J. Nig. Soc. Phys. Sci. 4 (2022) 620

Journal of the
Nigerian Society

of Physical
Sciences

A Study of the Relationship Between Southward BZ > −10 nT
and Storm Time Disturbance Index During Solar Cycle 23

T. W. Davida,b,∗, B. J. Adekoyaa, C. M. Michaelb, S. A. Adekoyaa, O. A. Adenugaa, S. O. Kareemc,
H. T. Oladunjoyea, A. E. Ajetunmobia, O. T. Williamsa, D. T. Ogundelea

aDepartment of Physics, Olabisi Onabanjo University, Ago-Iwoye, Nigeria
bDepartment of Physics and Astronomy, University of Leicester, Leicester, UK

cDepartment of Physics, Mountain Top University, Prayer City, Nigeria

Abstract

Magnetic reconnection can be used for studying the geoeffective processes in the coupled Sun–Solar wind – Magnetosphere dynamics leading to
geomagnetic disturbance. In this study, 1-hour resolution solar wind plasma parameters from OMNIweb were used to investigate the relationship
between moderate southward interplanetary magnetic field, IMF-Bz (i.e., Bz > −10 nT) and geomagnetic storm time disturbance, Dst , during the
ascending, maximum and descending phases of solar cycle 23. Occurrences of different classes of geomagnetic storms during moderate southward
Bz are reported. The occurrence of weak and moderate geomagnetic storms is more predominant during maximum solar activity than intense and
super intense storms. It was found that 10.11 % (181) of all the classes of the storm were intense, and 0.17 % (3) were super intense storms.
Furthermore, it was found that 4 (2.2 %) out of the 181 intense storms were caused by southward Bz > −10 nT which were associated with the
complex structure due to the high-speed solar wind stream and corotating interacting region. In such a complex structure and Bz > −10 nT, we
observed that an intense geomagnetic storm rarely occurs and if it does, would be predominant around solar maximum. It was found that long-
duration (∆t > 6 hrs) of southward Bz (i.e., −10 nT < Bz ≤−3.6 nT ) can also lead to an intense geomagnetic storm during the solar maximum and
descending phase (moderate solar activity) of a solar cycle. The complex structure of intense geomagnetic storms associated with the Bz > −10
nT is rare and possesses a special configuration of magnetic field and solar wind parameters structures which are CIR manifestations.

DOI:10.46481/jnsps.2022.620

Keywords: Magnetic reconnection, Dst , intense geomagnetic storm, moderate southward IMF- Bz, solar maximum, solar minimum, solar cycle.

Article History :
Received: 28 January 2022
Received in revised form: 15 September 2022
Accepted for publication: 16 September 2022
Published: 11 November 2022

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

1. Introduction

The Earth’s near-space environment is not surrounded
by vacuum, but by a highly dynamic and coupled system of
plasmas and magnetic fields, whose complex interplay with

∗Corresponding author tel. no: +2348055268531
Email address: david.testimony@yahoo.com;

david.timothy@oouagoiwoye.edu.ng (T. W. David )

sunspot number, coronal mass ejections (CMEs) and solar
flares eruption could cause a time-varying condition that
constitutes the subject of space weather [1-3]. The solar wind,
consisting mainly of protons and electrons, originates from the
sun and streams radially into space, pervading the solar system.
The Sun’s Magnetic field flows with these particles. The
magnetic field of the Earth poses an obstacle to this oncoming
flow of plasma from the Sun and thereby carves out the mag-
netosphere. The solar wind interacts with the Earth’s magnetic

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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 2

field and reconfigures its dipolar shape by compressing it on the
sunward side while stretching it to a tail-like shape on the night
side. During an anti-parallel orientation of the interplanetary
magnetic field (IMF) to the geomagnetic field lines, solar
wind energy, momentum and mass could be transferred into
the Earth’s magnetosphere, thereby influencing its dynamics
and geomagnetic storms. Landmark studies [3-9] have shown
that Bz, which is the north-south direction component of the
IMF, is a good index that plays a vital role in the reconnection
between the solar and terrestrial magnetic fields, leading to
additional energy in the magnetospheric flux tube and the
geoeffectiveness of geomagnetic storms. A southward Bz,
fluctuating in the corotating interacting regions (CIRs), is a
prerequisite for magnetic reconnection leading to the devel-
opment of geomagnetic storms [4] whereas, a northward Bz
rarely leads to storms except during extremely high solar wind
speed [5, 10]. On the other hand, the storm time disturbance
index, Dst, has been extensively used to measure the degree
of moderate magnetic perturbation experienced by the dipolar
field of the terrestrial planet [11]. The Dst index represents the
magnetic depletion resulting from the westward drift of the
ring current formed by ions and electron energy which would
be detectable by an appropriate ground-based instrument [10].

The interplanetary origin of intense geomagnetic storms
has been widely studied [3,12-21]. Many have explained the
interrelation between the southward interplanetary magnetic
field and the depletion in the D st index leading to intense
magnetic storms. They recognised that the orientation of the
interplanetary magnetic field played a great part in the strength
of the main phase of geomagnetic storms. Gonzalez et al.
[22, 23] were among the leading research work on the relation-
ship between the interplanetary magnetic field and the resulting
ring current system. Meanwhile, Gonzalez and Tsurutani [24]
and Gonzalez et al. [15] had drawn an inference that Bz and the
geomagnetic storm’s development are interrelated, where they
observed that the magnitude of the southward Bz leading to an
intense storm is ≤−10 nT and over a period exceeding 3 hours.
This intense nature of Bz appears to originate from the different
interplanetary and solar wind structures and the interaction
between them. Also, it was established that the Poynting flux
from the interplanetary medium is a driver of the main phase of
storm development in the magnetosphere and determines the
strength and magnitude of the storm [3, 15, 21].

Several studies [25-28] while studying the ring current,
tried to quantify the energy deposited in the magnetosphere
by the stream of charged particle/solar wind, coupled with
the solar magnetic field it drags. They also looked at the
magnetospheric dissipation rate of this energy. The stored
magnetosheath energy (i.e., pressure gradient force and mag-
netic tension force) realigns the magnetic field, the energy
along the field lines causes the westward ring current of the
plasma under the influence of gradient and curvature drift
[29]. The main phase of geomagnetic storms results from ring
current development, in which energisation depends on storm
time disturbance index, Dst , solar wind speed, ram pressure

and Bz component of the IMF [3, 26, 30]. The drivers of events
with large geomagnetic storms are described to be of complex
interplay [14]. The complexity includes several steps at the
main phase of the storm, the phase of the solar cycle, the oc-
currence of shock at the sheath, the speed of the interplanetary
coronal mass ejection (ICME), etc. Borovsky and Denton [16]
explained that while coronal mass ejection-driven storms are
inimical to the electrodynamics system on Earth, storms driven
by the corotating interacting region (CIR) affect assets in the
space region. Many of the CIRs have transient properties that
are similar to that of ICMEs and contain small ICME-like
transient, that is, the solar wind properties feature many ICME
signatures, such as smooth/coherent field rotation and enhanced
fields, but that is significantly reduced in duration (a few hours
on average) than typical large-scale ICMEs [31, 32, 33]. En-
trainment of such transients, when they have southward fields,
may enhance the geoeffectiveness of a CIR. The interaction
between such transients may enhance the geoeffectiveness of
a CIR, especially, when they have moderate southward fields
[32]. Adekoya and Chukwuma [3] reported that these types of
storms may be originated from small explosions that are more
intense than the CMEs-caused storms. And were caused by the
interactions between a shock driven by the symmetric transient
disturbances and the corotating stream [34]. Gonzalez et al.
[15] added Bs structures (southward magnetic field) to the list
of causative elements of events with large geomagnetic storms.
They pointed out that the long duration of the enhanced Bs
would offer support for a magnetic cloud to produce a large
magnetic storm. Kumar et al. [35] observed that the magnitude
and duration of the southward Bz are fundamental in the
occurrence and development of the geomagnetic storm. In
all, none of these investigations has been able to categorically
report or linked the geoeffectiveness of an intense magnetic
storm to a lower magnitude of southward Bz.

Similarly, studies exist on the interplay of solar wind
parameters and geomagnetic activity during the solar cycle 24.
For example, Rathore [36] in a case study of a geomagnetic
storm during the solar cycle 24 shows that IMF parameters
including the Bz component are linked to geomagnetic storm
given the increase in the value of Bz at the storm commence-
ment. This is relatable to a previous observation of a high Bz
value by Rawat et al. [37] during several intense geomagnetic
storms in solar cycles 23 and 24. However, the Bz cannot
be isolated as the main driver following Rathore [36], since
the value of other solar wind parameters such as solar wind
speed and plasma temperature were equally large during the
same period of the storm commencement. Pokharia et al.
[38] suggest that combining solar wind speed and Bz is a
better approach to depicting the production of geomagnetic
storms than considering both parameters separately. The
foregoing shows Bz is a relevant interplanetary condition for
geomagnetic storm commencement, which is in tandem with
the requirements suggested in Gonzalez and Tsurutani [24] for
intense geomagnetic activity.

This work looks at the statistical analysis of the occurrence
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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 3

of geomagnetic storms associated with the IMF-Bz as well
as the geoeffectiveness of Bz > −10 nT. In comparison to
previous works, a complete solar cycle will be investigated in
this study, which will allow every phase of the solar cycle to
be investigated. Previous studies [22, 24, 39] had argued that
an intense storm can only occur when the Bz component of
the IMF stays at least three hours in the southward direction
with a threshold of Bz ≤ −10 nT. Attention is restricted in the
present study to events during a southward turning of Bz such
that Bz > −10 nT. The term “moderate southward Bz ” in this
work refers to the range of Bz component of the IMF such
that −10 nT < Bz ≤ −5 nT. Solar cycle 23 has been chosen
not for any special reason, but it is worth mentioning that it
is the longest solar cycle in history. Figure 1 shows the time
series of the sunspot number enclosing the period of solar cycle
23, where the peak (solar maximum) shows a double hump
between the year 2000 - 2003 and a solar minimum in 2008
ending the cycle. The black line in Figure 1 is the daily total
while the red line is the yearly smoothed sunspot numbers. The
minimum and maximum sunspot numbers during the cycle are
respectively about 5 and 180.

Figure 1: The time series sunspot number enclosing the period of solar cycle
23.

2. Data source and method

The period under investigation is the solar cycle 23, with
a time interval from August 1996 to December 2008. For this
period, the solar wind plasma and geomagnetic parameters data
employed in this study consist of hourly values of the Bz com-
ponent of the Interplanetary Magnetic Field (Bz, nT), the storm
time disturbance index (Dst index, nT), plasma flow speed (Vsw,
km/s), Proton density (ρ, n/cm3) and corresponding plasma
temperature (T, K). These interplanetary and hourly geomag-
netic data are obtained from the Space Physics Data Facility
(SPDF) OMNIWEB website (http://omniweb.gsfc.nasa.gov/).
This research is focused on a statistical analysis of the differ-
ent classes of geomagnetic storms indicated by the storm time
disturbance index as a result of moderate southward Bz at the
nose of the Earth’s magnetopause. The geomagnetic storms

classifications are: weak (−30 nT ≤ Dst > −50 nT), moder-
ate (−50 nT ≥ Dst > −100), intense (−250 nT < Dst ≤ −100
nT), and super intense (Dst < −250 nT), while (Dst ≥ −30
nT) is regarded as period of quiet activity [39, 40, 41]. In this
study, the period at which the OMNI data set of solar wind
plasma parameters at the bow shock region of the Earth records
−10nT < Bz ≤ −5 nT is taken to be a moderate southward Bz
event. There were 1790 geomagnetic events during the solar
cycle 23, and the frequency of the hourly values is shown in
Table 1.

3. Result and Discussion

3.1. Hourly analysis of events

Table 2 indicates the hourly distribution (in UT) of geomag-
netic storms as indicated by the Dst index in Table 1. The data
in Table 2 shows the frequency of the hourly values of the 1790
events during the solar cycle 23 and its occurrence, which is
the frequency of a particular class at a particular hour divided
by the total frequency for that hour (see equation (1)). It is
clearly shown that weak geomagnetic storms dominate every
hour throughout the period under investigation, while the super
intense class is a rare phenomenon.

Figure 2 shows the bar chart of the temporal distribution
of events with weak, moderate, intense and super intense geo-
magnetic storms caused by moderate southward Bz during the
period under investigation. The hourly occurrence of the dif-
ferent classes of storms is calculated as the percentage ratio of
the number of events in each class to the total events caused by
moderate Bz at the particular hour (see Table 2).

DstOccurrence =
Total of each storm category

Total storm event
×100%.(1)

The blue, green, yellow, and red colours represent the per-
centage occurrence of the weak, moderate, intense and super
intense geomagnetic storms, respectively. As more field lines
are opened due to dayside re-connection, the open field lines
stretch in an anti-sun ward direction and the solar wind energy
is transported into the magnetosphere, where it is stored in
the magnetotail [42]. The eventual release of the energy as a
result of reconnection in the neutral sheet gives rise to varying
degrees of storm categories. It could be seen from Figure 2 that
apart from the super intense geomagnetic storms that rarely
occur, all other classes of geomagnetic storms are general
phenomena at all times. Furthermore, Figure 2 indicates that
though moderate geomagnetic storms have no distinct peak,
it attains a maximum occurrence of about 49 % during the
moderate southward Bz conditions. However, when the class
of geomagnetic storms is above moderate, the occurrence peak

Table 1: Frequency of different range of classes of Dst corresponding to mod-
erate southward Bz 165 during the solar cycle 23.

Dst Weak Moderate Intense Super Intense
Frequency 878 728 181 3

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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 4

Table 2: Frequency of hourly peak values and percentage occurrence for different classes of geomagnetic storms during solar cycle 23.

UT Frequency of Dst Dst Occurrence (%)
Weak Moderate Intense Super Intense Weak Moderate Intense Super Intense

0 42 28 7 0 54.55 36.36 9.09 0.00
1 39 28 7 0 52.7 37.84 9.46 0.00
2 29 34 7 0 41.43 48.57 10 0.00
3 30 31 7 0 44.12 45.59 10.29 0.00
4 32 30 7 0 46.38 43.48 10.14 0.00
5 34 28 8 0 48.57 40 11.43 0.00
6 33 30 13 0 43.42 39.47 17.11 0.00
7 34 33 5 0 47.22 45.83 6.94 0.00
8 48 34 5 0 55.17 39.08 5.75 0.00
9 31 24 5 0 51.67 40 8.33 0.00

10 37 37 5 0 46.84 46.84 6.33 0.00
11 29 29 6 0 45.31 45.31 9.38 0.00
12 45 37 8 0 50 41.11 8.89 0.00
13 45 28 8 0 55.56 34.57 9.88 0.00
14 45 34 8 0 51.72 39.08 9.2 0.00
15 33 26 3 0 53.23 41.94 4.84 0.00
16 38 30 4 0 52.78 41.67 5.56 0.00
17 33 31 4 0 48.53 45.59 5.88 0.00
18 36 38 7 0 44.44 46.91 8.64 0.00
19 39 27 14 0 48.75 33.75 17.5 0.00
20 33 31 14 0 42.31 39.74 17.95 0.00
21 28 24 13 2 41.79 35.82 19.4 2.99
22 47 30 9 0 54.65 34.88 10.47 0.00
23 38 26 7 1 52.78 36.11 9.72 1.39

Total 878 728 181 3

Figure 2: The hourly occurrence values for different classes of geomagnetic
storms associated with southward moderate Bz during solar cycle 23.

reduces below 20 %. A clear observation of Figure 2 shows
a higher occurrence of intense storms during the night sector
with respect to the universal time. Around 19 − 23 UT and
00 − 06 UT, the occurrence of an intense storm is higher in

comparison to during the period 08 − 18 UT. Less than 0.2 %
of the events are super intense storms, and about two-thirds are
driven by midnight mechanisms.

3.2. Yearly analysis of events
Table 3 indicates how the total number of 1790 events

indicated by the D st index in Table 1, is distributed across the
years in solar cycle 23. As stated earlier, frequency is the num-
ber of events for the different classes of geomagnetic storms
(measured by the Dst index) according to the southward Bz due
to the magnetic reconnection. The occurrence on the other hand
is the frequency of a particular class in a particular year divided
by the total frequency for that year. It can be seen that the
maximum frequency of all the classes of geomagnetic storms
is during solar maximum (see Figure 1). In all, the percentage
occurrence of intense and super intense storms peaked during
solar maximum, while the occurrence of weak geomagnetic
storms was dominant during solar minimum. This is partly
because the sunspot number being at maximum, increases solar
activity level and provides an opportunity for geoeffectiveness.
The occurrence of moderate geomagnetic storms was higher
at the declining phase of the solar cycle, which occurs at solar
moderate periods, meanwhile, the lowest occurrence rate was
at solar minimum. This result was congruent with the report

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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 5

of Echer et al. [10] who reported the highest rate of moderate
storm occurrence in the declining phase of the solar cycle 23.
The moderate storms were dominantly driven by CIRs and
high-speed streams (HSSs), but with variable contributions
from ICMEs, their shocks (sheaths), and combined occurrence
within the solar cycle [10, 21, 43]. Whereas, the weak class
of geomagnetic storm’s highest occurrence was found at the
solar minimum, lowest during the solar maximum periods,
the ascending and descending phases of the solar cycle shows
non-linear variations.

3.3. Analysis of the southward Bz > −10 nT and solar wind
conditions leading to an intense geomagnetic storm

The intense geomagnetic storms (Dst ≤ −100 nT) are
caused by the intense southwardly directed IMF-Bz of magni-
tude > 10 nT, with a duration greater than 3 hours [22, 24, 39].
However, not all intense storms are associated with the intense
nature of Bz [3, 10]. That is, there are intense storms that are
likely caused by moderate southward Bz, (−10 nT < Bz ≤ −5
nT) whose complex solar wind and interplanetary interplay
may be different from other storms [44, 45]. Kumar et al. [35]
observed that the magnitude and duration of the southward Bz
are fundamental in the occurrence and development of geomag-
netic storms. Therefore, onward in this section, the interplay
of the intense storms associated with the moderate southward
B z (−10 nT < Bz ≤ −5 nT) turning for long-duration of three
consecutive hours and solar wind conditions during the solar
cycle 23 is presented. This event is a rare occurrence and only
occurred during the solar maximum and descending phase
(moderate solar activity) of the solar cycle 23. Its properties
and geoeffectiveness as related to the moderate southward Bz
are explained below.

Figure 3 shows the interplanetary and solar wind plasma
characteristics during the geomagnetic storm event of 25 − 27
September 2001, representing the moderate southward Bz event
during the solar maximum phase of the solar cycle 23. The
region within the two red vertical lines presents the structure
of the solar wind characteristics associated with the moderate
southward Bz . The duration of the moderate southward Bz turn-
ing is represented with ∆t, that is, the changes in time at the first
and second vertical lines. Looking at Figure 3, the peak value of
southward Bz was -3.6 nT which is contrary to the earlier sug-
gested magnitude of the moderate southward Bz [19, 22]. From
the view of the solar wind plasma structure associated with this
southward Bz , the intense signature of Dst = −102 nT corre-
sponds with the respective high-scale variations of the plasma
density, ρ is 39.2 N/cm3, plasma temperature, T is 706094 K,
plasma flow speed, Vsw is 675 km/s above the typical value of
450 km/s and plasma Beta, β, is 4.88. Choi et al. [7] referred
to such an event with a duration ≥ 3 hrs as long-weak Bz and
has characteristics of HSSs/CIRs driven intense storms. The
event properties emanated from coronal holes and are associ-
ated with stream interaction regions [5] and are identified as
complex ejecta [3, 45].

In a similar configuration, the solar wind properties during

Figure 3: Interplanetary and Solar wind plasma parameters of a moderate south-
ward Bz turning caused intense storm during the solar maximum phase of the
solar cycle 23. The shaded region marked the corresponding interplanetary and
geomagnetic profiles associated with the moderate southward Bz. The Septem-
ber 25 − 27, 2001 geomagnetic storm event.

the intense geomagnetic storm of 3 − 5 April 2004 represent
the moderate southward Bz event during the descending phase
of the solar cycle 23 is presented in Figure 4. Looking at this
figure, the intense storm (Dst ≥ -100 nT) originated from the
long-duration (∆ t > 7 hours) moderate southward Bz turning
of magnitude -7.9 nT. The corresponding solar wind parame-
ters suggest that there is a high-scale variation of flow speed
with a peak magnitude of 504 km/s below the typical value
of 450 km/s. The plasma flow speed increases from 423 km/s
around 1300 UT on April 3 to a peak magnitude of 504 km/s
around 0000 UT on April 4 corresponding to the periods of the
moderate southward orientation of the Bz. Contrary to the high
plasma temperature of the events during the solar maximum
phase of the solar cycle, the plasma temperature during the de-
scending phase was reduced (the peak plasma temperature at
the confined period of the moderate southward Bz was 121,155
K) below the typical of 400,000 K [41]. Corresponding to the
moderate southward directed Bz are high proton density, ρ with
a peak value of 24.5 N/cm3 and high plasma Beta, β, with a
peak value of 3.46. The characteristic signature of this intense
storm is depression in the magnitude of the Dst resulting from
the westward ring current associated with the moderate south-
ward directed Bz system encircling the Earth. Following the
sudden storm commencement of the storm, the Dst decreases to
a minimum value of -117 nT at exactly 0000 UT on April 4.

During the window of the southward directed Bz, the char-
acteristic of this complex ejecta-driven storm during the solar

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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 6

Table 3: Frequency of yearly peak values and percentage occurrence for different classes of Dst during solar cycle 23.

Year Frequency of Dst Dst Occurrence (%)
Weak Moderate Intense Super Intense Weak Moderate Intense Super Intense

1996 13 3 1 0 76.47 17.65 5.88 0.00
1997 52 66 5 0 42.28 53.66 4.07 0.00
1998 120 61 22 0 59.11 30.05 10.84 0.00
1999 100 77 11 0 53.19 40.96 5.85 0.00
2000 173 105 26 1 56.72 34.43 8.52 0.33
2001 118 119 57 2 39.86 40.2 19.26 0.68
2002 50 97 38 0 27.03 52.43 20.54 0.00
2003 136 103 2 0 56.43 42.74 0.83 0.00
2004 20 25 10 0 36.36 45.45 18.18 0.00
2004 40 30 2 0 55.56 41.67 2.78 0.00
2005 26 30 7 0 41.27 47.62 11.11 0.00
2006 19 11 0 0 63.33 36.67 0.0 0.00
2007 11 1 0 0 91.67 8.33 0.0 0.00
2008 878 728 180 3

Figure 4: Same as Figure 3, but during the descending phase of the solar cycle
23. The April 3 − 5, 2004 geomagnetic storm event.

maximum and descending phase are presented in Table 4. In
Table 4, the peak value of the solar wind parameters and mag-
netic index associated with the moderate southward directed Bz
were highlighted. Four (4) intense geomagnetic storm events
were identified to be related to the Bz > −10 nT, three (3)
were during the solar maximum and one during the descending
phase (around moderate solar activity periods) of the solar
cycle 23. This rare occurrence event was not found during
the ascending phase of the solar cycle 23, which indicates the

possibility of not having such an event during the ascending
phase of a solar cycle. The occurrence rate of this moderate
southward Bz -driven storm is very rare. The only condition
for an increase in the occurrence of the moderate southward
Bz is when the geomagnetic storm classification is moderate
(i.e. −100 nT < Dst ≤ −50 nT) and during solar minimum
[5, 32]. From Table 4, one can see that the peak response of
southward Bz during the storm of 25 - 27 Sept. 2001 was -3.6
nT, which is above the typical value for moderate southward
Bz of (−10nT < Bz ≤ −5 nT). Aside from this low-weak Bz,
the parameters show high- scale variables compared to other
storms. Choi et al. [7] have suggested that this weakly event
of southward Bz should be considered significant from the
viewpoint of their geoeffectiveness. Therefore, the occurrence
rate may be too low to be considered, but the solar wind char-
acteristics and geoeffectiveness of the storm compared to the
other storms with a higher magnitude of southward Bz should
be classified as moderate southward Bz-driven intense storm.
The sudden increase and high flow speed and proton density
of the plasma indicate that the geoeffectiveness of stream
interacting region/high-speed streams can be explained by
solar wind properties. Therefore, either low-weak southward
Bz or moderate southward Bz-related intense storms should
be considered as geoeffective significant events that can affect
space-based and ground-based technology as much as those of
the intense southward Bz signature.

4. Summary and Conclusions

We have carried out a statistical analysis of the occurrence
of geomagnetic storms associated with the southward interplan-
etary magnetic field in the range of Bz ¿ -10 nT, using the com-
plete solar cycle 23 data. The complex structure of intense
geomagnetic storms associated with the Bz > -10 nT is rare

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T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 7

Table 4: The characteristics of the solar wind parameters associated with the southward directed Bz ( > −10 nT) with long-duration of intense geomagnetic storm
during solar cycle 23. The peak response of the parameter during the southward Bz turning was highlighted.

S/N YEAR DOY Bz (nT) ∆t (hr) T (K) Vsw (km/s) ρ (N/cm3) β Dst (nT)
1 2001 269 -3.6 > 8 706094 675 39.2 4.88 -104
2 2002 233 -9.2 > 12 35238 495 7 0.88 -106
3 2002 325 9.4 > 6 478599 728 54.8 1.26 -128
4 2004 95 -7.9 > 7 121155 504 24.5 3.46 -117

and possesses a special configuration of magnetic field and so-
lar wind parameters structures which are HSSs/CIR manifesta-
tions. It was found that 10.11 % (181) of all the classes of the
storm were intense, 0.17 % (3) were super intense storms, 40.67
% (728) were moderate geomagnetic storms while 49.05 %
(878) were weak storms. Furthermore, it was found that only 4
(2.2 %) out of the 181 intense storms were caused by the south-
ward Bz > −10 nT which were associated with the complex
structure due to the High-Speed solar wind stream and corotat-
ing interacting region. The results are further summarised as
follows:

• The complex structure and Bz > −10 nT event of
the intense geomagnetic storm is a rare occurrence and
only occurred during the solar maximum and descending
phase (moderate solar activity) of the solar cycle 23.

• Sometimes the southward turning of Bz > −5 nT with a
complex configuration of solar wind characteristics may
lead to an intense geomagnetic storm which may oc-
cur during solar maximum. Therefore, the geoeffective-
ness of an intense storm associated with the southward
Bz > −10 nT is controlled by the solar wind character-
istics (i.e., high plasma flow speed, high proton density
and complex structure of plasma beta).

• The yearly analysis shows a predominance in the weak
and moderate geomagnetic storms resulting from -10 nT
¡ Bz ≤−5 nT.

• The complex structure associated with the moderate geo-
magnetic storms is more predominance during solar min-
imum.

• The peak occurrence for all classes of geomagnetic
storms, associated with moderate southward Bz, is ob-
served during solar maximum.

• In contrast to previous studies that a 3-hour intense south-
ward Bz is a pre-requisite for an intense geomagnetic
storm, a 3-hour southward Bz > −10 nT with a complex
structure can lead to an intense geomagnetic storm at the
phases of the solar cycle.

• About 75 % of the southward Bz > −10 nT leads to
intense geomagnetic storms occurring at the maximum
phase of the solar cycle.

Acknowledgements

The authors appreciate the staff of Space
Physics Data Facility (SPDF) OMNIWEB (website:
http://omniweb.gsfc.nasa.gov/) for free accessibility of
data. We thank the Olabisi Onabanjo University, Ago-Iwoye,
Nigeria, for creating the enabling environment for this re-
search. The University of Leicester, United Kingdom, is deeply
appreciated for making UoL Spectre available for the analysis.

References

[1] C. G. Falthammar, “Magnetosphere Ionosphere Interactions - Near-Earth
Manifestations of the Plasma Universe”, IEEE Transactions on Plasma
Science 14 (1986) 616.

[2] G. S. Lakhina, S. Alex, & R. Rawat, An Overview of the Magnetosphere,
Substorms and Geomagnetic Storms. Turbulence, Dynamos, Accretion
Disks, Pulsars and Collective Plasma Processes, Astrophysics and Space
Science Proceedings, Springer, Netherland (2008).

[3] B. J. Adekoya & V. U. Chukwuma, “Classification and quan-
tification of solar wind driver gases leading to intense geo-
magnetic storms”, Advances in Space Research 61 (2018) 274.
https://doi.org/10.1016/j.asr.2017.09.036.

[4] B. T. Tsurutani, Ezequiel Echer, Fernando L. Guarnieri & Walter D.
Gonzalez, “The properties of two solar wind high speed streams and
related geomagnetic activity during the declining phase of solar cycle
23” Journal of Atmospheric and Solar-Terrestrial Physics 73 (2011) 164.
https://doi.org/10.1016/j.jastp.2010.04.003.

[5] M. Grandin, Aikio, A. T., & A. Kozlovsky, Properties and geoeffective-
ness of solar wind high-speed streams and stream interaction regions
during solar cycles 23 and 24. Journal of Geophysical Research: Space
Physics 124 (2019) 3871. https://doi.org/10.1029/2018JA026396.

[6] B. S. Rathore, Subhash C. Kaushik, K. A. Firoz, D. C. Gupta, A. K.
Shrivastava, Krishna Kant Parashar & R. M. Bhaduriya, “A Correlative
Study of Geomagnetic Storms Associated with Solar Wind and IMF Fea-
tures During Solar Cycle 23” International Journal of Applied Physics
and Mathematics 1 (2011) 149.

[7] K. -E. Choi, D.-Y. Lee, K.-C. Choi, & J. Kim, Statistical properties and
geoeffectiveness of southward interplanetary magnetic field with empha-
sis on weakly southward Bz events, Journal of Geophysical Research:
Space Physics 122 (2017) 4921. doi:10.1002/2016JA023836.

[8] Y. Kamide & W. Baumjohann, Magnetosphere-Ionosphere coupling,
Springer, Heidelberg, (1993).

[9] W. Baumjohann & R. A. Treumann, Basic Space Plasma Physics, Impe-
rial College Press, (1997).

[10] E. Echer, B. T. Tsurutani & W. D. “Gonzalez, Interplanetary origins of
moderate (−100 nT < Dst ≤ −50 nT) geomagnetic storms during solar
cycle 23 (1996-2008)”, Journal of Geophysical Research - Space Physics
118 (2013) 385. doi: 10.1029/2012JA018086

[11] E. Echer, W. D. Gonzalez & B. T. Tsurutani, “Statistical studies of
geomagnetic storms with peak Dst ≤ −50 nT from 1957 to 2008”,
Journal of Atmospheric and Solar-Terrestrial Physics 73 (2011) 1454.
doi:10.1016/j.jastp.2011.04.021.

[12] Tsurutani, B. T., Gonzalez, W. D., Tang, F., Akasofu, S. -I., & E. J. Smith,
“Origin of interplanetary southward magnetic fields responsible for major

7



T. W. David et al. / J. Nig. Soc. Phys. Sci. 4 (2022) 620 8

magnetic storms near solar maximum (1978-1979)”, Journal of Geophys-
ical Research 93 (1988) 8519.

[13] Y. Kamide, Yokoyama, N., Gonzalez, W., Tsurutani, B. T.,
Daglis, I.A., Brekke, A., & S. Masuda, “Two-step develop-
ment of geomagnetic storms” J. Geophys. Res. 103 (1998) 6917.
https://doi.org/10.1029/97JA03337.

[14] W. D. Gonzalez, B. T. Tsurutani & A. L. Clua De Gonzalez, “The in-
terplanetary causes of geomagnetic storms”, Space Science Review 88
(1999) 529.

[15] W. D. Gonzalez, A. L. Clúa de Gonzalez, J. H. A. Sobral, A. Dal Lago &
L. E. Vieira, “Solar and Interplanetary Causes of Very Intense Geomag-
netic Storms”, Journal of Atmospheric and Solar-Terrestrial Physics 63
(2001) 403.

[16] J. E. Borovsky & M. H. Denton, “Differences between CME-driven
storms and CIR-driven storms”, Journal of Geophysical Research 111
(2006) A07S08

[17] J. Zhang, I. G. Richardson, Webb, D.F., Gopalswamy, N., Huttunen, E.
Kasper, J. C., Nitta, N. V., Poomvises, W., Thompson, B. J., Wu, C.
-C., Yashiro, S. & A. N. Zhukov, “Solar and interplanetary sources of
major geomagnetic storms (Dst ≤ −100 nT) during 1996 - 2005”, Jour-
nal of Geophysical Research 112 (2007) A10102. https://doi.org/10.10
29/2007JA012321.

[18] E. Echer, W. D. Gonzalez, & B. T. Tsurutani, “Interplanetary condi-
tions leading to superintense geomagnetic storms (Dst ≤ −250 nT) dur-
ing solar cycle 23”, Geophysical Research Letter 35 (2008), L06S03.
https://doi.org/10.1029/2007GL031755.

[19] J. A. Hutchinson, D. M. Wright, & S. E. Milan, “Geomagnetic storms
over the last solar cycle: A superposed epoch analysis”, Journal of Geo-
physical Research 116 (2011), A09211, doi:10.1029/2011JA016463.

[20] E. K. J. Kilpua, H. Hietala, D. L. Turner, H. E. J. Koskinen, T.
I. Pulkkinen, J. V. Rodriguez, G. D. Reeves, S. G. Claudepierre,
& H. E. Spence, “Unraveling the drivers of the storm time radi-
ation belt response”, Geophysical Research Letter 42 (2015) 3076.
https://doi.org/10.1002/2015GL063542.

[21] P. I. Reyes, V. A. Pinto, & P. S. Moya, “Geomagnetic storm occurrence
and their relation with solar cycle phases”, Space Weather 19 (2021)
e2021SW002766. https://doi.org/10.1029/2021SW002766.

[22] W. D. Gonzalez, J. A. Joselyn, Y. Kamide, H. W. Kroehl, G. Ros-
toker, B. T. Tsurutani, & V. M. Vasyliunas, “What is a geomag-
netic storm?” Journal of Geophysical Research 99 (1994) 5771.
https://doi.org/10.1029/93JA02867.

[23] W. D. Gonzalez, E. Echer, A. L. Clua-Gonzalez & B. T Tsurutani, “Inter-
planetary origin of intense geomagnetic storms (Dst < −100 nT) dur-
ing solar cycle 23”, Geophysical Research Letter 34 (2007) L06101.
https://doi.org/10.1029/2006GL028879.

[24] W. D. Gonzalez & B. T. Tsurutani, “Criteria of interplanetary parameters
causing intense magnetic storms (Dst < −100 nT)”, Planetary and Space
Science 35 (1987) 1101.

[25] J. R. Kan & L. C. Lee, “Energy coupling function and solar wind-
magnetosphere dynamo”, Geophysical Research Letter 6 (1979) 577.

[26] W. D. Gonzalez, B. T. Tsurutani, A. L. C. Gonzalez, E. J. Smith, F.
Tang & S. -I. Akasofu, “Solar Wind-Magnetosphere Coupling During In-
tense Magnetic Storms (1978-1979)”, Journal of Geophysical Research
94 (1989) 8835.

[27] P. T. Newell, T. Sotirelis, K. Liou, C. -I. Meng, & F. J. Rich, “A nearly
universal solar wind-magnetosphere coupling function inferred from 10
magnetospheric state variables”, Journal of Geophysical Research 112
(2007) A01206.

[28] S. E. Milan, J. S. Gosling & B. Hubert, “Relationship between interplan-
etary parameters and the magnetopause reconnection rate quantified from
observations of the expanding polar cap”, Journal of Geophysical Re-
search 117 (2012) A03226. doi:10.1029/2011JA017082.

[29] W. Baumjohann, & R. A. Treumann, “Basic Space Plasma Physics”, Pub-
lished by Imperial College Press, 57, Shelton Street, Covent Garden, Lon-
don WC2H 9HE, ISBN 1-86094-X (1997).

[30] B. O. Adebesin, “Roles of interplanetary and geomagnetic parameters in
’intense’ and ’very intense’ magnetic storms generation and their geoef-
fectiveness”, Acta Geodaetica et Geophysica Hungarica 43 (2008) 383.
https://doi.org/10.1556/AGeod. 43.2008.4.2.

[31] E. K. J. Kilpua, J. G. Luhmann, J. Gosling, Y. Li, H. Elliott, C. T. Russell,
L. Jian, A. B. Galvin, D. Larson, P. Schroeder, K. Simunac, & G. Petrie,
“Small solar wind transients and their connection to the large-scale coro-
nal structure” Solar Physics 256 (2009) 327. doi:10.1007/s11207-009-
9366-1

[32] E. K. J. Kilpua, A. Balogh R. von Steiger & Y. D. Liu, “Geoeffective
Properties of Solar Transients and Stream Interaction Regions”, Space
Science Review (2017). doi:10.1007/s11214-017-0411-3.

[33] W. Yu, C. J. Farrugia, N. Lugaz, A. B. Galvin, E. K. J. Kilpua, H.
Kucharek, C. Möstl, M. Leitner, R. B. Torbert, K. D. C. Simunac, J. G.
Luhmann, A. Szabo, L. B. Wilson, K. W. Ogilvie & J. -A. Sauvaud, A
statistical analysis of properties of small transients in the solar wind 2007-
2009: STEREO and wind observations. J. Geophys. Res. Space Phys. 119
(2014) 689. doi:10.1002/2013JA019115

[34] L. F. Burlaga, K. W. Behannon, & L. W. Klein, “Compound streams,
magnetic clouds, and major geomagnetic storms”, Journal of Geophysical
Research 92 (1987) 5725.

[35] Santosh Kumar, M. P. Yadav & Amita Raizada, “Solar and Interplanetary
Disturbances causing Moderate Geomagnetic Storms”, Journal of Astro-
physics and Astronomy 29 (2008) 263.

[36] B. S. Rathore, “Effect of Solar outcomes on earth magnetosphere during
solar cycle-24” Indian Journal of Radio & Space Physics 50 (2021) 142.

[37] R. Rawat, E. Echer, & W. D. Gonzalez, “How different are the solar wind-
interplanetary conditions and the consequent geomagnetic activity dur-
ing the ascending and early descending phases of the solar cycles 23 and
24?”, Journal of Geophysical Research: Space Physics 123 (2018) 6621.
https://doi.org/10.1029/2018JA025683.

[38] Meena. Pokharia, Lalan Prasad, Chandrashekhar Bhoj & Chandni Math-
pal, “Study of Geomagnetic Storms and Solar and Interplanetary Pa-
rameters for Solar Cycle 22 and 24”, Solar Physics 293 (2018) 126.
https://doi.org/10.1007/s11207-018-1345-y

[39] W. D. Gonzalez, B. T. Tsurutani, R. P. Lepping & R. Schwenn, “Inter-
planetary phenomena associated with very intense geomagnetic storms”,
Journal of Atmospheric and Solar Terrestrial Physics 64 (2002) 173.

[40] T. W. David, A. N. Akintola & B. J. Adekoya, “Time/level of ionospheric
response to geomagnetic storm of 25-26 July 1981 at different latitudes”,
Indian journal of radio & space physics 40 (2011) 311.

[41] B. J. Adekoya & B. O. Adebesin, “Ionospheric and solar wind variation
during magnetic storm onset and main phase at low- and mid-latitudes”,
Acta Geophysica 63 (2015) 1150.

[42] S. E. Milan, J. S. Gosling & B. Hubert, “Relationship between interplan-
etary parameters and the magnetopause reconnection rate quantified from
observations of the expanding polar cap”, Journal of Geophysical Re-
search 117 (2012) A03226. doi:10.1029/2011JA017082.

[43] C. M. N. Candido, I. S. Batista, V. Klausner, P. M. de Siqueira Negreti,
F. Becker-Guedes, E. R. de Paula, J. Shi & E. S. Correia, “Response of
the total electron content at Brazilian low latitudes to corotating interac-
tion region and high-speed streams during solar minimum 2008”, Earth,
Planets and Space 70 (2018) 1.

[44] L. F. Burlaga, R. Skoug, C. W. Smith, & D. F. Webb,” Fast ejecta during
the ascending phase of solar cycle 23: ACE observations, 1998-1999”,
Journal of Geophysical Research 106 (2001) 20957.

[45] A. Ojeda-Gonzalez, V. Klausner, O. Mendes, M.O. Domingues & A.
Prestes, “Characterization of the complex ejecta measured in situ on 19 -
22 March 2001 by six Different methods”, Solar Physics 292 (2017) 160.

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