Spread-F occurrence during geomagnetic storms near the southern crest of the EIA in Argentina

TL;DR

This study analyzes ionospheric irregularities during geomagnetic storms near the southern crest of the EIA in Argentina, revealing how geomagnetic activity and electric fields influence spread-F occurrence and scintillation at low latitudes.

Contribution

First analysis of spread-F occurrence during geomagnetic storms at Tucumán, Argentina, using GPS and ionosonde data, highlighting electric field effects on irregularity development.

Findings

Geomagnetic storms create conditions for ionospheric irregularities.

Post-midnight irregularities are driven by eastward electric fields.

Strong scintillation correlates with strong spread-F during storms.

Abstract

This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucum\'an-Argentina, a low latitude station in the Southern American longitudinal sector ( 26.9 {\deg} S, 294.6 {\deg} E; magnetic latitude 15.5 {\deg} S), near the southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h'F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures. The results show that, for the three events studied, geomagnetic activity creates favorable conditions for the initiation of ionospheric irregularities, manifested by ionogram spread-F and TEC fluctuation. Post-midnight irregularities are developed due to the presence of eastward disturbance dynamo electric fields (DDEF). For the storm of May, an eastward over-shielding prompt penetration electric field (PPEF) is also acting. This PPEF is added to the DDEF and produces the uplifting of the F region that helps trigger the irregularities. What is more, during October and November, strong GPS L band scintillation is observed associated with strong range spread-F (SSF), that is, irregularities29 extending from the bottom-side to the topside of the F region.