region ponderomotive nonlinearity are examined for cases where each of these two theories exists exclusively or both of them exist simultaneously. According to the analysis and the simulation results presented in this paper, it is found that the generated VLF signal amplitude exhibits significant variation as a function of HF frequency in different source regions. Therefore, this characteristic can be utilised as a potential new approach to determine the physical mechanism and source location of BW.

Spectral Properties of Low‐Frequency Quasi‐periodic Oscillations in GRS 1915+105

2004 ◽  
Vol 615 (1) ◽  
pp. 416-421 ◽  
Author(s):  
J. Rodriguez ◽  
S. Corbel ◽  
D. C. Hannikainen ◽  
T. Belloni ◽  
A. Paizis ◽  
...  
Keyword(s):  
Spectral Properties ◽  
Low Frequency ◽  
Periodic Oscillations

scholarly journals Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

2004 ◽  
Vol 22 (6) ◽  
pp. 1989-2000 ◽  
Author(s):  
T. Bösinger ◽  
S. L. Shalimov
Keyword(s):  
Background Noise ◽  
Azimuthal Angle ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Major Axis ◽  
Resonance Structure ◽  
Frequency Range ◽  
Ionosphere Model ◽  
F Region ◽  
E Region

Abstract. Polarization properties of the magnetic background noise (MBN) and the spectral resonance structure (SRS) of the ionospheric Alfvén resonator (IAR) below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3) and analyzed using the existing SRS theory by Belyaev et al. (1989b). The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset) and vice versa (sunrise). We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b). The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night). Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz), where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20&deg.

scholarly journals A study of seasonal variations of gravity wave intensity in thelower thermosphere using LF D1 wind observations and a numerical model

2004 ◽  
Vol 22 (1) ◽  
pp. 35-45 ◽  
Author(s):  
N. M. Gavrilov ◽  
Ch. Jacobi
Keyword(s):  
Numerical Model ◽  
Drift Velocity ◽  
Seasonal Variations ◽  
Middle Atmosphere ◽  
Low Frequency ◽  
Internal Gravity Waves ◽  
Short Period ◽  
Summer Maximum ◽  
E Region ◽  
Standard Deviations

Abstract. The data of the regular low-frequency D1 E-region observations at Collm, Germany (52°N, 15°E) in 1983–1999 are used for estimations of the intensity of short-period perturbations of the horizontal drift velocity at 85–110 km altitude. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales of 0.7–3 h. The average monthly standard deviations of short-period perturbations of the zonal velocity near altitude 83 km have a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards the spring months, and a second maximum of perturbation amplitudes appears in autumn at altitudes near and above 100 km. The seasonal changes in the standard deviations of meridional velocity show the maxima in spring and summer. A numerical model describing the propagation of a set of harmonics modeling a spectrum of internal gravity waves in the atmosphere is used for the interpretation of observed seasonal variations of wind perturbation intensity. Numerical modeling reveals that the observed altitude changes in the seasonal variations of the drift velocity standard deviations may be explained by a superposition of IGWs generated at different levels in the troposphere and middle atmosphere. IGWs generated in the stratospheric and mesospheric jet stream may have substantial amplitudes at altitudes near and above 100 km, where they may modify the seasonal variations, which are typical for IGWs propagating from the troposphere. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides) – Ionosphere (ionospheric irregularities)

Sign in / Sign up

Export Citation Format

Share Document