Longitudinal Variation of the Ionospheric Response to the 26 August 2018 Geomagnetic Storm at Equatorial/Low Latitudes
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Pure and Applied Geophysics
Longitudinal Variation of the Ionospheric Response to the 26 August 2018 Geomagnetic Storm at Equatorial/Low Latitudes GUSTAVO A. MANSILLA1,2 and MARTA M. ZOSSI1,2 Abstract—We have studied the ionospheric response at nearequator latitudes during the geomagnetic storm of 26 August 2018, which was the strongest geomagnetic disturbance that year (minimum Dst value: -174 nT). For the analysis, we considered the F2layer critical frequency (foF2) and peak height (hmF2), as well as total electron content (TEC) data for Jicamarca (geographic coordinates: 12° S, 283.2° E; geomagnetic coordinates: 2.26° S, 4.09° W), Saoluis (geographic coordinates: 2.6° S, 315.8° E; geomagnetic coordinates: 5.94° N, 28.5° E), Guam (geographic coordinates: 13.4° N, 144.8° E; geomagnetic coordinates: 5.73° N, 143.2° W) and Libreville (geographic coordinates: 0.39° N, 9.45° E; geomagnetic coordinates: 1.64° N, 82.6° W). First, we observed pre-storm improvements, which could be due to previous moderate geomagnetic activity. Second, only one station (Jicamarca) clearly revealed a prompt penetration electric field (PPEF) effect when Bz turned strongly negative during the initial phase of the storm. Over the stations Saoluis and Guam, a PPEF effect was not evident. These stations presented pre-storm enhancements in foF2. In this case study, disturbed dynamo electric fields appear not to have played a crucial role in increasing electron density near equatorial regions during the recovery phase because the observed disturbances did not correspond with those produced by these electric fields, that is, negative (positive) storm effects on the dayside (night). Third, the increases in electron density observed during recovery are most likely caused by neutral composition changes. Keywords: Geomagnetic storm, ionospheric parameters, physical mechanisms.
1. Introduction During geomagnetic storms, there is a magnetospheric energy input into the polar upper atmosphere,
1
Departamento de Fı´sica, Facultad de Ciencias Exactas y Tecnologı´a, Universidad Nacional de Tucuma´n, Av. Independencia 1800, 4000 San Miguel de Tucuma´n, Argentina. E-mail: [email protected] 2 Consejo Nacional de Investigaciones Cientı´ficas y Te´cnicas, 2290 Godoy Cruz, CABA, Argentina.
which significantly modifies the chemical and dynamics/electrodynamics processes of the ionosphere-thermosphere system. In particular, the equatorial and low-latitude ionosphere exhibits remarkable variations during these events. Significant changes of the F2-layer critical frequency (foF2) from normal values during geomagnetic storms are called ionospheric storms (Buonsanto 1999). Basically, foF2 (proportional to the peak electron density of the F region), can either increase or decrease from its quiet time value during disturbed conditions (the so-called positive or negative ionospheric storms; e.g., Pro¨lss 1995, p. 200). The ionosphere presents complex disturbance characteristics driven by different interacting physical processes. Prompt penetration electric f
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