Development of an automatic procedure to estimate the reflection height of tweek atmospherics

Ohya, Hiroyo; Shiokawa, K.; Miyoshi, Y.

doi:10.1186/bf03352835

Cited by 25 publications

(24 citation statements)

References 15 publications

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“…where f is the frequency of the tweek waves, c is the light velocity, and a is the Earth's radius; for details, see Ohya et al [2008].…”

Section: Estimation Methods For Tweek Reflection Heightmentioning

confidence: 99%

“…[13] We developed an automatic procedure to estimate tweek parameters h and d for statistical analysis [Ohya et al, 2008]. For more accurate estimation, we adopted the maximum entropy method (MEM) to obtain tweek spectra instead of using the conventional fast Fourier transform (FFT) method.…”

Section: Estimation Methods For Tweek Reflection Heightmentioning

confidence: 99%

“…[53] We developed an automatic procedure to estimate the tweek parameters h and d for static analysis using the tweek spectra obtained by a conventional FFT method [Ohya et al, 2008]. For more accurate estimation of tweek reflection height, we compared tweek spectra obtained by the MEM and by the FFT.…”

Section: Appendix Amentioning

confidence: 99%

“…Ohya et al [2003Ohya et al [ , 2008 proposed a technique to measure the D region height variations using VLF and extremely low frequency (ELF) tweek atmospherics (1.5-10.0 kHz) originating from lightning discharges. Passive measurement of VLF/ELF tweeks is much easier and cheaper than measurement by active radar.…”

Section: Introductionmentioning

confidence: 99%

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Long-term variations in tweek reflection height in the D and lowerEregions of the ionosphere

2011

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[1] We investigated, for the first time, long-term variations in reflection heights of tweek atmospherics based on very low frequency (VLF) observations at Kagoshima, Japan. The results revealed the effects of the solar cycle on the nighttime lower ionosphere at low to middle latitudes. The tweek reflection heights on geomagnetically quiet days were analyzed every month over three solar cycles by using an automated spectral fitting procedure to estimate the cutoff frequency. The average and standard deviation of the reflection height were 95.9 km and ±3.1 km, respectively. Typical periods of time variation for the reflection height were 13.3, 3.2, 1.3, 1.0, 0.6, and 0.5 years. The variations in tweek reflection heights did not show simple anticorrelation with solar activity. The correlation coefficient between tweek reflection height and sunspot number was 0.03 throughout the three solar cycles. Hilbert-Huang transform analysis successfully indicated the presence of 0.5-1.5 year and ∼10 year variations as intrinsic mode functions (IMF). The decomposed IMF with the ∼10 year variation had a positive correlation with sunspot numbers and a negative correlation with galactic cosmic rays (GCRs). We hypothesize that these variations in tweek reflection heights could be caused by coupling of several ionization effects at the D and lower E regions, effects such as geocorona, GCRs, particle precipitation, and variations in neutral density in the lower thermosphere. Among these processes, the geocorona and particle precipitation could show negative correlation, while the GCRs and neutral density could show positive correlation with solar activities.Citation: Ohya, H., K. Shiokawa, and Y. Miyoshi (2011), Long-term variations in tweek reflection height in the D and lower E regions of the ionosphere,

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“…where f is the frequency of the tweek waves, c is the light velocity, and a is the Earth's radius; for details, see Ohya et al [2008].…”

Section: Estimation Methods For Tweek Reflection Heightmentioning

confidence: 99%

Section: Estimation Methods For Tweek Reflection Heightmentioning

confidence: 99%

Section: Appendix Amentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Long-term variations in tweek reflection height in the D and lowerEregions of the ionosphere

2011

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“…The tweek waveforms are better resolved and suffer less attenuation at night (typically \0.5 dB Mm -1 as compared to 5 dB Mm -1 during daytime) due to sharper D-region electron density profiles [4]. Dispersion analysis of tweeks yields information about the state of the D-region ionosphere along the path of propagation [5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Remote sensing of D-region ionosphere using multimode tweeks

et al. 2015

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Lightning discharges radiate electromagnetic waves in a wide frequency range, with maximum energy in extremely low frequency/very low frequency band. A part of the radiated extremely low frequency/very low frequency wave energy is trapped in the Earth-ionosphere waveguide and travels thousands of kilometers in different modes with lower attenuation. Amplitude, frequency and phase of these waves are used to study the less explored D-region ionosphere at lower latitudes. Extremely low frequency/very low frequency observations are recorded continuously by automatic whistler detector setup installed at low-latitude Indian station Lucknow (Geom. lat. 17.6°N; long. 154.5°E). In total, 149 cases of tweeks having modes ranging from 3 to 6 have been recorded by automatic whistler detector during December 2010 and analyzed. Result shows that the propagation distance in the Earth-ionosphere waveguide lies between 1.1 and 9.4 Mm. The electron density in the lower D-region varies between 25 and 150 cm -3 . The upper boundary of the waveguide varies between 80 and 95 km. The reported results are in good agreement with the earlier measurements at different latitudes and longitudes.

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Daytime tweek atmospherics

Ohya

Shiokawa

2015

JGR Space Physics

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We report the first observation of daytime tweek atmospherics based on measurements at Moshiri (44. 37°N, 142.27°E) and Kagoshima (31.48°N, 130.72°E), Japan, during nonsolar eclipse days for 5 months in 1980-1994. The daytime tweeks were observed on geomagnetically quiet and stormy days. The daytime tweeks had clear frequency dispersion with an average duration of 12 ms, which was shorter than that in the nighttime (~50 ms). The average occurrences of the daytime tweeks at Moshiri and Kagoshima were 0.6 and 0.1 tweeks per minute during 10:00-15:00 LT, respectively. Daytime tweeks up to the second-order mode were visible. There was no difference in the occurrence of each visible mode between storm time and magnetically quiet time. The daytime reflection heights were similar to those at night (85-100 km) but with greater variation. We evaluated the attenuation rate (α n ) of tweeks by strictly taking the ionospheric reflection coefficient into account. For each frequency, α n was evaluated as a function of the electron density, electron density gradient, and ionospheric height. We found that α n had an inverse relationship with the electron density (or conductivity), electron density gradient, and ionospheric height. We suggest that the best conditions for daytime tweek observations are when the bottomside of the ionosphere is sharply defined and the ionospheric height is high.

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Development of an automatic procedure to estimate the reflection height of tweek atmospherics

Cited by 25 publications

References 15 publications

Long-term variations in tweek reflection height in the D and lowerEregions of the ionosphere

Long-term variations in tweek reflection height in the D and lowerEregions of the ionosphere

Remote sensing of D-region ionosphere using multimode tweeks

Daytime tweek atmospherics

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