Effects of a Solar Eclipse on the Propagation of VLF-LF Signals: Observations and Results
01 Jan 2011-Terrestrial Atmospheric and Oceanic Sciences (Chinese Geoscience Union)-Vol. 22, Iss: 4, pp 435
TL;DR: The results from measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere) of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7%) are shown in this article.
Abstract: The results from the measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere) of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7%) are shown. This study summarizes our results from sferics signals at 81 kHz and subionospheric transmitted signals at 19.8 and 40 kHz recorded at Agartala, Tripura (latitude: 23°N, longitude: 91.4°E). We observed significant absorption in amplitude of these signals during the eclipse period compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the eclipse associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of the Earth-ionosphere waveguide to a value where the conductivity parameter was 10 6 unit. The absorption in 81 kHz sferics amplitude is high compared to the absorption in the amplitude of 40 kHz signal transmitted from Japan. The simultaneous changes in the amplitudes of sferics and in the amplitude of transmitted signals assert some sort of coupling between the upper atmosphere and the Earth’s near-surface atmosphere prevailing clouds during solar eclipse.
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TL;DR: In this paper, the effect of total solar eclipse (TSE) on the D-region of the ionosphere was investigated using ELF/VLF radio signal. And the modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis.
19 citations
TL;DR: In this paper, the effects of two solar eclipses on the propagation characteristics of VLF sferics in the Earth-ionosphere waveguide were investigated at a fixed receiver location (23.75°N, 91.25°E).
Abstract: [1] Effects of solar eclipses on the propagation characteristics of worldwide VLF sferics from lightning activity require more investigation. An attempt was made on the occasion of two solar eclipses during 22nd July, 2009 and 15th January, 2010 to study the effects of the two eclipses on the propagation characteristics of VLF sferics in the Earth-ionosphere waveguide. Identical experimental setups were used to study the VLF sferics during the two eclipse events. The spectral character of VLF sferics propagating inside the waveguide is studied at a fixed receiver location (23.75°N, 91.25°E) at six discrete frequencies in between 3 and 20 kHz. During both the eclipse events, it is observed that VLF sferics at all the six discrete frequencies is increased from the mean normal average ambient level. The increment peaks around 10–12 kHz with an overall increment of 6.4 dB with respect to its ambient level. The VLF spectral character of enhancement of sferics show similar characters in two eclipses. The percentage decrease in electron density using standard modeling equations is found to be 90% at the height of 71 km for both the eclipses, supporting linear variation of electron density with solar radiation at the D-region of the ionosphere. The results are explained qualitatively on the basis of a decrease in electron density at the lower ionosphere modifying the reflection coefficient which affected the propagation of VLF sferics in Earth-ionosphere waveguide during eclipsed condition.
14 citations
TL;DR: In this article, the authors report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009, where sixteen and sixty-three tweek signals were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the total solar eclipse were 0.458 and 0.966, respectively.
Abstract: [1] We report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009. Sixteen and sixty-three tweek atmospherics were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the solar eclipse were 0.458 and 0.966, respectively. This was the first observation of tweek atmospherics during a low-magnitude eclipse (0.458). The average and standard deviation of the reflection height were 94.9 ± 13.7 km at Moshiri and 87.2 ± 12.9 km at Kagoshima. The reflection height at Moshiri was almost the same as that for normal nighttime conditions in July (96.7 ± 12.6 km) in spite of the low magnitude of the eclipse. The reflection height at Kagoshima seems be divided into two parts: propagation across the total solar eclipse path and propagation in the partial solar eclipse path. During the eclipse, we also observed the phase variation in the LF transmitter signals. The average change in the phase delay of the LF signals was 109° for the paths that crossed the eclipse path and 27° for the paths that did not cross the eclipse path. Assuming a normal daytime height for LF waves of 65 km, a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5–6 km for the paths across the eclipse and 1–2 km for partial eclipse paths. The wide range of estimated tweek reflection heights at Kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses.
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06 Oct 2018
483 citations
TL;DR: In this article, the authors used measured field strengths from VLF transmitters to determine improved day-time values of ionospheric parameters to enable improved VlF propagation predictions.
165 citations
TL;DR: On a clear day, there is a downward electric field of 100 to 300 volts/meter at Earth's surface, although this field is not noticeable in daily life as discussed by the authors. But the field is there.
Abstract: On a clear day, there is a downward electric field of 100 to 300 volts/meter at Earth's surface, although this field is not noticeable in daily life. That is, one does not encounter a 1 kV potential difference when getting into a car on an upper floor in a parking garage, and electrocution is not the major hazard associated with jumping out of trees. The major reason why we don't notice the fair‐weather field is that virtually everything is a good conductor compared to air. Objects such as tree trunks and our bodies are excellent ionic conductors that short out the field and keep us from noticing it. But the field is there.
154 citations
"Effects of a Solar Eclipse on the P..." refers background in this paper
...The quasi-static electric field observed near the Earth’s surface, i.e., Fair Weather Field (FWF), is maintained by global thunderstorm activities (Bering et al. 1998; Rycroft et al. 2000)....
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TL;DR: In this article, the authors examined the effect of the total solar eclipse on meteorological variables across Greece and found that the amplitude of air temperature drop was not analogous to the obscuration percentage but was principally determined by the surrounding environment (mainly the sea influence), the background meteorological conditions and local cloudiness.
Abstract: This paper examines the effect of the total solar eclipse of 29 March 2006 on meteorological variables across Greece. Integrated micrometeorological measurements were conducted at Kastelorizo, a small island within the path of totality, and other sites within the Greek domain, with various degrees of solar obscuration. The observations showed a dramatic reduction in the incoming global radiation and subsequent, pronounced changes in surface air temperature with the lowest temperature values occurring about 15 min after the full phase. The amplitude of the air temperature drop was not analogous to the obscuration percentage but was principally determined by the surrounding environment (mainly the sea influence), the background meteorological conditions and local cloudiness. Surface wind-speed decreased in most sites as a result of the cooling and stabilization of the atmospheric boundary layer. This perturbation provided a unique opportunity to apply a sensitivity analysis on the effect of the eclipse to the Weather Research and Forecast (WRF) numerical mesoscale meteorological model. Strong anomalies, not associated with a dynamic response, were simulated over land especially in surface air temperature. The simulated temperature drop pattern was consistent with the observations.
105 citations
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