Abstract
Ionospheric irregularities can severely degrade radio communication and navigation systems. Geomagnetic storms may affect the generation of these irregularities in a way that is not yet fully understood. To improve the forecasting of this phenomenon, we need to study the ionosphere in different regions of the world, and in particular in the equatorial ionization anomaly (EIA) where irregularities are usually more intense. This study analyses the effect of geomagnetic storms on ionospheric irregularities. We examined the occurrence of irregularities at the southern crest of the EIA in Argentina (Tucumán, 26.9°S, 294.6°E, dip latitude 15.5°S) during three intense and one moderate geomagnetic storm of different solar sources, between 2015 and 2018. We used data from an ionosonde, a Global Positioning System receiver and magnetometers. Ionogram spread-F, the F-layer bottom side (h'F), the critical frequency of the F2-layer (foF2), the rate of TEC index and the S4 scintillation index were analysed. The data show irregularities were present as range spread-F and moderate TEC fluctuations in one storm: 27 May 2017 (a coronal mass ejection CME-driven storm occurred on local winter), and were absent in the other events. We suggest that eastward disturbance dynamo electric field and over-shielding prompt penetration electric fields may create favourable conditions for developing these irregularities, whereas westward storm time electric fields might inhibit the growth of irregularities during the other storms considered. During co-rotating interaction region CIR-driven storms, the westward disturbance dynamo electric field may be associated with the non-occurrence of irregularities.
Highlights
Ionospheric irregularities are regions in the ionosphere with electron density notably different from the background, with scale sizes ranging from tens of centimetres to hundreds of kilometres, and duration between minutes and several hours
Irregularities cause backscatter signatures called spread-F; Range spread-F (RSF) if the broadening is in height and frequency spread-F (FSF) if the broadening is in the frequencies (Piggott & Rawer, 1978)
We examined the occurrence of ionospheric irregularities during four geomagnetic storms at a station near the southern crest of the equatorial ionization anomaly (EIA) in South America (Tucumán, 26.9°S, 294.6°E, dip latitude 15.5° S)
Summary
Ionospheric irregularities are regions in the ionosphere with electron density notably different from the background, with scale sizes ranging from tens of centimetres to hundreds of kilometres, and duration between minutes and several hours. These irregularities are a major space weather issue because they can degrade navigational signals, disrupt satellite to ground communications and cause large positioning errors. Plasma density irregularities of several hundreds of meters can cause rapid fluctuations in the signal amplitude and phase in a received electromagnetic wave, called scintillation. Irregularities can manifest as Total Electron Content (TEC) depletions. GPS derived TEC and amplitude scintillations of Lband frequencies have been used to characterize the irregularities
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