## 1 Introduction
Although there are progressive results on the ionospheric irregularities and loss of lock mechanism in the past, the complex origin and the dynamics of the ionospheric irregularities relevant to their effects on GNSS and communication systems are not yet fully understood. Using data from the European Space Agency (ESA) Swarm mission, [PERSON] et al. [21; 22] inferred that plasma bubbles certainly exhibit scaling properties that are associated with large density gradients arising from the turbulent nature of the irregularities. Their studies suggest that the turbulent characters are reflected in the high rate of change in electron density index (RODI) values inside bubbles. [PERSON] et al. [23] highlighted that the GNSS loss of lock events is strongly correlated with well-defined values of both RODI and the rate of change in the TEC index (ROTI), suggesting their origin in the regions with high electron density gradients. Recent investigation of [PERSON] et al. [20] on loss of lock events using long-term Swarm observations reported that the GNSS loss of lock is very often confined to the turbulent plasma density irregularities with intermittent structures and extremely high RODI. Detecting EPBs is a challenging task as they are dynamic and often exhibit complex spatial and temporal characteristics. An EPB may travel across different longitudes and change its shape and strength of irregularities before diminishing in the background electron density [24]. Post-event detection methods provide us with a detailed description of bubble characteristics like bubble depth, bubble occurrence period, and the impact of the bubble on TEC depletion. Numerous techniques have been developed to detect EPBs using data from ground-based instruments, Radar observations [25], ionogram analysis [26], airglow data [10], and Global Navigation Satellite Systems (GNSS) [27; 28; 29] which include Global Positioning System (GPS), European Global Navigation System (Galileo), Russian Global Navigation Satellite System (GLONASS), Quasi-Zenith Satellite System (QZSS), Satellite-Based Augmentation System (SBAS), Chinese BeiDou Navigation Satellite System (BeiDou) [30; 31]. [PERSON] et al. [32] first observed the EPBs using the RADAR data as the plumes or wedges. The ionograms describe the presence of EPB as the equatorial spread F phenomenon in the ionospheric F layer [33]. The all-sky imager captures the night airglow in the optical imager 630 nm images in which the dark bands or intensity-depleted regions are the signatures of EPBs [5]. Continuous observational data of the F-region anomaly were observed in Sanya from 2009 to 2010 at the equinox months using VHF radar data, GPS observations, and ionosonde observations [34]. The results indicated that the observed field alignment irregularities, scintillation values, and TEC depletion may be related to the possible development of EPB. [PERSON] et al. [35] used the 630 nm airglow data from the visible light and infrared spectrum imager to identify the EPBs. The electron density inside the EPB decreases, which is visible as a dark patch in the airglow image, considering it as an EPB occurrence. The EPBs marked in the airglow data are in line with the EPB occurrence observed through the ionosonde and GPS observations. Studies on EPB occurrence based on GNSS-derived TEC depletion or ROTI are emphasized nowadays as there exists a direct relationship between the ROTI, irregularity strength, and scintillation indices [19]. [PERSON] and [PERSON] [36] highlighted the strong connection between phase fluctuation intensity specified by ROTI and degradation in precise GPS during an extreme EPB prevailing condition. [PERSON] et al. [37] analyzed the global ROTI maps along with data from other ground- and space-based observations during geomagnetic storm to present a global multi-instrumental overview of ionospheric TEC and electron density irregularities during the storm.