Ionospheric plasma blobs at low latitudes are localized regions of enhanced plasma density, substantially above the surrounding ambient plasma (Watanabe and Oya, 1986; Pimenta et al., 2004; Pimenta et al., 2007; Yokoyama et al., 2007; Huang et al., 2014; Tardelli-Coelho et al., 2017; Klenzing et al., 2011; Kil et al., 2019; Agyei-Yeboah et al., 2021; Park et al., 2022; Adebayo et al., 2023). The first observation of such localized plasma density enhancements, along with depletions in the nighttime tropical F-region, was reported by Watanabe and Oya (1986) using data from the Hinotori satellite. Their statistical analysis suggested that the occurrence probabilities of plasma depletions (bubbles) and enhancements (blobs) appear to be complementary, with plasma blobs typically confined to regions adjacent to those where plasma bubbles occur (Watanabe and Oya, 1986; Yokoyama et al., 2007; Huang et al., 2014; Adebayo et al., 2023). Subsequent observational and modeling studies have investigated the relationship between plasma blobs and other ionospheric phenomena, including Medium-scale Traveling Ionospheric Disturbances (MSTIDs), geomagnetic storms, and the Equatorial Ionization Anomaly (EIA) (Pimenta et al., 2007; Yokoyama et al., 2007; Klenzing et al., 2011; Kil et al., 2019; Park et al., 2022; Adebayo et al., 2023; Thokuluwa, 2025). Simultaneous observations of plasma blobs and plasma bubbles along the same magnetic meridian (Yokoyama et al., 2007; Huang et al., 2014), as well as numerical simulations (Ossakow et al., 1979; Zalesak et al., 1982; Carrasco et al., 2020), suggest a close connection between their generation mechanisms. However, the detection of blobs in the absence of bubbles (Klenzing et al., 2011) indicates that plasma bubbles are not a necessary condition for blob formation.

Recent studies have investigated various mechanisms to explain the formation of ionospheric plasma blobs (Park et al., 2022; Adebayo et al., 2023; Thokuluwa, 2025). For instance, Adebayo et al. (2023) reported the merging and bifurcation of plasma blobs in the Brazilian Amazon region. The merging was attributed to the influence of local neutral winds, while the bifurcation was linked to polarization electric fields within the associated equatorial plasma bubbles (EPBs). In this context, the amplification of polarization electric fields within developing plasma bubbles plays a key role in driving plasma upward, eventually leading to the formation of blobs (Huang et al., 2014; Adebayo et al., 2023). An alternative hypothesis attributes blob formation to meridional winds and nonuniform airflow in the ionosphere, which can modify the plasma distribution along a bubble’s magnetic flux tube, generating localized plasma enhancements or “blobs” (Klenzing et al., 2011; Wang et al., 2019). Also, observations in both the African and South American sectors have revealed occurrences of plasma bubbles without accompanying plasma blobs, highlighting the complex and variable nature of blob formation (Okoh et al., 2017; Chian et al., 2018; Adebayo, 2021). A recent case study over the African region by Park et al. (2023), using data from the GOLD satellite, associated plasma blob occurrences with activity in the Equatorial Ionization Anomaly (EIA). These blobs were found to remain near the EIA crest and poleward of adjacent plasma bubbles, consistent with earlier findings from the Central and South American sectors (Pimenta et al., 2007; Park et al., 2022).

While extensive research has been conducted over the Brazilian tropical sector and other sectors, studies focused on the African region remain limited and incomplete. In this paper, we present the first in-situ observations of ionospheric plasma blobs over the African sector during a deep solar minimum period (January 2018 – December 2020). This study aims to investigate the morphology, dynamics, and spatiotemporal characteristics of these plasma blobs. Key observational features are identified, analyzed, and discussed to improve our understanding of blob behavior in this underexplored region.

In this study, plasma blobs are identified as localized regions of enhanced electron density, typically exhibiting a 5%, or more, above ambient plasma density. To prevent potential artifacts, like small peak of electron density (Ne) around the dayside dip equator, as reported by Song et al. (2022), we excluded any enhancements located within ±5° of the 10°N latitude, as all artifacts were observed within this region. The identification of plasma blobs was carried out through a visual inspection (https://vires.services/) using both electron density data and Total Electron Content (TEC) data. Only electron density enhancements that coincided with corresponding TEC enhancements were considered valid. This is because known artifacts in the Swarm electron density data do not exhibit corresponding TEC enhancements (Song et al., 2022). Figure 1 illustrates the methodological workflow, beginning with data pre-processing followed by data analysis. To estimate the north-south scale size of the blobs, we used the along-track extension of the blobs. This extension was then converted into kilometers, where 1° of latitude was assumed to correspond to approximately 110 km. A similar approach was used by Le et al. (2003) for estimating the scale size of plasma blobs.

Swarm is a constellation mission by the European Space Agency (ESA) consisting of three identical satellites, namely, Swarm A, B, and C, launched into near-polar orbits in November 2013. Their initial pearl-of-strings configuration allowed for the study of Polar Cap Patches (PCP) evolution, as Spicher et al. (2017) explained. In addition, Park et al. (2015) used the same configuration of the satellites (A, B, C) to study the westward tilt of plasma blobs. By April 2014, the satellites’ orbits had been set, resulting in Swarm A and Swarm C orbiting at about 460 km and Swarm B at approximately 510 km. Each Swarm satellite carries an identical payload comprising several instruments; in this study, we used only the electron density (Ne) and the Total Electron Content (TEC) data from satellite C as A makes practically the same observation as C but with about 1.6° difference in longitude (however, in future work, we plan to incorporate data from Swarm A to examine the possible cross-track (zonal) structure of plasma blobs). Both the Ne and TEC are derived from Electric Field Instrument (EFI) and onboard GPS Receiver (GPSR) instruments, respectively (Jin et al., 2020). In this study, Swarm satellite C data obtained during the period from January 2018 to December 2020 (Low solar activity; average 10.7 cm solar radio flux <80 × l0⁻²²Wm^-2Hz^-1) were used to analyze the daily and seasonal occurrence of plasma blobs over the African Sector. Figure 2 shows an example of the trajectory of the Swarm satellite C (in blue) on 7 November 2018, and the magnetic equator (dashed line). In addition, the position of the detected plasma blob, and the crests of the EIA are shown as short red and magenta lines, respectively. Typically, Swarm satellite C passes over the African region six (6) times daily at varying longitudes.

This study presents the first comprehensive characterization of ionospheric plasma blob occurrences in the topside ionosphere over the African sector during a deep solar minimum. Plasma blobs, a type of ionospheric plasma irregularity, are known to disrupt radio communication through signal fluctuations and scintillation (Jin et al., 2020). To quantify plasma enhancement within blobs, we calculated the percentage increase in electron density relative to background levels (Figure 9). The results show a right-skewed distribution, with most events exhibiting enhancements between 5% and 100%, and a median around 25%. Unlike previous case-study-based reports, this statistical approach provides a broader perspective. Earlier studies (e.g., Watanabe and Oya, 1986) found enhancements up to 200% during high solar activity, but such levels are less common during deep solar minimum conditions. The lower enhancements observed here are consistent with reduced background densities and lower solar flux. Nevertheless, rare events with >100% enhancement may reflect geomagnetic storm-time effects, as noted by Pimenta et al. (2007). Overall, our findings show that during deep solar minimum, plasma blobs over the African sector typically enhance electron density by 5%–100%, with occasional events exceeding this range due to storm-time dynamics.

The analysis of plasma blob occurrences in the African sector from January 2018 to December 2020 provides valuable insights into their distribution, timing, and potential generation mechanisms. The results indicate that plasma blobs primarily occur during the post-sunset to post-midnight hours, with peak occurrences around pre-midnight. This pattern is consistent with previous studies in other sectors, such as those by Su et al. (2022), Adebayo (2021) and Park et al. (2010), which suggest a close association between plasma blob formation and nighttime ionospheric dynamics.

One of the leading mechanisms for plasma blob generation is the role of equatorial plasma bubbles (EPBs), which have been widely reported as a key driver (Park et al., 2003; Pimenta et al., 2007; Huang et al., 2014; Tardelli-Coelho et al., 2017; Agyei-Yeboah et al., 2021; Adebayo et al., 2023; Thokuluwa, 2025). EPBs typically form around the magnetic equator and are mapped along geomagnetic field lines to low latitudes, potentially seeding blob formation at varying latitudes during their evolution (Huang et al., 2014). Several cases observed in this study support this hypothesis, as shown in Figure 10 (2018-05-12, 2018-08-30, 2019-02-08). However, in the first panel (2018-05-12), a case study reveals a blob located only at the northern edge of the plasma bubble, with no corresponding southern edge counterpart similar to the report of Park et al. (2010), Figure 2, panel (e). This suggests that plasma blobs associated with EPBs may not always be symmetrical, contrary to the hypothesis put forth by Huang et al. (2014). Meridional thermospheric winds could play a significant role in this asymmetry, as previously suggested by Luo et al. (2018) and Krall et al. (2010). The presence of strong zonal and meridional winds can either enhance or suppress the development of EPBs (Aa et al., 2024), thereby influencing the spatial distribution of blobs. On the other hand, the difference between the northern and southern hemispheres in the spatial distribution of plasma blobs indicates that land–atmosphere–ionosphere coupling may play a key role in modulating both the Equatorial Ionization Anomaly (EIA) and thermospheric winds, thereby influencing the generation and distribution of blobs in the African sector during deep solar minimum.

Furthermore, we observed several instances where plasma bubbles were present without accompanying plasma blobs, and vice versa. Quantitatively, 44.8% of the blob events occurred in conjunction with EPBs, either in the same longitude or in adjacent longitudes, while 55.2% of blob events occurred in the absence of EPBs. The absence of EPBs indicates that no depletions were recorded along the trajectories on the days when blobs were detected. For example, the three cases shown in Figure 4 were detected in the absence of EPBs, but we noted deformations in the EIA structure, such as the merging of the two crests in the event of 25 October 2019. Adebayo (2021) observed similar cases of bubbles without blobs over the Brazilian sector using optical instruments, suggesting that polarization electric fields (E) might play a crucial role in the formation of plasma blobs associated with EPBs. They proposed that a threshold of polarization electric field strength might be required to trigger blob development, compared to the cases of bubbles without blobs. In addition, they stated that EPBs without blobs exhibited a relatively shorter depletion band compared to those associated with blobs. Interestingly, several symmetrical blobs were also observed in the EIA without EPBs in the African longitudes (e.g., 2020-01-17, Figure 10), raising the possibility that these blobs are related to fountain effects combined with local neutral wind dynamics as suggested by Pimenta et al. (2007).

Additionally, our results reveal for the first time a hemispheric asymmetry in plasma blob occurrence during the deep solar minimum. Blob occurrence frequency is concentrated primarily in the geographic latitude (GLAT) range of 15°–30° in the Northern Hemisphere, whereas in the Southern Hemisphere, it spans a wider range from 0° to 35°. This spatial difference between hemispheres suggests a significant role of both the Equatorial Ionization Anomaly (EIA) and thermospheric winds in the generation and distribution of plasma blobs in the African sector during periods of low solar activity. Based on these findings, we can infer that the generation of plasma blobs in the African sector is likely driven by a combination of factors, including geomagnetic field variations, EIA dynamics, EPBs, and neutral wind interactions. The diverse characteristics of the observed blobs suggest that a deeper understanding of their physical processes, such as development and morphology, could enhance our knowledge of ionospheric plasma irregularities, particularly in underexplored sectors like Africa.

This study provides the first comprehensive investigation into the occurrence and characteristics of plasma blobs in the topside ionosphere over the African sector during a deep solar minimum period (2018–2020). Using Swarm satellite data, we characterized the spatial, temporal, and seasonal patterns of blob occurrences, as well as their internal plasma enhancements. The results show that plasma blobs predominantly form between 16:00 UT and 02:00 UT, aligning with post-sunset ionospheric dynamics. A higher concentration of blobs was observed in northern Africa, likely due to land–atmosphere–ionosphere coupling, processes particularly relevant in the African context and the influence of local thermospheric wind patterns. While equatorial plasma bubbles (EPBs) were confirmed as a major driver of blob formation, our findings also reveal that approximately 55.2% of blobs occurred without any associated EPBs. These independent events suggest the presence of alternative mechanisms. We propose that lower atmospheric processes, such as enhanced atmospheric tides, gravity waves from deep convection, and the strong land–ocean thermal contrasts specific to the African sector, modulate thermospheric winds and electric fields, thus contributing to blob generation. Seasonal ITCZ migration and hemispheric heating asymmetries also appear to influence the latitudinal distribution and hemispheric occurrence of blobs. Our analysis of electron density enhancements within blobs shows a right-skewed distribution, with most events exhibiting a 5%–100% increase over background levels and a median enhancement around 25%. Rare cases exceeding 100% may be linked to geomagnetic storm-time activity, consistent with previous storm-related observations.

These findings show the complex, multifactorial nature of plasma blob formation in the African ionosphere, highlighting the role of regional geophysical conditions and lower atmosphere–ionosphere coupling. This study provides a valuable baseline for future work and reinforces the need for integrated observations across atmospheric layers. In future work, we plan to incorporate data from Swarm A to examine the cross-track (zonal) structure of plasma blobs. This will complement our current along-track (meridional) analysis and allow for a more complete characterization of blob morphology, although such efforts will require substantial re-processing of the dataset.