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Discussion papers
https://doi.org/10.5194/angeo-2019-73
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-73
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 13 Jun 2019

Regular paper | 13 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Latitudinal variation of Pc3-Pc5 geomagnetic pulsation amplitude across the dip equator in central South America

Graziela Belmira Dias da Silva, Antonio Lopes Padilha, and Lívia Ribeiro Alves Graziela Belmira Dias da Silva et al.
  • Space Geophysics Division, National Institute for Space Research (INPE), Sao Jose dos Campos, 12227-010, Brazil

Abstract. In order to clarify the equatorial electrojet effects on ground magnetic pulsations in central South America, we statistically analyzed the amplitude structure of Pc3 and Pc5 pulsations recorded during quiet to moderately disturbed days at multiple equatorial stations nearly aligned along the 10° magnetic meridian. It was observed that Pc3 amplitudes are attenuated around noon at the dip equator for periods shorter than ~ 35 s. It is proposed that daytime Pc3s are related to MHD compressional waves incident vertically on the ionosphere, with the screening effect induced by enhanced conductivity in the dip equator causing wave attenuation. Daytime Pc5s showed amplitude enhancement at all equatorial stations, which can be explained by the model of waves excited at higher latitudes and propagating equatorward in an Earth-ionosphere waveguide. However, a slight depression in Pc5 amplitude compared to neighboring equatorial stations and a phase lag in relation to an off-equatorial station were detected at the dip equator. This result cannot be explained by the ionospheric waveguide model alone and we propose that an alternative propagation model that allows ULF waves to penetrate directly from the magnetosphere to low latitudes could be operating simultaneously to produce these features at the dip equator. Significant effects of the sunrise terminator on Pc3 pulsations were also observed at the stations closest to the dip equator. Contrary to what is reported at other longitudes, in central South America the sunrise effect increases the H-to-D amplitude ratio. We suggest that these differences may arise from the unique characteristics of this sector, with a strong longitudinal variation in the magnetic declination and precipitation of energetic particles due to the presence of the South Atlantic Magnetic Anomaly. The H-component amplification can be explained by enhancements of the zonal electric field near the magnetic equator driven by F-region neutral winds during sunrise.

Graziela Belmira Dias da Silva et al.
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Graziela Belmira Dias da Silva et al.
Graziela Belmira Dias da Silva et al.
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Short summary
The paper shows a statistical analysis of Pc3 and Pc5 pulsations recorded during 60 days (September to November 1994) by a meridional magnetometer profile crossing the dip equator in central South America. This is the first time that a detailed mapping of latitudinal dependence of pulsation amplification at very low latitudes has been performed. One of the most prominent findings is that our equatorial Pc5s might be related to both horizontally and vertically incident MHD waves on the ionosphere
The paper shows a statistical analysis of Pc3 and Pc5 pulsations recorded during 60 days...
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