From December 1975 to June 1976 we observed

an evolving recurrent proton enhancement with IMP 7/8

and Helios 1/2 at different distances from the sun. The

corotating character is established over 4 solar rotations.

Due to the unique constellation in March 1976 simultaneous

measurements were possible which allowed a study of the

radial development undisturbed by temporal effects. The

intensity variation of the ~4 - 13 MeV protons between

0.43 and 1 AU revealed a sudden increase to a large positive gradient (+329 %/AU) in the leading edge of the

event. This value is consistent with a major source outside

1 AU. We suggest an interplanetary acceleration which

becomes sufficiently effective within a fast solar wind

stream

Green, G.

Hempe, H.

Kunow, H.

Müller-Mellin, R.

Wibberenz, G.

Witte, M.

Caltech Authors - Main

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SIMULTANEOUS OBSERVATIONS OF COSMIC RAY PARTICLES IN A 
COROTATING INTERPLANETARY STRUCTURE AT DIFFERENT SOLAR 
DISTANCES BETWEEN 0~3 AND 1 AU FROM HELlOS 1 AND 2 AND 
IMP 7 AND 8 
H. Kunow, G. Wibberenz, G. Green, R. Muller~Mellin, M. Witte, H. Hempe 
· Institut fUr Reine und Angewandte Kernphysik, Olshausenstr. 40~60, 23 Kiel, 
Federal Republic of Germany 
-
R.A. Mewaldt, E.C .. Stone, R.E. Vogt 
California Institute of Technology, Pasadena, California, 91125, U.S.A. 
Abstract. From December 1975 to June 1976 w.e observed 
an evolving recurrent proton enhancement with IMP 7/8 
and Helios 1/2 at different distances from the sun. The 
corotating character is established over 4 solar rotations. 
Due to the unique constellation in March 1976 simultaneous 
measurements were possible which allowed a study of the 
radial development undist~rbed by temporal effects. The 
intensity variation of the "'4 ~ 13 ~leV protons bet.ween 
0.43 and 1 AU revealed a sudden increase to a large posi~ 
tive gradient (+329 %/AU) in the leading edge of the 
event. This value is consi.stent with a major source outside 
1 AU. We suggest an interplanetary acceleration which 
becomes sufficiently effective within a fast solar wind 
stream. -
1. Introduction. The Pioneer 10 and 11 missions to Jupiter 
provided for the first time the opportunity to extend the studies 
on the radial dependence of recurrent proton enhancements over 
a much larg~r range of radial distances. McDonald et al. (1975) 
found that the average recurrent ~vents near 3 AU were up to 
"'10 times larger in intensity than the average events observed 
at 1 AU. Whereas initially a solar origin of these particles had 
been assumed, McDonald et al. now suggested that interplanetary 
acceleration was resonsible for the higher intensities observed 
beyond 1 AU. Barnes and Simpson (1976) reported evidence for 
interplanetary acceleration of nucleons in corotating interaction 
regions. In a statistical study, ~1arshall and Stone (1977) found 
that in the majority of the events observed at 1 AU the diffusive 
anisotropy of "'1.6 MeV protons was towards the sun, along the 
interplanetary magnetic field, ind~aating that there was a source 
of particles outside 1 AU and a sink inside. 
In this paper we present measurements of proton intensities in 
corotating events, taken by two spacecraft inside 1 AU simultane-
ously and by two spacecraft at 1 AU with only ~ very short time 
delay. 
I 
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2. OeveloHm~nt of the recurrent proton enhancement between 
January andpril 1976. From December 1975 until June 1976 an 
evolving recurrent proton enhancement has been observed in inter-
planetary spa~e. This period is characterized by a very low level 
of solar activity only a few months before the solar minimum. 
Be t wee n J a n u a r y 1 2 a n d M.a r c h 2 1 , 1 9 7 6 no so 1 a r f 1 a r e o f i m p o r-
tance 1f or larger had been observed. Figure 1 shows the intensi-
ty-time history of 4.0 - 12.5 MeV protons as measured by the 
Caltech Electron/Isotope Spectrometer on board IMP 8. The 4 
panels of figure 1 show the complete Carrington rotations 1637 
through 1640. The Carrington longitude scale on the bottom 
~escribes the magnetic field line connection of IMP 7/8 to the. 
solar surface assuming a constant solar wind velocfty of 550 km/s. 
T~e si~nificant feature of figure 1 is the 
recurrence of a proton intensity enhance-
ment with a period of~ 27 days over 4 
solar rotations centered around 280e Carring-
ton longitude. The event~velops considerably 
during three subsequent solar rotations. The 
slow increase in January lasts for nearly 10 
days with its maximum aftyr 6 days. !he rna~· 
x i mum i n ten s i t y 'i s 4 x 1 0 pro to n s I m s s r MeV. 
One rotation later, in February 1976, the 
maximum intensity is reached after a rise 
time of only four days. The first and second 
peak which are separated by three d~ys show 
nearly2the same intensity of 3 x 10 pro-tons/m s sr MeV. The decay appears to be 
much slower and shows two additional humps. 
During the third solar ro~ation the intensi-
t~ increases up to 7 x 10. particles/ 
m s sr MeV within 2.5 days. Here the first 
peak is much more pronounced than the 
following peaks. The decay ~hase, however, 
is disturbed by a prompt solar particle 
event due to a series of flares between 
March 21 and March 31, 1976. In April the co-
rotating feature has weakened by two orders 
of magnitude. However, the peak appears at 
the same Carrington longitude as before. 
This disturbance of the corotating struc-
• ~ • ~ ~ • & ~ • 
CARRING'ION LONGITUDE 
Fig.1: Recurrence of. 
an intensity enhance-
ment (shaded area) of 
4.0-12.5 MeV protons 
measured by IMP 7/8 
over 4 solar rotations 
(day 13-120, 1976). 
ture might be related to the series of flires which 
before the onset. 
ended 12 days 
While the corotating structure s£ems to develop for 3 complete 
solar rotations and to decay thereafter· significant features per-
sist at nearly the same Carrington longitude for 3 or 4 solar 
rotations. This demonstrates the recurrent character of the in-
tensity enhancements (shaded area in figure 1). For a more de-
tailed discussio~ we.shall concentrate in the following on the 
increase bet~een March 12 and March 20~ 1976· (days 72-80). 
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3. Spacecraft constellation. The March 1976 corotating event 
has been observed by 4 spacecraft simultaneously. The spacecraft 
constellation for March 15 is given in figure 2. Helios 1 was 
closest to the sun at a radial distance of 0.43AU 
and a heliographic latitude of -7.1o. Helios 2 
was located at a solar distance of 0.67 AU and 
a latitude of -7.2°. Both probes were connected 
via interplanetary magnetic field lines to the 
same region on the sun at 2680 Carrinton longitu-
de. The earth orbiting satellites IMP 7 and 8 
were at a solar distance of 0.994 AU and a .helio-
graphic latitude of -6.5°. On March 15 these sate-
llites were probably in a regime.of relatively 
low solar wind velocity and connected to the 
corona at 305° Carrington longitude. 
This spacecraft constellation is unique in so 
far as Helios 1 and Helios 2 are located at 
different solar radial distances but on the 
same interplanetary magnetic field line. We wish 
to point out that this includes the longitude as 
well as the latitude of the magnetic field line 
75.1976 
Fig.2: Constel-
lation of HELlOS 
1/2 and IMP 7/8 
on March 15,1976. 
connection to the sun. Only ~ 30 hours later the same interplane- . 
tary magnetic field line intercepts the IMP 7 and IMP 8 satellites. 
These relative spacecraft positions allow the radial development 
of the event to be studied undisturbed by temporal effects. 
4. Instrumentation. The observations on which this paper is 
based were made by the Caltech experiments on board IMP 7 and 8 
and by experiments of the University of Kiel on board Helios 1 and 
Helios 2. The detector telescope of the Helios 1 and 2 instruments 
is described in detail by Kunow et al. (1975) and by Kunow et al. 
(1977). In this paper we present coincidence data of detectors 1 
and 2. The original countrates were corrected for background 
using two-dimensional pulse height information of extended time 
·periods. The EIS experiment on board of IMP 7 and 8 is described 
by Hurford et al. (1974) and Mewaldt et al. (1976). The data pre-
sented in this paper are based on two-parameter particle identifi-
cation. 
An intercalibration of all 4 instruments was performed for 'the co-
rotating event periods in December 1975 and January 1976 when both 
Helios spacecraft were outside 0.9 AU and within an azimuthal 
distance of 24° from the earth. Taking into account the corotation 
delay all 4 instruments measured the same intensities to within 
+ 15 %. 
5. The March 1976 Corotating Event. The March 1976 corotating 
event, already introduced above, is shown in more detail in 
figure 3. Prior to the onset of the event a sector bounda~y sweeps 
past Helios 1 and 2 (G. Musmann and F. Neubauer, private communi-
cation). The intensity time profiles of 4 to 13 MeV protons are 
presented by 2-hour averages between March 12 and March 20, 1976. 
The profiles are similar at the three radial distances 0.43, 0.67 
and 1.0 AU. The intensity rises to the main maximum within about 
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50 hours. The event shows the double hump 
structure (best evident at 1 AU) frequent-
ly observed in corotating events at 
larger solar distances (Barnes et al., 
1976). We have visually identified the 
structures 3, 4 and 5 which are common to 
all three profiles.Application· of the 
backmapping technique using preliminary 
solar wind velocities (courtesy H. Rosen-
bauer, R. Schwenn) results in the same 
Carrington longitudes within + 3° for the 
corresponding structures. AddTtional 
times have been chosen for identic~l 
C a r ri n g ton 1 on g i t u d e s and a r e mar k e ·d 1 , 
2, 6 and 7. The increasing phase and the 
first maximum coincide roughly with the 
increase and maximum of a high speed so-
lar wind stream. The decreasing phase 
lasts for 4 days before it is masked by 
a prompt solar event (see figure 1). 
Special consideration should be given to 
the large step between marks 2 and 3 in-
dicating a moderate intensity increa~e 
by a factor of 2.5 at the position of 
Helios 1, but a drastic intensity in-
crease by a factor of ~to at 1 AU. 
DOn9'1& 
~ n n ~ ~ ~ n ~ n ~ 
1141' 718 
j 5 • uu 
A)./~ , \rt 
PROTONS 3.8 -12.6 MoY 
HELlOS 2 
, 0,67AU 
·;~· 
PROTONS 3.8 '12.8 MoY 
PROTONS 3. 7 -12.7 MeV 
10"' 12 13 14 15 16 17 18 19 20 
MAR1976 
Note also the radial depend~nce of the Fig.3:Two-hour averages 
intensity. The intensity level of the of proton intensities 
measured simultaneously 
main peak as observed by Helios 1 is at three different radial 
marked by solid triangles in each panel. distances. Marks 1 through 
The peak intensity of 4-13 MeV protons 
increases by a factor of 5.6 as the ra- 7 denote measurements on 
dial distance varies from 0.43 to 1.0 AU. the same interplanetary 
The radial dependence of the intensity magnetic field line. Note 
at the 7 marked levels in the profiles, that the energy interval 
which correspond to measurements on fo~ IMP 7/B.data has been 
essentially the same interplanetary adJusted sl~ght~y from 
_magnetic field line is shown in figure 4. that shown ln flg. l.to 
The Carrington longitude changes from agree m?re ~losely w1th 
310o to 227o between positions 1 and 7. the Hellos lnstruments. 
The intensity is plotted on a logarithmic scale versus radial 
distance on a linear scale. The·measurements can be fitted 
reasonably well by a straight lin.e. Thus we can describe the radial 
dependence of the intensity by radial gradient _ 1 x dl 
g - T err 
which is independent of r. Starting from the onset of the event 
(marked 1) the radial gradient g js negative:g = -(175 + 70) %/AU. 
The gradient increases with decreasing Carrington longi~ude, and 
switches suddenly to large positive values within less than 
5.hours in coincidence with the large step between position 2 and 
3. For the remaining part of the observable event (until it is 
masked by a prompt solar event on March 21) the gradient changes 
only little. For the main peak e.g. the gradient is g = + (329 
_:!: 20) %/AU. 
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It should be pointed out that ~ 
from approximately noon on day 74 
until noon on day 77 (IMP 8) and > 
from approximately noon on day ~ 
76 unti 1 the end of day 79 (IMP 7), ~ m' 
the IMP instruments were inside "::~: 
the earth's magnetopause ~ 30 ~ 
earth radic down the magnetotail. ~ 
Intercomparison of IMP - 7 and 8 ... 
d a t a d u ri n g t h e s e per i o d s i n d i - ~ •o' 
cates that the absolute intensi- ~ 
ties of 4 to 13 MeV protons were 
affected by ~ 20 % by the pre-
sence of the magnetopause. 
~ 
HELlOS 1 
0.4 0.5 
MG - 52 
HEI.,IOS 2 
0,6 0,7 0.8 
RADIAL DISTANCE (AU I 
IMP718 
0,9 1,0 
6. Discussion. · 
The material presented here i_s 
not sufficient to definitely 
confirm or rebut existing models 
Fig. 4: Radial depend~nce of the 
proton intensity at the 7 marked 
levels of Fig. 3. 
about the origin and nature of corotating events. The observed 
positive radial gradients certainly exclude a direct solar origin 
combined with pure interplanetary propagation, where ••pure" means 
that there is no local interplanetary acceleration. 
Let us for simplicity assume an 6uter source of particles pro-
duced well beyond the points of observation discussed in this 
paper. These particles penetrate into the inner solar system 
quite in the same way as particles ~f galactic origin. Under 
stationary conditions, a particularly simple form of the trans-
port equation is given by the force-field approximation (Gleeson 
and Axford, 1968), which is valid when the radial streaming Sr 
is zero. (This condition might apply here in contrast to par-
ticles of galactic origin in this energy range because of the 
steep energy spectrum, and, as a consequence, of the large Comp-
ton-Getting factor). From an experimental viewpoint, a vanishing 
radial streaming is related to a vanishing anisotropy in the 
radial direction. Preliminary analysis indicated that the a~iso­
tropies are small, consistent with the observations of Marshall 
and Stone (1977). If over the energy range 4~13 MeV we assume 
a power law spectrum ~E-Y, we have y ~ 4. This gives a Compton-
Getting factor C = 3.3. 
The force-field equation 
S r = C VU - K d U = 0 
r<>r 
1 ';) u 
allows to relate the gradient Gr = U~r to the diffusion coeffi-
cient Kr, once C and V are known. Inserting Gr = 32~ %/A~ 1 V = 550 km/sec and C = 3.3, we obtain Kr = 9.b x 10 ° em s- . 
Let us take v/c = s = 0.1 as a representative proton velocity 
for the energy range 4-13 MeV. This gives us for the radial mean 
free pathAr = 0.06 AU which is in good agreement with the average 
mean free path for cosmic ray particles as deduced from solar 
cosmic ray events (Wibberenz, 1974), and with that deduced by 
Marshall and Stone {1977) for ~1.6 MeV recurrent events at 1 AU. 
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The estimate does not explain the existance of recurrent events, 
but it shows that the observations are conststent with a major 
.sourc~ for these particles outside 1 AU. The onset of the posi-
tive radial gradient in coincidence with the leading edge of a 
fast solar wind stream indicates that the acceleration process 
becomes sufficiently effective within a fast stream. In the 
model suggested here the constancy of the radial gradient both 
with respect to radial distance and to longitudinal phase might 
be related to the constancy of the cosmic ray diffusion coeffi-
cient. The characteristic intensity profile may be due either 
to the boundary and injection conditions or to the variation of 
wave-particle interactions with phase within a fast solar wind 
stre·am. 
7. References 
Barnes, C.W. and J.A. Simpson, Astrophys. J. Lett., 210, L 91 -
L.96, 1976. 
Gleeson, L.J. and W.I. Axford, Astrophys. J., 154, 1011, 1968. 
Hurford, G.J., R.A. Mewaldt, E.C. Stone, and R:t: Vogt, 
Astrophys. J., 192, 541 - 546, 1974. 
Kunow, H., G. Wibberenz, G. Green, R. Muller-Mellin, M. Witte 
und H. Hempe, Raumfahrtforschung, 19, 253 - 258, 1975. 
Kunow, H., M. Witte, G. Wibberenz, H.~empe, R. Muller-Mellin, 
G. Green, B. Iwers und J. Fuckner, J. Geophys., To be 
published, 1977. 
Marshall, F.E. and E.C. Stone, Geophys. Res. Lett., 4, 57- 60, 
1977. -
McDonald, F.B., B.J. Teegarden, J.H. Trainor, T.T. von Rosenvinge 
and W.R. Webber, Astrophys. J., 203, l 149 - L 154, 1975. 
Mewaldt, R.E., E.C. Stone, S.B. Vidor, and R.E. Vogt, 
Astrophys. J., 205, 931- 937, 1976. 
·wibberenz, G., J. Geophys., 40, 667 - 700, 1974. 
© Bulgarian Academy of Sciences • Provided by the NASA Astrophysics Data System 


Simultaneous Observations of Cosmic Ray Particles in a Corotating Interplanetary Structure at Different Solar Distances between 0.3 and 1 AU from HELIOS 1 and 2 and IMP 7 and 8

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Simultaneous Observations of Cosmic Ray Particles in a Corotating Interplanetary Structure at Different Solar Distances between 0.3 and 1 AU from HELIOS 1 and 2 and IMP 7 and 8

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