J. Nig. Soc. Phys. Sci. 4 (2022) 54–58

Journal of the
Nigerian Society

of Physical
Sciences

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

B. O. Adebesina,b,c,∗, J. O. Adeniyia,b, I. A. Adimula1, S. J. Adebiyia,b, S. O. Ikubannia,b, B. J.
Adekoyae

a Climate Action SDG 13 Group (Space Weather and Environment), Landmark University, Nigeria.
b Department of Physical Sciences, Landmark University, P.M.B 1001, Omu-Aran, Kwara State, Nigeria.

c Landmark University Centre for Research, Innovation and Discoveries (LUCRID), Nigeria.
dDepartment of Physics, University of Ilorin, Ilorin, Nigeria

e Department of Physics, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria

Abstract

A short review of the pattern and morphology of the equatorial plasma drift velocities, particularly during the evening-time Pre-reversal enhance-
ment (PRE) period in the African region had been presented. The seasonal PRE peak values across some locations in the West-African region
were considered and compared with other sectors of the world. While most plasma drift observations in the African region were calculated from
ionosonde measurements, the observations from other sectors involved direct measurement from satellite and the Incoherent Scatter Radar (ISR)
observations. The importance of the PRE in ionospheric electrodynamics was highlighted, the better in the use of either the virtual or real heights
of the F-layer in inferring vertical drift velocities were enumerated, revealing the strengths and weakness of each method. The general observa-
tions revealed that PRE peak magnitude is commonly weaker in the African region in comparison with the American/Peruvian and Indian sectors,
seasonal and solar activity dependent, and could be higher during either magnetic quiet or disturbed activity than when both magnetic activity
conditions are combined. The first work to present a regional PRE model around the African equatorial ionization anomaly region (Adebesin et
al model) was mentioned. The relevance of the E × B drift in quantifying the daytime equatorial electrojet (EEJ) current was also discussed.

DOI:10.46481/jnsps.2021.327

Keywords: Vertical E x B Drift; Ionosphere, Plasma; Pre-reversal enhancement (PRE); African sector.

Article History :
Received: 31 July 2021
Accepted for publication: 04 February 2022
Published: 28 February 2022

c©2022 Journal of the Nigerian Society of Physical Sciences. All rights reserved.
Communicated by: O. J. Abimbola

1. Introduction

Equatorial vertical plasma drifts (V p) explain the extent
in terms of speed to which the ionospheric F-layer is moving
vertically with respect to time. 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

∗Corresponding author tel. no: +234(0)8058051253
Email address: adebesin.olufemi@lmu.edu.ng (B. O. Adebesin )

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. The lifting interrupts
the ionospheric density stability through the Rayleigh-Taylor
mechanism. Vertical drifts had also been useful in the de-
scription of electron density response to solar eclipses, thus
making the E x B drift an essential factor for ionospheric F2-
layer redistribution during eclipse period [5]. The vertical

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B. O. Adebesin et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 54–58 55

drift velocities had been widely investigated in most sectors
of the world including the Peruvian/American sector [6], and
Indian sector [7, 8, 9], with little done in the African sector
[10, 11, 12, 13, 14, 15].

The space-borne drift measurements through the use of the
Incoherent Scatter Radar (ISR) have been well documented
over Jicamarca and Millstone Hill and had been the major
source of data for modelling ionospheric vertical plasma drift
[16]. Data from the Jicamarca ISR and AEE satellite had been
employed by [16] to find a first global empirical model for dif-
ferent solar activity conditions and seasons in the F-region, and
subsequently injected into the IRI-2007 model. Other empirical
models of repute include [17] - using ionosonde observations,
[18] and [19] - obtained from ROCSAT-1 measurements, and
[20] - from CHAMP satellite. All of these models and many
more are predicted/forecasted outside the African sector. The
first work to report modelling of the vertical plasma drift veloc-
ity in the African region, to the best knowledge of the authors, is
the work of [14]. The Adebesin et al model used ground-based
ionosonde data observations from Ouagadougou (Geographic
lat. 12.4◦N, long. 358.6◦E and Geomagnetic lat. 0.59◦N, long.
71.5◦E) spanning 1966-1998. The model was used in inferring
a regional empirical model between the evening-time drift and
the solar activity index. The model presents a strong potential
for obtaining Vp magnitude around the evening/nighttime pe-
riod, especially in the African equatorial ionization anomaly
(EIA) region. The mathematical relation that describes the
model as a function of the solar activity condition is given by
the expression:

PRE = 0.158RZ + 1.495 (1)

While satellite and ISR measurements had been widely used
in the investigation of the E X B drift in the other sectors of
the world, the ground-based ionosonde/digisonde had been the
major source of data acquisition for inferring drift pattern in
the African sector. The contribution of real-time ionospheric
measurements from ionosondes/digisondes are useful parame-
ters in space weather study and forecasting [21]. The estimation
of the vertical plasma drift from ground-based ionosonde mea-
surements in the African sector had been achieved majorly by
either computing the time rate of change of the F2-layer height
of the peak electron density - d(hmF2)/dt, or by that of the vir-
tual height of reflection - d(h′F)/dt [13, 22, 23, 24]. The limita-
tion inherent in the description of Vp using ground-based mea-
surement is well documented in [12]. Consequently, a review
of both the quantitative and qualitative characteristics of pre-
vious works done on ionospheric drift pattern in the equatorial
African sector will add to our understanding on its morphology
when compared with other sectors of the world. From this point
forward, all observations reported are in the equatorial African
sector, except otherwise specified.

2. Variations in drift pattern obtained from Ground-based
ionosonde/digisonde real height and virtual height mea-
surements

Observations involving inferring vertical plasma drift from
both the height of the peak electron density (hmF2) and vir-
tual height of the F-layer (h′F) methods are well established.
Argument on the best V p inferring parameter between the two
(h′F and hmF2) is a continuous scientific debate. However,
works that describe both methods in a single paper are scarce,
even from other sectors. [15] describes the morphology of
V p obtained from each method of measurement (d(hmF2)/dt)
and d(h′F)/dt) using digisonde data obtained from Ilorin (Geo-
graphic 8.5◦N, 4.5◦E) in the West African region during a year
of low sunspot activity. For better interpretation, the result was
compared with those obtained from ISR observations (which
serves as the reference drift condition) spanning the same study
period. They reported a PRE highest magnitude around 19 LT
for the entire seasons with hmF2-Vp while that of h′F−V p also
recorded the maximum at 19 LT (except for December solstice
and September equinox, which peaked at 18 LT). The nighttime
downward reversals peak values range from −2 to −14 m/s and
−4 to −14 m/s respectively for the h′F−V p and hmF2−V p ob-
servations. Further, the PRE peak magnitude across the entire
seasons ranges from 4−14, 3−14 and 2−14 m/s respectively for
the ISR-Vp, hmF2-Vp and h′F − V p. A correlation percentage
of above 83% was recorded for the ISR-Vp versus hmF2-Vp
and ISR-Vp versus h′F −V p pairs of observations between 16-
20LT during equinoxes, but lower for solstices (¡ 40%).

Table 1 depicts the intra-hour bin time correlation values
for the ground-based ionosonde versus ISR observations re-
vealing the correlation magnitudes (R) expressed in percent-
age, between the pairs for different time intervals. While the
PRE magnitude of h′F − V p compares well with ISR-Vp dur-
ing equinoxes, that of hmF2-Vp is equitable to ISR-Vp during
solstices. Bearing in mind that both methodologies are gov-
erned by the same mechanism at night, it was concluded that
any of the two can be used as long as the 300 km threshold
magnitude condition suggested by Bertoni [25] and [26] is ful-
filled, else chemical modification may be necessary. See also
[27] for more discussion on this condition.

3. Seasonal variations in the PRE peak magnitude across
equatorial stations in Africa and comparison with other
sectors.

A summary of the evening-time maximum PRE magnitude
of the vertical plasma drift velocity across various stations in
Africa (and other sectors), including the type of methodology
involved in inferring the drift, as well as solar activity condi-
tions are presented in Table 2. The Table revealed that during
the combined magnetic disturbed and quiet conditions in the
African region, the maximum PRE magnitude for June solstice,
December solstice, and Equinox respectively generally spans
around 7.6-12.0 m/s, 8.0-15.2 m/s and 8.0-20.0 m/s (from the
PRE magnitudes presented by [14, 15, 28]). It was observed
that the maximum peak limit for each of these seasons during

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B. O. Adebesin et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 54–58 56

Table 1: Seasonal correlation coefficient (R) between ISR-Vp versus h′F − V p and ISR-Vp versus hmF2-Vp for different nighttime interval periods (** are periods
without data for the ISR observation)

Time interval Parameter Mar. equinox Sept. Equinox Jun. Solstice Dec. Solstice
16-19 LT ISR-Vp vs h′F − V p 83% ** 99% 33%

ISR-Vp vs hmF2-Vp 99% ** 78% 88%
19-21 LT ISR-Vp vs h′F − V p 88% 87% 68% 93%

ISR-Vp vs hmF2-Vp 94% 90% 86% 99%
21-06 LT ISR-Vp vs h′F − V p 67% 53% 87% 76%

ISR-Vp vs hmF2-Vp 72% 29% 82% 58%

this condition of combined quiet and disturbed magnetic con-
dition (12, 15, and 20 m/s) can be boosted either during only
magnetic disturbed or quiet condition as shown from the PRE
peak values reported by [10, 29, 30]. Besides, PRE peak values
are mostly higher during magnetic quiet period relative to dis-
turbed activities. [31] had submitted that quiet magnetic activ-
ities compare reasonably with the thremospheric ground state
owning to small rate of atomic oxygen (O+) during the time.
The separate magnetic quiet or disturbed during June solstice
is associated with high PRE peak values comparable to the val-
ues during equinoxes (i.e., [31]). Further, PRE peak values are
lesser during low solar activities when compared with high so-
lar activity magnitudes, establishing solar dependence of PRE.

This study also revealed that on the average, the PRE peak
value obtained from h′F is higher than that inferred from hmF2
for the entire seasons from the work of [15]. This higher value
associated with PRE obtained from h′F measurements may be
connected to the disappearance of both the D- and E-layer of
the ionospheric region at night, thereby leaving the F-layer ac-
tive. During this period, the F-layer bottomside time rate of
change is more accurate. Conversely for the F-layer peak height
(hmF2), the exact height may not be obtained accurately own-
ing to merging of all layers during its measurement.

It has been observed by [18] that PRE peak magnitude in the
American region is higher than those obtained from other sec-
tors including the African sector. This statement was confirmed
from Table 2. The Table showed that the PRE peak magni-
tude during the equinoxes is higher in the American sector in
comparison to the African region (with the exception of the one
by [15]; using ISR observations during low sunspot condition).
The situation is same for the December solstice period. It is also
worth noting that the evening time PRE peak presents inverse
linear relationship with the electron ionization gradient param-
eter defined by the height rate of change of the F2-layer peak
electron density, dN/dh [35].

4. Measuring the Electrojet current from ground-based
vertical drift measurements

Of the diverse relevance of the equatorial vertical plasma
drift velocities, its practical relation to physical events like the
equatorial ionization anomaly, fountain effect, and Spread-F are
outstanding as these phenomena can alter the reliability of com-
munication and navigation systems. The equatorial Spread-
F phenomena originates within the E-layer current system, in

form of an intense ionospheric daytime eastward current, and
narrowed within 3◦ dip latitude; often referred to as the equa-
torial electrojet (EEJ). Several studies have been done on the
electrojet strength using different approaches, methodologies,
and tools. The electrojet current is triggered by local intensi-
fied ionospheric currents as well as physical structures flowing
at the dip equator with high current strengths at daytime pe-
riod leading to variation in solar quiet (Sq) signature. While
the relationship between the measurement of the difference be-
tween the horizontal magnetic field component at an equatorial
and an off-equatorial station, at daytime, had been used to ob-
tain the equatorial vertical plasma drift [36], the quantification
of the daytime EEJ current with the plasma drift in the Ameri-
can and Indian longitudes had also been established [7, 36, 37].
While [38] and [39] had presented novel observation of the EEJ
current in the African sector, the relationship between electro-
jet current and the E x B drift were not considered. Based on
the authenticated outcome of E x B drift velocities - EEJ rela-
tionship around daytime hours obtained by [40] and [7] for the
American and Indian sectors respectively, [24] attempted same
in the African region, using data from Ilorin, being the first of
such study in the African sector.

MAGDAS and ionosonde inferred measurements at Ilorin
were used during solar minima year. The results obtained re-
vealed that a maximum morning time representative param-
eter defined by the expression Ew = [d(∆H)/dt]max at day-
time, representing the east-west electric field in electrojet cur-
rent matches considerably with the E × B drift, and therefore
can serve as a representation/proxy parameter in depicting the
magnitude of the vertical drift in the morning hour. The linear
correlation between the two parameters (Ew and plasma drift) is
0.94 and observed during low solar activity. [7] recorded a cor-
relation coefficient of 0.66 for a high solar activity condition in
the Indian sector, while [36] reported a correlation value of 0.87
at the American sector. The good relationship between the two
parameters is because an increase in the Ew magnitude implies
an intensification of the EIA, which subsequently reduces the
plasma density around the equator; thereby rapidly increasing
the plasma density along the crest regions. The plasma den-
sity reduction over the magnetic equator further diminishes the
effect of ion drag on neutrals, thus enhancing the zonal wind
prior to sunset. These processes create a large eastward electric
field raising the amplitude of the post-sunset E × B drift of the
F-layer.

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B. O. Adebesin et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 54–58 57

Table 2: Seasonal PRE peak magnitudes in the African and other sectors

Source
Data Instrument
/ Source

Sector/Station Solar activity
Equinox (m/s) Solstices (m/s)

March September June December

[28]
Ionosonde /
h′F median

Africa (Korhogo) Descending
phase of solar
cycle (SC) 22

12.6 8.7 8.0 12.0
Africa (Ouagadougou) 15.2 11.0 7.4 10.9

Africa (Dakar) 10.0 7.7 7.9 8.0
[29] Ionosonde/ h′F mean Africa Moderate 40.1 30.1 31.2 30.2

[14]
Ionosonde /
h′F mean

Africa (Ouagadougou) SC 20. 1966-
1976

18.6 16.3 10.7 10.6

Africa (Ouagadougou) SC 21. 1976-
1986

19.5 19.0 11.3 13.2

Africa (Ouagadougou) SC 22. 1986-
1996

19.1 18.0 10.1 14.7

Africa (Ouagadougou) 1966-1998 18.1 15.8 12.1 12.9

[15]
Digisonde / h′F mean Africa (Ilorin) Low 12.7 12.8 2.2 13.3

Digisonde / hmF2 mean Africa (Ilorin) Low 9.2 3.8 0.3 8.0
[11] Ionosonde / hmF2 mean Africa (Ouagadougou) High 17.1b 16.1 14.1
[30] Ionosonde / h′F2 median Africa (Ibadan) High 33.6b 26.9 26.7

[10] Ionosonde / h′F mean
Africa (Ibadan) Quiet High 33.0 28.0 42.0 28.0

Africa (Ibadan) Disturbed Low a 18.0 23.0 23.0
[15] ISR Peruvian (Jicamarca) Low 13.6 9.6 a 6.4
[32] ISR Peruvian (Jicamarca) High 32.0b 14.0 28.1
[16] ISR and AE-E Satellite Peruvian (Jicamarca) 1968-1992,

1977-1979
45.0b 35.0 38.1

[33] HF Sounder Indian (Kodaikanal) High 26.4b 25.0 20.8
[34] VHF Radar Peruvian (Jicamarca) High 50.0b 17.0 38.1

ainsignificant magnitude
bEquinoctial average values

5. Conclusion and Recommendation

A review of the morphology of vertical plasma drift in
the African region was presented. Reviewed literatures cap-
turing drift velocities in the West-African region including
Ibadan (Nigeria), Ilorin (Nigeria), Ouagadougou (Burkina
Faso), Dakar (Senegal), and Korhogo (Cote d’Ivorie), were
used, and compared with other observations especially during
the PRE period in the Peruvian/American sector. The obser-
vations include periods of high-, moderate-, and low-solar ac-
tivities, as well as 11-year and descending phases of solar ac-
tivities. It also includes different magnetic activity conditions.
The various observations point to the fact that the magnitude
of the drift pattern obtained from ground-based ionosondes in
the African region is lesser than those obtained from other sec-
tors. However, most ionospheric satellite observational stud-
ies have revealed exciting longitudinal pattern in equatorial re-
gion electrodynamics. The peak of these variations in terms
of irregularities is severe in the African sector owning to the
better alignment between the geomagnetic and geodetic equa-
tors, whereas in the American/Peruvian sector, the geomagnetic
equator dips, presenting fairly huge disparity between the geo-
magnetic and geodetic equator. This could have been responsi-
ble for the large excursion in the PRE. It has been observed by
Fejer et al. (2008) that PRE peak magnitude in the American re-
gion is higher than those obtained from other sectors including

the African sector. This statement was confirmed from Table
2. The Table showed that the PRE peak magnitude during the
equinoxes is higher in the American sector in comparison to
the African region (with the exception of the one by Adebesin
et al., 2015b; using ISR observations during low sunspot con-
dition). The situation is same for the December solstice period.
drift pattern observed with the Jicamarca ISR drift observation
in relation to those inferred from ionosonde measurements in
the African region. Consequently, having an ISR equipment in
Africa will further increase our understanding of the drift mor-
phology in explaining the uniqueness of ionospheric irregulari-
ties in the African sector as well as the possible mechanism that
initiates such unique structures.

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