Large coronal regions disconnected from any calcium plages and identified by their thermal emission at 169 mHz play a basic role in the sector structure of the interplanetary medium. It was concluded that these coronal regions are to be interpreted as streamers

Avignon, Y.

Axisa, F.

Martres, M. J.

Pick, M.

Simon, P.

English

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HELMET AND ACTIVE STREAMERS FROM RADIO OBSERVATIONS Y. Avignon, F. Axisa, 
M. J. Martres, M. Pick, 
and P. Simon 
Large coronal regions disconnected from any calcium plages and identified by their 
thermal emission at 169 mHz play a basic role in the sector structure of the 
interplanetary medium. We now conclude that these coronal regions are to be interpreted 
as streamers. 
ABSTRACT 
We have shown that the basic structure of helmet and 
active streamers would be traced by the presence, length, 
and orientation of filaments, the structure of both types 
of objects being determined by magnetic fields. Here we 
present some properties of active and helmet streamers 
based on radio observations, in particular some conse- 
quences concerning the medium corona and the inter- 
planetary medium [ Axisa et aZ., 197 11 . 
At 169 mHz, the slowly varying component of thermal 
origin is best explained in terms of emission by streamers 
at a typical altitude of 0.4 solar radius (fig. 1). A plasma 
frequency of 169 mHz corresponds to an electron 
density of 3.5 X lo8 e/cm3. Therefore, at an altitude of 
0.4 R,, the quiet sun can be considered practically 
transparent for such a frequency. So a value of 3.5 X 
lo8 e/cm3 may be considered as an upper limit for the 
actual density in streamers at 0.4 R,. In any case, it is 
seen that the electron density as deduced from our ratio 
data will be higher than proposed in Newkirk‘s model. It 
is in agreement with the electron density deduced from 
radio burst observations. At the same frequency, similar 
altitudes have been found for the sources of type I11 
emission [Mercier, 197 1 ] . 
As seen at 169 mHz, streamers schematically may be 
considered as dense plates extending from the filaments, 
with roughly the same length. The actual width of such 
Drs. Avignon, Martres, Pick, and Simon are at the Meudon 
Observatory, France; Dr. Axisa is at  the Service d’Electronique 
Physique, Centre d %tudes Nucle2ires de Saclay, France. 
plates cannot be estimated because of the limited 
resolving power of our instrument. But a recent study 
relative to type I11 bursts obtained with the Nancay 
radioheliograph leads to an estimation of 20,000 km 
[Merciw, 19711. Koutchmy deduced similar results 
from the March 1970 eclipse [Koutchmy, 19711 . 
We would like to discuss some implications concerning 
the coronal expansion. Independently, Schatten and 
Newkirk pointed out that through the medium corona, a 
very important filtering effect occurs and therefore the 
knowledge of coronal structure at a typical altitude of 
0.6 R,  is of great importance [Schatten, 1968;Newkirk 
et aZ., 19681. The coronal structures observed in 
radioastronomy at this level after the filtering effect 
have the same stability and longitudinal extent as the 
underlying filaments. Because large filaments reflect 
large regular magnetic field structures, it may help to 
understand physically why a relatively good correlation 
between interplanetary and photospheric large scale 
patterns has been found [Wileox and Ness, 19651. 
In connection with this problem, Martres et al. [ 19701 
have emphasized that large coronal regions disconnected 
from any calcium plages and identified by their thermal 
emission at 169 mHz play a basic role in the sector 
structure of the interplanetary medium (fig. 2). In the 
light of our present results, we now conclude that these 
coronal regions are to be interpreted as streamers. This 
result is in full agreement with BohEin’s [1970] paper 
showing the connection between an asymmetrical hel- 
met streamer and the interplanetary magnetic field. 
119 
https://ntrs.nasa.gov/search.jsp?R=19730002042 2020-03-17T07:23:01+00:00Z
1964 Oct. 15 
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120 
Finally, we would like to emphasize that as the slowly 
varying component observed near 169 mHz, contrasting 
with higher frequencies, is not at all representative of the 
solar activity (eruptive centers, calcium plages, coronal 
condensations, coronal enhancements), the pattern of 
the interplanetary sectors would not be simply linked to 
calcium plages. 
We now come to the solar wind expansion. Referring 
to the theoretical work of Pneuman [1969], we think 
that it is not so much the streamer itself that is of crucial 
importance, but the surrounding region. It is quite clear 
that solar activity will have a basic role to play by 
supplying energy. For the transfer of that energy 
throughout the medium corona, active streamers and 
helmet streamers will play an important role. 
Koutchmy, S.: Un modile de grant jet coronal avec 
renforcement de region active. Astron. Astrophys., 
1971 (in press). 
Martres, M. J.; Parks, G .  K.; and Pick, M.: The Origin of 
Interplanetary Sectors from Radio-0bservations.Solar 
Phys., Vol. 15, 1970, pp. 49-59. 
Mercier, C.: Altitude of Type I11 Bursts Observed at 169 
mHz, and Coronal Structure. Solar Phys., 1971 , to be 
submitted . 
Newkirk, G.; Altschuler, M. D.; and Harvey, J.: Influ- 
ence of Magnetic Fields on the Structure of the Solar 
Corona. I.A.U. Symposium No. 35,1968. 
Pneuman, G .  W.: Coronal Streamers. Solar Physics, Vol. 
6,1969, pp. 255-275. 
Schatten, K. H.: Large Scale Configuration of the 
Coronal Interplanetary Magnetic Field. Thesis, Uni- 
versity of California, Berkeley, 1968. 
REFERENCES 
Axisa, F.; Avignon, Y.; Martres, M. J.; Pick, M.; and 
Simon, P.: Streamers and Active Streamers from 
Radio Observations. Solar Phys., 1971 (in press). - .  
Bohlin, J. D.: Evolution of Discrete Features from the Wdcox, J. M.; and Ness, N. F.: Quasi-Stationary Corotat- 
Sun to 1 AU. Solar Phys., Vol. 13, 1970, ing Structure in the Interplanetary Medium. J. 
pp. 153-175. Geophys. Res., Vol. 70,1965, pp. 5793-5805, 
121 


Helmet and active streamers from radio observations

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