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INJECTION OF RELATIVISTIC ELECTRONS DURING THE GIANT SSC AND THE GREATEST MAGNETIC STORM OF THE SPACE ERA L. V. Tverskaya 1, E. A. Ginzburga,
N. N. Pavlovt,
and P. M. Svidskyz
ISkobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, I 19899, Russia 2Institute of Applied Geophysics, Rostokinskaya str., 9, Moscow, 129128, Russia
ABSTRACT We study the variations of relativistic electrons in the magnetosphere during the two extraordinary events of the space era: an SSC on 24 March 1991 and a superstorm on 13 March 1989. We analyze the experimental data from four sensors measured electrons in the energy range 0.17-S MeV on the METEOR satellites (polar orbit with -900 km altitude). For March 199 1, we study the developing of a new radiation belt of relativistic electrons which has been created in this event. A giant SSC built a “shock-injected” belt with its peak at L-2.8 (for >8 MeV electrons). During the main phase of the following strong magnetic storm (IDstlmax-300 nT), the peak moved to the lower L-shells and finally reached L-2.3. This position did not change on the recovery phase of the storm. Another, “storminjected” belt has been formed during the storm recovery at Lmax-3. In this latter belt, an intensity of the higher energy electrons increased with a delay in comparison with the intensity of lower-energy electrons (full energy range of the comparison is 0.17-3 MeV). Both new belts are well distinguished in our data. In the another case, 13 March 1989, we observed relativistic electrons during a superstorm with ~Dstlmax-600 nT. In this event, maximum intensity of the new “storm-injected” belt appeared at L-2.5 for all energies up to 8 MeV. L-position of the “storm-injected” belts in both observed cases of highamplitude Dst well agrees with the earlier developed formula: lDst(max=2.75.104/L4max. o 2003 COSPAR. Published
by Elsevier Science Ltd. All rights reserved.
INTRODUCTION Detailed theory of the particle drift in the electric and magnetic fields of sudden impulses has been developed in 60s (Tverskoy, 1964a,b; 1965; 1968). However in the direct observations, the role of particular sudden impulses in forming the radiation belts has been adequately realized only in the recent discovery (Blake et al., 1992). In the event 24 March 1991, the new belts of protons and electrons of tens of MeV appear in the slot region within about 1 minute. The causing impulse might be qualified as one of the largest for the whole history of the space era. This effect has been explained in the framework of the Tverskoy’s theory with an assumption of existence, in this case, of a -10 second positive impulse and a negative impulse which restored the field in -1 minute (Pavlov et al., 1993). The similar idea has been applied in a detailed computer simulation of the event (Li et al., 1993). Focusing on high-relativistic electrons we should note that CRRES has first found out a new shockinjected belt at L-2.5; and, three days after SC, the belt has occurred at L-2.3 although no data on Llocation of the maximum of this belt for the period 25-27 March was reported (Blake et al., 1992). It seems interesting to look in more details at how the new electron belt developed, and whether is somewhat effect of the following storm on this belt, and how does all this compare with a usual storm injection of relativistic electrons into the outer radiation belt. A& Space Res. Vol. 31, No. 4, pp. 1033-1038,2003 0 2003 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177/03 $30.00 + 0.00
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12.V. Tverskay:i e, II/
Shock injections like the case of 24 March 1991 occur very seldomly. One similar event was observed in February 1986 (Gussenhoven et al., 1989). More one case may be a candidate: it is possible to suppose a second peak of the >2_5MeV protons measured by Explorer-14 at L-2.2 in 1962 (McIlwain. 1963) to be a result of the shock injection. We wonder, can a usual storm injection compete with the shock-injected events? In the other words. is it realizable that a peak of high-relativistic electrons appears at L-2.5, as a result of a storm, without a large sudden impulse within the storm period ? If yes, what might be its peak intensity in comparison with the peak intensity of the event March 1991? Below we will try to answer these questions basing on the analysis of an injection of high-relativistic electrons during the greatest storm of the space era, 13 March 1989. OBSERVATIONS AND DISCUSSIONS To get the necessary details we got the data from METEOR that has a 90-minute polar orbit, 900 km height. The sensors involved in the analysis are as follows: (a) the gas-discharge counters measured an intensity of electrons with Ee>O. 17, >0.7, >1.5 and >3 MeV; (b) a Cherenkov detector measured an intensity of electrons with Ee>8 MeV; (c) a scintillation detector which was dedicated to measure protons with Ep>30 MeV, however in the outer belt it counted electrons with Ee>2 MeV (Ginzburg et al., 1993). Event in March 1991 Figure 1 illustrates the evolution of a shock-injected radiation belt of Ee>8 MeV electrons during a strong magnetic storm in March 1991, lDst(max-300 nT; preliminary results are published in (Ginzburg et al., 2000). The lower plot presents a Dst’index (left axis) and a position (Lmax) of the intensity 103-
ME’I’EOR ‘\
24. 27.03.1991
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Fig. 1. Evolution of the shock-injected electron belt of March 1991. Bottom: Dst index (left axis) and L-position of an intensity maximum of Ee>8 MeV electrons (crosses, right axis). Top: L-profiles from the Ee>8 MeV METEOR’s channel. Arrows indicate the times of the profile recording.
Injection of Relativistic
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Electrons
maximum of the new belt (crosses, right axis). L-profiles given in the upper plot provide more details on the form of the new radiation belt. Arrows in the lower plot indicate when the profiles were recorded. At the time of SSC, 03:42UT, METEOR was at high latitudes in the south hemisphere and it first recorded the newly injected electrons near the South Atlantic anomaly. A peak of the >8 MeV electron belt has been found at L-2.8 at 05:22UT. With further developing of the ring current, the belt moved As seen from the data on 27 March, this variation has occurred deeper and finally reached L-2.3. irreversible. Figure 2 presents three L-sections of the radiation belt prepared for the same event in five energy ranges. The first plot shows a state before the storm, the second is made at the beginning of the recovery phase, and the third shows the situation two days after the storm maximum. All data are picked for a similar strength of the magnetic field B. Before the storm (the first plot) the slot region is well identified; the outer belt electrons of Ee>S MeV are recorded at the background. In next plots, a peak around L-2.3 is well seen, as described above with respect to Ee>8 MeV (Figure 1). Another notable increase of lower-energy electrons is well identified in that plots around L-3. Although the channel of Ee>O. 17 MeV electrons is saturated at its top countrates, and all other gas-discharge sensors show the increased background countrates due to contamination with solar protons, but nevertheless it is obvious that a new peak grows up in the channels EeB0.7 MeV, Ee>1.5 MeV and Ee>3 MeV at L-3 in the period 25-27 March. As seen, the lower energy electrons precede the more energetic components in forming this peak. The almost complete filling of the slot region with electrons of Ee>O. 17 MeV is observed by 27 March. An observed delay in increasing of the higher energy components in comparison with the lower energy electrons may be a consequence of several causes. The first cause may be a different duration of establishing the equilibrium in a particle distribution along a field line for the low- and high-energy electrons after their injection into the radiation belts (Williams et al., 1968). Another cause may be a gradual electron acceleration on the storm recovery phase. A giant SSC on 24 March 1991 has created a shock-injected belt of relativistic electrons. The following strong magnetic storm decreased electron intensity in the regions Ll2.5 and created another belt (we name it “storm-injected belt”) with its intensity maximum at L-3. The response of Lmax-3 onto IDstlmax-300 nT well agrees with the rule JDstlmax=2.75.104/L4max (Tverskaya, 1986, 1998). Several mechanisms are known as responsible for the electron intensity drop at the main phase of a storm: an adiabatic variation caused by the developing ring current (Dessler and Karplus, 196 1; Tverskoy, METEOR before storm
start of recovery phase
24.03.1991 lo4
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.
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Fig. 2. L-profiles acquired from METEOR for the south hemisphere, with the similar strength of the magnetic field B, in March 1991. The data on the plots were recorded before storm (left), at the beginning of the recovery phase (mid), and two days after the storm maximum (right).
1964b; Mcllwain, 1966) and a drift to the magnetopause in periods when the daysidc magnctosph~rc 15 compressed by solar wind (Tverskoy, 1964a,b, 1968). More one significant mechanism of the relativistic clcctron precipitation during a magnetic storm is a parasitic resonance of electrons on the waves produzctl by the cyclotron instability of the ring current near the plasmapause (Thorne and Kennel, 1971 ). Several mechanisms may be applied to explain the acceleration of electrons at a specific L.-shell in a s~rnl: electrons of less than 200-300 keV energy may be accelerated by the large-scale substorm electric ticld while their transporting from the higher I.-shells during a storm (Rondareva and ‘l‘\.crskaya, 1973: 1.i c! 1969) and in ;I al.. 1998): relativistic electrons may be accelerated in a dipolarization process (‘l’vc~d~oq~. wave-particle interaction process (Rostoker et al., 1998; Horne and Thorne, 1998; Antonova et al., 2000; Summers and Ma, 2000). Additional adiabatic acceleration of electrons is provided by the recovering magnetic field on the storm recovery phase (Tverskaya. 1986 and references therein: Kim and C’han. 1997).
Event in March 1989 I-igure 3 illustrates the dynamics of relativistic electrons in the outer magnetosphere during the superstorm 13-14 March, 1989. On the plot of Dst-variation (IDstlmax=600 nT), arrows mark the times when METEOR crossed the radiation belts (the data from two satellites are available). The upper part of Figure 3 shows L-profiles from METEOR-l. Data of the three sequential plots are taken for the magnetic field magnitudes close to each other. The similar profiles from METEOR-2 are given in the right-bottom part of Figure 3. The intensities from METEOR-l and METEOR-2 should not be compared direct]!, since B is different in that cases. On March 9. several days before the superstorm, the peak of the outer radiation belt is at L-3.4. Cherenkov detector measuring electrons of Ee>8 MeV records only the background countrates (thin dashes). The passage of March 15 falls on a recovery after the storm. Electrons with Ee>S MeV appeal METEOR
1 II; Ivlarct-I. ccl.wT
15 March
9 March before the storm
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. m . . 2 days after storm rnz lo3 F .
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>8 MeV
B ,“,
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-600 8
10
12 MARCH,
14
16
1989
Fig. 3. L-profiles measured on METEOR-l in the south hemisphere for the similar strength of magnetic field B in March 1989 (at the top). Dst-variations and the data from METEOR-2 are at the bottom. Solid arrows mark the storm-injected peaks and the dashed arrows point to the peaks that have moved onto the lower L-shells.
Injection of Relativistic
Electrons
1037
and an electron intensity in the channels Eel1.5 MeV and Ee>3 MeV increases too. A peak of this storm-injected belt is at L-2.5, which well corresponds to the formula IDstJmax=2.75.104/L4max, as well as with the storm-injected belt of March 1991. We used the data from the identical Cherenkov detectors in both Figures 2 and at the upper part of Figure 3; and a magnetic field strength B is almost the same in these plots. The comparison shows that the peak countrate in the shock-injected belt in March 199 1 is one order higher than the peak countrate in the storm-injected belt in March 1989. Therefore, even a superstorm with its amplitude 600 nT, that happens to occur as seldom as once in 120 years (Allen et al., 1989), does not generate such high-energy electrons with such efficiency as the giant SSC in March 1991 does. An interesting effect is observed on the recovery phase in the data from the two simultaneously flying METEORS. It is well seen in the passages of 16 March 1989, plotted in the right, the peaks of the lower-energy electrons Ee>lS MeV and Ee>2 MeV move to L-2.2 meanwhile the peaks of higherenergy electrons Ee>3 MeV and Ee>8 MeV stay at their original L-2.5. The observed fast radial shift occurs to be different for the different-energy relativistic electrons. This effect may result from the global quasi-periodical geomagnetic disturbances that may selectively accelerate the particles whose drift period is equal to the period of the disturbances (Cladis, 1966). At high altitudes, at L-2-2.5, the similar effect was observed on MOLNIYA-1 (Vernov et al., 1972; Vakulov et al., 1976). In our case, at L-2.2, the drift period of -2 MeV electrons is about 20 minutes, therefore the geomagnetic disturbances with that period are supposed. CONCLUSIONS The dynamics of the >8 MeV electron belt created during a giant sudden commencement on 24 March 1991 is studied. The belt maximum initially occurred at L-2.8. On the main phase of the following strong magnetic storm (/Dstlmax-300 nT) the maximum moved to L-2.3. This variation has occurred irreversible. More one new electron belt, with its maximum at L-3, appeared on the recovery phase of the storm. As a result of the superstorm in March 1989, a storm-injected belt of relativistic electrons has been formed with a peak at L-2.5. Its maximum intensity in the Ee>8 MeV channel is several times smaller than the maximum intensity of the shock-injected electron belt appeared in March 1991. In the event March 1989, we observed the fast radial shift of electrons with Eel2 MeV into the inner radiation belt, onto L-2.2, however the peak of higher-energy electrons kept staying at L-2.5. Probably. this effect is caused by the resonant acceleration due to global quasi-periodical magnetospheric disturbances with the period of about 20 minutes. ACKNOWLEDGEMENT This work was supported by RFFI grant No. 00-15-96623. REFERENCES Allen, J., H. Sauer, L. Frank, and P. Reiff, Effects of the March 1989 Solar Activity, Trans. AGU, 70, N46, 1479-1488, 1989. Antonova, A.E., Yu.1. Gubar’, and A.P. Kropotkin, A Model of Spatio-temporal Structure of the Substorm Electromagnetic Disturbance and Its Consequences, Phys. and Chem. of the Earth, 25, (C), Nl-2,4346, 2000. Blake, J.B.. M.S. Gussenhoven, E.G. Mullen, and R.W. Fillius, Identification of Unexpected Space Radiation Hazard, IEEE Trans. Nucl. Sci., 39, 1761-1764, 1992. Bondareva T.B. and L.V. Tverskaya, On the Radiation Belt Particles Drift During Substorms. Geomagn. i Aeron., 13,723-729, 1973. C’ladis, J.B., Acceleration of Geomagnetically Trapped Electrons by Variations of Ionospheric Currents, J. Geophys. Rex, 71, 5019-5027, 1966. Dessler, A.I. and R. Karplus, Some Effects of Diamagnetic Ring Currents on Van Allen Radiation, J. Geophys. Res., 66, 2289-2297, 1961.
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