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Proceedings ArticleDOI

Spatio-temporal characteristics of sub-ionospheric perturbations associated with annular solar eclipse over Japan: Network observations and modeling

01 Aug 2014-pp 1-3
TL;DR: In this paper, the amplitude data from the UEC's VLF/LF transmitter observation network associated with an annular solar eclipse in 2012 were analyzed using 2D-FDTD method.
Abstract: The UEC's VLF/LF transmitter observation network has been operating years in order to monitor the ionospheric perturbations caused by various physical phenomena. A solar eclipse is one of the factors that produce disturbances in the lower ionosphere. In this paper, we analyze VLF amplitude data from our network associated with annular solar eclipse in 2012. Clear temporal dependences of the VLF/LF amplitude were identified at various VLF/LF receivers. Numerical computations of VLF/LF signals with the ionospheric perturbations due to the solar eclipse were carried out by using 2D-FDTD method. As a result, temporal variations of the VLF/LF amplitude are in rather good agreement with those from the numerical modeling.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors carried out the prediction of daily nighttime mean very low frequency (VLF) amplitude by using Nonlinear Autoregressive with Exogenous Input Neural Network (NARX NN), which was built based on the daily input variables of various physical parameters such as stratospheric temperature, total column ozone, cosmic rays, Dst, and Kp indices.
Abstract: The electric field amplitude of very low frequency (VLF) transmitter from Hawaii (NPM) has been continuously recorded at Chofu (CHF), Tokyo, Japan. The VLF amplitude variability indicates lower ionospheric perturbation in the D region (60–90 km altitude range) around the NPM-CHF propagation path. We carried out the prediction of daily nighttime mean VLF amplitude by using Nonlinear Autoregressive with Exogenous Input Neural Network (NARX NN). The NARX NN model, which was built based on the daily input variables of various physical parameters such as stratospheric temperature, total column ozone, cosmic rays, Dst, and Kp indices possess good accuracy during the model building. The fitted model was constructed within the training period from 1 January 2011 to 4 February 2013 by using three algorithms, namely, Bayesian Neural Network (BRANN), Levenberg Marquardt Neural Network (LMANN), and Scaled Conjugate Gradient (SCG). The LMANN has the largest Pearson correlation coefficient (r) of 0.94 and smallest root-mean-square error (RMSE) of 1.19 dB. The constructed models by using LMANN were applied to predict the VLF amplitude from 5 February 2013 to 31 December 2013. As a result the one step (1 day) ahead predicted nighttime VLF amplitude has the r of 0.93 and RMSE of 2.25 dB. We conclude that the model built according to the proposed methodology provides good predictions of the electric field amplitude of VLF waves for NPM-CHF (midlatitude) propagation path.

9 citations

Journal ArticleDOI
TL;DR: In this article, a review on ULF, ELF and VLF signals within the waveguide in terms of different geophysical and extra-terrestrial events like lightning, earthquakes, Leonid meteor shower, solar flares, solar eclipse, geomagnetic storms, and TLEs etc.
Abstract: The space between the two spherical conducting shells, Earth surface and the lower boundary of the ionosphere, behaves as a spherical cavity in which some electromagnetic signals can propagate a long distance and is called Earth-ionosphere waveguide. Through this waveguide ultra low frequency (ULF), extremely low frequency (ELF) and very low frequency (VLF) signals can propagate efficiently with low attenuation. Resonances which occur for ELF waves due to round-the-world propagation interfering with $2n \pi $ phase difference are called Schumann resonances. Lightnings are the main sources of energy continuously producing these electromagnetic radiations from the troposphere. Some fixed frequency signals are also transmitted through the waveguide from different stations for navigation purposes. The intensity and phase of these signals at a particular position depend on the waveguide characteristics which are highly influenced by different natural events. Thus the signatures of different geophysical and extra-terrestrial events may be investigated by studying these signals through proper monitoring of the time series data using suitable techniques. In this article, we provide a review on ULF, ELF and VLF signals within the waveguide in terms of different geophysical and extra-terrestrial events like lightning, earthquakes, Leonid meteor shower, solar flares, solar eclipse, geomagnetic storms, and TLEs etc.

6 citations

Proceedings ArticleDOI
01 Aug 2017
TL;DR: In this article, the NARXNN was used as a method for predicting the daily nighttime mean amplitude of VLF transmitter signals indicating the ionospheric perturbation around the transmitter-receiver path.
Abstract: The electromagnetic field amplitude of the subionospheric Very Low Frequency (VLF) propagation is sensitive to the lower ionospheric conditions. Accordingly, VLF waves have been proposed to study and monitor the lower ionosphere (D/E region). In this paper, the NARXNN (Nonlinear Autoregressive with Exogenous Input Neural Network) is used as a method for predicting the daily nighttime mean amplitude of VLF transmitter signals indicating the ionospheric perturbation around the transmitter-receiver path. The NARXNN has a good accuracy in predicting time series data and thus are more suitable for dynamic modeling. The NARX constructed model, which was built based on daily input variables of various physical parameters with the time interval from 1 January 2011 to 4 February 2013 such as stratospheric and mesospheric temperatures, cosmic rays, total column ozone, F10.7, Kp, AE, and Dst indices. We used the constructed model to predict high-(NLK-CHF), middle-(NPM-CHF) and low-latitude (NWC-CHF) paths. As a result, the constructed models are capable of performing reasonably good 5-day ahead predictions of the daily nighttime of VLF electric field amplitude for NPM-CHF path with the Pearson correlation coefficient (r) of 0.84 and with Root Mean Square Error (RMSE) of 3.12 dB, NLK-CHF (r = 0.80, RMSE = 3.57 dB) and NWC-CHF (r = 0.79, RMSE = 2.60 dB). We conclude that the constructed NARX NN model is capable of predicting the VLF electric field amplitude variation for different latitude paths.

3 citations

Proceedings ArticleDOI
01 Mar 2019
TL;DR: In this paper, the temporal dependences of very low frequency (VLF) electric amplitude perturbation from two Japanese VLF transmitters (JJI (22.2kHz) and JJY (40.0kHz) were analyzed.
Abstract: A large part of the path of the Annular Solar Eclipse of May 20,2012 (magnitude 0.9439) (ASE-2012) was over southern Japan. The D-region ionospheric changes associated with the ASE-2012, led to several degree of observable perturbations of sub-ionospheric very low frequency (VLF) radio signal. The solar eclipse associated signal changes were identified in VLF several receiving stations $(R_{x})$ simultaneously for the VLF signals coming from both Japanese and US VLF transmitters ($T_{x}$). In this work, we have analyzed temporal dependences of VLF electric amplitude perturbation $(\Delta A_{ecl,obs}(t))$ from two Japanese VLF transmitters (JJI (22.2kHz) and JJY (40.0kHz)), and the spatio-temporal characteristics of respective subionospheric perturbations are studied in detail. We consider the 2-parameter D-region ionospheric model with the exponential electron density profile. To model the shadow effect on the D-region ionosphere due to obscuration of solar disk, we assume a generalized space-time dependent 2-Dimensional Elliptical Gaussian distribution Model (2DEGM) for ionospheric parameters, such as, effective reflection height $(h')$ and sharpness factor $(\beta )$. In the vicinity of the eclipse zone, we compute the subionospheric VLF signal propagation for several signal propagation paths. In the simulation, we obtain the perturbation of VLF signal amplitude ($\Delta A_{ecl,LWPC}(t))$ at each station and compare with its observtaional counterpart $(\Delta A_{ecl,obs}(t))$.

1 citations

Proceedings ArticleDOI
01 Jul 2018
TL;DR: In this paper, nonlinear physical processes of VLF signals propagation can be well represented by nonlinear autoregressive with exogenous input neural network (NARXNN) model.
Abstract: Very low frequency (VLF) waves have been used as a powerful tool to monitor and study the lower ionosphere (D/E region). In this paper, nonlinear physical processes of VLF signals propagation can be well represented by nonlinear autoregressive with exogenous input neural network (NARXNN) model. Further, a study of NARXNN model to predict the daily nighttime mean amplitude of VLF propagation wave to recognize the ionospheric perturbation along the great circle path. The NARXNN model is powerful in predicting time series data and suitable representations of a variation of nonlinear models. The daily input variables of various physical parameters with the time interval from 15 March 2014 to 26 May 2016 were used to build prediction model. The results of the built models are performing reasonably good for one-step ahead (OSA) predictions of the daily nighttime of VLF electric field amplitude. The NARXNN model has good performance for predicting the VLF amplitude variation for different latitude paths.

1 citations

References
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Journal ArticleDOI
TL;DR: In this article, the amplitude and phase of four VLF transmitters in the frequency range 16-24 kHz were measured during the total solar eclipse observed in Europe on August 11, 1999.
Abstract: During the total solar eclipse observed in Europe on August 11, 1999, measurements were made of the amplitude and phase of four VLF transmitters in the frequency range 16–24 kHz Five receiver sites were set up, and significant variations in phase and amplitude are reported for 17 paths, more than any previously during an eclipse Distances from transmitter to receiver ranged from 90 to 14,510 km, although the majority were 10,000 km Negative phase changes were observed on most paths, independent of path length Although there was significant variation from path to path, the typical changes observed were ∼3 dB and ∼50° The changes observed were modeled using the Long Wave Propagation Capability waveguide code Maximum eclipse effects occurred when the Wait inverse scale height parameter β was 05 km−1 and the effective ionospheric height parameter H′ was 79 km, compared with β=043 km−1 and H′=71 km for normal daytime conditions The resulting changes in modeled amplitude and phase show good agreement with the majority of the observations The modeling undertaken provides an interpretation of why previous estimates of height change during eclipses have shown such a range of values A D region gas-chemistry model was compared with electron concentration estimates inferred from the observations made during the solar eclipse Quiet-day H′ and β parameters were used to define the initial ionospheric profile The gas-chemistry model was then driven only by eclipse-related solar radiation levels The calculated electron concentration values at 77 km altitude throughout the period of the solar eclipse show good agreement with the values determined from observations at all times, which suggests that a linear variation in electron production rate with solar ionizing radiation is reasonable At times of minimum electron concentration the chemical model predicts that the D region profile would be parameterized by the same β and H′ as the LWPC model values, and rocket profiles, during totality and can be considered a validation of the chemical processes defined within the model

98 citations

Journal ArticleDOI
TL;DR: In this paper, a week-long campaign was conducted in the Indian sub-continent to study the low-latitude D-region ionosphere using the very low frequency (VLF) signal from the Indian Navy transmitter (call sign: VTX3) operating at 18.2 kHz.

41 citations


"Spatio-temporal characteristics of ..." refers result in this paper

  • ...Earlier works, found in literature, mainly compared the experimental data with the results of numerical modeling by using Long Wavelength Propagation Capability (LWPC) code and the number of VLF propagation paths were limited [1,2]....

    [...]

Journal ArticleDOI
TL;DR: In this article, the amplitude and phase of a radio ground wave are calculated for an oblique crossing of a flat-lying coast line, where the surface impedance is allowed to change in a continuous and gradual manner in the vicinity of the coast line.
Abstract: The amplitude and phase of a radio ground wave are calculated for an oblique crossing of a flat-lying coast line. The surface impedance is allowed to change in a continuous and gradual manner in the vicinity of the coast line. The earlier results for an abrupt boundary are recovered as the width of the transition zone is reduced to zero. In general, it is found that the presence of the transition region will not produce a significant modification of the transmitted field. On the other hand, the reflected waves and the behavior of the field near the coast line are profoundly influenced by the width of the transition. In particular, certain singular behavior of the field associated with an abrupt boundary is virtually eliminated when the transition zone has a finite width.

20 citations


"Spatio-temporal characteristics of ..." refers background in this paper

  • ...Ionospheric perturbation [3] is assumed to be a Gaussian function propagating along the path of solar eclipse from west to east....

    [...]