Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 1165-1176, 2017
https://doi.org/10.5194/angeo-35-1165-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
27 Oct 2017
Evidence of prompt penetration electric fields during HILDCAA events
Regia Pereira Silva, Jose Humberto Andrade Sobral, Daiki Koga, and Jonas Rodrigues Souza Instituto Nacional de Pesquisas Espaciais (INPE), São José dos Campos, 12227-010, São Paulo, Brazil
Abstract. High-intensity, long-duration continuous auroral electrojet (AE) activity (HILDCAA) events may occur during a long-lasting recovery phase of a geomagnetic storm. They are a special kind of geomagnetic activity, different from magnetic storms or substorms. Ionized particles are pumped into the auroral region by the action of Alfvén waves, increasing the auroral current system. The Dst index, however, does not present a significant downward swing as it occurs during geomagnetic storms. During the HILDCAA occurrence, the AE index presents an intense and continuous activity. In this paper, the response of Brazilian equatorial ionosphere is studied during three HILDCAA events that occurred in the year of 2006 (the descending phase of solar cycle 23) using the digisonde data located at São Luís, Brazil (2.33° S, 44.2° W; dip latitude 1.75° S). Geomagnetic indices and interplanetary parameters were used to calculate a cross-correlation coefficient between the Ey component of the interplanetary electric field and the F2 electron density peak height variations during two situations: the first of them for two sets daytime and nighttime ranges, and the second one for the time around the pre-reversal enhancement (PRE) peak. The results showed that the pumping action of particle precipitation into the auroral zone has moderately modified the equatorial F2 peak height. However, F2 peak height seems to be more sensitive to HILDCAA effects during PRE time, showing the highest variations and sinusoidal oscillations in the cross-correlation indices.

Citation: Silva, R. P., Sobral, J. H. A., Koga, D., and Souza, J. R.: Evidence of prompt penetration electric fields during HILDCAA events, Ann. Geophys., 35, 1165-1176, https://doi.org/10.5194/angeo-35-1165-2017, 2017.
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In this work the response of the Brazilian equatorial ionosphere is studied during three HILDCAA events that occurred in the year of 2006 using the digisonde data. Geomagnetic indices and interplanetary parameters were used to calculate a cross-correlation coefficient between the Ey and the hmF2. The results showed that the pumping action of particle precipitation into the auroral zone has moderately modified the equatorial hmF2, being more sensitive during PRE time.
In this work the response of the Brazilian equatorial ionosphere is studied during three HILDCAA...
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