The temporal and spatial variability of Earth’s ionosphere is significant in space weather. The variability is highly influenced by multiple strong coupling processes (Saranya et al., 2015). Solar activity such as Coronal Mass Ejections (CMEs) and high-speed solar wind streams, interact with the Earth’s magnetosphere to cause geomagnetic storms. The interactions cause greater plasma circulation within the magnetosphere, resulting in high electric currents and fields (Gonzalez et al., 1994). Storms have an impact on the Earth's ionosphere, causing fluctuations in Total Electron Content (TEC). TEC is an important indicator that quantifies the number of electrons inside a vertical column of the ionosphere, spanning from 50 km to 1000 km above the Earth’s surface (Bhattarai et al., 2018) and 1 TEC unit = 1×1016 electrons/m2. Significant information on the effects of space weather on satellite systems, communication, and navigation may be obtained by comprehending the latitudinal response of ionospheric thermoelectric conduction during geomagnetic storms (Kintner et al., 2007).
Specific features of low-latitude and equatorial ionosphere include the electrodynamics of the plasma fountain, the equatorial electrojet (EEJ), the equatorial ionization anomaly (EIA), and the development of equatorial plasma bubbles after sunset (Panda et al., 2013; Harsha et al., 2020; Ghanshyam et al., 2023). The EIA consists of two crests of increased TEC centered around ± 15° magnetic latitude, separated by a trough along the magnetic equator (Appleton 1946; Olwendo et al., 2017; Ghanshyam et al., 2023). The equatorial plasma fountain phenomenon elevates ionospheric plasma to greater heights, resulting in its dispersion along magnetic field lines and the formation of crests (Anderson, 1981). The EIA results from the eastward electric fields that occur during daytime, which also contribute to the equatorial ionospheric fountain effect (Appleton, 1946). This phenomenon is caused by an upward drift in E×B a result of the interaction between the horizontal northward magnetic fields and the eastward electric fields near the equator. Panda et al. (2013) state that the plasma is elevated by a vertical movement and transported to greater altitudes. From there, it moves to higher latitudes via magnetic field lines. The plasma flow at magnetic latitudes ± 15° is responsible for the production of EIA peaks (Kelley, 2009).
The ionosphere receives a large amount of energy from powerful geomagnetic storms that occur at high latitudes. This energy is responsible for the production of currents, electric fields, and Joule heating. Disturbed winds and disturbance dynamo processes may have an impact on ionospheric electric currents and fields. These storms may disrupt the equatorial ionosphere by shifting electric fields from high to low latitudes (Sastri et al., 2000). Storms cause two groups of electric fields. The first one is called the disturbance dynamo electric field (DDEF), which can persist for more than a day. It counteracts the normal zonal electric field during quiet periods and shifts westward during the day and eastward during the night. The second type is the transitory prompt penetration electric field (PPEF), generated by the solar wind's magnetospheric dynamo. This electric field moves westward at night and eastward during the day. This PPEF lasts only a few hours. That means that during a storm, the eastward electric field during the daytime can change, which can increase or decrease the plasma fountain effect (Lin et al., 2007; Olwendo et al., 2017).
Mannucci et al. (2005) investigated the impact of a Halloween storm, with a disturbance storm time index (Dst) of -390 nT, on fluctuations in the total electron content of the ionosphere. The study showed that plasma transport towards the pole and potential uplift at mid-latitudes contribute to significant increase in mid-latitude plasma, which may lead to high TEC differences and TEC plumes resulting from subauroral electric fields. Sharma et al. (2011) conducted a study on the TEC of the ionosphere at low latitudes in response to a geomagnetic storm that occurred on August 25, 2005. The storm had a Dst value of -184 nT. During the storm, the TEC records a peak with two distinct humps, which have an amplitude about twice as large as that observed on a quiet day. The second peak belongs to the plasma fountain effect, whereas the first peak is assigned to the PPEF. In addition, it has been shown that the impact of the PPEF is nearly uniform in the longitudinal direction. Ikubanni et al. (2020) studied the impact of intense geomagnetic storms on TEC in the low-latitude area of Africa. March 17, 2013, geomagnetic storm (Dst = -132 nT) had a substantial influence at commencement of recovery phase, particularly at Equatorial Ionization Anomaly (EIA) crest site. On the other hand, March 17, 2015 storm (Dst = -234 nT) event had a significant impact near the end of the main phase and during recovery phase. VTEC reactions have been analysed during a geomagnetic storm (Dst = -175 nT) from August 24 to 31, 2018, and found that the VTEC peak on August 26, 2018 was produced by the PPEF from a geomagnetic storm (Sur et al. 2020). The corresponding decrease in VTEC over the subsequent days was attributed to DDEF during the storm’s recovery phase. The impact of four strong geomagnetic storms that occurred between 2010 and 2015 on fluctuations in Total Electron Content (TEC) in low-latitude areas of India (Singh et al. 2021). They found that the notable changes in TEC during the storm period were mostly attributed to the electric field and neutral winds associated with the storms.
Geomagnetic storms cause substantial fluctuations in the electron density of the ionosphere, which are often measured as total electron content (TEC). These storms induce ionospheric perturbations that may either increase or decrease electron density. This research investigates the variations in ionospheric TEC at various locations across the planet Earth during the May 11, 2024, which is the most severe (Dst = -412 nT) to be observed after the Halloween storm that occurred on October 29–30, 2003 (Dst = -390 nT).