Power spectral analyses of modulated earth-ionosphere cavity resonances

Hughes, H. G.

doi:10.1029/jz069i021p04709

Cited by 9 publications

(6 citation statements)

References 2 publications

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“…The asymmetry conditions are permanent, and hence (2n + 1)-fold splitting of the resonance peaks should be a common feature in Schumann resonance spectrums. The fact that such splitting is only infrequently observed [Hughes, 1964;Rycroft, 1965 (who deduced that his fine structure was spurious); Larsen and Egeland, 1968] or requires special techniques for observation [Bormotov et al, 1973] is attributed to the low Q factors for the resonance modes which prevent resolution of the fine structure. Jones [1974] suggests that the splitting observed by Hughes [1964], Rycroft [1965], and Larsen and Egeland [1968] could have arisen from the analysis of too short a data sample, and he further states that in his own data, marked mode splitting is an unusual feature when sufficiently long (15 min) data samples are analyzed.…”

Section: Previous Work By Horton and Hoffman [1962] Santirocco And Pmentioning

confidence: 99%

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Fraser–Smith¹,

Buxton²

1975

J. Geophys. Res

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A high-sensitivity superconducting magnetometer has been used to measure geomagnetic activity at Stanford, California, in the 0.1-to 14-Hz frequency range. The measurements, which covered the 2-month interval January 26 to March 26, 1974, consistently show a minimum of activity in the interval 3-7 Hz, where conventional measurement systems are likely to be limited by their internal noise. At frequencies, below the minimum, in the range 0.1-3 Hz, there is typically a monotonic decrease of background activity with frequencyf. The variation is approximately of the form f-' 25 for the Pc 1 frequency range (0.2-5 Hz). At frequencies above the minimum, in the range 7-14 Hz, the activity is dominated by the first Schumann resonance. The peak amplitude of this activity is usually low in comparison with the amplitude of the background activity at 1 Hz. No splitting of the first Schumann resonance peak into a triplet could be detected, but a doublet structure was observed on 7 days in the 2-month measurement interval. This paper reports high-sensitivity measurements of geomagnetic activity in the frequency range 0.1-14 Hz made with a superconducting magnetometer system [Buxton andFraser-Smith, 1974] at a mid-latitude location (Stanford, California; geomagnetic latitude 43.5øN). The data are new in two respects. First, unlike past measurements, which emphasize the properties of particular large-amplitude events, our measurements are concerned primarily with the properties of the underlying component of geomagnetic activity in the Pc I pulsation frequency range (0.2-5 Hz) which forms a comparatively stable background to the better studied largeamplitude events. We believe that the data presented here are the first fully calibrated measurements of this background activity. Second, our measurements consistently show a minimum of activity in the interval 3-7 Hz (i.e., at the junction of the ultralow frequency band (ULF: frequencies less than •5 Hz) with the extremely low frequency band (ELF: frequencies in the range •5 Hz to 3kHz)), where conventional ULF/ELF measurement systems are likely to be limited by their internal noise. The internal noise level of the Stanford superconducting magnetometer is significantly lower than the noise level in these conventional systems, and it has been shown to be lower than the level of natural background activity in the frequency range 3-7 Hz [Buxton and Fraser-Smith, 1974]. Thus our data are probably the first largely noise-free measurements of geomagnetic activity at frequencies near 5 Hz. In addition to these two features of our data the superconducting magnetometer measurements fill a gap between background measurements made by other investigators at frequencies below 1 Hz and above 7 Hz (both frequencies are approximate; superconducting magnetometer measurements at lower frequencies have recently been reported by Zimmerman and Campbell [1975]). It is possible as a result to relate the natural background in the frequency range 0.1-14 Hz to the background outside the frequency range, i.e.,...

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Section: Previous Work By Horton and Hoffman [1962] Santirocco And Pmentioning

confidence: 99%

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Fraser–Smith¹,

Buxton²

1975

J. Geophys. Res

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“…This fact should be attributed to the kind of the sources rather than distances to the sources. Hughes (1964) showed the recorded samples of modulated oscillations which exhibit earth-ionosphere resonant frequencies which might belong to the present Q-type bursts. One of our most beautiful samples of Q-type bursts recorded at 8 h 01 m 37.6s GMT on May 8, 1966 is shown in Fig.…”

Section: Observations Of Natural Elf and Vlf Electromagnetic Noises Bmentioning

confidence: 99%

“…Some workers recognized that the resonated signals are hidden in the background noises and they appear only by frequency analysis of measured noises (Balser and Wagner, 1960;Madden and Thompson, 1965), while some others clearly showed characteristic oscillations in the meas- (443) ured records (Polk and Fitchen, 1962;Polk, 1964;Hughes, 1964). They seem to have concerned apparently with different phenomena.…”

Section: Introductionmentioning

confidence: 99%

“…Other workers are interested in the study of the relation of ELF noise origin to the worldwide thunderstorm activity. Since Schumann (1952Schumann ( a, b, 1957 presented the resonance theory that FLF electromagnetic waves resonate in the cavity between the good conducting earth and ionosphere, a number of experimental investigations were made to detect actual resonant frequencies in natural electromagnetic phenomena (Balser and Wagner, 1960;Polk and Fitchen, 1962;Chapman and Jones, 1964;Gendrin and Stef ant, 1964;Rycrof t and Wormell, 1964;Hughes, 1964).…”

Section: Introductionmentioning

confidence: 99%

“…For example Balser and Wagner (1960) used the high tower of 37 m in height, while Rycroft and Wormell (1964) used the horizontal antenna of 190 m in length. Chapman and Jones (1964) used the 3 m vertical rod antenna, and Hughes (1964) used the vertical whip antenna of 10 m in length. The present measuring system reported here includes a simple type of capacitive conductor antenna which is called the "ball antenna ".…”

Section: Introductionmentioning

confidence: 99%

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Observations of Natural ELF and VLF Electromagnetic Noises by Using Ball Antennas

Ogawa

Tanaka

Miura

et al. 1966

J. geomagn. geoelec

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A simple observing system for the measurements of vertical electric field component of natural ELF and VLF electromagnetic noises by using ball antennas is described. With this system it is possible to measure long traveled natural ELF noises discriminated from natural local noises due to such as atmospheric electric space-charge fluctuations. Some of the typical recorded noises are shown. Observed ELF noises are divided into three characteristic types; "ELF flash", "ELF burst" (N-and Q-types), and "ELF continuous". ELF flashes originate from the lightning discharges in the area within about 1, 000 km from the observing station. Occurrences of ELF bursts are more frequent in the daytime than in the nighttime, and are characterized by sudden increase at the time of local sunrise, suggesting the related mechanism of their generation to the solar position relative to the earth. N-type bursts are followed by VLF noises. Source distances of these bursts which are followed by tweek-type atmospherics in the night are estimated to be in the range from 2, 500 km to 5,000km. Q-type bursts often show clear oscillations of the frequencies of Schumann resonances. The daily variations of the mean amplitude of "ELF continuous" which composes the background noises are quite similar to the daily variations of the world thunderstorm activity.

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Detection of line splitting of Schumann resonances from ordinary data

Tanahashi

1976

Journal of Atmospheric and Terrestrial Physics

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Power spectral analyses of modulated earth-ionosphere cavity resonances

Cited by 9 publications

References 2 publications

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Observations of Natural ELF and VLF Electromagnetic Noises by Using Ball Antennas

Detection of line splitting of Schumann resonances from ordinary data

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