relativistic electrons and ulf-activity dynamics …

RELATIVISTIC ELECTRONS AND ULF-ACTIVITY DYNAMICS DURING

CIR- AND CME-STORMS IN MAY 2005

Myagkova I.N.1, Kozyreva O.V.

2, 3

1Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow;

2Institute of Physics

of the Earth of RAS, Moscow; 3Space Research Institute of RAS, Moscow,e-mail: [email protected]

Abstract. The electron acceleration and ULF activity during two magnetic storms in May 2005

have been analyzed. The first magnetic storms (May, 7-9) caused by the corotating interactive

region and high speed stream of solar wind (CIR-storm) as well the second one (May, 15-16)

caused by the coronal mass ejecta (CME-storm). We have studied relativistic electron dynamics in

the Outer Earth’s Radiation Belt (OERB) based on CORONAS-F (1.5-3 MeV) and

Universitetskiy-Tatiana (>3.5 MeV) satellite measurements. These data have been compared with

the ground and magnetosphere ULF (2-7 mHz) activity. The global maps of the ULF space-

temporal distribution have been constructed. We have found that the relativistic electron flux

measured by both satellites significantly decreased during the main phase of both CIR and CME

geomagnetic storms. Then during the recovery phase of both geomagnetic storms (and even

several days after that), the electron flux was pronouncedly increased, the electron’s belt widened.

The possible role of ULF-waves in the OERB dynamics is discussed.

INTRODUCTION

Space weather is the conditions and processes occurring in the space which have the potential to affect the

near-Earth environment. The effects of space weather can range from damage to satellites to disruption of

power grids on Earth. Earth’s ERB dynamics is one of the most important factors of space weather. It is well

known that strong increases of relativistic and sub-relativistic electron fluxes in the Outer Earth's Radiation

Belts (OERB) is physical processes occurring during magnetic disturbances (e.g. Tu 2009 et al.; Li et al.,

2005). Such electrons are sometimes named "killer electrons" as they are very dangerous to electronic

devices, in particular the microcircuits that are used in spacecraft and breakdown their normal operation.

Therefore, the measurement of relativistic electron dynamics has both practical and scientific interest (e.g.

Fridel et al., 2002).

The purpose of this study is the analysis of the dynamics of the relativistic electrons in the outer Earth

radiation belt (OERB) and the ULF (2-7 mHz) wave activity on the ground during magnetic storms.

OBSERVATIONS AND ANALYSIS RESULTS

CORONAS-F satellite data

One of the main goals of the Russian solar observatory CORONAS-F (Complex ORbital Observations in the

Near-Earth space of the Activity of the Sun) was the study of space weather effects, i.e. CME and CIR

influence on the Earth’s magnetosphere.

CORONAS-F was launched to the orbit with the inclination 82.5o, initial altitude about 500 km and final

one 350 km, on July 31, 2001 and was operated until December 12, 2005. The orbital period is 94.8 min.

Charged particles in different energy ranges (protons with energy 1-90 MeV, electrons 0.3-12 MeV) were

measured by semiconductor and plastic scintillator detectors (Kuznetzov et al., 2002).

Universitetskiy-Tatiana satellite data

Universitetskiy-Tatiana satellite was launched to the orbit with the inclination 83o, initial altitude about 1000

km on January 20, 2005). The main scientific tasks of this satellite was monitoring of the radiation

environment in the near Earth space (Sadovnichy et al., 2007). In this work we have used proton data with

energies 2–14, 7–16, 15–40 and 40–100 MeV and electron data with energies >70 keV, 300–600 keV, 700–

Proceedings of the 9th Intl Conf. “Problems of Geocosmos” (Oct 8-12, 2012, St. Petersburg, Russia)

347

Fig. 1. The variations of Dst-index, velocity (V) and density(Np) of solar wind, Bz component of IMF (upper

panel); the relativistic electron flux dynamics in the outer radiation belt during May 2005 (two

bottom panels).

900 keV and >3.5 MeV. The data was measured by two semiconductor detectors and one scintillation

detector (for details see Sadovnichy et al., 2007, Myagkova et al., 2009).

Solar wind, IMF and relativistic electrons in Earth’s outer radiation belt observations in May 2005

We have studied two magnetic storms in May 2005 (Fig. 1): the first storm on 07-10 May 2005 caused by

the passage of the corotating interaction region (CIR) and the high speed stream to the Earth’s

magnetosphere (so named CIR-storm); the second storm on 14-16 May 2005 caused by the passage of the

coronal mass ejection (CME) to the Earth (so named CME-storm).

The variations of Dst-index (Dst), the solar wind velocity (V) and density (Np), the Bz component of

interplanetary magnetic field (http://cdaweb.gsfc.nasa.gov) are shown in the upper panel of Fig. 1. Two

bottom panels of Fig.1 demonstrate the relativistic electron in May 2005 according to CORONAS-F (1.5-3

MeV) and Universitetskiy-Tatiana (>3.5 MeV) measurements. The electron flux intensity is shown by

colour.

We can see that the amplitudes of the V, Dst and Bz variations during CME-storm were significantly

large than during CIR-storm.

Variations of electron measured at altitudes 360 km (CORONAS-F) and 1000 km (Universitetskiy-

Tatiana) at in both magnetic storms the dynamics of relativistic electrons was similar:


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http://cdaweb.gsfc.nasa.gov/

Fig. 2. The profiles of the radiation belt electron fluxes on based CORONAS-F (300-600 keV, 600-1500 keV,

1.5-3 MeV; upper panel) and Universitetskiy-Tatiana (300-600 keV, 700-900 keV, >3.5 MeV; bottom

panel) data during the first storm (May, 7-9; left panel) and the second one (May, 14-16; right panel).

- during the main phase of the both magnetic storms (May, 8 and 15) the relativistic electrons flux

decreased;

- during the recovery phase of the both magnetic storms (May, 9 and 16) the relativistic electron flux

increased.

Figure 2 demonstrates the profiles of the radiation belt electron fluxes on based CORONAS-F (300-600

keV, 600-1500 keV, 1.5-3 MeV; upper panel) and Universitetskiy-Tatiana (300-600 keV, 700-900 keV, >3.5

MeV; bottom panel) data during the first storm (May, 7-9; left panel) and the second one (May, 14-16; right

panel).

During the CIR-storm (May, 7-9; left panel) and the second one (May, 14-16; right panel) we have

analyzed consequently, 7/05 and 14/05 (thin solid lines), 7/05 and 15/05 (thick solid lines), 9/05 and 16/05

(thin dashed lines). One can see that in both storms the belt maximum shifted to smaller L during main

phase.

The relativistic electrons flux measured by CORONAS-F and Universitetskiy-Tatiana significantly

decreased during the main phase of geomagnetic storms (during the storms on May During the recovery

phase of geomagnetic storms (and even several days after that) the relativistic electron flux of the OERB is

pronouncedly increased, the electron’s belt is widened and the belt maximum is shifted to smaller L. It is

clearly seen in Figure 2 after the first weaker storm on May 8 in the data from both satellites. During the

recovery phase the Earth’s magnetosphere is slowly expanding again, and the outer radiation belt is forming

much closer to the Earth. During the next days the belt comes back to its position before the storm.

Simultaneously, a significant increase of relativistic electron flux at L=4-5.5 was observed both at 350 km

(CORONAS-F) and 1000 km (Universitetskiy-Tatiana). We observed this electron flux increase not only

after the strong geomagnetic storm on May 15, but also after a significantly weaker storm on May 8.


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Fig.3. Left panel: The variations of Dst-index, velocity(V) and density(Np) of solar wind, Bx, By, Bz

components of IMF (upper panel), the variations of ULF-index in interplanetary magnetic field,

magnetosphere (Goes 11) and on ground (bottom panel) during the first storm (May,7-10) the maps of

global spatial distribution of ULF-activity on the ground for selected peaks during different phases of this

magnetic storm (right panel).

Therefore, significant changes in the outer ERB occur both during both strong CME and moderate CIR

magnetospheric storms. We suppose that a strong reduction of the electron flux observed during the main

phase of a geomagnetic storm is possibly connected to a strong reduction of the size of the Earth’s

magnetosphere, as discussed in (Myagkova et al., 2009).

The major processes believed to play a role in the electron acceleration are: radial diffusion (Falthammar,

1965; Selesnick et al., 1997; Hilmer et al., 2000) and local heating via wave-particle interactions (Horne and

Thorne, 1998; Li et al 2007). However, the relative importance of these mechanisms is still unknown.

Preliminary results of the analysis produced by Antonova et al. (2008) also demonstrate the possibility of

the formation local isolines of constant value of magnetic field at the equatorial plane which do not surround

the Earth, i.e. demonstrate the possibility of the of local particle traps formation in the high latitude

magnetosphere.

During the specified time periods of wave activity increasing (ULF) was observed at several high-altitude

stations. We assume that observed enhancements of relativistic electron flux can be connected with the ULF

wave activity increasing.

ULF wave activity dynamics

We have studied the ULF-activity using ULF-index (Kozyreva et al., 2007). ULF-index estimates the level

of magnetic field variations in frequency range 2-7 mHz. ULF-index in interplanetary magnetic field,

magnetosphere (Goes 11) and on ground is shown in 3 left bottom panels of Fig.3 (the first storm) and Fig.4

(the second storm).


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Fig.4. Left panel: The variations of Dst-index, velocity(V) and density(Np) of solar wind, Bx, By, Bz components

of IMF (upper panel), the variations of ULF-index in interplanetary magnetic field, magnetosphere (Goes

11) and on ground (bottom panel) during the second storm (May,14-16) the maps of global spatial

distribution of ULF-activity on the ground for selected peaks during different phases of this magnetic

storm (right panel).

The right panels of Fig.3 (the first storm) and Fig.4 (the second storm) demonstrate the maps of global

spatial distribution of ULF-activity on the ground for selected peaks during initial, main and recovery phases

of magnetic storm. You can see that:

- in the initial phase the maximum of ULF-activity was observed at ~70o

- in the main phase the ULF-activity shifted to more low latitudes at~60-70o

- in recovery phase the maximum of ULF-activity moved to higher latitudes at ~65-70o.

The ULF-activity dynamics was similar during CIR-storm (the first storm) and CME-storm (the second

storm), but ULF variations in CIR-storm were less intensive and the maximum of ULF-activity was observed

at more high latitudes than in CME-storm.

CONCLUSIONS

We have studied the dynamics of the relativistic electrons in the outer Earth radiation belt (OERB) and the

ULF (2-7 mHz) activity on the ground during CIR-storm (2005, May 8-10) and CME-storm (2005, May 14-

16).

o It was found that the relativistic electron flux in OERB significantly decreased during the main phase

of both CIR and CME storms. Then during the recovery phase of both CIR and CME storms, the

electron flux was pronouncedly increased, the electron’s belt widened and become more intensive.


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o The ULF-activity dynamics was also similar during and CME-storms, but ULF variations in CIR-

storm were less intensive and the maximum of ULF-activity was observed at more high latitudes

than in CME-storm. o We suppose that the obtained dynamics of the relativistic electrons flux in OERB reduction and ULF

activity during during CIR-storm (2005, May 8-10) and CME-storm (2005, May 14-16) may be a

result of the changing size of the dayside magnetosphere caused by the changing solar wind dynamic

pressure. ACKNOWLEDGEMENTS

The authors thank the participants of the CORONAS-F and the Universitetskiy-Tatiana experiments for

valuable advices in the process of discussion of the results of the work. The work was supported by Russian

Foundation for Basic Research (12-05-01030) и by Ministry of Science and Education of Russian Federation

(project no 2012-1.2.2-12-000-1012-003).

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