Solar and galactic particle fluxes and interplanetary magnetic field after 1967 flar

Lindgren, S.

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FSolar and galactic coeraic rays and the interplaneta y
ma[rnet_ic field 28 JanunrY - 15 Feb_ ark/ 1967.
Stig Lindgren
Cosmic Ray Group, University of Uppsala, Uppsala, Sweden.
Abstract
Solar and galactic particle fluxes after the 28 January	
v
1967 particle flare are discussed in relation to interplane-
tary field observations. A soft pre-event began at 0214 on 	 r	 ^
28 January. It shows modulation features carried by the so-
A
r
lar wind from Explorer 33, 67 RE upstream, to IMP-3,
 15 RE
downstream from the earth. The interplanetary magnetic fiel
shows a sudden, major change of direction in coincidence
with the onset of the main event, whicn begins at 0835. New
injections of energetic protons take place late on 2 and
13 February.
The enhanced diurnal variation seen by neutron monitors
31 January - 7 February coincides well with a two-fold
increase in the magnitude of the interplanetary magnetic
field. Several hours before a magnetic storm at the end of
this period, the interplanetary magnetic field appears to
be strongly bqueezed; it enters the ecliptic plane from be-
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Introduction
The 28 January 1967 particle flare has been discussed in
several papers (Baird et al., 1967; Lockwood, 1968; Masley
and Goedeke, 1968; Mathews and Wilson, 1968; Paulikas and
rBlakey 1969). The most outstanding features of this event
arc: (1) the high particle fluxes at MeV energies; (2)
essentially as a consequence o •f' thats the long duration at
MeV energies; (3) the .lack of anisotropy at the onset; (4)
the absence of a reasonable parent flare on the solar disk.
Lockwood (1968) has suCecated a flare site 600 beyond the
west limb.
The purpose of the present paper is to present additional
data on the 28 January events mainly to add information on
the small particle event which preceded the ruin event by
6 hours, and to look for interactions between the inter-
planetary magnetic field and the flux of low energy solar
protons (E > t).5 MeV).
General characteristics of solar and galactic 2article fluxes
An overall picture of observed particle fluxes and the geo-
t
F'",
magneti c., activity is given in Fig. 1. The low
data come from K.A. Anderson's experiments on
33) and IMP-3. The pre-event can be seen most
IMP-3 "open" counter, which is a conventional
Unfortunately, the scale shows a rate which i
high. The count rate increases from 0.4 to 10
energy particle
4IMP-1 (Exploror
clearly in the
Geiger counter.
3 10 times too
counts/sec
and remains at the higher level for five hours until the main
event brings the rate up to a maximum level well three orders
of magnitude above the initial background rate. The charac-
teristic decay time of the ion chamber pulse rate is close to
2 days during the first four days after the peak rate. hater
in the events 11 - 13 February ' the decay time is much longer,
close to six days. The top diagram shows that two particle
increases are superimposed on the main event. The first
additional event begins late on 2 Februarys the second ev,.;nt
r
3late on 13 February. The clashed lines are meant to show what
the main event would have looked like without the two super-
imposed events. It is our definite impression that fluxes
from the 28 January flare are still present at the end of the
13 February event, implying a total duration of three weeks.
The raost outstanding feature in the galactic cosmic ray inten-
sity f apart from the increase on 28 - 29 January t is the en-
hanced diurnal variation from 1 to 7 February (Venkatesan and
Mathows. 1968; Hashim and Thanbyahpillai. 1969)p a period
which is geomagnetically quiet and completely free from For-
bush type modulations.
The interplanetary magnetic ,
 field.
Hourly overages of the interplanetary magnetic field are
presented in Figs. 2-4. The field was measured by the AMES
magnetometer experiment on Explorer 33 (Milhalov et al..
1968). The diagrams show three sets of data, with intermediate
gaps due to perigee pas es on 1-2 February and 14-15 February.
Figure 2 shows magnitude and phi-angle in the solar equatorial
system. Figure 3 magnitude and theta-angle.
From 0100 to 0900 on 28 January the field flows into the
region observed by Explorer 33 from above the equatorial
plane (theta,-45 0 ) and from a direction (phi,,,/2150 ) per-
pendicuiar to the garden-hose angle (0700 in Fig. 2 should be
0100 t as in	 Fig. 3). The field switches to a normal di-
rection at the time when the pre-Event is succeeded by the
main event.
Figure 2 shows that there are several periods t lasting about
a day ' when the field is more or less perpendicular to the
garden-hose direction (31 Jan. - 1 Feb.. 7 Feb.. 11-12 Feb.,
__ f
r
- 4 -
15 Feb. Y 17 Feb.). There are also extended periods when thu
magnetic flux enters the t luatorial plane from below at
large theta-angles (7 Feb., 9-13 Feb.). During the first
15 hours of 7 February the field appears to be strongly
aqueezc:d: it comes up into the equatorial plane at a thuta-
angle of —60 0  :axed is very strong (,v 10 garx-,ias) . An SSC is
observed at the earth at 1636 UT (Fig. .;}. After the SSC the
field is roughly in tho equatorial planer although point,inrr,
in a strange direction (phi-ar_jlu ~2550).
During tho period 31 Janua2y - 8 February the field is
roughly twice as strong; as before and after this period
(Fig. 4). The very strong field on 7-8 February should be
related to the SSC at 1636 on 7 February. It is clear that
this period of high field magnitudes coincides very well with .
a period of strongly enhanced diurnal variation. "le feel
that the strong magnetic field explains the enhanced diurnal
amplitude in this case, sin g e no modulation of the Ferbusl.
type is present to furnish an explanation in terms of a
disturbed density distribution.
Soiao remarks on the solar particle fluxes.
The pro-event which begins at 0214 on 28 January is illustrn--
ted in Fig. 5. The "open" counter on IMP-3 is a conventional
Geiger counter, which accepts protons >0.5 MeV and electrons
>40 keV. The scatter counter is sensitive only to electrons
>45 keV, scattered into the counter from a,;old foil. Besides;
both counters accept penetrating particles, protons >55 '!AeV
and electrons >5 MeV. The ITIT-3 ion chamber is sensitive, to
protons >15 MeV and electrons >1 bleV, the Explorer  33 chamber
to protons >12 MeV and electron3 >0.7 MeV.
It is possible to get a roughs qualitative picture of tlae
ML
r
- 5 -
spectrum of the observed solar particles by taking the ratio
between the open and scatter counters. With only penetrating
particles present, the ratio ahould bu 1, j: flux of sub-rela-
tivistic electrons only, E < 5 MoV, should ,give the ratio 19.
Soft protons, S < 55 MeV, should increase the ratio to a very
yarge value, since the scatter counter has a very low efficiency
for sucl protons. As Figure 5 Shows, the pre-event is charac-
terized by a ratio just below 15 9 a value which is reached
very late during the main uvont, on 6 February (Fig. 6). At
the -time when sea level neutron zionitors see the maximum
relativistic proton flux, ~1100 UT on 28 January, the ratio
is at its lowest value, ` 3. What is seen during the pre-
event appears to be sub-relativistic electrons, followed by
protons.
As Figure 5 indicates, Explorer-33 seems to observe certain
features 20 - 25 min before IMP-3. Explorer 33 is 82 RE or
522,500 km closer to the sun at this time, which leads to a
solar wind velocity of 350 - 435 km/sec, a reasonable value.
The onset time of the main event is estimated to 0835 from
the data shown in Fig. 5. The solar observatory at Culgoora
observed a type II herringbone burst on the meter and decameter
bands 075 15 - 0855 9 of intensity 2 on the decameter band. If we
assume that the scatter counter sees only protons at the time
of maximum count rato, — 1800 on 28 January, we arrive at a
maximum flux of 900 protons/cm2 sec at E > 55 MeV.
Figure 6 shows a decrease in the ratio between the open and
scatter counters late on 2 February, in coincidence with a
rate increase in the open counter. This implies an additional
injection of more energetic protons. The onset is gradual,
--., 1915 UT, and maximum intensity is reached five hours later by
r
e
I
r
	
"'!
- 6 -
the Gc:i; er couiiturs .
The increr;se iii 'the open counte,: 1500-1630 UT on 4 robruary
is pr^..eent alsa) in the scatter couiiter but not in the ion
ehaiibers. The nature of this increase is not known.
On 5 February al]. detectors suffer a te,.iporary rcducti,)n of
the count rate. The decrease is :sudden in the Gei er counters,
where: it occurs at 0343 UT, but very slow in the ion chaiabers,
extending; over > 3 hours. Complete recovery has taken place;
in all detectors at 2100 UT. The interplanetary field shows
a coLiplicated structure on 5 Fobruary (Fig;. 2). At BeV ener-
;ies the strong anisotropy disappears touporarily near mid-
night 4-5 February (Fig. 1; also Ha,shiLi and ThU .b;, -hpillai,
1969). The possibility of an interaction between the inter-
planetary riediui.i and the cosLlic rays cannot be excluded. HiZh
fluxes of soft protons are present before and after the SSC at
1636 on 7 February (Fib;. 6)- The same situation is repeated on
15- 16 February (Fig. 1).
The only increase during this period which can be associated
with a definite optical flare io the event at 1840 oil 13
February, beyond any doubt due to an importance 3 flare at
N21, 7;10.
Acknowledy eie nts
This work has been supported by the Swedish Science Research
Council, the Swedish Space Cormittee, and NASA (Contract: NGL-
05-003-017; Contractor: Dr. K.A. Anderson, Space Sciences Labo-
ratory, Berkeley). The AMES naGnetoraeter da-4'Ja were kindly supp-
lied by Dr. C.P. Sonett, the particle data from I12-3 and Ex-
plorer 33 by Dr. K.A. Juiderson.
r
References
1. Bairap G.A.p Bell, G.G.p Duggal f S.P. and Pomerantzv M.A.
Sclaz' Physic s
 2 f
 491 ( 1967).
2. HaehiLap A. and Thambyahpillaiq T. p barge Amplitude Wavo
Trains in the Cosmic Ray .ntensity^ Proprint ( 1969)0
3. Lo ckwoodp J.A. f J. Geophys. Res. 73 9 4247 (1968).
4. Masleyp A.J. and Goodeke f A.D. ' Can. J. Phys. 46 t S 766
(1968).
5. Vmthews t T. aid Wilson, B.G.p Can.J. Phys. 46 p S 776,
(1968).
6. Mihalovq J.D. Colburn, D.S. 9 Curriep R.G. and Sonettq
C.P. 9 J. Geophys. Res. 73, 943 (1968)•
7. Paulikasq G.A. and Blake t J.B. 9 J. Geophys. Res. 749
2161 (1969)0
8. Venkatesan, D. and Mathews f T. f Can. J. Phys. 46, S 794
(1968).
^t
,`t
Figuru Caitions
Fig. 1. Flux of solar and Ualac:tic cos-.iie rays 28 Jan. -
- 25 Feb. 1967. Scale of I-3 open counter shows ratua
10 timo3 too high. Sudden commencements in goomagnotic
activity marked by wed,fes.
Fit;. 2. Magnitw'.e and phi-angle of interplanetary raagnc:tio
field observed on Explore" 33 by C.F. Sonett, 11MES. Su-
lax equatorial. coordinates. Flags 	 2 4 00 UT. (0700 on
28 Jan. should be 0100. )
Fig. 3. ldagnitudcr and theta-angle of interplanetary magenetic
field observed on Explorer 33. Solar equatorial coordinates.
Flags ;:lark 2400 UT.
Fig. 4. This figure shows that a period of unhanced diurnal
variation closoly coincides with a twofold increase in
the strength of the interplanetary magnetic field.
Fig. 5. D 04-ni lod time profiles of pre-event, beginning at
0214 on 28 January. Certain features appear 20 - 25 nin
earlier at Explorer 33, 82 RE closer to the sun than
IMP-3. Ratio at bottom reflects gardening of spectrum
when main event begins.
Fig. 6. Illustrates how particle injections on 28 Jan. and
2 Feb. reduce ratio between open and scatter counters.
High ratios 7 - 8 Feb. indicate fluxes of soft protons
before and after SSC.
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Solar and galactic cosmic rays and the interplanetary magnetic field, 28 January - 25 February 1967

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