Abstract
Higher harmonic tweeks observed for the first time at the low latitude station Varanasi (geomag. lat. 14‡ 55′ N) are reported. The analysis of data shows that higher harmonic tweeks are usually not associated with whistlers and occur when the ionization in the lower ionosphere would not increases with height. The Earth-ionosphere waveguide dispersion features play an important role in the propagation of broad band lightning generated signals and their occasional observation as higher harmonic tweeks. It is shown that the conductivity of ground and sea mixed path, forming the lower surface of the waveguide, provide an estimate of the travelled distances of higher harmonic tweeks in the waveguide. The attenuation factors are computed which shows that as the harmonic number increases their probability of observation decreases. The attenuation increases as the frequencies approach the cut-off frequencies and also as the layer height falls. The tweek activity is found to increase during periods of magnetic disturbances.
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Barr, R.: 1974, in Holtel, J. A. (ed.), ELF-VLF Radio Wave Propagation, Reidel, Dordrecht, Holland, p. 225.
Budden, K. G.: 1953, The Propagation of Very-Low-Frequency Radio Waves to Great Distances, Phil. Mag. 44, 504.
Burton, E. T. and Boardman, E. M.: 1933, (a) Effects of Solar Eclipse on Audio Frequency Atmospherics, Nature 131, 81–82; (b) ‘Audio-Frequency Atmospherics’, Proc. IRE 21(10), 1476–1494.
Hamar, D., Tarcsai, Gy., Lichtenberger, J., Smith, A. J., and Yearby, K. H.: 1990, Fine Structure of Whistlers Recorded Digitally at Halley, Antarctica, J. Atmos. Terres. Phys. 52(9), 801–810.
Hayakawa, M. and Shimakura, S.: 1978, Trans. IEEE, Japan E61, 15.
Hayakawa, M.: 1988, Direction Finding of Half-Gyrofrequency VLF-Emissions in the off Equatorial Region of the Magnetosphere, Proc. Natn. Inst. Polar Res. Symp. Upper Atmos. Phys. 1, 168–172.
Hayakawa, M., Ohto, K., and Shimakura, S.: 1990, Spaced Direction Finding of Nighttime Whistlers at Low and Equatorial Latitudes and Their Propagation Mechanism, J. Geophys. Res. 25(A9), 15,091–15,102.
Hayakawa, M., Ohta, K., and Baba, K.: 1994, J. Geophys. Res. 99, 10,733.
Helliwell, R. A.: 1965, Whistlers and Related Ionospheric Phenomena, Stanford University Press, Stanford, California.
Kamiyama, H.: 1970, Ann. de Geophys. 26, 625.
Kashiwagi, M. and Ohtsu, J.: 1970, Proc. Res. Ins. Atmospherics, Nagoya Univ. 17, 125.
Lynn, K. J. W. and Crouchley, J.: 1987, Aust. J. Phys. 20, 101.
Muto, H., Hayakawa, M., Parrot, M., and Fefeuvre, F.: 1987, Direction Finding of Half Gyrofrequency VLF Emissions in the off Equatorial Region of the Magnetosphere and Their Generation and Propagation, J. Geophys. Res. 92, 7538–7552. Outsu, J.: 1960, “Numerical Study of Tweeks Based on Waveguide Mode Theory’, J. Proc. Res. Inst. Atmos., Nagoya Univ. 7, 58–71.
Prasad, R.: 1981, Effects of Land and Sea Parameters on the Dispersion of Tweek Atmospherics, J. Atmos. Terres. Phys. 43, 1271–1277.
Reeve, C. D. and Rycroft, M. J.: 1972, J. Atmos. Terres. Phys. 34, 667.
Singh, R. N., Singh, R. P., Singh, U. P., and Singh, A. K.: 1992, Some Features of Low Latitude Second and Third Harmonic Tweeks, Ind. J. Rad. Spa. Phys. 21, 377–380.
Synder, P. and Pappert, A.: 1969, Rad. Sci. 4, 213.
Wait, J. R.: 1957, The Mode Theory of Ionospheric Propagation for Finite Ground Conductivity, Proc. IRE 45, 760.
Wait, J. R.: 1970, Electromagnetic Waves to Stratified Media, Pergamon Press, Oxford.
Westerlund, S.: 1974, in Holtel (ed.), ELF-VLF Radiowave Propagation, Reidel, Dordrecht, Holland, p. 117.
Yamashita, M.: 1978, Propagation of Tweek Atmospherics, J.Atmos. Terres. Phys. 40, 151–156.
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Singh, A.K., Singh, R.P. Propagational features of higher harmonic tweeks at low latitudes. Earth Moon Planet 73, 277–290 (1996). https://doi.org/10.1007/BF00115886
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DOI: https://doi.org/10.1007/BF00115886