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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012

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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 3

Space Physics Laboratory, Federal University of Technology, Akure, Nigeria

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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012

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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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012 3.0

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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). For the high latitude station: H O =

H5 + H6 + H7 + H8 4

For the mid latitude station: H O =

H6 + H7 + H8 + H9 4

For the equatorial station: H O =

3.1

H 9 + H 10 + H 11 + H 12 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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012 The

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ZO and δZ were determined according to equations (3.1 and 3.2), then the inductance were found

using equation 3.3

δI = 4.0 4.1

δZ δH

3.3

Results and Discussions 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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012

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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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012 4.3

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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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Advances in Physics Theories and Applications ISSN 2224-719X (Paper) ISSN 2225-0638 (Online) Vol 4, 2012

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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, 323–334

J. Atmospheric and Solar-Terrestrial Physics 73 (2011)

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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Advances in Physics Theories and Applications 1.0 Introduction 28 HIGH LAT Baker Lake 64.319 96.10 STATION’S NAME LAT ( o ) LONG ( o ) Advan...

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