Ionospheric Scale Index Map Based on TEC Data During the Saint Patrick Magnetic Storm and EPBs

Abstract

This study examines the variability of the ionospheric content during the period around the 2015 Saint Patrick magnetic storm and when equatorial plasma bubbles (EPBs) are observed during the quiet time over South America during two other events. It uses the ionospheric scales index map based on the disturbance ionospheric index (DIX). The results are compared to the traces of the ionograms obtained at three different ionospheric stations (Fortaleza, Campo Grande, and Cachoeira Paulista) in Brazil acquired in the same period and at the same time rate. The index is based on the TEC map developed at the "Brazilian Studies and Monitoring of Space Weather" (Embrace/INPE). It covers the whole South America (latitudes from 20°N to 60°S and longitudes from 90°W to 30°W) with 0.5°× 0.5°resolution cells (60 × 60 km 2). Among the results, the DIX map revealed some patches of "Disturbed" and "Weakly Disturbed" ionospheric conditions during the magnetically quiet time before the storm, which were associated with range and frequency Spread-F over the same area as observed in ionograms. Also, the information from the southern portion of the dip equator showed a transition from occurrences of Spread-F prior to sunrise to a condition favorable enough to develop a F3 layer after sunrise. Magnetic storms have also been investigated in a large number of works in several different ways. For instance, the Saint Patrick magnetic storm has been investigated by Astafyeva et al. (2015) using a global multi-instrumental overview of the ionospheric impact of this magnetic storm. Nevertheless, the map present in their Figure 2 has very low resolution. Besides, the maps presented in their Figure 5 have several gaps. In another portion of the study (e.g., Figure 4 that deals with sectoral analysis), they basically used profiles of NmF2 from a single station. In the other study, Venkatesh et al. (2017) did provide quite high-resolution maps, but TEC maps (see their Figures 6 and 9), not disturbances maps. For the disturbance, they used

Study of the equatorial and low-latitude total electron content response to plasma bubbles during solar cycle 24–25 over the Brazilian region using a Disturbance Ionosphere indeX

“…However, as the irregularities start to develop spread F in the CAJ2M ionograms (03:50 to 06:50 UT), we can see a gradual increase in DIX, which reaches a peak at 06:50 UT. This feature reinforces that the DIX is strongly related to the physical variations in the ionosphere that are measured by the ionosonde (Denardini et al, 2020b).…”

“…Moreover, the authors discussed the DIX response to pre-storm effects and other phenomena, such as sporadic E layers. Denardini et al (2020b) analyzed DIX maps calculated for South America during extreme geomagnetic storms and plasma bubbles. Besides the magnetic storm analysis, the authors associated local disturbances in DIX with the equatorial spread F (ESF) observed over the same area of study.…”

Equatorial Plasma Bubbles Observed at Dawn and After Sunrise Over South America During the 2015 St. Patrick's Day Storm

“…The focus of this work is the evolution of the plasma bubbles generated in the recovery phase of this storm. Other perturbations during this storm have been studied by several authors (e.g., Astafyeva et al, 2015;Denardini et al, 2020;Kuai et al, 2016;Venkatesh et al, 2017;Verkhoglyadova et al, 2016;Zhang et al, 2017). These EPBs structures were so intense that even with sunrise and photoionization effects active were not enough for these structures to cease.…”

“…The ionospheric response to the St. Patrick's Day magnetic storm (17–18 March 2015) has been analyzed in many studies (e.g., Astafyeva et al., 2015; Denardini et al., 2020; Fagundes et al., 2016; Figueiredo et al., 2017; Venkatesh et al., 2017). However, in‐depth analyses of pre‐ and post‐sunrise plasma bubbles generated during the St. Patrick's geomagnetic storm in the South American sector have not been reported in the literature.…”

“…The EPBs are defined as plasma depletion formed by Rayleigh‐Taylor Instability (RTI) processes (Kelley, 2009). Different instruments and methodologies can be used to detect these EPBs, such as Ionosondes (Abdu et al., 2003, 2012), All‐Sky Imager (Pimenta et al., 2007; Vargas et al., 2020), total electron content (TEC) (Barros et al., 2018; Silva et al., 2019), Very High Frequency (VHF) radars (Abdu et al., 2009), scintillation index (S4) (De Paula et al., 2007; De Rezende et al., 2007), disturbance ionospheric index (DIX) (Denardini et al., 2020), and Rate Of TEC Index (ROTI) (Carmo et al., 2021; de Jesus et al., 2020). These irregularities are commonly generated after sunset (Abdu et al., 2003; Agyei‐Yeboah et al., 2021; Magdaleno et al., 2012; Vargas et al., 2020).…”