Coronal loops and active region structure |
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Authors: | D F Webb H Zirin |
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Institution: | (1) American Science and Engineering, Inc., 02139 Cambridge, Mass., U.S.A.;(2) California Institute of Technology, 91125 Pasadena, Calif., U.S.A. |
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Abstract: | We intercompared synoptic H , Ca K, magnetograph and Skylab soft X-ray and EUV data for the purpose of identifying the basic coronal magnetic structure of loops in a typical active region and studying its evolution. We focussed on a complex of activity in July 1973, especially McMath 12417. Our principal results are: (1) Most of the brightest loops connected the bright f plage to either the sunspot penumbra or to p satellite spots; no non-flaring X-ray loops end in umbrae; (2) short, bright loops had one or both ends in regions of emergent flux, strong fields or high field gradients; (3) stable, strongly sheared loop arcades formed over filaments; (4) EFRs were always associated with compact X-ray arcades; and (5) loops connecting to other active regions had their bases in outlying plage of weak field strength in McM 417 where H fibrils marked the direction of the loops. We conclude that a typical loop brightens in response to magnetic field activity at its feet, which heats the plasma. This suggests that the loop acts as a trap for gas convected from its base. |
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