First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All‐Sky Airglow Imager and GNSS Receivers

Abstract

This is the first paper that reports the occurrence frequency of equatorial plasma bubbles and their dependences of local time, season, and geomagnetic activity based on airglow imaging observations at West Africa. The all‐sky imager, situated in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S), has a 180° fisheye view covering almost the entire airspace of Nigeria. Plasma bubbles are observed for 70 nights of the 147 clear‐sky nights from 9 June 2015 to 31 January 2017. Differences between nighttime and daytime ROTIs were also computed as a proxy of plasma bubbles using Global Navigation Satellite Systems (GNSS) receivers within the coverage of the all‐sky imager. Most plasma bubble occurrences are found during equinoxes and least occurrences during solstices. The occurrence rate of plasma bubbles was highest around local midnight and lower for hours farther away. Most of the postmidnight plasma bubbles were observed around the months of December to March, a period that coincides with the harmattan period in Nigeria. The on/off status of plasma bubble in airglow and GNSS observations were in agreement for 67.2% of the total 768 h, while we suggest several reasons responsible for the remaining 32.8% when the airglow and GNSS bubble status are inconsistent. A majority of the plasma bubbles were observed under relatively quiet geomagnetic conditions (Dst ≥ −40 and Kp ≤ 3), but there was no significant pattern observed in the occurrence rate of plasma bubbles as a function of geomagnetic activity. We suggest that geomagnetic activities could have either suppressed or promoted the occurrence of plasma bubbles.

Spread F occurrence features at different longitudinal regions during low and moderate solar activity

“…In the case of the West African sector, past studies (Okoh et al, 2017;Yizengaw et al, 2013) have presented a similar discussion about the role of GW in the observed large RSF occurrence during a solstice month. Yizengaw et al, (2013) attributed the post-midnight enhancement of the eastward polarization electric field in the West African region to the presence of the localized charged particle.…”

Study of Equatorial Plasma Bubbles Using ASI and GPS Systems

“…The influence of solar and magnetic cycle is also studied. Magdaleno et al [42] studied the Climatology characterization of EPB using GPS data for the period 1998-2008. They have considered the slant total electron content (sTEC) derived from global positioning system (GPS) data from 67 International GNSS Service (IGS) stations distributed worldwide around the geomagnetic equator and the region of the ionospheric equatorial anomaly (IEA).…”

“…First time study of the occurrence frequency of EPB over West Africa is done by Okoh et al [42] using an ASI and GNSS Receivers from June 9, 2015 to January 31, 2017. This ASI is installed at Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S) which covers almost the entire airspace of Nigeria.…”

Current Understanding of the Equatorial E x B Drift velocities in the African Sector: A Short Review

“…V p plays a significant factor in describing and specifying many ionospheric models across the globe. It has also been found to be a significant factor in the manifestation of plasma bubbles and Equatorial Spread-F [1,2,3,4] through the action of the evening-time Pre-reversal enhancement (PRE) activity. The PRE is the evening-time enhanced E x B drifts driven by the eastward electric field., and consequently lifts the ionosphere.…”