Recordings on relativistic solar flare protons observed at Sanae, Antarctic, show that the percentage increase in counting rates of the neutron moderated detector (4NMD) is larger than the percentage increase in counting rates of the 3NM64 neutron monitor. These relative increases are described by solar proton differential spectra j sub s(P) = AP(beta). The power beta is determined for each event and the hardnesses of the temporal variations of beta, found for the ground level events (GLE) of 7 May, 1978 and 22 November, 1977

Stoker, P. H.

English

NASA Technical Reports Server

114
SH 1.3-14
SPECTRA OF SOLAR PROTON GROUND LEVEL EVENTS USING
NEUTRON MONITOR AND NEUTRON MODERATED DETECTOR RECORDINGS
P.H. Stoker
PU-CSIR Cosmic Ray Research Unit
Department of Physics
Potchefstroom University for CHE
POTCHEFSTROOM 2520
South Africa
ABSTRACT
Recordings on relativistic solar flare protons observed
at Sanae, Antarctic, show that the percentage increase
in counting rates of the neutron moderated detector
(4NMD) is larger than the percentage increase In
counting rates of the 3NM64 neutron monitor. These
relative increases are described by solar proton diffe-
rential spectra js(P) = AP-B. The power _ is determined
for each event and the hardnesses of the temporal
variations of 8, found for the GLE's of 7 May, 1978and
22 November, 1977,are related to the results of
Debrunner et al. (1980).
I. Introduction. Neutron monitors record at ground level solar protons of
energies _ 0.5 GeV, while satellite data generally covers the energy range
below 0.5 GeV. Debrunner et al. (1984) combined the two sets of observa-
tions for the solar proton events on 7 May, 1978 and 22 November, 1977, and
deduced for various phases the solar proton energy spectra from 50 MeV to
about 10 GeV.
These two events and several other solar proton events were recorded during
the present solar cycle at Sanae with a cutoff rigidity of 0.86 GV in
Antarctica. When looking at an event from only a single position on Earth,
a particular spectral function has to be assumed in order to deduce the
spectrum of solar protons entering the atmosphere. Since rigidity is the
appropriate parameter for the combined effect of protons, s-particles and
heavier particles for earth bound recordings, a rigidity dependent spectral
function was considered. A power law rigidity spectrum j = AP-B appears to
fit the spectra given by Debrunner et al. (1984) in the rigidity range
~ 0.5 GV - 10 GV better than the exponential rigidity spectrum
j = A exp(-P/Po).
The neutron moderated detector 4NMD and super neutron monitor 3NM64 record
at Sanae primary cosmic rays wlth different rigidity dependent sensltlvi-
tles. In order to derive solar proton spectra for ground level events from
these recordings, the specific yield functions of these two detectors have
to be obtained accurately for rigidities % I GV. Solar proton ground level
events recorded at Sanae during the present solar activity cycle are
analyzed accordingly in this paper.
2. Method. A sp_c:flc yield function was comput_ fo_ each detector from
S(P)=n_,t)/j(P,t). The primary dlfferential rigidity spectrum j(P,t) was
obtained from the 1965 cosmic ray proton and helium particle spectra com-
piled by Webber (1973), while the differentlal response functions n(P,t)
were deduced from a least square fitting (Van der Walt, 1983) of the Dorman
function N(P) = No(l-exp(-_P-k)) to the data of the 1976 sea level survey
(Potgieter et al., 1980). The differential response functions for the NMD
114 
SH 1.3-14 
SPECTRA OF SOLAR PROTON GROUND LEVEL EVENTS USING 
NEUTRON MONITOR AND NEUTRON MODERATED DETECTOR RECORDINGS 
P.H. Stoker 
PU-CSIR Cosmic 
Department of 
Potchefstroom 
POTCHEFSTROOM 
South Africa 
ABSTRACT 
Ray Research Unit 
PhysIcs 
University for CHE 
2520 
Recordings on relativistic solar flare protons observed 
at Sanae, Antarctic, show that the percentage Increase 
In counting rates of the neutron moderated detector 
(4NMD) is larger than the percentage increase In 
counting rates of the 3NM64 neutron monitor. These 
relative increases are described by solar proton diffe-
rential spectra Js(p) = AP-S. The power S is determined 
for each event and the hardnesses of the temporal 
variations of S, found for the GLE's of 7 May, 1978 and 
22 November, 1977, are related to the results of 
Debrunner et al. (1980). 
1. Introduction. Neutron monitors record at ground level solar protons of 
energies> 0.5 GeV, while satellite data generally covers the energy range 
below 0.5 GeV. Debrunner et al. (1984) combined the two sets of observa-
tions for the solar proton events on 7 May, 1978 and 22 November, 1977, and 
deduced for various phases the solar proton energy spectra from 50 MeV to 
about 10 GeV. 
These two events and several other solar proton events were recorded during 
the present solar cycle at Sanae with a cutoff rigidity of 0.86 GV in 
Antarctica. When looking at an event fr m only a single positi n on Earth, 
a particular spectral function has to be assumed In order to deduce the 
spectrum f solar proto s entering the atmosphere. Since rigidity IS the 
appropriate parameter for the combined effect of protons, a-particles and 
heavier particles for earth bound recordings, a rigidity dependent spectral 
function was consi ered. A power law rigidity spectrum J = AP-S appears to 
fit th  spectra given by Debrullner et al. (1984) In the rigidity range 
- 0.5 GV - 10 GV better than the exponential rigidity spectrum 
J = A exp(-P/P ). 
o 
The neutron moderated detector 4NMD and super neutron monitor 3NM64 record 
t Sanae primary cosmic rays with different rigidity dependent sensitivi-
ties. In order to d rive solar proton spectra for ground level events from 
these recordings, the specific Yield functions of these two detectors have 
to be obtained accurately for rigidities> 1 GV. Solar proton ground level 
events recorded at Sanae during the present solar activity cycle are 
analyzed accordingly in this paper. 
2. Method. A s~~c;flc yield function was computc~ f0~ each detector from 
S(P) = n{ ,t)/j(p,t). The primary differential rigidity spectrum j(F,t) was 
obtained from the 1965 cosmic ray proton and helium particle spectra com-
piled by Webber (1973), whil  the differential response functions n(P,t) 
were deduced from a least square fitting (Van der Walt, 1983) of the Dorman 
function N(P) = No (l-exp(-ap-k» to the data of the 1976 sea evel survey (Potgieter et al., 1980). The differential response functions for the NMD 
https://ntrs.nasa.gov/search.jsp?R=19850026446 2020-03-20T17:02:55+00:00Z
115
SH 1.3-14
and NM64 thus obtained were applied to reproduce correctly the relative
counting rates recorded for the 15 February, 1978 Forbush decrease (Stoker
and Louw, 1983).
If js(P,t) represents the primary solar proton differential spectrum, the
enhanced counting rate due to a solar proton GLE is given by
ANs(m,t) = _S(P)Js(P,t)dP
c
with is(P) = AP-B. The ratio of the enhanced counting rates recorded by
the two detectors then becomes
ANsNMD IpcSNMD p-B dP
=
&Ns NM64 IpcsNM64 P-BdP
3O
' I ' I ' I ' I ' I I ' I ' I
3O
2o
A _
......z
10
I0
, t, I , I, I, I, ?, t ' t 0
1 Z 3 Z. S 6 7 tt 10 20 30
% INCREASE3NM6_
Figure I Figure 2
In Figure I the calculated ratio of enhanced counting rates is shown as a
function of the power B, with P_ = 0.86 GV. The constants of the Dorman
function used in calculating S(P) are No = 151.67, _ = exp 2.13 and
k = 0.894 for the 3NM64, while for the 4NMD the values are No = 157.68,
= exp 1.99 and exp 2.06, k = 0.898 and 0.940 respectively for the solid
and broken lines A and B in the Figure. For both of these two sets of
constants the Dorman functions lie within the statistical regression limits
determined from fittinqs to latitude survey data for the NMD. The ratio
of enhanced counting rates is not 1.00 for _ = 0 because the two differen-
tial response functions for the 4NMD and that of the 3NM64 are normalized
at P = 17 GV. The two curves in Figure I are considered to present the
upper and lower limits of the ratio of the enhancements at a particular
power B.
5 
 .  
d  t us btained ere plied to r produce orrectly the elative 
counting rates recorded for the 15 February, 1978 Forbush decrease (Stoker 
and ou , 1983). 
If js(P,t) represents the primary solar proton differential spectrum, the 
enhanced counting rate due to a solar proton GLE is given by 
00 
liN (p, t) (S (p) j (p, t) d P 
s Jp s 
 
with js(P) = AP-S. The ratio of the enhanced countlng rates recorded by 
e  tectors en  
0 
1  1. __ .--_ .",.-
o 
{J 
Figure 
liN NMD 
s 
liN NM64 
s 
o ~ 20 
~ 
.... 
VI 
< 
.... 
a:: 
...... 
~ 
";f!. 0 
OL-~~~~~-L~~~~~~~ 
0 ~ 0 
 CREASE M64 
Figure 2 
In Figure 1 the calculated ratio of enhanced counting rates is sho n as a 
function of the po er S, ith Pc = 0.86 GV. The constants of the or an 
function used in calculating S(P) are N = 151.67, a = exp 2.13 and 
k = 0.894 for the 3NM64, while for the ~NMD the values are No = 157.68, 
a = exp 1.99 and exp 2.06, k = 0.898 and 0.940 respectively for the solid 
and broken I ines  and  in the i re. or both f t ese two sets f 
stants t  r  f tio  I i  it i  th  t ti ti l r r i  limit  
deter ined from fittin s t  l titu  survey ata f r the . he r ti  
f  nti  r t s is t .0  f r S   s  t  tw  iff r -
tial response functions for the 4NMD and that of the 3NM64 are nor al ized 
at P = 17 GV. The two curves in Figure 1 are considered to present the 
upper and lower I i its of the ratio of the enhance ents at a particular 
po er S. 
116
SH 1.3-14
3. The GLE of 7 May, 1978. In Figure 2 the enhanced pressure corrected
ten minute and hourly counting rates for the 4NMD are plotted as a function
of the similar counting rates of the 3NM64, for the GLE of 7 May, 1978. The
galactic contributions have been normalized to 100. From this Figure it
follows that the first particles arrived at Sanae in the time interval
0335-0340 UT (signified by 0340) followed by a fast rise in counting rates
during 0340-0350 UT. With ANMD/ANM64 = 0.95 for the enhancement until
0350 UT, B _ 1.3, suggesting a flat initial spectrum, which presumably is
the result of the earlier arrival of the more energetic protons. Subse-
quently the intensity of the slower particles are increasing, causing the
displacement in the plot from 0350 to 0400, with the ratio ANMD/ANM64
changing to 1.49, giving B = 3.4-3.5 from Figure I for curves A and B
respectively. After 0400 the solar proton spectrum becomes even softer.
The average of the enhanced counting rates for the hour 0400-0500, indi-
cated by 05 in the Figure, represents a ratio ANMD/ANM64 1.63, giving
= 3.8-4.2. At 0450 UT ANMD/ANM64 = 1.99, and _ = 4.9 for the upper curve
A in Figure I.
When the 7 May, 1978 solar proton spectra of Debrunner et al. (1984), for
the rigidity interval of about 0.8 - 5 GV, are represented by the power law
Js _ p-8, the power values are B _ 3.3, 3.6, 4.0 and 4.9 respectively for
the time periods 0335-0345, 0345-0400, 0400-0415 and 0430-0500. These
values are about the same as we have obtained from Figure I.
9O
30
3 -I "
_ 0 _
o
-60
-90 • , , ., ,
3O0 0 60 120 180 2/.0
GEOGRAPHICLONGITUDE
Figure 3 is in part a reproduction of Figure 3 of Debrunner and Lockwood
(1980). The apparent source position and contours for angular distances of
30°, 60° and 90° are shown for the 7 May, 1978 event. Added to the Figure
are the asymtotic directions of vertical incident particles for Sanae (Shea
and Smart, 1971). From this Figure follows that the proton spectrum inci-
dent on top of the atmosphere at Sanae should be equivalent to the free
space spectrum at I AU.
116 
SH 1.3-14 
3. The GLE of 7 May, 1978. In Figure 2 the enhanced pressure corrected 
ten minute and hourly counting rates for the 4NMD are plotted as a function 
of the similar counting rates of the 3NM64, for the GLE of 7 May, 1978. The 
galactic contributions have been normal ized to 100. From this Figure it 
follows that the first particles arrived at Sanae in the time interval 
0335-0340 UT (signified by 0340) followed by a fast rise in counting rates 
during 0340-0350 UT. With 6NMD/6NM64 = 0.95 for the enhancement until 
0350 UT, B ~ 1.3, suggesting a flat initial spectrum, which presumably is 
the result of the earl ier arrival of the more energetic protons. Subse-
quently the intensity of the slower particles are increasing, causing the 
displacement in the plot from 0350 to 0400, with the ratio 6NMD/6NM64 
changing to 1.49, giving B = 3.4-3.5 from Figure 1 for curves A and B 
respectively. After 0400 the solar proton spectrum becomes even softer. 
The average of the enhanced counting rates for the hour 0400-0500, indi-
cated by 05 in the Figure, represents a ratio 6NMD/6NM64 1.63, giving 
B = 3.8-4.2. At 0450 UT 6NMD/6NM64 = 1.99, and B = 4.9 for the upper curve 
A in Figure 1. 
When the 7 May, 1978 solar proton spectra of Debrunner et al. (1984), for 
the rigidity interval of about 0.8 - 5 GV, are represented by the power law 
J s cr p-B, the power values are B ~ .3, 3.6, 4.0 and 4.9 respectively for 
the time periods 0335-0345, 0345-0400, 0400-0415 and 0430-0500. These 
values are about the same as we have obtained from Figure 1. 
90r-------,---------------------------~ 
UJ 
c::J 
=> I-
i= 
.:( 
-J 0 u 
:E 
Q.. 
.:( 
c:: 
-30 t.:J 
0 
UJ 
t.:J 
-60 
-90 
300 0 60 120 180 240 
GEOGRAPHIC LONGITUDE 
Figure 3 is in part a reproduction of Figure 3 of Debrunner and Lockwood 
(1980). The apparent source position and contours for angular distances of 
30°, 60° and 90° are shown for the 7 May, 1978 event. Added to the Figure 
are the asymtotic directions of vertical incident particles for Sanae (Shea 
and Smart, 1971). From this Figure follows that the pr ton spectrum Inci-
dent on top of the atmosphere at Sanae should be equivalent to the free 
space spectrum at 1 AU. 
117
SH 1.3-14
4. The GLE of 22 November, 1977. , , , , t .... I ....
In Figure 4 the enhanced pressure _i04a
corrected ten minute and hourly 22 NOV.1977 J
counting rates for the 4NMD are //
plotted as a function of corres- 30 _osH_o3o
pond0ng counting rates of the 111 °Vo,i,.
3NM64 for the GLE of 22 November, I_/41_00
1977. Here again the spectrum Y
to soften from the _ 1_'/"m°appears
eleventh to the twelfth hour UT. _z 1140.f/ )'/1|
The ratio ANMD/ANM64 for the _ 20
y.,y
first ten minutes I010-I020 UT _ 121o_/15o
IS ~0.9, suggesting _ _ O, pre-
sumably again due to the earlier
arrival of the more energetic _ 13/,_/
protons. The ratlo ANMD/ANM64 = fO /_20
1.30 at 1030 which is also the /_/io2o
average for the hour 1000-1100, _4
implies B = 2.7 ± 0.1. At 1040
,jthe ratio of the enhancements =
1.41, with _ = 3.1 For the 0 r, , , , I , , , , I , , , ,• I0 20 ]0
decaying phase of this event the "1_INCREASE3NM64
ratios of the enhancements show
fluctuations around these values.
For 1050-1100, 6NMD/&NM64 = 1.23, and B = 2.5; 1100-1110, the ratio in-
creased to 1.48 and _ to 3.4. For the twelfth and thlrtienth hour, the
average ratio = 1.38 and B = 3.0.
When representing the 22 November, 1977 solar proton spectra of Debrunner
et al. (1984) by a power law for the rigidity range~ I -6 GV, the power
values are B = 5.5, 4.6 and 4.9 respectively for the tlme periods 1035-
1046, 1055-1105 and 1200-1215. These values are larger than we found, but
the fluctuations tn hardness follow the same trend as we are observing.
The lower power values deduced for Sanae may be attributed to an apparent
source direction to the left 0° geographic longtttude in Figure 3, favou-
ring the higher rlgtdtty protons to enter the atmosphere. Thus a harder
solar proton rigidity spectrum was possibly incident at Sanae comparlng to
the free space spectrum as I AU.
5. Conclusions. Spectra of relattv0sttc protons recorded at Sanae may be
deduced from the relatlve enhancements In countlng rates of the 4NMD and
3NM64 detectors. For GLE solar proton spectra of 23 September, 1978, 8
December, 1982 and 16 Februarie, 1984 average powers _ = 4.5±0.2, 2.8 ±
0.1 and 2.6 ± 0.1 were obtained respectively.
Acknowledqements. The financial controbution and logtstlc support by the
Department of Transport for Antarctic research are gratefully acknowledged.
References
Debrunner, H., Fl_ckiger, E., Lockwood, J.A. and McGulre, R.E., J. Geophys.
Res. 8_99,769, 1984.
Debrunner, H., and Lockwood, J.A., J. Geophys. Res. 8__55,6853, 1980.
Potgieter, M.S., Raubenheimer, B.C., Stoker, P.H., and Van der Walt, A.J.,
S. Afr. J. Phys. 3, 77, 1980.
Shea, M.A., and Smart, D.F., AFCRL-TR-75-0247, May, 1975.
Stoker, P.H., and Louw, P.A., 18th ICRC, Bangalore, Conf. Papers 4, 181, 1983.
Van der Walt, A.J., 18th ICRC, Bangalore, Conf. Papers 10, 287, 1983.
Webber, W.R., 13th ICRC, Denver, Conf. Papers 5, 3568, I--973.
4. The GLE of 22 November, 1977. 
(n Figure 4 the enhanced pressure 
corrected ten minute and hourly 
counting rates for the 4NMD are 
plotted as a function of corres-
ponding counti g rates of the 
3NM64 for the GLE of 22 November, 
1977. Here again the spectrum 
appears to soften from the 
eleventh to the twelfth hour UT. 
The ratio 6NMD/6NM64 for the 
first ten minutes 1010-1020 UT 
IS - 0.9, suggesting (3 :> 0, pre-
sumably again due to the earl ier 
arrival of the more energetic 
protons. The ratio ~NMD/~NM64 = 
1.30 at 1030 which is also the 
average for the hour 1000-1100, 
impl ies (3 = 2.7 ± 0.1. At 1040 
the ratio of the enhancements = 
1.41, with (3 = 3.1. For the 
decaYing phase of this event the 
ratios of the enhancements show 
fluctuations around these values. 
17 
30 
10 
SH 1.3-14 
1040 
22 NOV, 1977 
30 
For 1050-1100, 6NMD/6NM64 = 1.23, and (3 = 2.5; 1100-1110, the ratio in-
creased to 1.48 and S to 3.4. For the twelfth and thlrtienth hour, the 
average ratio = 1.38 and (3 = 3.0. 
When representing the 22 November, 1977 solar proton spectra of Debrunner 
et al. (1984) by a power law for the rigidity range-l -6 GV, the power 
values are S = 5.5, 4.6 and 4.9 respectively for the time periods 1035-
1046, 1055-1105 and 1200-1215. These values are larger than we found, but 
the fluctuations In hardness follow the same trend as we are observing. 
The lower power values deduced for Sanae may be attributed to an apparent 
source direction to the left 0° geographic longtltude in Figure 3, favou-
ring the higher rigidity protons to enter the atmosphere. Thus a harder 
solar proton rigidity spectrum was possibly incident at Sanae comparing to 
the free space spectrum as 1 AU. 
5. Conclusions. Spectra of relativistic protons recorded at Sanae may be 
deduced from the relative enhancements In counting rates of the 4NMD and 
3NM64 detectors. For GLE solar proton spectra of 23 September, 1978, 8 
December, 1982 and 16 Februarie, 1984 average powers (3 = 4.5 ± 0.2, 2.8 ± 
0.1 and 2.6 ± 0.1 were obtained respectIvely. 
Acknowledgements. The financial controbution and lOgiStiC support by the 
Department of Transport for Antarct IC research are gratefully acknowledged. 
References 
Debrunner, H., Fluckiger, E., Lockwood, J.A. and McGuire, R.E., J. Geophys. 
Res. 89, 769, 1984. 
Debrunner,IH., and Lockwood, J.A., J. Geophys. Res. 85, 6853, 1980. 
Potgieter, M.S., Raubenheimer, B.C., Stoker, P.H., and Van der Walt, A.J., 
S. Afr. J. Phys. 3, 77, 1980. 
Shea, M.A., and Smart,-D.F., AFCRL-TR-75-0247, May, 1975. 
Stoker, P.H., and Louw, P.A., 18th (CRC, Bangalore, Conf. Papers 4, 181,1983. 
Van der Walt, A.J., 18th (CRC, Bangalore, Conf. Papers 10, 287, 1983. 
Webber, W.R., 13th (CRC, Denver, Conf. Papers 2, 3568,1973. 


Spectra of solar proton ground level events using neutron monitor and neutron moderated detector recordings

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server