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Diurnal variation of VLF power spectral density between 100 Hz and 20 kHz at Byrd station, Antarctica
Planet.
Space Sci. 1968.
Vol. 16. pp. 1069 to 1070.
Pergamon
Press.
Printed
in Northern
Ireland
RESEARCH NOTES
DIURNAL
VARIATION
OF VLF POWER SPECTRAL DENSITY BETWEEN
100 Hz AND 20 kHz AT BYRD STATION, ANTARCTICA (Received 16 February 1968) Harang et e1.u’ presented a table of peak values of VLF emissions at frequencies ranging from 2.3 kHz to 14.7 kHz. In the band 4-7 kHz the densities of strong bursts were of the order of l-2 x lo-l6 W/ma/Hz. The intensity increased strongly with increasing frequency, and at 15 kHz the intensity had increased up to 6 N 7 x lo-l6 Wm*Hz. Jorgensen~*’ presented a summary of the power spectral density of VLF emissions measured by various research workers. All the available VLF power spectral-density data taken at high latitude so far have been computed either on the peak value for the day or for the average for the entire day. We present here the diurnal variation of the VLF power spectral density between 100 Hz and 20 kHz on contour map. (*) This was obtained by scaling the VLF noise recorded on a Panoramic Sonic Analyzer. Examples of the records are shown in Fig. 1. lp) We scaled upper profile of the amplitudes of VLF noise at 15 selected frequencies. They are: 100,400,600,800,1 k, 15 k, 2 k, 2.3 k, 3 k, 4 k, 5 k, 6 k, 8 k, 125 k, and 20 kHz. Data points were taken every 30 min. Then the average of these values was computed and plotted in Fig. 2 .o) The contours show one month’s average VLF power spectral density in 5 dB intervals KC/S
MARCH
(FALL1
KC/q
20
JUNE~WINTEA)
zo-
125 a 6 5 4
1?5 8 6 5 4
3 2.3 2
2.3 2
3
I.5 1 .8
1.5 I .8 .6 .4
.6 .4 .I
KC/S
KC/c
20
20125 8 6 5
125 8 6 5 4 3 2.3 2
DECEMBER
(SUMMER)
4 3 2.3 2
1.5 1 *8 ‘6 ‘4
1.5 1 *a .6 a4
-1
.I 0
6
12
FIG. 2. VLF
18 POWER
SPECTRAL
DENSITY, 1069
BYRD STATION,
1962.
1070
RESEARCH
NOTES
above the reference power density lo-r8 W/ma/Hz. Therefore the contour marked 10 in in the figure indicates 10-l’ W/ml/Hz, etc. Note, in the contour map, that there are two regions where the VLF intensity is high. One exists around 20 kHz and about 0300 UT, which is generally known as VLF hiss. The other exists around 600 Hz and about 1600 UT, which is generally known as VLF chorus. In this note, we present a contour of VLF power spectral density. The result is preliminary because we scaled the upper profile of the VLF noise amplitude recorded on a Panoramic Sonic Analyzer. There is about a 10 dB difference between the upper profile and the lower profile (see Fig. 1). The midpoint between the upper and the lower value looks reasonable, however when the lower value is lower than the noise level of the recorder, the midpoint loses its meaning. BY
17
1600
AUG 62
UT
n/m%s
HISS
RECORDER VALUES
I.
6.7
x IO-l6
2.
6.0
x IO-‘5
3.
4.8
x 10-15
4.
I.0
x 10-15
5.
6.6
I ID-‘5
6.
2.4
I IO-l5
7.
35
x 10-15
6.
I-I
x 10-17
p + ‘;
kc
Ro.3.
COMPARISON
OF
VLF
NOISE RECORDED ON PANORAMIC READING VOLT METER.
ANALYSER
AND
MINIhfUM
In Fig. 3o’ the readings taken from a Hiss recorder (minimum reading voltmeter) is superposed on a panoramic record obtained at Byrd Station on 17 August 1962. It is evident from the figure that the peak protile values taken from the panoramic record is always 5 to 12 dB higher than those taken from a Hiss recorder. In order to facilitate comparison among several research workers, standardization in measuring and scaling technique is recommended. Acknowledgements-We acknowledge the Antarctic Research Program of the National Science Foundation for providing the research opportunity. Professor R. A. Helliwell of Radio Science Laboratory, Stanford University provided the valuable data. Thanks are due to Dr. J. B. Cladis of Lockheed Palo Alto Research Laboratory for his criticism. General Electric Company Syracuse, New York 13201
HENRY
M.
MOROZUMI
REFERENCES 1. 2. 3.
HARANG, L., R. LARSEN and J~GENSEN, T. S., J. geophys. MOROZUMI, H. M. and R.
J. SKOGTVRDT, J. atmos. terr. Phys. 27, 1147-1150, 1965. Res. 71, 1966. A. HRLLIWELL, Technical Report No. 2, Radioscience Stanford University, Stanford, California 1966. 4. HELLWELL, R. A., Stanford University Press, 1965.
Laboratory,
FIG. 1. VLF
NOISE RECORDEDON PANORAMICANALYZER AT BYRD STATION, ANTARCTICA.
107
Space Sci. 1968.
Vol. 16. pp. 1069 to 1070.
Pergamon
Press.
Printed
in Northern
Ireland
RESEARCH NOTES
DIURNAL
VARIATION
OF VLF POWER SPECTRAL DENSITY BETWEEN
100 Hz AND 20 kHz AT BYRD STATION, ANTARCTICA (Received 16 February 1968) Harang et e1.u’ presented a table of peak values of VLF emissions at frequencies ranging from 2.3 kHz to 14.7 kHz. In the band 4-7 kHz the densities of strong bursts were of the order of l-2 x lo-l6 W/ma/Hz. The intensity increased strongly with increasing frequency, and at 15 kHz the intensity had increased up to 6 N 7 x lo-l6 Wm*Hz. Jorgensen~*’ presented a summary of the power spectral density of VLF emissions measured by various research workers. All the available VLF power spectral-density data taken at high latitude so far have been computed either on the peak value for the day or for the average for the entire day. We present here the diurnal variation of the VLF power spectral density between 100 Hz and 20 kHz on contour map. (*) This was obtained by scaling the VLF noise recorded on a Panoramic Sonic Analyzer. Examples of the records are shown in Fig. 1. lp) We scaled upper profile of the amplitudes of VLF noise at 15 selected frequencies. They are: 100,400,600,800,1 k, 15 k, 2 k, 2.3 k, 3 k, 4 k, 5 k, 6 k, 8 k, 125 k, and 20 kHz. Data points were taken every 30 min. Then the average of these values was computed and plotted in Fig. 2 .o) The contours show one month’s average VLF power spectral density in 5 dB intervals KC/S
MARCH
(FALL1
KC/q
20
JUNE~WINTEA)
zo-
125 a 6 5 4
1?5 8 6 5 4
3 2.3 2
2.3 2
3
I.5 1 .8
1.5 I .8 .6 .4
.6 .4 .I
KC/S
KC/c
20
20125 8 6 5
125 8 6 5 4 3 2.3 2
DECEMBER
(SUMMER)
4 3 2.3 2
1.5 1 *8 ‘6 ‘4
1.5 1 *a .6 a4
-1
.I 0
6
12
FIG. 2. VLF
18 POWER
SPECTRAL
DENSITY, 1069
BYRD STATION,
1962.
1070
RESEARCH
NOTES
above the reference power density lo-r8 W/ma/Hz. Therefore the contour marked 10 in in the figure indicates 10-l’ W/ml/Hz, etc. Note, in the contour map, that there are two regions where the VLF intensity is high. One exists around 20 kHz and about 0300 UT, which is generally known as VLF hiss. The other exists around 600 Hz and about 1600 UT, which is generally known as VLF chorus. In this note, we present a contour of VLF power spectral density. The result is preliminary because we scaled the upper profile of the VLF noise amplitude recorded on a Panoramic Sonic Analyzer. There is about a 10 dB difference between the upper profile and the lower profile (see Fig. 1). The midpoint between the upper and the lower value looks reasonable, however when the lower value is lower than the noise level of the recorder, the midpoint loses its meaning. BY
17
1600
AUG 62
UT
n/m%s
HISS
RECORDER VALUES
I.
6.7
x IO-l6
2.
6.0
x IO-‘5
3.
4.8
x 10-15
4.
I.0
x 10-15
5.
6.6
I ID-‘5
6.
2.4
I IO-l5
7.
35
x 10-15
6.
I-I
x 10-17
p + ‘;
kc
Ro.3.
COMPARISON
OF
VLF
NOISE RECORDED ON PANORAMIC READING VOLT METER.
ANALYSER
AND
MINIhfUM
In Fig. 3o’ the readings taken from a Hiss recorder (minimum reading voltmeter) is superposed on a panoramic record obtained at Byrd Station on 17 August 1962. It is evident from the figure that the peak protile values taken from the panoramic record is always 5 to 12 dB higher than those taken from a Hiss recorder. In order to facilitate comparison among several research workers, standardization in measuring and scaling technique is recommended. Acknowledgements-We acknowledge the Antarctic Research Program of the National Science Foundation for providing the research opportunity. Professor R. A. Helliwell of Radio Science Laboratory, Stanford University provided the valuable data. Thanks are due to Dr. J. B. Cladis of Lockheed Palo Alto Research Laboratory for his criticism. General Electric Company Syracuse, New York 13201
HENRY
M.
MOROZUMI
REFERENCES 1. 2. 3.
HARANG, L., R. LARSEN and J~GENSEN, T. S., J. geophys. MOROZUMI, H. M. and R.
J. SKOGTVRDT, J. atmos. terr. Phys. 27, 1147-1150, 1965. Res. 71, 1966. A. HRLLIWELL, Technical Report No. 2, Radioscience Stanford University, Stanford, California 1966. 4. HELLWELL, R. A., Stanford University Press, 1965.
Laboratory,
FIG. 1. VLF
NOISE RECORDEDON PANORAMICANALYZER AT BYRD STATION, ANTARCTICA.
107