## 1 Introduction  
Abrupt depletion in the equatorial ionospheric plasma density satellite data generally observed during nighttime is defined as an Equatorial Plasma Bubble (EPB) [1]. EPBs have various spatial ranges (50-1000 km) noticed in the equatorial ionosphere inside a narrow band of \(\pm 20^{\circ}\) magnetic latitude and include a broad area of altitudes from the bottom side ionosphere up to 1000 km [1, 2]. EPBs are created in the bottom side F region, where the boundary between the E and F regions develops to be unstable at night. During the post sunset, the ionization rate in the low latitude region decreases dramatically, therefore the density gradient at the bottom side of the F layer ionosphere goes into an abrupt state due to rapid loss of molecular ions. Under the action of gravity at the equatorial region, a polarization electric field is created, which raises the ionospheric plasma at the bottom side to higher altitudes. This mechanism of exchanging plasma between ionospheric regions is known as the Rayleigh-Taylor (R-T) instability [1; 3]. The plasma density depletion relative to the background ionosphere, which is several hundred kilometers in width and extending from the bottom side ionosphere to higher altitudes, is being observed [4; 5]. Depletion manifests itself in different names according to the measurement technique. It is denoted by plasma plumes due to its presence in radar displays [2], diffused echoes in ionogram data related to the name range spread F [6; 7; 8], and in the optical images, they appeared as emission depletions expanding along the magnetic field lines [9; 10] or ionospheric scintillation in radio wave signals. Due to the importance of EPBs in space physics, the authors of [7] derived an index related to the depletion of plasma observed by Swarm electron density \(n_{e}\) data, which is denoted by the Ionospheric Bubble Index (IBI). In addition to the decrease of plasma density associated with EPBs, which changes from some tens of percent to three orders of magnitude, an enhancement of the local magnetic field can extend to middle latitudes along EPBs region [7; 11; 12; 13]. EPBs regularly persist until after midnight since their creation around sunset and vanish after sunrise and their large-scale structures can be traced in successive satellite orbits [14]. The EPB phenomenon exists during quiet and active periods, but several studies found a higher correlation between its occurrence rate and active periods than quiet periods. Not only, the EPB occurrence rate is activity-dependent, but it also depends on the phase of the geomagnetic storm; it is much higher during the growth and main phase and it is rarely observed during the recovery phase [15; 16; 17]. Geomagnetic storms are considered one of the major natural hazards [18]. The main reason for the high correlation between solar activity and EPB occurrence rate is the less upward plasma gradient experienced due to the less ionization taking place during low solar active periods, but during high solar activity, the ionization rate is very large due to the increase in solar Extreme Ultraviolet (EUV) radiation; therefore, the plasma gradient is extremely high, leading to a high occurrence rate of EPBs [19]. During geomagnetic disturbances, huge quantities of energy and momentum associated with the perturbed solar wind are ejected into the Earth's ionosphere-thermosphere at auroral latitudes, which subsequently creates intense convection in the polar cap region. The enhanced plasma convection considers the fastest response in the high-latitude ionosphere. The swift sunward (anti-sunward) plasma flows over the auroral latitudes leading neutral winds through ion-neutral collisions and creating a large-scale dawn-to-dusk ionospheric electric field [20]. This high latitude electric field can extend nearly spontaneously down to equatorial regions. In this case, the electric field is named the Prompt Penetration Electric Field (PPEF) [13; 21; 22].