Equatorial ionospheric response to storm-time electric fields during two intense geomagnetic storms over the Brazilian region using a Disturbance Ionosphere indeX

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

“…This behavior is observed similarly but not identically over the four equatorial GNSS stations, which reinforces the idea that the DIX provides a localized response to the TEC variations associated with the occurrence of ionospheric disturbances (as suggested by Picanço et al, 2021). Moreover, since the ROTI is one of the most reliable indices for detecting TEC changes due to ionospheric irregularities, the simultaneous response of both indices is a good indication that the DIX is also capable of perceiving the presence of TEC fluctuations generated by plasma bubble events (Carmo et al, 2021). However, to ascertain the most likely origin of these disturbances, we analyzed OI 630 nm airglow images taken at CA (Fig.…”

“…The DIX is an index developed for representing the ionosphere perturbation degree during several types of phenomena (e.g., disturbed electric fields, plasma bubbles, and spo- Extremely disturbed radic E layers). Therefore, we highlight that the ionospheric responses observed using this index are generally caused by the sum of concomitant events which can be caused by internal and/or external drives (Denardini et al, 2020a, b;Picanço et al, 2020Picanço et al, , 2021. Thus, those studies demonstrate that the current DIX methodology provides a straight response to space weather events in which it is possible to estimate the intensity and duration of ionospheric disturbances.…”

“…The ROTI is given by the deviation of ROT within a 5 min time interval, as presented in Eq. (3) as follows (Pi et al, 1997;Carmo et al, 2021):…”

“…Therefore, several ionospheric indices have been developed aiming to measure the ionospheric TEC effects due to EPBs. Among them, the rate of TEC index (ROTI) is a technique for quantifying the amplitude of GNSS phase fluctuations and is commonly used as a direct measure of the EPBs occurrence (Pi et al, 1997;Cherniak et al 2018;Carrano et al, 2019;Liu et al, 2019a, b;Borries et al, 2020;Carmo et al, 2021). Another widely used index for monitoring the EPB effects is the scintillation index (S4), which represents a value of ionospheric scintillation on GNSS signals mainly in the equatorial and low-latitude regions and is capable of estimating the magnitude of the EPB-related scintillations (Aarons, 1982;Kintner et al, 2007).…”

“…The authors stated that the new DIX approach proved to be effective in detecting ionospheric disturbances due to internal sources and that the new method for calculating the DIX non-perturbed reference also made the index more sensitive to short-term TEC time variations. Afterward, Picanço et al (2021) used the same DIX version to provide an analysis of the equatorial and low-latitude ionospheric response to disturbed electric fields during extreme geomagnetic storms over the Brazilian region. Moreover, the authors discussed the DIX response to pre-storm effects and other phenomena, such as sporadic E layers.…”