Indexing
All Issues
Submission
Author Guidelines
Reviewers
Editorial Members
Publication Fee
Vol.2 , No. 3, Publication Date: May 21, 2015, Page: 68-79
&description=Records of geomagnetic field variations obtained during September 2011, at six sites in the eastern parts of the Amazon region, have been employed for a better understanding of diurnal changes and the relative influences of solar quiet variations and Equatorial Electro Jet (EEJ) at low latitudes in Brazil. Analysis of these data sets provide new insights into the nature of superposition of solar quiet (Sq) and EEJ variations. Model studies reveal that the center of symmetry of EEJ variations is located at the mean latitude of approximately two degrees north. Comparison with results of earlier studies point to a northward shift of four degrees in the position of EEJ, during the period of 1999 to 2011. Inverse power law fit to selected data sets indicates that horizontal and vertical variations at the source regions of EEJ are greater by at least a factor of two when compared with values recorded by ground level magnetometers. Analysis of data sets have also allowed a better understanding of high frequency variations of geomagnetic field at ground level. Occurrences of micro pulsations, with amplitude greater than two nanotesla (nT), are found to characterize perturbed periods of geomagnetic fields relative to those of the calm periods. In addition, results of spectral analysis reveal that variations in the power spectral density (PSD) of micro pulsations have distinctly different characteristics during calm relative to those of the perturbed periods of geomagnetic fields. It has been possible to identify two distinct trends in the frequency dependence of PSD. Thus, for frequencies less than 0.0025 Hz the decrease in PSD follow a liner trend, while for those higher than 0.003 Hz changes in PSD are nearly independent of the frequency.&picture=http://www.aascit.org/aascit/decorators/img/journal/899.jpg)
| [1] | Werneck De Carvalho V. J. O., Department of Geophysics, National Observatory – ON Rio de Janeiro, Brazil. |
| [2] | Hamza V. M., Department of Geophysics, National Observatory – ON Rio de Janeiro, Brazil. |
| [3] | Benyosef L. C. C., Department of Geophysics, National Observatory – ON Rio de Janeiro, Brazil. |
Records of geomagnetic field variations obtained during September 2011, at six sites in the eastern parts of the Amazon region, have been employed for a better understanding of diurnal changes and the relative influences of solar quiet variations and Equatorial Electro Jet (EEJ) at low latitudes in Brazil. Analysis of these data sets provide new insights into the nature of superposition of solar quiet (Sq) and EEJ variations. Model studies reveal that the center of symmetry of EEJ variations is located at the mean latitude of approximately two degrees north. Comparison with results of earlier studies point to a northward shift of four degrees in the position of EEJ, during the period of 1999 to 2011. Inverse power law fit to selected data sets indicates that horizontal and vertical variations at the source regions of EEJ are greater by at least a factor of two when compared with values recorded by ground level magnetometers. Analysis of data sets have also allowed a better understanding of high frequency variations of geomagnetic field at ground level. Occurrences of micro pulsations, with amplitude greater than two nanotesla (nT), are found to characterize perturbed periods of geomagnetic fields relative to those of the calm periods. In addition, results of spectral analysis reveal that variations in the power spectral density (PSD) of micro pulsations have distinctly different characteristics during calm relative to those of the perturbed periods of geomagnetic fields. It has been possible to identify two distinct trends in the frequency dependence of PSD. Thus, for frequencies less than 0.0025 Hz the decrease in PSD follow a liner trend, while for those higher than 0.003 Hz changes in PSD are nearly independent of the frequency.
Keywords
Geomagnetic Variations, Amazon Region, Equatorial Electro Jet, Diurnal Changes, Micro Pulsations, Power Spectral Density
Reference
| [01] | Chapman, S., Bartels, J. (1940) “Geomagnetism”. University Press, Oxford, Vol. 2, 1049 pp. |
| [02] | Merrill, R.T., McElhinny, M.W., McFadden, P.L. (1996) “The Magnetic Field of the Earth”. Academic Press Inc. |
| [03] | Chapman, S. (1951) “Some phenomena of the upper atmosphere”. Proc. Phys. Soc. London, B, 64, 833–843. |
| [04] | Malin, S.R.C. (1987) “Historical introduction to geomagnetism”, in Geomagnetism, Vol. 1, edited by J.A. Jacobs, Academic Press Inc., pp. 1-49. |
| [05] | Abdu, M. A. Ramkumar, T K., Batista, I.S., Brum, C.G.M., Takahashi, M., Reinisch, B.W., Sobral, J.H.A.(2006) “Planetary wave signatures in the equatorial atmosphere-ionosphere system, and mesosphere- E- and F region coupling”. Journal of Atmospheric and Solar-Terrestrial Physics, 68: 509-522. |
| [06] | Pinto Jr, O., Gonzalez, W.D., Pinto, I.R.C.A., Gonzalez, A.L.C., Mendes Jr, O. (1992) “The South Atlantic Magnetic Anomaly: three decades of research”. J. Atmos Solar-Terr. Phys, 54: 1129–1134. |
| [07] | Hartmann, G.A., Pacca, I.G. (2009) “Time evolution of the South Atlantic Magnetic Anomaly”, Annals of the Brazilian Academy of Sciences, 81(2): 243-255. |
| [08] | Chapman, S. (1951) “The equatorial electrojet as detected from the abnormal electric current distribution above Huancayo, Peru, and elsewhere”. Arch. Meteorol. Geophys. Bioclimatol. A, 4: 368–390. |
| [09] | Onwumechili, C.A. (1967) “Geomagnetic variations in the equatorial zone”, in Physics of Geomagnetic Phenomena, edited by S. Matsushita and W.H. Campbell, pp. 425–507, Academic Press, New York. |
| [10] | Gama, L.J. (1948) “Magnetic effects observed at Vassouras, Brazil, during solar eclipse of May 20, 1947”. J. Terrestrial Magnetism and Atmospheric Electricity, 53, 3. |
| [11] | Gama, L.I. (1965) “Campo magnético normal e sua variação secular no Brasil em 1960”, Publ. Serv. Magn., No.9, Observatório Nacional (Brazil). |
| [12] | Gama, L.I. (1969) “Recommendations from the South American Meeting on Geomagnetism”, IAGA News, 8. |
| [13] | Hesse, D. (1982) “An investigation of the equatorial electrojet by means of ground based magnetic measurements in Brazil”, Ann. Geophys., 38, 315–320. |
| [14] | Kane, R.P., Trivedi, N.B. (1982) “Comparison of Equatorial Electrojet characteristics at Huancayo and Euzebio (Fortaleza) in the South American region”. J. Atmosph. Terres. Physics, 44, 785–792. |
| [15] | Barreto, L.M. (1988) “Secular variation and geomagnetic normal field modelling in Brazil”. Deutsch Hydrograph Zeitsch, 41. |
| [16] | Zanandrea, A. (1994) “Micropulsações Geomagnéticas em Santa Maria – RS”. UnpublishedM.Sc. Thesis, Instituto Nacional de Pesquisas Espaciais - INPE, São Jose dos Campos, Brazil. |
| [17] | Zanandrea, A., (1999) “Estudo de micropulsações geomagnéticas Pc3-5 em latitudes muito baixas, no Brasil”. Rev. Bras. Geof., 17: 216-217. |
| [18] | Zanandrea, A., Padilha, A.L., Trivedi, N.B., Da Costa, J.M., Dutra, S.L.G., Schuch, N.J., Kitamura, T., Tachihara, H., Shinohara, M., Akaki, H. (1996) “Geomagnetic micro pulsationsat Santa Maria – RS”. In: Fourth Latin American Conference on Space Physics, Universidad Nacional de Tucuman, Tucuman - Argentina, 22-28. |
| [19] | Trivedi, N.B.; Arora, B.R.; Padilha, A.L.; Da Costa, J.M.; Dutra, S.L.G.; Chamalaun F.H., Rigoti, A. (1997) “Global Pc5 geomagnetic pulsation of march 24, 1991, as observed along the American sector”. Geophysical Research Letters, v.24, 13, 1683-1686. |
| [20] | Vieira, L.E.A. (1998) “Estudo de Micropulsações do Campo Geomagnético de Longos Períodos, Classe Pc5, em Baixas Latitudes. São Jose dos Campos”. UnpublishedM.Sc. Thesis, 113p. Instituto Nacional de Pesquisas Espaciais - INPE, São Jose dos Campos, Brazil. |
| [21] | Rigoti, A., Chamalaun, F.H., Trivedi, N.B., Padilha, A.L. (1999) “Characteristics of the Equatorial Electrojet determined from an array of magnetometers in N-NE Brazil” Earth Planets Space, 51, 115–128. |
| [22] | Zanandrea, A., (1999) “Estudo das Micropulsações Geomagnéticas em Latitudes Muito Baixas, no Brasil” Unpublished Ph.D. Thesis, Instituto Nacional de Pesquisas Espaciais - INPE, São Jose dos Campos, Brazil. |
| [23] | Rigon Silva, W. (2009) “Variação com o ciclo solar das pulsações geomagnéticas de períodos longos (1,0 – 10 mHz) na região da anomalia magnética do atlântico sul – AMAS”. Report 102220/2008-5, INPE, São Jose dos Campos, Brazil. |
| [24] | Klausner, V. (2012) “Estudo das variações geomagnéticas usando técnicas wavelet” Unpublished Ph.D. Thesis, Observatório Nacional, Rio de Janeiro, Brazil. |
| [25] | Bartels, J. (1962) “Collection of geomagnetic planetary indices Kp and derived daily indices Ap and Cp for the years 1932 to 1961”, IAGA Bull.18, IUGG Publication. |
| [26] | Rangarajan, G.K. and Iyemori, T. (1997) “Time variations of geomagnetic activity indices Kp and Ap: an update”. Ann. Geophysicae 15, 1271-1290. |
| [27] | Campbell, W.H. (1989) “The regular geomagnetic field variation during quiet solar conditions”, in: Geomagnetism, (Ed) Jacobs, J. A., 3: 385. |
| [28] | Takeda, M., Araki, T. (1985) “Electric conductivity of the ionosphere and nocturnal currents”, J. Atmos. Terr. Phys., 47, 601–609. |
| [29] | Yumoto, K., Ikeda, A., Shinohara, M., Uozumi, T., Nozaki, K., Watari, S., Kitamura, K., Bychkov, V.V.,Shevtsov, M., (2007)“Electric and magnetic field variations at low and equatorial latitudes during SC, DP2, and Pi2 events”, Adv. Geosci., 14, 197–212. |
| [30] | Duhau, S.,Romanelli, L. (1979)“Electromagnetic induction at the South American geomagnetic equator as determined from measured ionospheric currents”, J. Geophys. Res., 84, 1849–1854. |
| [31] | Abdu, M.A., Batista, I.S.,Muralikrishna, P., Sobral, J.H.S. (1996)“Long Term Trends In Sporadic e Layers and Electric Fields Over Fortaleza, Brazil”. Geophysical Research Letters, 23: 757-760. |
| [32] | Marple, S.L., (1987) “Digital spectral analysis with applications”, New Jersey: PTR Prentice Hall. |
| [33] | Bath, M. (1974) “Spectral Analysis in Geophysics”,Elsevier Scientific Publ. Comp. |
| [34] | Ney Avelino Barbosa Seixas, N.A.B. (1997) “Clima de Ondas na Bacia de Campos: Análise dos dados e Proposta de Parametrização”Unpublished Ph.D. Thesis Observatório Nacional, Brazil. |
