Abstract
A unique combination of photographic and K-coronameter data were used to study the structure and evolution of two known coronal streamers. In addition, two other K-coronameter enhancements were studied as representing ideal second examples of the known streamers. As a general rule the observations indicate that these features were direct coronal manifestations of photospheric bipolar magnetic regions (BMR) and were of two basic types:active region, by which is meant a coronal streamer which develops radially over a low-latitude active region; andhelmet which denotes a streamer whose structure and development appear to be a consequence of a long-lived complex of activity, composed of both trailing magnetic fields and a parent center of disk activity.
The similarity of growth rates during the first solar rotation of life led to derivation of a total streamer density of 4–5 × 108 cm−3 atr = 1.125R ⊙. This density may represent a characteristic maximum density at the base of streamers. The intensity gradient of the inner (r⩽1.5R ⊙) corona was used to establish a qualitative evolutionary model of streamers which synthesizes the observations. Briefly, streamers initially develop over active regions; the streamer growth rate may be as rapid as the disk activity, or at worst lags flare activity by ⪝\(\tfrac{1}{2}\) solar rotation. The streamer can be the cause of interplanetary and geomagnetic effects at 1 AU within a solar rotation after birth. Thereafter the streamer follows an evolution dictated by the underlying solar magnetic fields. In any case the lowest level of the coronal enhancement has a lifetime not exceeding that of the solar disk activity.
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Bohlin, J.D. Solar coronal streamers. Sol Phys 13, 153–175 (1970). https://doi.org/10.1007/BF00963949
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DOI: https://doi.org/10.1007/BF00963949