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11.the response of interplanetary medium to the geomagnetic storm of april 2010www.iiste.org call for paper
1. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
The Response of Interplanetary Medium to the Geomagnetic
Storm of April 2010
R.O Salami* 1,2 A.B Rabiu2,3 E.O. Falayi2,4 F.O Oluyemi2,5
1
Dept of Physics, Afe Babalola University, Ado-Ekiti, Nigeria
2
Space Physics Laboratory, Federal University of Technology, Akure, Nigeria
3
National Space Research & Development Agency, NASRDA, Abuja, Nigeria
4
Dept of Physics, Tai Solarin University of Education, Ijagun, Nigeria
5
Dept of Physics, Federal Polytechnic, Ado-Ekiti, Nigeria
*e-mail of the corresponding author: olawunmmisalam@yahoo.com
Abstract
Knowledge of the activities within our own solar system is of fundamental importance in our attempts to
understand the processes that occur in the upper reaches of our atmosphere; because, space weather is
greatly influenced by the speed and density of solar wind and Interplanetary Magnetic Field (IMF) carried
by solar wind plasma. For this reason, behaviours of the interplanetary medium during the storm of 5-7
April 2010 were examined using the routinely observed values of southward component of the
Interplanetary Magnetic Field, Bz, Disturbance storm time Index, Dst, Solar Wind Speed. Data of H and Z
components of the Earth’s magnetic field recorded at some equatorial and polar stations were also
considered to investigate ionospheric responses to the storm. Strong solar wind hit the Earth’s
magnetosphere about 0800UT on 5 April 2010 and sparked first geomagnetic storm of the new solar cycle.
The storm was the largest geomagnetic storm of the Sun caused in the past three years. The commencement,
main phase, and recovery phase of the storm were discussed vis-à-vis response of the interplanetary
medium. Probable magnetic processes responsible for the storm as well as the ionospheric implications
were also highlighted.
Keywords: Geomagnetic storm, interplanetary magnetic field, solar speed and disturbance storm time
index
1.0 Introduction
Space weather describes the interaction between the Sun and Earth. Storms on the Sun can produce bursts of
charged particles. These shoot out into space, and sometimes end up hitting the Earth. The effects of solar
storms can be as beautiful as an aurora or can cause damage to the satellites and health risks to astronauts and
aircraft crews. Meanwhile, our modern lifestyle depends heavily on space technology, for example, for TV
and mobile phone communications, internet. We cannot prevent geomagnetic disturbance, but we can
monitor the Sun and give some warning when stormy weather is approaching the Earth. Hopefully,
appropriate action can be taken to limit any damage. Thus, the physical phenomena which are associated
with space weather such as the speed and density of the solar wind, the interplanetary magnetic field (IMF)
carried by the solar wind plasma and geomagnetically induced currents at Earth's surface must be considered
at every time interval.
One of the disturbances that can be monitored on Earth to provide estimates of the level of the
magnetospheric activity is the Disturbance Storm Time Index, Dst.
Dst is a geomagnetic index which monitors the world wide geomagnetic storm level. It is constructed by
averaging the horizontal component of the geomagnetic field from mid-latitude and equatorial magnetograms
from all over the world. Negative Dst values indicate a geomagnetic storm is in progress, the more negative
Dst, the more intense the geomagnetic storm. The negative deflections in the Dst index are caused by the
storm time ring current which flows around the Earth from east to west in the equatorial plane. The ring
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
current results from the differential gradient and curvature drifts of electrons and protons in the near Earth
region and its strength is coupled to the solar wind conditions. Geomagnetic storms as seen in Dst commonly
have three phases: a sudden commencement, a main phase and a recovery phase. (Burton et al, 1975). The
sudden commencement occurs as the initial impact of increased solar wind dynamic pressure sharply
compresses the magnetopause. At the ground, this is observed as a sharp increase in horizontal magnetic field
intensity on time scales of less than 1h. The main phase and recovery phases are characterized by a decrease
in horizontal magnetic field intensity and then slow return to baseline. The strength of a geomagnetic storm
is described by the minimum reached during the main phase (Gonzalez et al., 1994).
Another disturbance that can be monitored on Earth to provide estimates of the level of the magnetospheric
activity is the southward component of the interplanetary magnetic field, Bz. The southward component of the
interplanetary magnetic field, Bz has been associated with geomagnetic activity in general (Foster et al.,
1971) and the geomagnetic storm main phase in particular (Russel et al., 1974).
Rostoker and Falthammar, (1967) found that the storm main phase was associated with a sustained
southward, Bz. Russel et al., (1974) found that the southward, Bz had to exceed an apparent threshold level,
possibly Dst -dependent, in order to trigger a storm main phase. Rostoker and Falthammar, (1967) also noted
the recovery phase was associated with a decrease or switching off of the southward, Bz.
Also, ground-based magnetic field observations have a component that is reflective of the Earth’s space
environment and provide important information about the state of geomagnetic activity. The competing
balance between Earth’s intrinsic magnetic field and solar wind dynamic pressure drives much of the
variation of the Earth’s space environment three independent elements are required to specify the magnetic
field at any location (Ganon and Love, 2010). The field is specified either by rectangular components X, Y
and Z or H, D and Z. These components are being measured at various magnetic observatories all over the
globe (Rabiu, 2000). In this paper, we looked at the H and Z component of the Earth magnetic field for the
month of April and the inductance during the geomagnetic storm period.
2.0 Data Collection
For the present work we have studied geomagnetic storm of April 2010 which occurred between 5 and 7
April 2010. The studying parameters are southward component of the interplanetary magnetic field, Bz ,
disturbance storm time index, Dst and solar wind speed. The data were taken from OMNIWEB
(omniweb.gsfc.nasa.gov/ow.html) at 1hour interval over 30 days. While the X, Y, Z components of the
earth’s magnetic field data were obtained from Intermagnet Geomagnetic Observatory at one minute interval.
STATION’S NAME LAT (o) LONG (o)
HIGH LAT Baker Lake 64.319 96.10
MID LAT Tucson 32.181 110.58
EQUATOR Guam 13.590 144.45
Table 1: Geomagnetic Observatory and their Coordinate
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
3.0 Methodology
The southward component of the interplanetary magnetic field, Bz, disturbance storm time index, Dst and
solar wind speed hourly values for all the days of April 2010 were plotted against universal time. The X , Y,
Z values of the Earth magnetic field at the polar, mid-latitude and equatorial stations collected at one minute
interval were averaged to hourly values for all the days of April 2010. And the H component values of the
Earth magnetic field for all the days of April 2010 were obtained following equation 1.1.
H = (X 2
+Y 2
) 1.1
X - The component of the Earth along horizontal geographic north;
Y - Horizontal geographic east components
H - Horizontal intensity; the horizontal magnetic intensity due to the X and Y component;
3 .1 Inductance
The inductance of the of the storm time from 4th-9th of April 2010 were determined using equations (3.1 –
3.3)
3.1.1 Midnight Baseline Value, Ho
Mean of 4 hourly values of each magnetic components flanking local midnight values (Rabiu et al, 2007 and
Chandra et. al., 2000).
H5 + H6 + H7 + H8
For the high latitude station: H O =
4
H6 + H7 + H8 + H9
For the mid latitude station: H O = 3.1
4
H 9 + H 10 + H 11 + H 12
For the equatorial station: H O =
4
3.2 Hourly Departure
Hourly departure from the midnight value of time, t at local time (LT) were analysed by subtracting midnight
baseline value from each hourly values t1 to t24 hour for each of the component from 4th-9th of April 2010.
δH = H t − H o 3.2
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
The ZO and δZ were determined according to equations (3.1 and 3.2), then the inductance were found
using equation 3.3
δZ
δI = 3.3
δH
4.0 Results and Discussions
4.1 Hourly Variations of Interplanetary Indices & H with Dst
Figure 1a shows the hourly average plot of, Bz, solar wind speed and Dst. A sudden increase in the value
of Bz was seen just before the sudden commencement of the storm. The value increased from 0.1nT at
10:00UT to -11.4nT at 11:00UT on April 5 2010. An hour later, solar wind speed increased from
730km/s at 12:00UT to 783km/s at 13:00UT. The southward component of the interplanetary magnetic
field, Bz, causes magnetic reconnection of the dayside magnetopause, rapidly injecting magnetic and
particle energy into the Earth's magnetosphere. Thus, leading to sudden increase in solar wind speed
which compresses the day-side magnetopause, resulting in enhancements and rearrangements of the
complex current systems near the Earth. These current system changes are as well observed as magnetic
field fluctuations at ground-level (McPherron, 1995). This is evident in figure 1b in which depletion
was seen in H component of the Earth’s magnetic field across all the latitudes, as the geomagnetic
storm occurred.
Figure 1a: Hourly variations of interplanetary indices and Dst Figure 1b: Hourly variations of H component at high
latitude (Baker Lake), mid-latitude (Tucson) and equatorial region (Guam)
4.2 Diurnal Variations of Interplanetary Indices, Dst, Z and H.
Figures 2a-2c showed the diurnal variations of Bz, solar wind speed and Dst respectively. The plots showed a
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
sharp increase in the negative value of Bz just before the storm and solar wind value increases positively
before the storm. Figures 3a-3c is the plots of diurnal variations of H over April 2010 and it showed the
values of H for each day of the month. There is a sharp decrease in the values of H across all the latitudes
during the geomagnetic storm. Geomagnetic storms occur during longer periods of steady southward IMF
and are characterised with a global decrease of the horizontal geomagnetic field component at middle and
low latitudes. For example, (Gonzalez et al., 1994) observed that at the ground, the main phase and recovery
phases of a storm are characterized by a decrease in horizontal magnetic field intensity and then slow return
to baseline.
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
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ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
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4.3 The Storm Phase
Figure 5: The sudden commencement, main phase and recovery phase of April 4th -8th 2010 storm
From figure 5, the southward component of the interplanetary magnetic field (IMF), Bz , increases sharply to
the magnitude of 11.4nT at 1100UT from 0.1nT at 1000UT on April 5. Immediately the sudden increase in,
Bz a sharp increase was seen in the magnitude of solar wind speed which shows the sudden commencement
of the storm at -53nT on April 5. This result is in agreement with (Burton et al, 1975) observation that geo
effectiveness of solar wind depends upon the speed and embedded southward magnetic field. And, (Yadav,
2005) observed that 70% of GMSs are associated with southward component of IMF, Bz ,alone. Furthermore,
it is observed that the product of V and B directly modulates the geomagnetic activity.
On April 6, at 0700UT the storm magnitude increased to -67nT which shows the main-phase of the storm and
this increased to -73nT at 1400UT of April 6. The recovery phase occurred during the period of negative
field. However, immediately the storm of April 6 has recovered, an increase was seen again in the value of Bz
at 0700UT on April 7 which shows another storm but the magnitude was low (-50nT) compared to the
former.
5.0 Conclusions
The daily and hourly averages of the interplanetary indices with Dst showed a sharp increase in the
magnitude of, Bz which is at 12hours before the sudden commencement of the storm. The solar wind speed
increases suddenly prior to the main phase. The recovery phase is seen as, Bz drops and solar wind decrease.
There is a sharp decrease in the magnitude of H which cut across all the latitudes. The main phase and
recovery phases are characterized by a decrease in horizontal magnetic field intensity and then slow return to
baseline. The magnitude of the vertical component, Z, increases across all the latitudes during the storm.
Acknowledgements. The results of the horizontal and vertical component of the Earth’s magnetic field
presented in this paper rely on data collected at magnetic observatories. We thank the national institutes that
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8. Advances in Physics Theories and Applications www.iiste.org
ISSN 2224-719X (Paper) ISSN 2225-0638 (Online)
Vol 4, 2012
support them and INTERMAGNET for promoting high standards of magnetic observatory practice
(www.intermagnet.org). We also thank the OMNIWEB (omniweb.gsfc.nasa.gov/ow.html) for the
interplanetary indices data.
References
Burton et al, 1975, ‘An empirical relationship between Interplanetary Conditions and Dst’
J.Geophys. Res., vol 80, No 31.
Chandra, H., Sinha, H. S. S and Rastogi, R. G. (2000), Equatorial Electrojet studies from rocket and ground
measurements, Earth Planets Space, Vol. 52, pp 111-120
Foster, J. C., D. H. Fairfield, K. W. Ogilvie, and T. J. Rosenberg. (1971),’ Relationship of interplanetary
parameters and occurrence of magnetospheric substorms’, J. Geophys. Res., 76, 6971
Gonzalez, W.D., et al., (1994), What is a geomagnetic storm? Journal of Geophysical Research 99,
5771-5792.
Ganon and Love (2010), USGS 1-min Dst index, J. Atmospheric and Solar-Terrestrial Physics 73 (2011)
323–334
McPherron, R.L. (1995), Magnetospheric dynamics. In: Russell, C.T., Kivelson, M.G. (Eds.), Introduction to
Space Physics. Cambridge University Press, Cambridge, UK, pp. 400–458.
Russel et al., 1974, ‘On the causes of geomagnetic storms’, J.Geophys. Res, 79, 1105.
Rostoker and Falthammar (1967), Relationship between changes in the interplanetary magnetic filed and
variations in the magnetic field at the Earth’s surface, J.Geophys. Res., 72(23), 5853.
Rabiu, A.B. (2000), Geomagnetic variations at middle latitude, PhD thesis submitted to the department of
Physics and Astronomy, Univ. of Nsuka, Nigeria.
Rabiu, A. B., Mamukuyomi, A. I. and Joshua, E. O., (2007), Variability of equatorial ionosphere inferred
from geomagnetic field measurements. Bulletin of the Astronomical Society of India, Vol. 35, pp 607-618
Yadav, M.P. (2005), Comparative study of SWP and IMF parameters with DST ≤ - 100 nT in association
with large geomagnetic storms. 29th International Cosmic Ray Conference Pune (2005) 00,101-104
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