Geophysical Research Abstracts Vol. 12, EGU2010-3023, 2010 EGU General Assembly 2010 © Author(s) 2010
Wave and wave-particle processes induced by interplanetary high-speed stream impact on the magnetosphere under conditions of the moderate and very low solar activity Alexander Potapov and Tatyana Polyushkina Institute of Solar-Terrestrial Physics, Magnetospheric Department, Irkutsk, Russian Federation (
[email protected], +7 3952511675)
Unusually prolonged minimum of solar activity in 2008–2009 gave to scientists a unique opportunity to retrace solar-magnetospheric phenomena in their pure form, without a superposition of concurrent events or extraneous disturbances. In this work, we study a wave aspect of the solar wind – magnetosphere interaction by way of two examples of high-speed streams flowing around the magnetosphere. One of these streams was observed in January 2005 when the solar activity was moderate during the declining phase of the 23rd sunspot cycle. The other event occurred in March 2009 against the background of very low solar activity. In the latter case we found a clear demonstration of direct penetration of the ULF waves from the solar wind into the magnetosphere. In the January 2005 event, however, indications of the direct wave penetration are far less evident. The reason is a high level of magnetic disturbance caused by an interplanetary shock wave forestalling the high speed stream in January 2005. In spite of different kinds of conditions for magnetospheric ULF wave generation in these two cases, both events launch similar chains of processes leading to enhancement of relativistic electron flux at the geosynchronous orbit within two days after a peak of a high-speed solar wind stream. This suggests that even with the very low solar activity the high energy particles can present problem for satellite electronics. The mechanisms of particles acceleration under the action of Alfvèn waves in the magnetosphere are discussed briefly. The work was partly supported by RFBR grants 09-06-00048 and 10-05-00661.
Wave and wave-particle processes induced by interplanetary high-speed stream impact on the magnetosphere under conditions of the moderate and very low solar activity A.S. Potapov and T.N. Polyushkina Institute of Solar-Terrestrial Physics SB RAS, Irkutsk, Russia / E-mail:
[email protected]
1
Introductory Clause Unusually prolonged minimum of solar activity in 2008–2009 gave to scientists a unique opportunity to retrace solar-magnetospheric phenomena in their pure form, without a superposition of concurrent events or extraneous disturbances.
2
Solar wind parameters and Dst during the two events In this work, we study a wave aspect of the solar wind – magnetosphere interaction by way of two examples of high-speed streams flowing around the magnetosphere. January, 2005
ACE Bz
0 -20
1000
N, cm-3
ACE Vsw
20 ACE N
500
Dst, nT
0
Dst
-15 -30 20
Wind Bz
10 0 -10
550
-20
30
500
Wind Vsw
450
20
400 350
10
Wind Np
0 0:00
Vsw, km/s
40
Vsw, km/s
-40 60
Bz_GSE, nT
20
15
N, cm-3
Bz_GSE, nT
40
40 0 -40 -80 -120
Dst (nT)
Dst
March, 2009
12:00 0:00 12:00 21-22 January 2005
0:00 UT
0 0:00
0:00
0:00
0:00
0:00
13-16 March 2009
One of these streams was observed in January 2005 when the solar activity was moderate during the declining phase of the 23rd sunspot cycle. The other event occurred in March 2009 against the background of very low solar activity. 3
Oscillations in the solar wind March12-13, 2009
January 21-22, 2005
ACE IMF Bz
ACE IMF Bz 0.1
Spectral Power
After ISW
13.03.09 0.1
12.03.09
Before ISW
0.01
0.01
1
Frequency, mHz
1
Frequency (mHz)
Both events demonstrated appearance of the stable spectral peak between 3 and 4 mHz in the solar wind upstream of the magnetosphere when a high-speed stream passed the L1 monitoring satellite. 4
Oscillations inside the magnetosphere January 21-22, 2005
March 13, 2009
Spectral Density (relative units)
Hp
1
GOES-10 Hp Pc5 range
GOES-11 0.1
GOES-12 Hp
GOES-12
0.1 3 1 Frequency (mHz)
1
Frequency (mHz)
Inside the magnetosphere at the geosynchronous orbit, on March 13, 2009, we see a spectral peak at the same frequency 3–4 mHz as in the solar wind. In January 2005, however, there are many spectral peaks including one in the range between 3 and 4 mHz, but it is lost among the others peaks. 5
Geomagnetic pulsations on the ground March, 2009
March, 2009
14.03.09
13.03.09
Spectral power
Spectral power
1
13.03.09
1
SOD
Bx
CMO
Bx
14.03.09
0.1
16.03.09
0.1
16.03.09
1
2
3
Frequency (mHz)
5
1
2
3
5
Frequency (mHz)
At these plots we see spectra of ULF oscillations observed in March 2009 on ground at two high-latitude stations spaced in longitude by 185 degrees. On March 13 the 3-4 mHz peak dominates at both observatories. 6
Geomagnetic pulsations on the ground January 21-22, 2005
March, 2009
BRW H
10
(70.1, 251.4)
STJ
CMO X
10
13.03.09
0.1
(65.1, 264.2)
SIT X
3
Spectral power
14.03.09
Spectral Power
(59.8, 280.3)
Bx
2
SHU X
1
(53.1, 258.6)
1
EYR H (-50, 256.2)
HON H (21.2, 270)
0.1 5
16.03.09
0.01
PBQ X
2
(65.6, 358.6)
5
MEA X (62.0, 306)
2
1
2
3
5
1
2
3
5
Frequency (mHz)
Frequency (mHz)
The same spectral peak is observed also at the mid-latitudinal observatory St John's, its intensity is much smaller though. On the contrary, we do not see this peak at spectra calculated for the 21-22 January 2005 event. 7
Chain of processes leading to enhanced electron flux at the geosynchronous orbit March, 2009 600
Vsw
Vsw (km/s)
900
Wind
600
Vsw
ACE
500
400 0.16
0.4 0.3
GOES
0.2
S
Spectral Power Jel(E>2 MeV) nT2/Hz (count s-1 st-1 cm-2)
Fluence Spectral Power Electrons/cm2-day-sr nT2/Hz
Vsw (km/s)
January, 2005
0.12
f = 3-4 mHz
GOES
0.08
0.1
f = 3-4 mHz S
0.04
0
1x109
Jel
8
5x10
GOES
0
0x10
21-Jan
23-Jan
25-Jan
27-Jan
0 3000
Jel
2000
GOES
1000 0
12-Mar
14-Mar
16-Mar
The sequence of processes for the two events does not differ in anything with the exception of their intensity.
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Electron flux behaviour during March 2009 event 1E+006
1000
100 GOES-10 daily max GOES-11 daily max GOES-12 daily max GOES-11 5 min ave
10
1
Electron flux (s-1 ster-1 cm-2)
Electron flux (s-1ster-1cm-2)
E > 2 MeV
E > 0.6 MeV
1E+005 GOES-10 daily max GOES-11 daily max GOES-11 5 min ave
1E+004
1E+003
12.03
15.03
18.03 2009
12.03
15.03
18.03 2009
The fastest, one order increase of the E > 2 MeV electron flux occurred on March 14, when the ULF wave activity in the magnetosphere dropped two- or three-fold as compared to March 13 flux. On the contrary, for the E > 0.6 electrons, the flux intensified fastest on March 13, when the ULF wave activity level was highest. Our interpretation see in Discussion and Conclusions. 9
Discussion and Conclusions 1. The major finding of this study is the first observation of the direct penetration of the ULF waves from the solar wind into the magnetosphere. On March 13-14, 2009 a weak disturbance in the solar wind caused by high speed plasma flow from a coronal hole was followed by the enhancement of the ULF wave activity, both in the interplanetary medium and inside the magnetosphere [1]. An important point is that frequency spectra of the waves in all regions were very close having the same dominant frequency peaks. 2. Following the amplification of wave activity lasted not more than two days, the enhancement of E > 2 MeV electron flux at the geosynchronous orbit occurred. On the first day the effectiveness of the E > 0.6 MeV electron acceleration by the ULF waves is high due to high activity of the oscillations in the magnetosphere. However, the relativistic electron fluxes (E > 2 MeV) do not increase as fast as that because a number of the “seed” electrons of moderate energy is not so high. On the second day of the disturbance a number of the moderate energy particles is sufficient to fast increase of relativistic electron fluxes even under the reduced wave activity. 10
Discussion and Conclusions 3. Another important conclusion of the work is that even under the conditions of the extremely low solar activity typical for the second half of 2008 and the first half of 2009 a mechanism of the electron acceleration by the ULF waves does work and provides appearance of the relativistic electron fluxes in the outer radiation belt were geosynchronous orbit lies. The intensity of the fluxes is sufficient to create a threat for the on-board electronics. This confirms a conclusion of Baker et al. [2]. 4. Comparison between the two events observed under different levels of solar and magnetic disturbance shows that the low solar activity provides favorable conditions for analysis of individual events. For the weak activity wave penetration from the interplanetary medium is easily traced. On contrary, during the strong and even moderate disturbances, the penetrating oscillations are concealed by the irregular oscillations of the magnetic field caused by the dynamic pressure pulses of the solar wind. 5. In conclusion it should be noted that the ULF oscillations, beside their role in acceleration of relativistic electrons, are able to redistribute background ions in the magnetosphere due to ponderomotive forces they cause. In paper [3] an example of such a redistribution is illustrated. 11
References 1. Potapov, A.S., T.N. Polyushkina. Evidence for direct penetration of the ULF waves from the solar wind and their contribution to acceleration of the radiation belt electrons. Geomagnetism and Aeronomy 50(7), 2010 (in press). 2. Baker, D.N. et al. Recurrent geomagnetic storms and relativistic electron enhancements in the outer magnetosphere: ISTP coordinated measurements. J. Geophys. Res. 102 (A7), 14,14114,148, 1997. 3. Guglielmi, A.V., A.S. Potapov. On the latitudinal structure of the magnetohydrodynamic Alfvén resonances. Izvestiya Physics of the Solid Earth 45(10), 845-849, 2009.
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