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International Journal of Astrophysics and Space Science
2019; 7(1): 1-11
http://www.sciencepublishinggroup.com/j/ijass
doi: 10.11648/j.ijass.20190701.11
ISSN: 2376-7014 (Print); ISSN: 2376-7022 (Online)
Study of Response of Extreme Meso-Scale Field-Aligned
Current to Interplanetary Magnetic Field Components BX,
BY and BZ During Geomagnetic Storm
Adero Ochieng Awuor1, *, Paul Baki1, Olwendo Joseph2, Pierre Cilliers3, Pieter Kotze3
1Department of Physics and Space Science, Technical University of Kenya, Nairobi, Kenya
2Department of Mathematics and Physical Sciences, Pwani University, Mombasa, Kenya
3South Africa National Space Agency, SANSA Space Center, Hermanus, South Africa
Email address:
*Corresponding author
To cite this article:
Adero Ochieng Awuor, Paul Baki, Joseph Olwendo, Pierre Cilliers, Pieter Kotze. Study of Response of Extreme Meso-Scale Field-Aligned
Current to Interplanetary Magnetic Field Components BX, BY and BZ During Geomagnetic Storm. International Journal of Astrophysics and
Space Science. Vol. 7, No. 1, 2019, pp. 1-11. doi: 10.11648/j.ijass.20190701.11
Received: October 6, 2018; Accepted: November 26, 2018; Published: August 6, 2019
Abstract: The influence of IMF components on meso-scale field-aligned currents (FACs) is investigated with an aim to
establish how different IMF components influence the occurrence and distribution of FACs. The field-aligned currents (FACs)
are calculated from the curl of the Ampere’s law to the magnetic field recorded by CHAMP satellite during 24 major
geomagnetic storms. To determine the field-aligned currents at extreme mesoscale range ∼150 - 250 km, a low-pass filter to
FACs with a cutoff period of 20s is applied. The peak-to-peak amplitude of FAC density, with the maximum difference ≤ 30
MLAT, is determined and used to define the FAC range. The results indicate high occurrence of FACs centered about IMF ≈ 0,
for large values of Dst. The magnitude of FACs is in general affected by all the three IMF components, alongside other
ionospheric factors such as solar wind speed and density. Magnetic reconnection, under -BZ is a major FACs drivers and is
significant in the dayside northern hemisphere. The reconnection is not symmetric in both hemispheres. We find a possible
electrodynamic similarity between the dayside northern hemisphere and nightside southern hemisphere, prominent along BX
when BZ is negative. This interesting observation can further be investigated.
Keywords: Auroral Ionosphere, High-latitude Current Systems, Magnetosphere-ionosphere Coupling
1. Introduction
A number of systems of global-scale electrical currents are
generated in the near-Earth environments due to the
interaction between the solar wind and interplanetary
magnetic field. One of such currents is the field-aligned
currents (FACs), commonly referred to as Birkeland currents
after he first suggested their existence in the upper
atmosphere in 1908. This current system plays a role in
coupling the energy from the magnetosphere to the high
latitude conducting ionospheres. This coupling can lead to
magnetospheric perturbations and currents which have been
shown to be the cause of various devastating effects on
Earth’s atmosphere, such as, geomagnetically induced
currents (GICs) on power grids, railways, and other long-
distance conducting structures [12]. The dynamics of the
high-latitude thermosphere is greatly affected by the energy
input from the solar wind via Joule heating and particle
precipitation [21, 30]. Further, Joule heating of the
thermosphere can have undesired effects on satellites in low
Earth orbits [7]. These effects result from large currents,
totaling approximately 4 MA for typical solar wind and IMF
conditions and increasing as more extreme driving occurs
[34]. Thus, a better understanding of the FAC distribution
under various geomagnetic conditions and IMF orientations
is important for understanding energy transfer in the
magnetosphere-ionosphere system. The IMF BY component
significantly changes the patterns of FACs in both the
ionosphere and the magnetosphere [11]. The BY deflections
2 Adero et al.: Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic
Field Components BX, BY and BZ During Geomagnetic Storm
has been hypothesized to be due to field-aligned currents
(FACs) [28]. The effect of polarity of IMF BY on the FACs
topology is reversed in the southern hemisphere due to the
antisymmetry of the reconnection site with respect to the
noon-midnight meridian [10].
Four types of FACs are known to exist, e.g., Region 1
(R1), Region 2 (R2), northward IMF Bz (NBZ), and IMF BY
modulated (DPY) FACs [16, 17]. R1 FACs flow into the
ionosphere in the morning sector and out of the ionosphere in
the evening sector, and R2 FACs are located equatorward of
the R1 FACs with opposite polarities. For northward IMF Bz,
NBZ FACs dominate in the polar cap poleward of R1 FACs
[17]. This current system, NBZ FACs, have been interpreted
in terms of the antiparallel reconnection on field lines
tailward of the dayside cusp [17, 31, 32]. When IMF BY
becomes dominant DPY FACs form around the noon sector
while positive BY, in the northern hemisphere results in
upward field-aligned current located poleward of the
downward current, and vice versa in the southern hemisphere
[16, 2]. The poleward part of DPY currents could be
associated with the plasma mantle/cusp precipitation, while
the equatorward part is an intrusion of dawnside (BY > 0) or
duskside (BY < 0) R1 currents [e.g., 8, 35]. The high-latitude
ionospheric convection pattern strongly depends on the
orientation of IMF [13]. Normally, for southward IMF two-
cell convection flow pattern exists, while for northward IMF
four-cell flow pattern emerges due to high-latitude
reconnection. IMF BY will distort the convection map and
cause dawn-dusk and interhemispheric asymmetries. The
locations of the auroral oval and its activity have been found
to strongly depend on the IMF configuration [14]. High
auroral power is observed for all negative IMF components
[29]. A brighter dayside aurora has also been observed for
BX< 0 than for BX > 0 during southward IMF, while the
nightside aurora brightness is less dependent on IMF BX, and
the duskside auroral brightness for northward IMF is not so
much brighter for BX < 0 than for Bx > 0 [36].
The overall response of both the ionospheric convection
and field-aligned current distribution to IMF BZ, BX and BY
has been established. However, the mutual relationship of
these components has not been comprehensively examined.
The relationship would, for instance, help us understand the
mapping of the field-aligned currents from the ionosphere to
the magnetosphere. In this study, we will examine the effect
of IMF BX, BY, and BZ on the ionospheric distribution of
FACs by defining a new parameter called FAC range. We
define FAC range as peak-to-peak amplitude of FAC density,
filtered by a 20s low-pass filter. The location of maximum
and minimum peaks is determined by the magnetic latitude
(MLAT), with the maximum difference ≤ 30 MLAT,
alongside the corresponding magnetic local time (MLT) and
universal time (UT). The satellite passes with the peaks
which are far apart (>30 MLAT) are discarded. This was done
to avoid using peaks in different MLT sectors. The FAC
range comprises R0, R1 and R2 FACs.
The paper is organized as follows; the data set and
methodology are described in section 2. The results are
presented in section 3 while section 4 outlines the
discussions. Finally, the conclusion is given in section 5.
2. Data Set and Methodology
2.1. CHAMP Satellite Data
The geoscientific satellite CHAMP was launched on 15
July 2000 into a near circular, near-polar orbit (87.30
inclination) [23, 25]. With initial altitude at 456 km the orbit
decayed to about 350 km after 5 years. The orbital plane
precesses at rate of 1 h in local time (LT) per 11 days, thus
covering all local times within 131 days. The data used here
are the vector magnetic field measurements of the Fluxgate
Magnetometer (FGM). FGM instrument delivers vector field
readings at a rate of 50 Hz. The satellite data used in this
study are the pre-processed (level 2) fluxgate magnetometer
vector data from CHAMP in sensor frame (product identifier
CH-ME-2-FGM-FGM), which has been down sampled to 1.0
Hz.
2.2. Geomagnetic and OMNI IMF/Solar Wind Data
The Dst, IMF BZ (in GSM coordinates) and solar wind
dynamic pressure are taken from NASA/Goddard Space
Flight Center’s (GSFC’s) OMNI data set through the
OMNIWeb interface. The OMNI data set provides time series
of solar wind parameters propagated to their impact on the
bowshock [24]. The solar wind data has been time shifted for
15 min to take into account the solar wind propagation
through the magnetosheath from the bow shock nose to the
magnetopause [5].
2.3. Field-Aligned Currents Density Calculation
The FAC density is determined according to Ampere’s law
from the vector magnetic field data by solving the curl-B,
that is, =
−
where is the vacuum
permeability, Bx and By are the transverse magnetic field
deflections caused by the currents. We have assumed that
FACs is infinite sheets aligned with the mean location of the
auroral oval [33]. Since we do not have multipoint
measurements, we convert spatial gradients into temporal
variations by considering the velocity under the assumption
of the stationary of the current during the time of satellite
passage. After discrete sampling is introduced, we obtain
=
where vx is the velocity perpendicular to the
current sheet and By is the magnetic deflection component
parallel to the sheet [22].
3. Observations
3.1. IMF-FAC Range Variation in Different MLT Sectors
The Figures 1-8 show the variations of FAC range with
IMF BX, BY and BZ components. The data are classified
according to the geomagnetic activity levels and MLT
sectors; dayside (0800-1600 MLT), nightside (2000-0400
International Journal of Astrophysics and Space Science 2019; 7(1): 1-11 3
MLT), dawnside (0500-0700 MLT) and duskside (1700-1900
MLT). We however take note of relatively limited number of
data points for some MLT sectors, which could lead to
uncertainties in the interpretations.
From left to right, the panels in Figures 1-8 correspond to
IMF BX, BY and BZ while from top to bottom, we have
dayside, nightside, dawnside and duskside sectors
respectively. Indeed, the IMF BX and BY component affect
both dayside and nightside Polar Regions. The increase of
FAC range magnitude corresponded fairly well to an
increasing |BZ| during southward IMF, while the magnitude
remained fairly constant regardless of |BZ| during northward
IMF, clearly seen on the nightside MLT sector. The other
IMF components, on the hand, did not show, in general, the
increasing FAC range magnitude with increasing IMF.
Figure 1. FAC range against various IMF components. Panels a, b and c (dayside), d, e and f (nightside), g, h and i (dawnside) and j, k and l (duskside) in the
northern hemisphere. The Dst value between −119 −100.
The distribution of FAC range varied differently in all
MLT sectors for different IMF components, depending of the
negative and positive deflection of the components. Higher
FAC range occurrence is exhibited during positive IMF BX
than during negative IMF BX during the dayside MLT sector
and the reverse is observed in the nightside. For the IMF BY
component, higher occurrence of FAC range is observed
when the component is negatively deflecting than during
positive deflecting. The reverse is observed during the dawn
MLT sector. Figure 1 (c and f panels) show IMF BZ, as
expected, higher occurrence of FAC range with larger
densities is observed during the negative deflection than
during the positive deflection. The occurrence of FAC range
is also higher during the dayside MLT sector than the rest of
other sectors.
The magnitude of FAC range density increased
significantly, possibly responding to the increase in storm
magnitude. The increase is more pronounced during the
dayside (Figure 2, a-c) MLT sectors. High FAC range
occurrence is observed during the negative IMF BX in all
MLT sectors while for IMF BY the distribution is almost
symmetrical about IMF BY ≈ 0, but with high magnitudes of
FAC range during the negative IMF BY. The response of FAC
range distribution observed during the negative IMF BZ is
consistent throughout the MLT sectors.
Figure 2. Same as Figure 1 for Dst value between−150 −120.
4 Adero et al.: Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic
Field Components BX, BY and BZ During Geomagnetic Storm
Figure 3. Same as Figure 1 for Dst value between−200 −151.
The magnitude of FAC range did not respond significantly
to the decrease in the storm main phase (−151
−200 ! . The distribution of FAC range is however
showing meaningful differences in different MLT sectors.
While during the dayside, the occurrence of FAC range is
higher for negative deflection of IMF BX (Figure 3a) and IMF
BZ (Figure 3c) than during the positive deflections in both
cases, the IMF BY (Figure 3b) is centered about IMF BY ≈
±5nT. The nightside MLT sector exhibited the same trend.
Both dawnside and duskside MLT sectors showed negative
deflections of IMF components to favor the occurrence of the
FAC range compared to positive deflection.
Figure 4. Same as Figure 1 for Dst value "−200 .
Figure 4, panels (d-f), show significant increase in the
FAC range magnitude. The most remarkable difference is
observed during the dayside MLT sector, panels (a-c), where
the distribution of FAC range is almost symmetrical
about −10 #$% 10 . The FAC range intensities
are stronger for large positive and negative values of the BZ
(Figure 4, c and f).
Figure 5. Same as Figure 1 in the southern hemisphere.
International Journal of Astrophysics and Space Science 2019; 7(1): 1-11 5
There is less occurrence of FAC range in the southern
hemisphere compared to similar conditions in the northern
hemisphere (Figure 1) with the FAC range distribution about the
−10 #$% 10 . This could imply asymmetry in
reconnection in southern and northern hemispheres. Higher FAC
range occurrence is exhibited during positive IMF BX than
during negative IMF BX during the dayside MLT sector and the
reverse is observed in the nightside. For the IMF BY component,
higher occurrence of FAC range is observed when the
component is negatively deflecting than during positive
deflecting. The reverse is observed during the dawn MLT sector.
Figure 1(c and f panels) show IMF BZ, as expected, higher
occurrence of FAC range with larger densities is observed
during the negative deflection than during the positive deflection.
The occurrence of FAC range is also higher during the dayside
MLT sector than the rest of other sectors.
Figure 6. Same as Figure 2 in the southern hemisphere.
Figure 6 shows less occurrence of FAC range in all MLT
sectors, with higher magnitudes and distributions during
negative IMF BZ component compare to during positive IMF
BZ. The IMF BY component exhibited a roughly symmetric
distribution about IMF ≈ 0, spreading wider during the
dayside and nightside MLT sectors compared to dawn-dusk
sectors. The IMF BX component had dayside FAC range
distribution and magnitude responding to positive IMF BX
compared to negative IMF BX while the reverse is observed
during the nightside MLT sector (Figure 6d).
Figure 7. Same as Figure 3 in the southern hemisphere.
The occurrence of FAC range is evidently higher during the
&'" 0, in all MLT sectors. For IMF BY, the dayside MLT
sector (Figure 7b) showed, to some extent, symmetrical
distribution of FAC range for both negative and positive
deflections. The same is observed during the dusksise MLT
sector (Figure 7k). During the nightside MLT sector, the
distribution of FAC range was evidently high for &() 0
(Figure 7e) and the reverse observation is made for the dawnside
MLT sector (Figure7h). The IMF BZ components, as expected
had higher distribution of FAC range during &*" 0 as
compared to &*) 0, in all MLT sectors, however with high
occurrence during the dayside MLT sector (Figure7c).
6 Adero et al.: Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic
Field Components BX, BY and BZ During Geomagnetic Storm
Figure 8. Same as Figure 4 in the southern hemisphere.
The distribution of FAC range tends to concentrate between
−10 #$% 10 for dayside and nightside MLT sectors. The
same trend is exhibited in dawnside and duskside sectors though
with less symmetric distribution about the IMF ≈ 0. The dayside
MLT sector still exhibited higher occurrence of FAC range
compared to nightside sector. The magnitude of FAC range did
not vary much correspondingly to the increase in Dst.
3.2. Day-night FAC Range Dependence on the Orientation
of IMF
In this section, we investigate the FAC range cases in IMF
BX-BZ and IMF BY-BZ planes in different orientations
(positive and negative deflections) in northern and southern
hemispheres. The position of the circle is determined by the
corresponding values of the IMF components while the size
of the circle represents the magnitude of the FAC range. The
IMF orientations are categorized as +&*) 0,&') 0! ,
+&*" 0,&'" 0!, +&*) 0,&'" 0! and +&*" 0,&') 0!
for IMF BX-BZ plane and the same conditions are considered
for IMF BY-BZ plane.
Figure 9. Relationship between the IMF BX, IMF BY and BZ with the FAC range. Area of the circle represents the magnitude of FAC range, dayside northern
hemisphere.
From the plots, some general observations could be made such as for IMF BZ < 0 and BY > 0, the occurrence of FAC
International Journal of Astrophysics and Space Science 2019; 7(1): 1-11 7
range is prevalent along the IMF BZ compared to IMF BY in
all cases (Figure 9h, 10h, 11h and 12h). This indicates the
dominance of negative IMF BZ over positive IMF BY. The
positive IMF BZ component was dominant over negative BX
in the northern hemisphere (Figures 9c and 10c), with more
FAC range cases occurring along the IMF BZ > 0. This is not
the case in the corresponding day-night sectors in the
southern hemisphere (Figures 11c and 12c). A nearly linear
relationship between IMF +BZ and IMF +BX is observed in
both hemispheres, with a clear linear dependence in the
northern hemisphere night sector (Figure 10 a, b) and
southern day sector (Figure 11a, b), indicating a possible
electrodynamic similarities between nightside northern
hemisphere and dayside southern hemisphere. The similarity
can be further investigated. The FAC range magnitudes are
stronger for large -BZ compared to large +BZ. FAC range
occurrence and magnitude seem to favor large values of |IMF
BY|, prominent in northern hemisphere than in southern
hemisphere whenever IMF BZ < 0. The north-south
hemispheres asymmetry is observed in the IMF BX
component. The northern hemisphere dayside (Figure 9a)
FAC occurrence showed a similar behaviour as the southern
nightside FAC cases (Figure 12a). Similar observations are
made between northern hemisphere nightside (Figure 10a)
and the dayside FAC range occurrence in the southern
hemisphere (Figure 11a).
High occurrence of FAC range is observed for small values
of IMF components. For &*) 0,&') 0, large FAC range
density occur when IMF BZ is small and BX ~ 10 nT (Figure
9a). The distribution of FAC range favored the large values
of BX, corresponding to large values of BZ. For southward
IMF BZ and negative IMF BX (Figure 9b), the large FAC
range density occurs for large IMF BZ with more cases of
FAC range occurring for small negative IMF BX. Figure 9c
compares FAC range cases for positive IMF BZ and negative
IMF BX. Few cases of FAC range is exhibited under this
condition, with large FAC range density occurring for small
BZ and BX. The large FAC range occurred during large
negative IMF BZ (Figure 9d). While comparing the FAC
range occurrence with different orientations of IMF BZ and
IMF BY, the FAC range cases are more prevalent during IMF
BZ < 0, (Figure 9f and 9h). During IMF BZ > 0, larger FAC
range occurred during negative BY (Figure 9g) compared to
positive BY, (Figure 9e). However, the FAC ranges with large
densities tend to occur in the large |IMF BY| and small |IMF
BZ| region in all cases in IMF BZ-BY plane.
Figure 10. Same as Figure 9 for nightside northern hemisphere.
The nightside FAC range seemingly enjoy a linear
relationship in the IMF BZ-BX plane, when both components
are positive (Figure 10a). Large FAC range densities are
however observed for small IMF BZ and BX. When both
components are negative (Figure 10b), the negative IMF BZ
components dominates in terms of FAC range occurrence and
also large values of FAC range are seen during large values
of negative IMF BZ. Interchanging the directions of the IMF
components, with positive IMF BZ and negative IMF BX
(Figure 10c) leave no components preferred for the
occurrence of FAC range. The large density FAC range occur
for the small values of the IMF components in this condition.
For the case of negative IMF BZ and BX > 0 (Figure 10d),
more FAC range occurred along IMF BZ. Large FAC range
density are observed during large values of IMF BZ < 0 and
small IMF BX > 0. In the IMF BZ-BY plane, the occurrence of
FAC range was prevalent in BY component than along BZ
except for IMF BZ < 0 and BY > 0 (Figure 10h). Large FAC
range density occurred during large IMF BZ and small IMF
BY whenever BZ < 0 (Figure 10f and 10h).
8 Adero et al.: Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic
Field Components BX, BY and BZ During Geomagnetic Storm
Figure 11. Same as Figure 9 for dayside southern hemisphere.
The possible linear relationship between the IMF BZ-BX
plane FAC range when both components are possible (Figure
11a) while the larger FAC range are observed for small values
of IMF BZ and BX. Similar observations are exhibited when
IMF BZ and BX are negative (Figure 11b). For IMF BZ > 0 and
BX < 0, few cases of FAC range are observed with the large
density FAC range occurring when IMF BZ is very small
(Figure 11c). In Figure 11d, large values of FAC range density
are observed during large values of IMF BZ. In the IMF BZ-BY
plane, except for both positive IMF BZ and BY (Figure 11e)
where large values occurred for small values of IMF BZ and
BY, Figure 11f, g and h, shows dominant occurrence of FAC
range along the IMF BZ component. Large values of FAC
range are observed when IMF BY is very small.
Figure 12. Same as Figure 9 for nightside southern hemisphere.
The nightside southern hemisphere, Figure 12, showed occurrence of large FAC range values in both components for
International Journal of Astrophysics and Space Science 2019; 7(1): 1-11 9
the both large values of IMF BZ and BX positive (Figure 12a)
and IMF BZ and BX negative (Figure 12b). For BZ > 0 and BX
< 0 large FAC range values are observed for large values of
IMF BX (Figure 12c). For IMF BZ < 0 and IMF BX > 0, the
large values of FAC range occurred during large values of
IMF BZ. The IMF BZ-BY plane had large values of FAC range
when BY was large and small BZ (Figure 12e) while large
values of FAC range are observed for large values of IMF BZ
and small magnitude of IMF BY for IMF BZ < 0, IMF BY > 0
(Figure 12h).
4. Discussions
Interplanetary magnetic field (IMF) influences on the
occurrence of large-scale FACs has been long recognized
[31, 19, 1]. The IMF influence on the FACs is however not
from only a single IMF component but a contribution from
all the IMF components. For instance, it has been found that
in the polar region the distribution, scale, and magnitude of
the Joule heating region, and the corresponding FACs, are
controlled mainly by the IMF clock angle, which is
determined by the BY and BZ components of the IMF [20].
The occurrences and patterns of the high-latitude field-
aligned currents (FACs) observed in Figures 1-12 are an
indication of the solar wind-magnetosphere-ionosphere
coupling. Using geomagnetic data from CHAMP satellite,
during geomagnetic storm, the study has investigated the
occurrences and intensifications of FAC range for different
interplanetary magnetic field (IMF) orientations and
amplitudes for 24 different storms. The intensification of
FACs manifested in large magnitudes of FAC range during
southward IMF BZ compared to northward IMF BZ (Figures
1-8, IMF BZ column) indicating that the magnetopause is
closer to Earth under southward IMF than under northward
IMF BZ. Similar observations are made in IMF planes,
whenever IMF BZ < 0, (Figures 9-12). The dayside sector has
exhibited high occurrences of FAC range indicating
significant influence of dayside magnetic reconnection.
Magnetic reconnection has also been alluded to as the main
driver for strong FACs originating from magnetopause
boundary during the southward IMF [15, 4]. This implies that
the merging between the IMF and Earth’s magnetic field
creates open field lines that are transported tailward by the
magnetosheath flow in accordance to [6]. During IMF -BZ,
magnetic flux is removed from the dayside and added into
the tail flux tubes. The open flux is then closed by subsequent
reconnection in the magnetotail and returned to the dayside
by sunward convection. The magnetotail reconnection
explains the observed nightside high occurrence of FAC
range cases (Figures 1-8, second row).
The influence of the level of geomagnetic activity on FAC
range is evident on both hemispheres. With the increase in
the activity level (Dst < -200 nT), the FAC range magnitude
remains fairly constant for |IMF| (Figures 4 and 8). The
observed enhanced fluctuations are consistent with the
enhanced FACs reported by [3].
For geomagnetic activity ≥ - 200 nT, Figures 1-3, northern
hemisphere and Figures 5-7, southern hemisphere, the
occurrence and magnitude of FAC range fairly depended on
the orientation of IMF. This concurs with the observation that
high-latitude ionospheric convection pattern strongly
depends on the orientation of IMF [13]. The occurrences and
intensity of FAC range is higher during the negative
deflection of IMF components compared to positive
deflection, affirming the observations by [29, 35].
The nightside FAC range showed a clear dependence on
IMF BZ (Figures 1f, 2f, 5f, 6f and 7f), with increasing
magnitude of FAC range with increasing IMF -BZ and a
fairly constant FAC range magnitude during IMF +BZ
compared to their dayside counterparts. This apparent
dependence on IMF Bz could be due to the relationship
between IMF Bz and AL index [9]. A similar observation was
also made by [18].
The magnitude of FAC range increased, to some extent,
with increasing |IMF BY| while higher occurrence as
observed around −10 ≤ |#$%&(|≤ 10 during both dayside
and nightside (Figures 1-8). Figures 9-12 also showed
increasing occurrence and magnitude of FAC range cases
with increasing |IMF BY|, whenever BZ < 0. This affirms that
IMF BY component affects not only the dayside polar region
but also the nightside polar region and consistent with the
observations by a number of scholars. The influence of IMF
BY on the FACs near the midnight auroral oval, where the
intensity of the currents increases with |BY| was observed by
[27]. Further, the coherent BY-controlled convection exists
near the midnight auroral oval when IMF is stable, and when
its magnitude is large, and that the distribution of the FACs is
associated with BY-controlled convection [26]. IMF BY
component changes the location of the reconnection site on
the magnetopause, leading to a number of asymmetric
features. On the dayside, finite IMF BY shifts the dayside
reconnection site from the subsolar point, toward high-
latitude flanks, where antiparallel reconnection is dominant.
The north-south asymmetry in the IMF BX component
could be due to the magnetopause reconnection location. For
BZ < 0, a positive (negative) BX might be expected to move
the preferred reconnection location northward (southward)
along the closed dayside field line. Closed dayside flux may
be transferred to open nightside flux and the ionospheric
projection would be expected to behave the same way as the
southward IMF. For BZ > 0, a positive (negative) BX is
expected to favor open-to-open lobe reconnection in the
southern (northern) hemisphere.
5. Conclusion
The higher occurrence of FAC range cases during the
dayside sector, with IMF -BZ is not unusual as these
conditions favor dayside reconnections. However, we
find a dominant occurrence of FAC range in northern
hemispheres compared to southern hemisphere
suggesting a possible asymmetry in reconnection sites in
southern and northern hemispheres. All the IMF
components influence the distribution of FACs.
10 Adero et al.: Study of Response of Extreme Meso-Scale Field-Aligned Current to Interplanetary Magnetic
Field Components BX, BY and BZ During Geomagnetic Storm
Although the IMF magnitude affects the
magnitude/intensity of FACs, other ionospheric
parameter s such as solar wind speed and density (not
studied here), may also be of great influence. T he IMF
BX drives the north-south asymmetry, with the north
dayside depicting a similar electrodynamic to the south
nightside.
Acknowledgements
The operational support of the CHAMP satellite mission,
the World Data Center, Kyoto, the GSFC/SPDF OMNIWeb
interface at http://omniweb.gsfc.nasa.gov, from where the
data used in this study was obtained, are sincerely
acknowledged. This work was also supported by the South
Africa National Space Agency (SANSA), Technical
University of Kenya (TUK) and the National Commission for
Science, Technology and Innovation (NACOSTI).
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