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Pc3-4 geomagnetic pulsations at very low latitude in Brazil |
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| Authors: | Ademilson Zanandrea JM Da Costa SLG Dutra T Kitamura H Tachihara O Saotome |
| Institution: | a Electronic Engineering Division—IEE, Technological Institute of Aeronautic—ITA, Praca Marechal E. Gomes, 50 Sao Jose dos Campos—SP, CEP 12228-900, Brazil b Department of Mathematics and Physics, University of Taubaté—UNITAU, Taubaté—SP, 12020-270, Brazil c Division of Space Geophysics—DGE, National Institute for Space Research—INPE, Sao Jose dos Campos—SP, CEP 12201-970, Brazil d Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812, Japan |
| Abstract: | In order to investigate Pc3-4 geomagnetic pulsations at very low and equatorial latitudes, L=1.0 to 1.2, we analyzed simultaneous geomagnetic data from Brazilian stations for 26 days during October-November 1994. The multitaper spectral method based on Fourier transform and singular value decomposition was used to obtain pulsation power spectra, polarization parameters and phase. Eighty-one (81) simultaneous highly polarized Pc3-4 events occurring mainly during daytime were selected for the study. The diurnal events showed enhancement in the polarized power density of about 3.2 times for pulsations observed at stations close to the magnetic equator in comparison to the more distant ones. The phase of pulsation observed at stations near the magnetic equator showed a delay of 48-62° in relation to the most distant one. The peculiarities shown by these Pc3-4 pulsations close to the dip equator are attributed to the increase of the ionospheric conductivity and the intensification of the equatorial electrojet during daytime that regulates the propagation of compressional waves generated in the foreshock region and transmitted to the magnetosphere and ionosphere at low latitudes. The source mechanism of these compressional Pc3-4 modes may be the compressional global mode or the trapped fast mode in the plasmasphere driving forced field line oscillations at very low and equatorial latitudes. |
| Keywords: | Geomagnetic pulsations Micropulsations Pc3-4 pulsations Multitaper polarization analysis ULF hydromagnetic waves |
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