Spread-F characteristics at the southern anomaly crest in South America during the descending phase of solar cycle 24

Abstract

Ionospheric F-region irregularities can acutely affect navigation and communication systems. To develop predictive capabilities on their occurrence, it is key to understand their variabilities in a wide range of time scales. Previous studies at low latitudes in South America have been performed mostly for the eastern sector, and fewer efforts have been done in the Argentinian region. This work presents the analysis of the spread-F (range spread-F, frequency spread-F and strong spread-F) and plasma bubble occurrence characteristics near the southern crest of the Equatorial Ionization Anomaly (Tucumán, 26.8°S, 65.2°W; magnetic latitude 15.5°S). We used ionosonde and Global Positioning System (GPS) data from November 2014 to December 2019 for different solar and geomagnetic conditions. The data shows that spread-F and plasma bubble occurrence rates peak in summer and are minimum in equinox and winter, respectively. There is, usually, a negative correlation between each type of spread-F and solar activity, whereas the opposite happens for plasma bubbles. Geomagnetic activity suppresses the generation of spread-F in equinox and summer and enhances it in winter. Plasma bubble occurrence is higher during disturbed days than during quiet days, but under medium solar activity, summer months register more plasma bubbles in quiet conditions. Range spread-F observed in winter under low solar activity is not associated with plasma bubbles originated at the magnetic equator. These results contribute to the knowledge necessary to improve the prediction of the spatial and temporal distribution of the night-time ionospheric irregularities.

Ionospheric irregularities during disturbed geomagnetic conditions over Argentinian EIA region

“…In Tucumán, during the descending phase of solar cycle 24, the low spread-F occurrence season was equinox and the high spread-F season was summer except in 2018 when the highest spread-F occurrence was winter (González, 2021)…”

Ionospheric Irregularities During Disturbed Geomagnetic Conditions Over Argentinian EIA Region

“…In Tucumán, during the descending phase of solar cycle 24, the low spread-F occurrence season was equinox and the high spread-F season was summer except in 2018 when the highest spread-F occurrence was winter (González, 2021). In this study, spread-F was absent during the storms of October 2015, March 2016 (equinox) and August 2018 (local winter), whereas it was present during the May 2017 storm (local winter).…”