Evolution of coronal helmets during the ascending phase of solar cycle 20 |
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| Authors: | Shirley F Hansen Richard T Hansen Charles J Garcia |
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| Institution: | (1) High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colo., U.S.A. |
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| Abstract: | The principal polar-crown coronal helmet structures were selected from nearly three years (May, 1965–January, 1968) of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii. Six isolated and long-lived helmet systems were found at latitudes of 45° and above. Their developments are compared with underlying chromospheric and photospheric activity and a simple phenomenological model is presented showing that a coronal system is formed over an active region. Thereafter the center of gravity of the system gradually drifts poleward with the trailing unipolar magnetic region (UMR), and it becomes a high latitude coronal helmet, arched over a polar crown filament.By comparison of these coronal helmets with observations of the outer corona (to circa 4 R
 ) made at solar eclipse, lunar sunset, and with balloon and rocket-borne externally occulted corona-graphs, it appears that ground-based K-coronameter measurements to a distance of 1.5–2.0 R
are sufficient to detect the coronal streamers.The National Center for Atmospheric Research is sponsored by the National Science Foundation. |
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