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Peculiarities of the solar proton events of 19 October 1989 and 23 March 1991 according to the measurements onboard the Mir space station
Adv. SpaceRes. Vol. 14, No. 10, pp. (10)645-(10)650, 1994 Copyright© 1994COSPAR Printed haGreat Britain.All rightsreserved. 0273-1177/94 $7.00 + 0.00
Pergamon
PECULIARITIES OF THE SOLAR PROTON EVENTS OF19 OCTOBER 1989 AND 23 MARCH 1991 ACCORDING TO THE MEASUREMENTS ONBOARD THE MIR SPACE STATION V. M. Pelrov,* V. S. M a h k m t o v , * N. A. Panova,* V. A. S h u r s h a k o v , * Ts. P. Dachev,** J. V. S e m k o v a * * and Yu. P. M a t v i j c h u k * * * Institute of Biomedical Problems, Moscow 123007, Russia ** Solar- Terrestrial Influences Laboratory, Bulgaria
ABSTRACT Flux and dose rate dynamics of solar cosmic rays were measured by the L y u lin dosimeter during the events 19 October 1989 and 23 March 1991. The maximum dose rate registered was 0.4, 0.12 and 0.01 cGy/hour, respectively. Based on the latitude distribution of particle flux a power law form for the energy spectra of solar protons in the anisotropic phase of the events on 19 October 1989 and 23 March 1991 was determined. It was obtained that after the development of geomagnetic storm protons with energies more than I GeV were registered. INTRODUCTION Radiation monitoring with the dosimeter-radiometer Lyulin has been conducted for a long time aboard the orbital station Mir. The instrument is located in the main large-diameter module and its positioning is presumed to remain unchanged throughout the whole period of measurement. Therefore, mass distribution in reference to the instrument is constant and all oscillations in the radiation environment measured with the instrument result from changes in the radiation fields along the trajectory. The average thickness of the screening material is estimated to be 5-15 g.cm-2; the actual shielding due to spacecraft structure ranges between 2.5 and 150 g.cm -2. Hence, the largest contribution is made by protons with energies above 70-100 MeV. Thus the aquired data base of dose rate and flax along the station orbits gives the opportunity to investigate regularities or alterations of the radiation situation in the near-Earth space related to solar cosmic rays (SOR) and geomagnetic disturbances. In the present paper characteristics of the SCR in the period from 19 October 1989 up to 23 March 1991 responsible for radiation disturbances in the terrestrial magnetosphere and noticeable rise in dose rate in the Mir modules are discussed. EQUIPMENT AND RESULTS The Lyulin instrument is a highly sensitive semiconductive dosimeter which has been designed and put into operation during the second SU-Bulgarian joint mission aboard Mir in 1988. The detailed description of the instrument was given in /I/. The instrument provides concurrent measurements of dose rate and the flux of cosmic radiation. The detecting element is a semiconductor detector, the sensitive layer of which is 300 p~n thick and 2 cm 2 in area. The geometric factor amounts to 6 cm2.sr (for the flux from a hemisphere); the dose sensitivity (absorbed dose per one impulse at the outlet) is equal to IO.5.10 -10 Gy.impulse. The accuracy o f the dose measurements is +_20%, and the time of averaging of the dose rate and flux amounts to 10-1OO s. In September-October 1989 the instrument was in operation except for October 10-13 and 21-25. It was switched on during the solar proton events (SPE) in March 1991 and this allowed us to acquire detail information about flux distributions and dose rates along the Mir trajectory. Ten-second time averages of the radiation environment along each orbit was determined by measurements in more than 550 points. Each (10)645
(10)646
V.M. Petrov et al.
point was linked to geographic, L,B-ooordinates and time. Great detail of investigations and good statistics owin~ to high sensitivity of the instrument make it possible to use changes Lu the geomagnetic rigidity of outoff along the trajectory for determination of the S0R spectrum. This can be done by analyzing the flux distribution according to L values and vertical rigidity R (ratio R=14.8.L -2) or out-off energy E, which are the functions of L. As L values are determined from the model descriptions of the movement of particles in the geomagnetic field and the field itself, it would be useful to evaluate the effect of various geophysical factors on the vertical rigidity R. Among them there are three most slgnifioant: the direction of movement, local time and geomagnetic disturbance. The effect of direction of movement can be taken into account by means of the relation /2/ 4R I R(R l,t0)=.
, GV [
(1),
1+ / l - c o s O (R±/14.8) 3/4"12
where R(RI, 0J) is the cut-off rigidity representative of the vertical rigidity R± in a given point in orbit for the particles moving at angle with the East-West direction (~=0 for the particles coming from the East, ~0=~ for the particles coming from the West). If X=Rwest/Reast, this relation varies in the range from 4 to 1.1 while L changes from I to 7. The spectrum is normally estimated when the station passes the segments of the orbit with L>2.5 so that the real rigidity differs from vertical by no more than 15%. The influence of the local time on the estimation of the effective geomagnetic threshold R± can be defined with the use of relation /3/ for magnetically quiet period (Dst<50 nT): RI RI =
1
(2) + A(Ri,t m)
Correction A(Ri, tm) which depends on vertical threshold R± and local geomagnetic time tm at the point of measurement is calculated empirically using the equation formed on the basis of experimental data analysis: 2% 0.67 1.1+1.62 cos [ ~ 1.42 [ R--~- ]
(tm+O.66)]
A =
(3)
exp {1.72( Rl )2 [1+0.66 sin ( 2~ (t +2.o))]} O. 67
12
m
Oaloulations have shown that in the region RI<0.6 GV (EI<170 UeV), the correction A exceeds 0.5. In the region of RI>IGV (Ei>400 MeV), the value of A does not exceed 0.1 and rapidly diminishes with the increase of R I. In the region of RI>0.7 GV(EI>230 MeV) the correction runs 0.25. Hence, the neglect of local time can somewhat corrupt the SOR spectrum in the area of low energies (<150 MeV), basically by hardening, and will have practically no effect on the high energy region of the spectrum. The influence of geomagnetic disturbances must b{ also considered in the procedure for determining the vertical rigidity R I at the points of measurement. This can be accomplished, for instance, by usLu~ techniques proposed in /4,5/. Results of calculations of threshold rigzdity R I at various levels of disturbance (to amplitude of the Dst variation in nT) is shown in Table I. The analysis of data included in Table I indicated that
Peculiarities of SPE of 19 October 1989 and 23 March 1991
(10)647
the method of determining the 8CR spectrum on the basis of measurements of the particle fluxes during the flight of satellites in the geomagnetic field is unsuitable for geomagnetic disturbance (Dst>25 nT) since even in the region of energies above 250 MeV the error in the estimation of the cut-off vertical rigidity may exceed 50%. The method is best suited, from the standpoint of geomagnetic disturbance, for the cut-off energies more than 400 MeV (L<4) and weak geomagnetic disturbance (Dst<25 nT). TABLE 1
Vertical Rigidity and ~ e r g i e s of the Geomagnetic Threshold Cut-off as a Function of the Amplitude of Dst Variation
Dst=O
Dst = 25 nT
Dst = 50 nN
Dst= l O O n N
L RIGV
TIGeV
R± OV
TI0eV
R i GV
TiGeV
R i OV
TIGeV
1.0
14.80
13.90
14.76
13.85
14.72
13.80
14.63
13.72
I .5 2 .O
6.58 3.70
5.71 2.88
6.50 3.59
5.63 2.77
6.42 3.48
5.55 2.67
6.26 3.26
5.40 2.46
2.5 3.0
2.37 1.64
1.61 0.96
2.23 1.48
1.48 0.81
2.09 1.31
1.3 0.67
1.81 0.97
1.10 0.41
3.5
I .21
0.59
1 .O1
0.44
0.81
0.30
0.42
0.22
4.0 4.5 5.0 5.5
0.92 0.73 0.5 0,49
0.38 0.2 0.17 0.12
0.70 0.48 0.31 0.18
0.25 0.11 0.0 0.02
0.47 0.22 0.03 0.02
0.11 0.03 -
0.02 -
0.09 -
Finally, the form of the SCR spectrum has its specific influence on the correctness of the effective cut-off rigidity estimation. To quote estimations /6/, in the trajectories such as that of the Mir station the difference between R I and R I for the spectra with characteristic rigidity R o in the interval 50-100 MV for L parameter varying within 2.5-3 does not exceed 20%. We analyzed the periods of the SCR increases (19-20 October, 1989 and 23-24 March, 1991) when the geomagnetic disturbance amplitude (Dst-Variation) was not higher than 15-20 nT, and the following estimation of vertical cut-off rigidity accuracy can be made. For L values in the range 2.5-4.5 R I the values of the effective cut-off rigidity had errors no more than 40% for EI>250 UeV and no more than 30% for EI>I GeV. A rise in E I causes a decrease of error. 10
[
.\
E
v,
T~
I___ I
×
% 0
#N 0,1
•
\
\
.1,,
~-~.01 0,I
I E, GeV
Fig.1. SCR spectrum measured onboard the NIR station in 19 October 1989; I - 13.O7-13.21 UT; 2 - 13.49-14.10 UT
10
(10)648
V.M. Pelxovet al.
The energetic particle spectra for the initial phase of the SPE on 19 Oc tober 1989 were calculated with the use of the approximation techniques. The spectrum was determined for the region of the spacecraft orbit in the interval of L values between 2 and 5 in the period from 13.07 UT to 13.21 UT. The calculated results are shown in Figure I. It is evident,that the spectral form can be described by the function E-,7 7 being 2.2 in this period. For the period from 13.49 to 14.10 UT the spectrum in the f i ~ e is given under No 2, 7 parameter at that time was equal to 0.3. Similar calculations were carried out for the SPE which occurred on 23 March 1991. The geophysical situation remained undisturbed until 2.30 UT on 24 March 1991 when two successive magnetic storms with sudden commencements (black triangles) and a sharp Forbush decrease (Figure 2) of the GOR rate was registered. The figure displays the characteristics of geomagnetic activity,neutron monitor counting rate and solar flares ( segments ). On the whole the period is described by a great number of solar flares ( six during 21-23 March 1991 ) /7/. The SPE was apparently caused by one of the flares that took place at 22.43 UT on 22 March 1991 and at 02.19 UT on 23 March 1991. The satellite GOES-7 registered the beginning of an increase in Solar protons flux with E>IO MeV at 08 UT on 23 March 1991 .The proton
6500
I I I I I
N.M. Apatiti
~
I
2
3
6
4
7 8 9
5
GOES - 7 , Ip (> I OMeV )
IO
stratosphere Nit station
I I
6000 ~
5500
5000
_ ~ . ~ . j Z
8
Kp
-'--" I
6
--L.,I11
I
I
5 10 15 22.0.3,1991
20
-- -
0
I
i
5 10 15 2_3.03.1991
2
I
r
20
0
I
,
5 10 15 24.03,1991
,
20
Fig.2. Heliogeophysical environment during SPE in March 1991.
I 10 -I=KE-7
I "-~ 1 .0
r=~
.X.
in aeV I i n prot~cm2*s - 1 × s t 1
velue
0.1
I 0.1
~, G,~V
I
e
!
K
6.%J0~
1
7
2.6
@
@
5403 0.27 3.6
47
1.0
Fig.3. SCR spectrum measured onboard the MIR station in 03.23.1991. I - 20.50-21.00 UT; 2- 21.30-21.40 UT; 3 - 04.30-04.50 UT O3.24.1991; I and 3 - S-hemisphere, 2 - N-hemisphere
(10)649
Peculiarities of SPE of 19 October 1989 and 23 March 1991
flux was monotonically increasing up in the range of energies from 10 to 500 MeV and then a sharp increase followed at 04.06 UT on 24 March 1991 which was concurrent with a sudden commencement , m ~ e t i c storm. Figure 3 shows the SOR energetic particle spectra at two tsJne points before this abrupt increase ( and 2) and one - after the increase (3). The spectra are approximated by the function K,E-~ The parameters of this function for the indicaof the magnetic storm) the particle spectrum is typical for particles accelerated on the Sun and travelling in the interplanetary magnetic field. This is also evident from the softening of the spectrum later during the initial increase. The shock wave brought drastic changes into the pattern as particles with energies exceeding I GeV and a soft spectrum (7=4.7) emerged. The dynamics of the spectrum is typical for the transport of the SCR in a m.a~netic trap with additional acceleration processes up to high energies. Thzs seems to be the case during the 23 March 1991 event. The coincidence of abrupt onset of the magnetic storm and the appearance of extra particle fluxes was the reason for a considerable rise of the dose rate aboard Mir which reached 2.2 mrad/hr from 04.30 to 05 UT.
iven time points are shown in Table 2. The analysis of these data ~ es that prior to the arrival of the shock wave ( the beginning
TABLE 2 Integral Spectra of the SPE on 23 March 1991 at Different Time Points Date and Time of Measurements Parameter
20.50-21.00 UT 23 March 1991
21.30-21.40 UT 23 March 1991
04.30-04.50 UT 24 March 1991
6.8.10 -3 2.6
5.10 -3 3.6
0.27 4.7
R,cv -2. sr -I V
As a whole, the diurnal dynamics of the dose rate reflected the dynamics of particle fluxes during the SPE. The measured levels of the dose rates during the initial phase of the SPE on 19 October 1989 can exemplify this assumption ( Tigure 4 ). The dotted line shows the mean diurnal dose rates 101
10 4
S
103
"a
lo 0
o 3,
R,_.
~D ~
10"t
10 2
E
o 10"2
lo 1
~°°
6
~
?2
1'.
=:, 1°+ Hour UT
19 October. 1989
Pig.4. Dose rate dynamics measured by the LYULIN device and proton flux behavior, measured on the spacecraft GOES-7 at L=5-7 during the 19 October 1989 SPE. The dashed line is a dose at L=5-7 averaged for two days before the SPE. prior to the SPE, vertical lines - dose rates registered by the Lyulin instrument, solid curve - the proton flux registered by the GOES-7 satellite in the interval of energies between 84 and 200 MeV /7/. It is apparent that firstly, the dose that, firstly, the dose rate is highly proportional to flux and, secondly, the maximum dose rate reaches 4.10 -2 Gy.day -I suggesting a significant increase in the radiation environment even inside the space station and need for protective measures.
(10)650
V.M. Pe~rov et al.
CONCLUSION Measurements of the SGR fluxe distributions at various L-shells with the help of the Lyulin instrument elicited anomalies when large particle fluxes contributed to the high-energy region of the spectrum. This is manifested through an increase of extra SCR flux in the range of L=1.2-3.0 resulting from subtraction of baok~ground flux at these L values as measured during quiet periods. The flux of SCR measured by Lyulin device exceeds several times proton fluxes registered in the proton channel of the GOF~-7 spectrometer. The SCR spectra deduced from the analysis of the flux latitudinal distribution, particularly after arrival of the initial particles during the SPE on 19 October 1989, appeared to be anomalously rigid and contradictory to the current cosmophysic concepts of SCR proton acceleration. The ratio of dose rate_~o partigle flux measured by Lyulin varies in the range of (1.8-4.5).10 ~ G y . c m ~ ( for L from 1.4 to 6.1, respectively ) and agrees with the estimations of the ratio for protons with energy of 500-1000 MeV and-electrons with energy of 5-10 MeV. It should be noted that, according to the data from the GOES-7, the flux of electrons in the SCR with the energy >2 HeV exceeded the flux of protons with the energy of 640-850 MeV by a factor of five. Hence, we may infer that spectral hardening, as follows from the obtained data, is associated with mixed proton/electron relativistic component with prevalent input from electron fluxes. This hypothesis will require explanation of how relativistic electrons penetrate to the Mir orbit. The effect, probably, results from the quasi-capture of solar relativistic electrons in the outer regions of magnetosphere and subsequent rapid radial transport onto drift shells with a small L-parameter. These characteristics must be taken into account when the latitudinal effect is applied to reconstruct the SCR spectra. REF~CIES 1. Ts.P. Dachev, Yu.P.Natvichuk, J.V.Semkova,et al. Space radiation dosimetry with active detections for, the scientific program of the second bulgarian cosmonaut on board the "Mir" space station. Adv. Spece Res., 9, 247-251,1989. 2. R.A.Nimmik Some questions concerning the calculation of the penetration function. Cosm~ch. IssUed., V.28, • 2, pp.306-309, 1990. 3. R.A.Nimmik Daily variations of geomagnetic cutoff boundaries and penetration function. Co8m~ch. IssUed., V.29, ~ 3, pp 491-493, 1991. 4. V.V.Zil, F.V. Rjlomenskiy, V.M.Petrov Solar cosmic rays dose decrease due to geomagnetic field. Co8m~ch. ~ssZed., V.24, ~ 6, pp 944-947, 1986. 5. J.H.Adams, J.R.Letaw, D.F.Smart Cosmic Ray Effects on Microelectronics. Part II: The Geomagnetic Cutoff Effects. Naval Research Laboratory Memorandum Report 5099. 1983. Washington D.C. 6. P.I.Shavrin To determination of the solar proton spectra rigidity using geomagnetic cutoff along the trajectory of satellite. Cosm~ch. Iss~ea., V.13, ~ 4, pp 503-507, 1975. 7. Solar-Geophysical Data, ~ 560, 561, 565, Boulder, USA,1991.
Pergamon
PECULIARITIES OF THE SOLAR PROTON EVENTS OF19 OCTOBER 1989 AND 23 MARCH 1991 ACCORDING TO THE MEASUREMENTS ONBOARD THE MIR SPACE STATION V. M. Pelrov,* V. S. M a h k m t o v , * N. A. Panova,* V. A. S h u r s h a k o v , * Ts. P. Dachev,** J. V. S e m k o v a * * and Yu. P. M a t v i j c h u k * * * Institute of Biomedical Problems, Moscow 123007, Russia ** Solar- Terrestrial Influences Laboratory, Bulgaria
ABSTRACT Flux and dose rate dynamics of solar cosmic rays were measured by the L y u lin dosimeter during the events 19 October 1989 and 23 March 1991. The maximum dose rate registered was 0.4, 0.12 and 0.01 cGy/hour, respectively. Based on the latitude distribution of particle flux a power law form for the energy spectra of solar protons in the anisotropic phase of the events on 19 October 1989 and 23 March 1991 was determined. It was obtained that after the development of geomagnetic storm protons with energies more than I GeV were registered. INTRODUCTION Radiation monitoring with the dosimeter-radiometer Lyulin has been conducted for a long time aboard the orbital station Mir. The instrument is located in the main large-diameter module and its positioning is presumed to remain unchanged throughout the whole period of measurement. Therefore, mass distribution in reference to the instrument is constant and all oscillations in the radiation environment measured with the instrument result from changes in the radiation fields along the trajectory. The average thickness of the screening material is estimated to be 5-15 g.cm-2; the actual shielding due to spacecraft structure ranges between 2.5 and 150 g.cm -2. Hence, the largest contribution is made by protons with energies above 70-100 MeV. Thus the aquired data base of dose rate and flax along the station orbits gives the opportunity to investigate regularities or alterations of the radiation situation in the near-Earth space related to solar cosmic rays (SOR) and geomagnetic disturbances. In the present paper characteristics of the SCR in the period from 19 October 1989 up to 23 March 1991 responsible for radiation disturbances in the terrestrial magnetosphere and noticeable rise in dose rate in the Mir modules are discussed. EQUIPMENT AND RESULTS The Lyulin instrument is a highly sensitive semiconductive dosimeter which has been designed and put into operation during the second SU-Bulgarian joint mission aboard Mir in 1988. The detailed description of the instrument was given in /I/. The instrument provides concurrent measurements of dose rate and the flux of cosmic radiation. The detecting element is a semiconductor detector, the sensitive layer of which is 300 p~n thick and 2 cm 2 in area. The geometric factor amounts to 6 cm2.sr (for the flux from a hemisphere); the dose sensitivity (absorbed dose per one impulse at the outlet) is equal to IO.5.10 -10 Gy.impulse. The accuracy o f the dose measurements is +_20%, and the time of averaging of the dose rate and flux amounts to 10-1OO s. In September-October 1989 the instrument was in operation except for October 10-13 and 21-25. It was switched on during the solar proton events (SPE) in March 1991 and this allowed us to acquire detail information about flux distributions and dose rates along the Mir trajectory. Ten-second time averages of the radiation environment along each orbit was determined by measurements in more than 550 points. Each (10)645
(10)646
V.M. Petrov et al.
point was linked to geographic, L,B-ooordinates and time. Great detail of investigations and good statistics owin~ to high sensitivity of the instrument make it possible to use changes Lu the geomagnetic rigidity of outoff along the trajectory for determination of the S0R spectrum. This can be done by analyzing the flux distribution according to L values and vertical rigidity R (ratio R=14.8.L -2) or out-off energy E, which are the functions of L. As L values are determined from the model descriptions of the movement of particles in the geomagnetic field and the field itself, it would be useful to evaluate the effect of various geophysical factors on the vertical rigidity R. Among them there are three most slgnifioant: the direction of movement, local time and geomagnetic disturbance. The effect of direction of movement can be taken into account by means of the relation /2/ 4R I R(R l,t0)=.
, GV [
(1),
1+ / l - c o s O (R±/14.8) 3/4"12
where R(RI, 0J) is the cut-off rigidity representative of the vertical rigidity R± in a given point in orbit for the particles moving at angle with the East-West direction (~=0 for the particles coming from the East, ~0=~ for the particles coming from the West). If X=Rwest/Reast, this relation varies in the range from 4 to 1.1 while L changes from I to 7. The spectrum is normally estimated when the station passes the segments of the orbit with L>2.5 so that the real rigidity differs from vertical by no more than 15%. The influence of the local time on the estimation of the effective geomagnetic threshold R± can be defined with the use of relation /3/ for magnetically quiet period (Dst<50 nT): RI RI =
1
(2) + A(Ri,t m)
Correction A(Ri, tm) which depends on vertical threshold R± and local geomagnetic time tm at the point of measurement is calculated empirically using the equation formed on the basis of experimental data analysis: 2% 0.67 1.1+1.62 cos [ ~ 1.42 [ R--~- ]
(tm+O.66)]
A =
(3)
exp {1.72( Rl )2 [1+0.66 sin ( 2~ (t +2.o))]} O. 67
12
m
Oaloulations have shown that in the region RI<0.6 GV (EI<170 UeV), the correction A exceeds 0.5. In the region of RI>IGV (Ei>400 MeV), the value of A does not exceed 0.1 and rapidly diminishes with the increase of R I. In the region of RI>0.7 GV(EI>230 MeV) the correction runs 0.25. Hence, the neglect of local time can somewhat corrupt the SOR spectrum in the area of low energies (<150 MeV), basically by hardening, and will have practically no effect on the high energy region of the spectrum. The influence of geomagnetic disturbances must b{ also considered in the procedure for determining the vertical rigidity R I at the points of measurement. This can be accomplished, for instance, by usLu~ techniques proposed in /4,5/. Results of calculations of threshold rigzdity R I at various levels of disturbance (to amplitude of the Dst variation in nT) is shown in Table I. The analysis of data included in Table I indicated that
Peculiarities of SPE of 19 October 1989 and 23 March 1991
(10)647
the method of determining the 8CR spectrum on the basis of measurements of the particle fluxes during the flight of satellites in the geomagnetic field is unsuitable for geomagnetic disturbance (Dst>25 nT) since even in the region of energies above 250 MeV the error in the estimation of the cut-off vertical rigidity may exceed 50%. The method is best suited, from the standpoint of geomagnetic disturbance, for the cut-off energies more than 400 MeV (L<4) and weak geomagnetic disturbance (Dst<25 nT). TABLE 1
Vertical Rigidity and ~ e r g i e s of the Geomagnetic Threshold Cut-off as a Function of the Amplitude of Dst Variation
Dst=O
Dst = 25 nT
Dst = 50 nN
Dst= l O O n N
L RIGV
TIGeV
R± OV
TI0eV
R i GV
TiGeV
R i OV
TIGeV
1.0
14.80
13.90
14.76
13.85
14.72
13.80
14.63
13.72
I .5 2 .O
6.58 3.70
5.71 2.88
6.50 3.59
5.63 2.77
6.42 3.48
5.55 2.67
6.26 3.26
5.40 2.46
2.5 3.0
2.37 1.64
1.61 0.96
2.23 1.48
1.48 0.81
2.09 1.31
1.3 0.67
1.81 0.97
1.10 0.41
3.5
I .21
0.59
1 .O1
0.44
0.81
0.30
0.42
0.22
4.0 4.5 5.0 5.5
0.92 0.73 0.5 0,49
0.38 0.2 0.17 0.12
0.70 0.48 0.31 0.18
0.25 0.11 0.0 0.02
0.47 0.22 0.03 0.02
0.11 0.03 -
0.02 -
0.09 -
Finally, the form of the SCR spectrum has its specific influence on the correctness of the effective cut-off rigidity estimation. To quote estimations /6/, in the trajectories such as that of the Mir station the difference between R I and R I for the spectra with characteristic rigidity R o in the interval 50-100 MV for L parameter varying within 2.5-3 does not exceed 20%. We analyzed the periods of the SCR increases (19-20 October, 1989 and 23-24 March, 1991) when the geomagnetic disturbance amplitude (Dst-Variation) was not higher than 15-20 nT, and the following estimation of vertical cut-off rigidity accuracy can be made. For L values in the range 2.5-4.5 R I the values of the effective cut-off rigidity had errors no more than 40% for EI>250 UeV and no more than 30% for EI>I GeV. A rise in E I causes a decrease of error. 10
[
.\
E
v,
T~
I___ I
×
% 0
#N 0,1
•
\
\
.1,,
~-~.01 0,I
I E, GeV
Fig.1. SCR spectrum measured onboard the NIR station in 19 October 1989; I - 13.O7-13.21 UT; 2 - 13.49-14.10 UT
10
(10)648
V.M. Pelxovet al.
The energetic particle spectra for the initial phase of the SPE on 19 Oc tober 1989 were calculated with the use of the approximation techniques. The spectrum was determined for the region of the spacecraft orbit in the interval of L values between 2 and 5 in the period from 13.07 UT to 13.21 UT. The calculated results are shown in Figure I. It is evident,that the spectral form can be described by the function E-,7 7 being 2.2 in this period. For the period from 13.49 to 14.10 UT the spectrum in the f i ~ e is given under No 2, 7 parameter at that time was equal to 0.3. Similar calculations were carried out for the SPE which occurred on 23 March 1991. The geophysical situation remained undisturbed until 2.30 UT on 24 March 1991 when two successive magnetic storms with sudden commencements (black triangles) and a sharp Forbush decrease (Figure 2) of the GOR rate was registered. The figure displays the characteristics of geomagnetic activity,neutron monitor counting rate and solar flares ( segments ). On the whole the period is described by a great number of solar flares ( six during 21-23 March 1991 ) /7/. The SPE was apparently caused by one of the flares that took place at 22.43 UT on 22 March 1991 and at 02.19 UT on 23 March 1991. The satellite GOES-7 registered the beginning of an increase in Solar protons flux with E>IO MeV at 08 UT on 23 March 1991 .The proton
6500
I I I I I
N.M. Apatiti
~
I
2
3
6
4
7 8 9
5
GOES - 7 , Ip (> I OMeV )
IO
stratosphere Nit station
I I
6000 ~
5500
5000
_ ~ . ~ . j Z
8
Kp
-'--" I
6
--L.,I11
I
I
5 10 15 22.0.3,1991
20
-- -
0
I
i
5 10 15 2_3.03.1991
2
I
r
20
0
I
,
5 10 15 24.03,1991
,
20
Fig.2. Heliogeophysical environment during SPE in March 1991.
I 10 -I=KE-7
I "-~ 1 .0
r=~
.X.
in aeV I i n prot~cm2*s - 1 × s t 1
velue
0.1
I 0.1
~, G,~V
I
e
!
K
6.%J0~
1
7
2.6
@
@
5403 0.27 3.6
47
1.0
Fig.3. SCR spectrum measured onboard the MIR station in 03.23.1991. I - 20.50-21.00 UT; 2- 21.30-21.40 UT; 3 - 04.30-04.50 UT O3.24.1991; I and 3 - S-hemisphere, 2 - N-hemisphere
(10)649
Peculiarities of SPE of 19 October 1989 and 23 March 1991
flux was monotonically increasing up in the range of energies from 10 to 500 MeV and then a sharp increase followed at 04.06 UT on 24 March 1991 which was concurrent with a sudden commencement , m ~ e t i c storm. Figure 3 shows the SOR energetic particle spectra at two tsJne points before this abrupt increase ( and 2) and one - after the increase (3). The spectra are approximated by the function K,E-~ The parameters of this function for the indicaof the magnetic storm) the particle spectrum is typical for particles accelerated on the Sun and travelling in the interplanetary magnetic field. This is also evident from the softening of the spectrum later during the initial increase. The shock wave brought drastic changes into the pattern as particles with energies exceeding I GeV and a soft spectrum (7=4.7) emerged. The dynamics of the spectrum is typical for the transport of the SCR in a m.a~netic trap with additional acceleration processes up to high energies. Thzs seems to be the case during the 23 March 1991 event. The coincidence of abrupt onset of the magnetic storm and the appearance of extra particle fluxes was the reason for a considerable rise of the dose rate aboard Mir which reached 2.2 mrad/hr from 04.30 to 05 UT.
iven time points are shown in Table 2. The analysis of these data ~ es that prior to the arrival of the shock wave ( the beginning
TABLE 2 Integral Spectra of the SPE on 23 March 1991 at Different Time Points Date and Time of Measurements Parameter
20.50-21.00 UT 23 March 1991
21.30-21.40 UT 23 March 1991
04.30-04.50 UT 24 March 1991
6.8.10 -3 2.6
5.10 -3 3.6
0.27 4.7
R,cv -2. sr -I V
As a whole, the diurnal dynamics of the dose rate reflected the dynamics of particle fluxes during the SPE. The measured levels of the dose rates during the initial phase of the SPE on 19 October 1989 can exemplify this assumption ( Tigure 4 ). The dotted line shows the mean diurnal dose rates 101
10 4
S
103
"a
lo 0
o 3,
R,_.
~D ~
10"t
10 2
E
o 10"2
lo 1
~°°
6
~
?2
1'.
=:, 1°+ Hour UT
19 October. 1989
Pig.4. Dose rate dynamics measured by the LYULIN device and proton flux behavior, measured on the spacecraft GOES-7 at L=5-7 during the 19 October 1989 SPE. The dashed line is a dose at L=5-7 averaged for two days before the SPE. prior to the SPE, vertical lines - dose rates registered by the Lyulin instrument, solid curve - the proton flux registered by the GOES-7 satellite in the interval of energies between 84 and 200 MeV /7/. It is apparent that firstly, the dose that, firstly, the dose rate is highly proportional to flux and, secondly, the maximum dose rate reaches 4.10 -2 Gy.day -I suggesting a significant increase in the radiation environment even inside the space station and need for protective measures.
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V.M. Pe~rov et al.
CONCLUSION Measurements of the SGR fluxe distributions at various L-shells with the help of the Lyulin instrument elicited anomalies when large particle fluxes contributed to the high-energy region of the spectrum. This is manifested through an increase of extra SCR flux in the range of L=1.2-3.0 resulting from subtraction of baok~ground flux at these L values as measured during quiet periods. The flux of SCR measured by Lyulin device exceeds several times proton fluxes registered in the proton channel of the GOF~-7 spectrometer. The SCR spectra deduced from the analysis of the flux latitudinal distribution, particularly after arrival of the initial particles during the SPE on 19 October 1989, appeared to be anomalously rigid and contradictory to the current cosmophysic concepts of SCR proton acceleration. The ratio of dose rate_~o partigle flux measured by Lyulin varies in the range of (1.8-4.5).10 ~ G y . c m ~ ( for L from 1.4 to 6.1, respectively ) and agrees with the estimations of the ratio for protons with energy of 500-1000 MeV and-electrons with energy of 5-10 MeV. It should be noted that, according to the data from the GOES-7, the flux of electrons in the SCR with the energy >2 HeV exceeded the flux of protons with the energy of 640-850 MeV by a factor of five. Hence, we may infer that spectral hardening, as follows from the obtained data, is associated with mixed proton/electron relativistic component with prevalent input from electron fluxes. This hypothesis will require explanation of how relativistic electrons penetrate to the Mir orbit. The effect, probably, results from the quasi-capture of solar relativistic electrons in the outer regions of magnetosphere and subsequent rapid radial transport onto drift shells with a small L-parameter. These characteristics must be taken into account when the latitudinal effect is applied to reconstruct the SCR spectra. REF~CIES 1. Ts.P. Dachev, Yu.P.Natvichuk, J.V.Semkova,et al. Space radiation dosimetry with active detections for, the scientific program of the second bulgarian cosmonaut on board the "Mir" space station. Adv. Spece Res., 9, 247-251,1989. 2. R.A.Nimmik Some questions concerning the calculation of the penetration function. Cosm~ch. IssUed., V.28, • 2, pp.306-309, 1990. 3. R.A.Nimmik Daily variations of geomagnetic cutoff boundaries and penetration function. Co8m~ch. IssUed., V.29, ~ 3, pp 491-493, 1991. 4. V.V.Zil, F.V. Rjlomenskiy, V.M.Petrov Solar cosmic rays dose decrease due to geomagnetic field. Co8m~ch. ~ssZed., V.24, ~ 6, pp 944-947, 1986. 5. J.H.Adams, J.R.Letaw, D.F.Smart Cosmic Ray Effects on Microelectronics. Part II: The Geomagnetic Cutoff Effects. Naval Research Laboratory Memorandum Report 5099. 1983. Washington D.C. 6. P.I.Shavrin To determination of the solar proton spectra rigidity using geomagnetic cutoff along the trajectory of satellite. Cosm~ch. Iss~ea., V.13, ~ 4, pp 503-507, 1975. 7. Solar-Geophysical Data, ~ 560, 561, 565, Boulder, USA,1991.