CREATION OF SOLAR PROTON BELTS DURING MAGNETIC STORMS: COMPARISON OF TWO MODELS. L.L. Lazutin

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1 CREATION OF SOLAR PROTON BELTS DURING MAGNETIC STORMS: COMPARISON OF TWO MODELS L.L. Lazutin Moscow State University, Scobeltsyn Institute for Nuclear Physics, Space Physics Division, Vorob'evy Gory, Moscow, , Russia, After strong magnetic storms enhanced fluxes of trapped proton with energy 1-20 MeV were registered at L=2-4. Solar cosmic rays are regarded as a source of this new proton population. There are two mechanisms proposed for the explanation how SCR became trapped. The first mechanism suggests that particles are radially injected into the inner magnetosphere at the beginning of the magnetic storm by the electric pulse induced by SC compression of the magnetosphere. By the second mechanism SCR penetrates directly to the inner magnetosphere during the main phase of the magnetic storm and during the recovery phase remains at the closed drift shells if the recovery of the magnetosphere is fast enough compared with particle magnetic drift period. Detailed analysis of the particle dynamics during two magnetic storms based on lowaltitude satellites CORONAS-F and SERVIS-1 presented in this paper shows that it is direct trapping during recovery phase which is responsible for the enhanced proton radiation belts arriving after the strong magnetic storms. 1. INTRDUCTION Proton radiation belt situated on L=1.3-5 shells has been studied sufficiently well. Formation of the proton belt with particle energy from 0.1 to 100 MeV and spatial distribution are described by the theory of radial diffusion caused by the magnetic microimpulses (Parker, 1960, Tverskoy, 1965). Proton belt was regarded as a stable formation with certain substorm associated variations only at the outer belt boundaries. Nevertheless, there were several evidences of considerable proton intensity variations in the inner magnetosphere as well during strong magnetic bays. Slocum et al., [2002] found 11 events when new radiation belts appear after magnetic storms accompanied by solar cosmic ray events from 2000 to They claimed that one of new belts which arrive on November 24, 2001, was registered at least to July Lorentzen et al., [2002] found cases of solar 2-15 MeV proton trapping during strong magnetic storms in 1998 and Solar origin of these particles follows from the existence of helium ions. First of the possible explanation of the solar proton belt formation was proposed when satellite CRRES registered fast increase of the energetic electrons and ions during several minutes of sudden commencement (SC) of the magnetic storm of March 24, 1991 [Blake et al., 1992]. It was suggested that particles were injected inward and accelerated by the electric field impulse induced by magnetosphere compression during SC [Li et al., 1993, Pavlov et al., 1993]. Although similar direct measurements with sufficient temporal resolution have not been repeated, model of the SC-injection became preferable if not the only one for the explanation of the other observation of new solar proton belt formation during magnetic storms. Second mechanisms of the solar proton trapping at the recovery phase of the magnetic storms was proposed by Lazutin et al., [2006], and Lazutin and Kuznetsov, [2007]. Radial injection was not supposed as a main trapping force. It was claimed that solar protons penetrate directly deep into the inner magnetosphere during the main phase and when penetration boundary retreats during the storm recovery phase, low energy (1-20 MeV) protons remain at the closed drift shells due to the fast magnetosphere configuration recovery. It should be noted that both mechanisms are physically possible and both were observed experimentally, therefore our aim is not to show that one of them is erroneous, but to found which of two proposed mechanism really creates solar proton radiation belts. After short description of these mechanisms, and then analyze the details of the proton dynamics during two magnetic storms of October 29-31, 2003 and November 24, SC-INJECTION MODEL The process of the Sc-injection is the same as in a classical diffusion theory of the proton belt formation except that in this case instead of the series of small magnetic field pulses we have only one but with large magnitude. The effectiveness of this mechanism depends on the particle energy. Protons shifted earthward 152

2 by SC-impulse at the dayside must have magnetic drift velocity sufficient to carry them to the night side before the end of the impulse, otherwise its will be returned adiabatically to the starting drift shell with zero acceleration. Magnetic drift period may be found as: 44 T = (1) LE where Т in minutes and E particle energy in MeV For the proton energy 1 and 5 MeV and L=4 T= 11 and 22 minutes consequently, which is exceed significantly typical duration of the SC (< 30s). Therefore 1-5 MeV protons cannot be directly accelerated by this mechanism. Kress et al., [2007] proposed a modified SC-injection of the surfing type, when protons with starting energy ~ 1MeV at 5Re are drifting together with the SC wave gaining energy up to 15 MeV at ~3Re. Presented results of the modeling sufficiently explained captured intensity of the 15 MeV, but due to the resonant feature of the surfing-type acceleration, it cannot explain capture of the 1 MeV protons. Experimental support of this work was based on SAMPEX measurements which have no low-energy proton channels and therefore authors do not know that enhanced 1 MeV proton flux arrived efter the strong magnetic storms. Second restriction of the effectiveness of SC-injection came from the demand of large SC amplitude to obtain necessary proton acceleration. The radial shift δl might be calculated using Tverskoy equation [Pavlov et al., 1993]: 5 8 h L + L max f i δl = L L = (2) f i 21 Ho 2 where L f and L i are initial and final particle position, h max, and H o maximal deviation and total magnitude of the magnetic field at the Earths surface. For example, before the SC of proton penetration boundary (PB) was located at L=3.7 and maximum of 1-5 MeV solar proton radiation belt was found at the end of the main phase of magnetic storm at L=2.4. To receive such shift one must have h max =- 400nT, which exceeds observed SC value more than 4 times. 2.1 Proton radial profiles during SC. CORONAS-F Figure 1 presents 8 radial profiles of NeV proton channel of CORONAS-F particle spectrometer MKL. CORONAS-F satellite operates from July, 30, 2001 till December, 2005 on polar circular orbit with an inclination of ~82.5 o. The altitude of an orbit was 500 km in an initial stage of work, and it gradually decreased to ~350 km at The MKL spectrometer onboard CORONAS-F satellite has two semiconductor detectors with thicknesses of 0.05 mm and 2.0 mm and a CsI crystal with the thickness of 1.0 cm that was surrounded by an anti-coincidence plastic scintillator with thickness equal to 0.5 cm. The geometry factor was ~0.4 cm 2 sr. Electrons from 0.3 up to 12 MeV and protons from 1 up to 90 MeV in different energy ranges were registered [Kuznetsov et al., 2002]. First four profiles on Fig.1 were measured before the magnetic storm. Proton penetrates freely into the polar cap and quasitrapping region. The fourth profile was measured right before the SC (06.12 UT). Profile number five was measured minutes after SC, but no consequences of the proton injection were found in this or other proton channels. Last three profiles measured during storm main phase were shifted earthward as usual in such conditions again without any traces of the enhanced particle intensity. Second example shows similar CORONAS-F measurements before and after SC on UT magnetic storm (Fig. 2). In this case after SC along with the earthward shift of the PB considerable increase of the proton intensity was registered. But again the origin of this increase was not related to the SC injection, because homogeneous increase was registered on all penetration regions, including the polar cap. As one can se at inserted box, simultaneous increases was registered in interplanetary space and it is clear, that it was caused by additional solar cosmic ray acceleration by the same interplanetary shock which caused SC compression of the magnetosphere. 3. DIRECT TRAPPING MODEL During the main phase of the strong magnetic storm the penetration boundary of the solar cosmic rays approached toward the Earth to L=2-3. Closer to the Earth magnetic field is dipollike, while outer field lines are distorted and the protons are quasitrapped; their drift shells are not closed. 153

3 Fig Orbits 1-4 = UT UT. 5 = UT 6-8 = UT.. Profile temporal sequence is shown from top to the bottom. Red color belongs to the daytime local times, blue ones belong to the nighttime profiles. Fig. 2. Radial profiles of 1-5 MeV protons measured by CORONAS-F before and after SC of magnetic storm (Lazutin, Kuznetsov, 2007). In a box measurements electrons and protons of MeV energy range by АСЕ. For the solution of the problem of creation of solar cosmic ray belt it is important to know the ratio of the particle magnetic drift period and the time of the magnetosphere reconfiguration. Which in turn means the conservation or not of the third adiabatic invariant. For the fast drifting particle recovery of the magnetosphere configuration vent too slow and particles enter and leave magnetosphere not mentioning changes, only new particles enter point moves outward according to the PB movement. For the low energy protons magnetosphere changes are too fast and they may remain on the closed drift shells before they are able to leave magnetosphere. There are two important differences of this mechanism and SC-injection model, namely it does not demand injection, it is direct trapping, and in took place not at the beginning but at the recovery phase of the magnetic storm. 3.1 Effect of the double penetration boundary of the 1-5 MeV solar protons Complicated radial profile which we named as double PB occurs when the old low energy protons remain at the closed drift shells and the new low energy protons enter magnetosphere at some distance because of to the PB outward motion on magnetic storm recovery phase. Particle detector on board the satellite CORONAS-F recorded double PB for first time during magnetic storm of [Lazutin et al., 2006]. It was a composition of three storms, as one can see from Fig.3. The closes PB position was registered at L = at the beginning of October 30 and at the end of the same day. Both moments denote the end of the main phase of the second and the third magnetic storms. From the late evening of the October 30 PB started to move outward which was possible to follow by the measurements of three higher energy channels with energy range MeV. Low energy channel 1-5 MeV shows at the same time double PB structure. Fig 4 shows 1-5 MeV radial profiles during two orbits (8 profiles) starting from 00 UT October 31. Double PB was recorded at all profiles both at the North and South and independent on the local time, except the last profile when the single PB recovered. The outer parts of all profiles coincide with single PB of higher energy protons. Trapped solar protons remain at L= while PB moves outward to L= The flux of the detected trapped protons at the inner PB decreases quickly which is not surprising. Low altitude satellite registered only precipitation particles, which input from interplanetary space stopped when PB moved outward. As magnetic field lines became dipollike, pith-angle distribution changes from isotropic toward trapping and for the satellite detector protons became invisible at the most of the orbit except those over Brazilian Magnetic Anomaly (BMA). In this specific orbits enhanced proton were recorded days and months after the storm. 154

4 Fig. 3. Dst- index (SIM) during extremely strong magnetic storm of Fig. 4. The same as Fig. 1 with a double PB structure during the final magnetic storm recovery 4. PROTON BELT DURING OCTOBER 27-31, 2003 MAGNETIC STORMS Several radial profiles over BMA are shown on Fig. 5. Two flights belong to the pre-storm days; other four profiles were registered during the storm at the times shown by arrows on fig Radial profile is typical for the quiet time with maximum at L=3 for the 1 MeV protons Also pre-storm time with differences created by solar protons, which occupied polar cap and quasitrapping region down to L= Proton belt maximum at the same place, L= , ~0630 UT. Penetration boundary approached earthward to L=2.3, and proton belts situated at L=3 disappeared because particle drift orbits became open and protons enter and leave magnetosphere without trapping ~07.40 UT The middle of the recovery phase of the second magnetic storm. Penetration boundary at the end of the growth phase was near L=2.2 and during PB retreat new solar proton belt was created with maximum at L= , 22-23UT. The end of the main phase of the last magnetic storm. PB approached as close as L=2. Previously created SCR proton belt at L=3.4 disappeared , 07 UT. During PB retreat from L=2 to L=3-3.5 new solar proton belt was created at L=2.2. This belt will survive at the enhanced level during one year. At the bottom part of the fig 5 similar profiles are shown for MeV spectrometer channel. Only last SCR belt is visible at this energy while PB positions are the same as for 1-5 proton profiles. 5. PROTON BELT DURING JULY 22-30, 2003 MAGNETIC STORMS. Similar analysis was performed for a chain of three magnetic storms at the end of July, 2004 using SERVIS- 1 energetic particle measurements. It was also polar orbiter with altitude of 1000 km and therefore satellite contact with radiation belts was longer and more stable as compared with KORONAS-F. We will use results of the study of solar proton dynamics during these events presented in details in [Lazutin et al., 2008]. Three magnetic storms with a maximum Dst deviation 100, 150 and 200 nt were registered on July 22, 25 and 27, as shown by Fig.6. Arrows indicate the moments of the proton radial profiles measured by SERVIS- 1 spectrometer and shown on fig 7. Again we will follow proton radial profile transformation from day to day Pre-storm quiet day radial profile with typical intensity and the maximum position (L=3) Measurements were done after SC, during the main phase of the first magnetic storm. There were no changes of the profile compared with the quiet day and no effects of the SC injections To the end of the main phase of the first storm solar proton penetration boundary approached to L~3.5 and SCR intensity was at the maximum. It was the middle of the recovery phase when this profile was measured and one can see that low energy solar protons became trapped with maximum at L= Proton radial profile remains the same before the beginning of the main phase of the second magnetic storm. No traces of the injection at the beginning of this storm are present. 155

5 Fig 5. Radial profiles measured by CORONAS-F spectrometer from October 27 to 30, Channels 1-5 MeV (left) and MeV (right) Fig 6 Storm-time variation during magnetic storms, July 2004 Fig. 7 Radial profiles of the 1.2 MeV protons, SERVIS-1. All profiles were taken at the same longitude over BMA Important changes of the radial profiles were registered after the main phase of the second magnetic storm. Previously created proton belt disappeared because it was occupied by the region of the direct SCR penetration, the quasitrapping region. What was the fate of this trapped protons do they escaped from the magnetopause into the solar wind or were lost by diffusion into the loss cone, or they survive due to the radial diffusion from L=3.7 to L=3.2? Anyway, new proton belt was created during the initial part of the recovery phase of the second storm Before the beginning of the last magnetic storm one can see that intensity of the proton belt increased and maximum shifted a little earthward. That we can ascribe to the action of the recovery phase It seems that this new (solar) proton belt was too close to the Earth to be affected by the PB motion during the main phase of the third magnetic storm. As was mentioned previously, there were no effects indicating on the particle SC injection (see Fig. 2) During the recovery phase of the third magnetic storm one can see an increase of the intensity and earthward shift of the proton belt maximum. It is evident from the radial profile transformation discussed above, that it was created and accelerated at the recovery phase of the magnetic storm, not by the SC-injection. 6. DISCUSSION AND CONCLUSION Process of the solar proton capture to the proton belt at L=2-3 was confirmed by the observation during several magnetic storms, there are no doubts on the reality of this process. But there are different opinions on the mechanisms of this process. We analyzed here two models which were discussed in publications. 156

6 First model of resonant particle injection into the inner magnetosphere by SC pulse was described in details theoretically, was registered experimentally during the magnetic storm of March 24, 1991 and accepted for the explanation of the poststorm increase of the proton population in radiation belt in other cases. There are three aspects of the SC injection model, which restrict its acceptance as a source of the solar proton capture. First one relates to the restriction of the energy of trapped protons which cannot be lower than ~ 15 MeV as was discussed earlier. Second restriction comes from the demand of exceptional large magnitude of the SC pulse for the effective injection. And the last factor follows from the fact that even if SC injection was effective, there is strong probability that this new belt will be swept out when the boundary of quasitrapping region will move closer to the Earth during the main phase of the magnetic storm. The second mechanism of direct solar proton trapping during the recovery phase found confirmation by detailed analysis of the particle dynamics during several magnetic storms. New proton belt was found outward from the last position of the SCR penetration boundary, i.e. on the magnetic field lines which previously were at the quasitrapping region and then became dipollike, keeping protons at the closed drift shells. This mechanism has also restriction on proton energy, but different from the SC injection mechanism. Here exists upper limit of the trapped protons somewhere between 10 and 20 MeV. For high energy particles magnetosphere recovery is too slow and third adiabatic invariant conserves. This restriction on energy also is confirmed by the observations. Therefore we can conclude that from the proposed two mechanisms of the SCR capture to the radiation belt only the second one, mechanism of the direct trapping at the magnetic storm recovery phase effectively supported by the direct measurements. References Blake, J.B., Kolasinski W.A., Fillius R.W, and Mullen E.G. (1992) Injection of electrons and protons with energies of tens of MeV into L > 4 on 24 March 1991, Geophys. Res. Lett., 19, 821. Kress, B.T., M. K. Hudson, M. D. Looper, J. Albert, J. G. Lyon, C. C. Goodrich, (2007) Global MHD Test- Particle Simulations of >10 MeV Radiation Belt Electrons During Storm Sudden Commencement, J. Geophys. Res., 112, A09215, doi: /2006ja Kuznetsov S.N., K.Kudela, S.P. Ryumin, Y.V. Gotselyuk, (2002) CORONAS-F satellite - tasks for study of particle acceleration, Adv. Sp. Res. 30, 223 Lazutin L.L., Kuznetsov S.N., Podorolsky A.N. (2006) Solar proton belts in the inner magnetosphere during magnetic storms., In: Proceedings of the 2d International Symposium Solar Extreme Events: Fundamental Science and Applied Aspects, September 2005, Nor-Amberd, Armenia, ed. by A. Chilingarian and G. Karapetyan, CRD, Alikhanyan Physics Institute, Yerevan, Armenia, 67 Lazutin L. L., Kuznetsov S. N., and Podorolsky A.N. (2007) Creation and distruction of the solar proton belts during magnetic storms, Geomag. and aeronomy, 47(2), Lazutin L., E. Muravjeva, N. Hasebe, K. Sukurai and M. Hareyama, (2008) Comparative analysis of the energetic electron and solar proton dynamics during strong magnetic storms, Physics of Auroral Phenomena, Proc. XXXI Annual Seminar, Apatity Li, X., Roth I., Temerin M., Wygant J.R., Hudson M.K., and Blake J.B. (1993) Simulations of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC, Geophys. Res. Lett., 20, Looper, M. D., J. B. Blake, and R. A. Mewaldt, (2004) Response of the inner radiation belt to the violent Sun-Earth connection events of October November 2003, Geophys. Res. Lett., 32, L03S06, doi: /2004gl Lorentzen, K.R., Mazur J.E., Loper M.E., Fennell J.F., and Blake J.B. (2002) Multisatellite observations of MeV ion injections during storms, J. Geophys. Res., 107, 1231 Parker E.N. (1960) Geomagnetic fluctuations and the form of the outer zone of the Van Allen radiation belt. J. Geophys. Res., 65, Pavlov N.N., Tverskaya L.V., Tverskoy B.A., Chuchkov E.A., (1993) Variations of the radiation belt particle flux during strong magnetic storm of March 24, 1991, Geomag. and aeronomie, 33(6), Slocum, P.L., Lorentzen K.R., Blake J.B., Fennell J.F., Hudson M.K, Looper M.D., Masson G.M., and Mazur J.E., (2002) Observations of ion injections during large solar particle events, AGU Fall Meeting, SH61A-0501 Tverskoy B.A. (1965) Transport and acceleration of the charged particles in the Earths magnetosphere, Geomag. and aeronomy, 5, (R) 157