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STUDY OF DOSE RATE AND FLUX DISTRIBUTION AFTER SOLAR PROTON EVENTS IN 1989-1994 TIME INTERVAL

Ts.P. Dachev^1, B. T. Tomov^1, Yu.N. Matviichulc, R. T. Koleva^1, J. V. Semkova^1, V.M. Petrov2, V. V. Benghin^2, Yu. V. Ivanov2, V.A. Shurshakov2, J. Lemaire³

1 Solar-Terrestrial Influences Laboratory, Bulgaria, stilrad@hgcict.acad.bg

2 Institute of Biomedical Problems, Russia, shurshakov@mmcc.ibmp.rssi.ru

3 Belgian Institute for Space Aeronomy, Belgium, jl@oma.be Review of Liulin SPE data

Data of September, 29 1989; October 18, 1989; March, 23 1991; June 8, 1991 and June 15, 1991 are plotted on Figure 1. The thick lines correspond to the flux data, while thin lines represent the dose data.

Descending node parts of the orbits in southern hemisphere are chosen. The usual path of the station crosses at high geographic latitude the region northward of the South magnetic pole. The orbits in the last 2 panels crosses the equator westward than in the first 3 panels. That's why the "new maximum" at L=2 is observed in the flux channel on the last panel. Figure 1 reviels that both dose and flux data showed a similar features/characteristics depending on L value. In all cases a marked "knee" in the data is detected at L about 3.5. Horizontal lines represent GOES-7 5 minutes averages proton data in counts/cm² sec sr MeV for the higher than I 00 MeV channel. The universal time (UT) of the place of the comparison is mentioned on each panel. Liulin integral flux data at high L values for the most of SPEs are close to the GOES-7 differential flux measurements outside of the magnetosphere. This result could be easy explained by the fact that our detector because of the shielding (> 5 gram/cm²⁾ was able to observe protons with energies higher than 100 MeV.

Figure 2 shows data after March 23, 1991 SPE and the following SSC. The dose and flux data (thick lines) are plotted against the L value. The figure points out the intensive dynamics of the inner magnetosphere as a result of SPE from March till June,

1991. All parts of orbits are taken for the descending node orbits crossing the geographic equator at 50°-60° West longitude and about 7° south-east from the position of the main SAA maximum.

The top panel presents data from November 6, 1989. They remain conditions when second maximum or outer radiation belt is observed at L=3 after SPE and magnetic storm.

Usually no remarkable doses are observed inside of this maximum. This is the reason why we consider that the vast majority of its particles were electrons with energies higher than 10 Me V depositing few tents (nGy cm²)/particle. The second panel from the top introduces data measured on March 22, 1991. It is used as referent because presents

"quiet" data - only one maximum is observed in both dose and flux at about L=l.2-1.3. The third panel presents the first observation of the "new radiation belt" created after the SSC on March 24. It is seen in flux (thick line) data at L=2.2. The energy deposition in the new maximum is negligible. As a result a small increase in the doses were detected. At this orbit no second maximum at L=3 is noticed. The second belt is shown on the next panel presenting data from March 29. It is at first found at L=2.8 on March 27. The measured flux is lower than the one measured on March 29. That's why we assume that the time

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rate necessary for the creation of a second maximum is longer than the new one. As it was already mention no sufficient increase in the second maximum dose was observed.

The next panel (May 21, 1991) reveals that as a result of several magnetic storms the new belt is enhanced and ^u moved toward the main maximum peak at L=2. l. This ~ phenomenon is realized in about 50 days. The second belt N

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disappeared (June 14, 6 1991) but was created again after E the SPE on June 15, 1991. It is well marked on the second "iii u

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storm on June 1 7, 1991. The maximum values of this Cll a,

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from the bottom panel). From June 20 to June 30 the ~

observed very high values of the dose rate and flux data u:

began gradually to decrease.

Figure 3. shows data registered from 1992 to 1994. All condition in Fig. 3 are same as those on Fig. 2.

The top panel presents data from April 24, 1992. It is obvious that the new maximum in flux data has disappeared. and moved toward the main maximum. The second maximum at L=3 has disappeared too.

Second panel from the top: as a result of the SPE and magnetic storm on May 11, 1991 the new and second maxima were again intensified. They both disappear about

1.5 mounts later (see third panel, June 24, 1992).

The fourth panel shows that the new belt is still detectable on May 8, 1993. It has not fully disappeared. Unfortunately, these are the last available data for 1993.

The fifth panel (data from 1994) do not show any peculiarities close to the main SAA maximum. The second maximum seen on this panel was created first after February 21, 1994 SPE and magnetic storm and additionally intensified after the events on April, 16 1994.

CONCLUSIONS The presence of solar particles in the Earth vicinity is a necessary but not sufficient condition for creation of peculiarities in the inner magnetosphere. Only in a case when a magnetic storm starts close after the beginning of SPE, remarkable effects in the inner magnetosphere are observed.

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ACKNOWLEDGEMENTS Bulgarian team and J.L. gratefully acknowledge support from the Belgium BISA.

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