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Solar particle dynamics during magnetic storms of July 23-27, 2004.

S.N. Kuznetsov+, L.L. Lazutin, M.I. Panasyuk, L.I. Starostin, Yu.V.
Gotseliuk, (a)
N. Hasebe, K. Sukurai and M. Hareyama (b)

a) Moscow State University, Scobeltsyn Institute for Nuclear Physics,
Space Physics Division
Vorob'evy Gory, Moscow119992, Russia
b) Research Institute for Science and Engineering, Waseda University, 3-4-1
Okubo, Shinjuku, Tokyo 169-8555 Japan
lll@srd.sinp.msu.ru


Abstract

It is a case study of a chain of three magnetic storms with a special
attention to the particle dynamics based on CORONAS-F and SERVIS-1 low
altitude satellite measurements. Solar proton penetration inside the polar
cap and inner magnetosphere and dynamics at different phases of the
magnetic storms were studied. We found, that solar protons were captured
to the inner radiation belt at the recovery phase of the first and the
second magnetic storms and additionally accelerated during the last one.
No evidence of SC particle injection was found. Enhanced solar proton belt
intensity with small pitch angles decreased slowly during satellite orbits
for 30 days until the next magnetic storm. Then in 20-30 hours we
registered strong precipitation of these protons followed by the trapped
proton flux dropout. Intensity decrease was more pronounced at lower
altitudes and higher particle energies.

1. Introduction

During magnetic storms usually stable inner proton radiation belt
exhibit intensity variations of a short time scale. Bostrem et al. (1970)
observed low-energy (1-15 MeV) proton intensity increases and decreases on
L=2-4. Mineev et al. (1983) supposed that increase of particle flux is
associated with solar cosmic rays (SCR). Slocum et al. (2002) found 11
events when new radiation belts appeared during magnetic storms from 2000
to 2002. Lorenzen et al. (2002) found additional trapping regions of 2-15
MeV protons during strong magnetic storms of 1998 and 2000. Solar origin
of this particles follows from the presence of the helium ions.

After the sudden commencement (SC) of the March 24, 1991 magnetic storm,
energetic ions and electrons enhancements were registered by CRRES
satellite in the inner magnetosphere (Blake et al., 1992). It was explained
by the particles resonant acceleration and inward injection by the E-
field induced by SC pulse (Li et al., 1993, Pavlov et al., 1993, Hudson et
al., 1997). The SC injection became accepted as a main source of the solar
cosmic ray trapping into the inner radiation belt.
Alternative model was suggested by Lazutin et al., (2006), when direct
trapping of the 1-5 MeV solar protons was registered by CORONAS-F particle
detectors during extreme magnetic storms of October 29-31, 2003. They found
that when proton cutoff latitude or penetration boundary (PB) started to
retreat during magnetic storm recovery phase, low energy protons remain on
the closed drift orbits creating new or changing the old inner radiation
belts at L=2-4. PB retreat model was supported by analysis of the
measurements during two November 2001 magnetic storms (Lazutin et al.,
2007).
During moderate magnetic storms of July 2004 energetic proton and
electron trapping was registered by particle detectors of the SERVIS-1
satellites (Kodaira et al., 2005). Present paper offers analysis of this
event based on the measurements of the energetic protons and electrons by
the particle spectrometers on board of two polar satellites CORONAS-F and
SERVIS-1, which operates on different altitudes. This allows to found new
effects of the SCR dynamics inside the magnetosphere in general and of
the trapping process particularly.

2. Observations

CORONAS-F (C-F) particle detector has four proton differential channels
(1-5, 14-26, 26-50 and 50-90 MeV). At the altitude of 500 km trapped
particles may be seen only over the Brazilian Magnetic anomaly (BMA), and
adjacent South-Atlantic region, while on the majority of the trajectories
only precipitating particles were recorded. SERVIS-1 (S-1) Light Particle
Detectors (LPDs) measured protons and electrons in the energy range from
1.2 to 130 MeV and 0.3 - 10 MeV, respectively. Altitude of 1000 km and
inclination of 100њ on the solar synchronous orbit allows to register
trapping particles more often.
[pic]

Fig. 1. Solar wind (ACE) and magnetic indexes during July 2004 magnetic
storms.

2.1 Event description

Solar wind and magnetic activity indexes are shown by Fig. 1. There were
three moderate magnetic storms. During all magnetic storms IMF Bz was
negative and auroral activity index was at high level. Table 1 presents
characteristic time of the magnetic storms development.

Table 1. Main time-marks of three July 2004 magnetic storms
|SC SC |MaMain phase |Re |Dst |
| |end |Recove|Dst |
| | |ry |Ma |
| | |phapha|max, |
| | |se end|nT |
| | |end | |
|22 07 |22.07 21 UT | 24.07|10 |
|1036 UT| |06 T |100 |
|24 07 |24.07 12 UT - |26.07 |15 |
|0614 UT|25.07 10 UT |16 UT |150 |
|26 07 |26.07 23 UT - |30.07 |20 |
|2249 UT|27.07 14 UT |12 UT |200 |

Solar wind velocity was at moderate level of 500-700 km/s during first
two storms and up to 1000 km/s during the third one. Short enhancements of
the solar wind pressure were recorded at the main phases of all three
storms and associated position of the subsolar magnetosphere boundary
approached the Earth to 7-8 Re as calculated by Kuznetsov and Suvorova
(1996) method.
Solar cosmic rays, electrons and protons were registered in IMF by ACE
and inside the magnetosphere by both S-1 and C-F satellites.

2.2 Penetration boundary definition and dynamics

There are no exact definition of the PB position. One reason comes from
the dependence of the cutoff rigidity from the particle energy. More
energetic protons penetrate closer to the Earth as shown by Fig. 2a. Also
PB position might be defined eider by the background
[pic]
Fig. 2a. Energy dependence of the radial profiles of the solar protons,
CORONAS-F satellite.

counting level (PBb) or by last maximum intensity position (PBm), as
shown by Fig 2b. Finally, if the PB position overlaps with previously
trapped population, then PB boundary can not be found. It was the case for
the most of S-1 orbits, the comparison of the S-1 and C-F proton radial
profiles shown by Fig. 2b illustrates this statement. Therefore we used C-F
to define the PB position and S-1 for the study of the dynamics of trapped
radiation.
[pic]
Fig. 2b. Comparison of the radial profiles of solar protons, SERVIS-1
(solid lines) and CORONAS-F (dotted lines). Positions of the penetration
boundaries defined at background (PBb) and maximum (PBm) intensity levels
are shown by arrows. two energy ranges are shown, ~ 1 MeV and 12-14 MeV.

Figure 3 shows both PBb and PBm dynamics. We use C-F 1-5 MeV proton
data, because in other C-F
[pic]
Fig. 3. Dynamics of the 1-5 MeV proton penetration boundary (PBb and PBm)
and Dst index (solid line)

channels intensity was not high enough all that period. During last
magnetic storm proton precipitation from the newly trapped belt was high
and definition of the PB positions was not accurate. From the Fig 3 one can
see that PB approached the Earth to L=3 and therefore trapping of SCR to
the inner belt was possible.

2.3. Trapping history of 1-15 MeV protons

Two time intervals every day S-1 orbit enters South Atlantic (or
Brazilian) magnetic anomaly (BMA).
We chouse 17-19 UT BMA orbits every day from July 22 to 30, 2004 to
follow changes of the particle radial profiles. Fig. 4 shows the resulting
comparison. First two profiles, July 21 and 22 have a maximum at L=3,
such position is typical for the inner belt of 1 MeV protons. The July 22
profile was measured after the SC but no possible results of the SC
injection were seen. July 23 and 24 profiles were measured during the
recovery phase of the first magnetic storm. We found there additional
enhanced maximum at L=3.8. Penetration boundary at the end of the main
phase was as close as L=3.5 and therefore this new belt might be the
result of solar proton trapping during the retreat of the PB at the
recovery phase.
[pic]
Fig. 4. Latitudinal dependence of the 1 MeV solar proton intensities over
BMA, taken one per each day at 20-22 UT from July 21 to 29, 2004, S-1 data.


Next profile transformation was registered on July 25 again during
recovery phase. Maximum at L=3.8 disappeared because PB during the main
phase of the second magnetic storm approached closer to the Earth and
previously trapped particles found themselves at the open drift shells.
After PB retreat new maximum arrived located at L=3.
Evening pass of the July 26 was at the end of the recovery phase, maximum
position remains at the same place, but intensity increased twofold.
Similar intensity increase continued next four days, all profiles measured
during recovery phase of the third magnetic storm. Maximum position was
shifting gradually earthward, which indicates to the action of the electric
(ExB) drift where electric field might be induced by the magnetic field
increase during the decay of the ring current. It is possibly also that
magnetic field pulsations increase the rate of the inward radiation drift.
Radial profiles measured by S-1 12.5 MeV proton channel looks similar to 1
MeV ones.
[pic]
Fig. 5. The same as Fig.4. for C-F measurements.

Radial profiles of 1-5 MeV protons measured by C-F at the 500 km altitude
looks rather different (Fig. 5). We do not see trapping protons after the
first and the second magnetic storms: loss cone became empty in a short
time. After the third storm trapping proton intensity increased
significantly and C-F registered trapped particles over BMA, and also
precipitating protons in other longitudes.
We will discuss energetic electron dynamics in a separate paper, here
will only mention that there is remarkable similarity of proton and
relativistic electrons dynamics.
The last magnetic storm has a strongest SC amplitude ( 40 nT in Honolulu)
therefore we inspected particle measurements in nearby orbits is search of

[pic]
Fig. 6. C-F 1-5 MeV proton radial intensity profiles before and after the
SC (26.07 22.49 UT)

possible SC injection effect. Fig 6 presents radial profiles of 1-5 MeV
protons measured by C-F 5 minutes before and 25 minutes after the SC. There
was large shift of the penetration boundary and measurable increase of the
proton intensity which cannot be associated with SC injection. Increase
magnitude was the same over all the polar cap and evidently follows the
proton increase outside the magnetosphere in the solar wind created by the
Fermi acceleration at the front of the CME flux. We also did not find SC
injection signatures in other channel of C-F and S-1 as well.

2.4. Time history of a new trapped belts

New created solar proton radiation belts registered by Coronas-F and
investigated in previous studies
(Lazutin et al., 2006, 2007) remain observed not for a long time. After two
November 2001 magnetic storms particle flux decreased by an order in 15-20
days. After October 29-30, 2003 extreme magnetic storms 1 MeV proton belt
exists at the same intensity during 20 days, until the next superstorm and
after it disappeared rapidly.
[pic]
Fig. 7. Temporal behavior of the proton intensity at L=3 after July 22-28
magnetic storms.
[pic]
Fig. 8. Several orbits of the C-F with proton and electron measurements,
August 30, 2004. By dotted line L-values are shown. Peaks of the
precipitation were recorded at L=2.5-4.

In our case during whole August 2004 there were no magnetic storms, and
substorm activity was rather low. As a consequence newly trapped particles,
both electrons and protons, remain at constant level or decreased much more
gradually than after November 2001 storms. Figure 7 shows new radiation
belts time history. Trapped 1 MeV proton intensity at S-1 altitude
decreased rapidly during several days starting at July 28 until August 3.
After that nearly constant intensity level was registered by 1.2 MeV
channel and only slow decay by 12.5 MeV channel. At the C-F altitude
similar decay rate was registered by 1-5 MeV channel.
Then during whole day of August 30 gradual main phase of the magnetic
storm was observed with minimum Dst=-130 nT. Also during this whole day
magnetospheric substorm activity was registered in auroral zone. As a
result, fast decrease of the particle intensity was observed. The rate of
the intensity jump was greater at C-F as compared with S-1 and for higher
electron or proton energy.
The reason of the intensity dropouts was in strong precipitation observed
during more than 12 hours of August 30, 2004. Fig 8 shows example of the
proton and electron precipitation measured by C-F detectors. Similar
particle behavior was registered by S-1 detectors.
Again we will note that both slow intensity decrease and July 30 dropout
were registered also by energetic electron channels of both satellites, but
detailed consideration of electron dynamics will be regarded separately.

3. Summary and conclusion

Joint analysis of the particle measurements on board of two polar
satellites with different altitude not only allows to confirm validity of
the low energy solar proton trapping mechanism described earlier, but
reveals several new features of the solar proton dynamics inside the
magnetosphere during magnetic storms.
1. For the first time we have the possibility not only to find the
trapping effect, but to record detailed time history of the PB radial
motion and associated effects during magnetic storms. Solar protons
penetrate directly to low L shells during the main phases of the magnetic
storms and during the recovery phase 1-15 MeV protons remain there trapped
while more energetic particles were drifting off the magnetosphere.
First solar proton freshly trapped flux was recorded during the first
magnetic storm recovery, but in was destroyed when PB went earthward to
smaller L during the second storm. Distortion of the magnetosphere during
the second storm allows previously trapped protons to escape from this
region which transit to the quasitrapping regime.
At the recovery phase of the second magnetic storm new solar proton
trapping occurs with maximum at L=3. During the recovery of the last, third
magnetic storm intensity of this belt was gradually increasing and the
position of the maximum shifts earthward. Therefore three basic processes
are taking place during magnetic storms:
- sweeping away of previously trapped protons beside the penetration
boundary caused by the losses of the adiabacity because of the
magnetosphere distortion during the main phase of the magnetic storm,
- trapping of the solar protons during the fast magnetosphere recovery
during magnetic storm recovery phase,
- acceleration of the newly trapped protons not only due to in situ
increase of the magnetic field magnitude, but also due to the
earthward shift of the magnetic drift orbits. This shift may be caused
by induced electric field or/and fast radial diffusion caused by
interaction with electromagnetic emissions.
2. We did not find effects of the solar proton injection and acceleration
by SC induced mechanism.
3. After magnetic storm, time history of the trapped solar protons have
two regimes. In the absence of the magnetospheric disturbances slow
intensity decrease was recorded with the decay factor greater for more
energetic protons and for lower altitude of the satellite i.e. lower
altitude of the mirror point. Particle interaction with atmosphere may
possibly explain these relations. It is therefore appropriate to suppose
that 90? (trapped) particle intensity will remain constant for a long time.
During magnetic disturbances, storms or substorms, fast intensity decay
can took place. One obvious reason is wave-particle interaction leading to
pitch-angle diffusion into the loss cone.
Second type of the pitch-angle diffusion might be caused by the loss of
the adiabacity, namely when magnetic field line radius of the curvature
decreased and became comparable with the trapped particle Larmor radius.
For more energetic particles this second type diffusion rate is higher
which is in accordance with observed relation of the intensity dropouts
measured by S-1 and C-F on August 30, 2004.
Solar particle trapping to the inner radiation belt during recovery of
the strong magnetic storms therefore might be regarded as a important
source of the Earth inner radiation belt.

Acknowledgements

This study was partly supported by the grant ? 06-05-64225 of the
Russian foundation for Basic Research. One of the authors (LL) is grateful
to professor Yu.I. Logachev for a helpfull discussion.


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