34th Solar Physics Division Meeting, June 2003
Session 10 Transequatorial and other Coronal Structures
Oral, Tuesday, June 17, 2003, 9:00am-12:00noon, Auditorium

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[10.03] Transequatorial Loops and the Solar Magnetic Cycle

J.G. Luhmann, Yan Li (Space Sciences Laboratory, UC Berkeley), C.N. Arge (CIRES, U. of Colorado and NOAA-SEC), R. Ulrich (Department of Physics and Astronomy, UCLA)

Transequatorial coronal field lines exist during much of the solar magnetic cycle, especially at inactive times when the global dipole moment contribution to the coronal magnetic field is large, and its axis relatively untilted. These field lines are manifested in the simple near-equatorial helmet streamer belt observed with coronagraphs around solar minimum. However, they are not generally illuminated more than their surrounding counterparts, and are thus undistinguished when seen against the disk in soft x-rays. A point to note in this regard is that they are usually rooted at both ends in the quiet Sun. What is special about the subset of transequatorial field lines or flux tubes known as transequatorial loops is their brightness. A widely held view of soft x-ray loop brightness is that it is related to the magnetic field strength at the field line footpoints. The observation that transequatorial loops are usually rooted at one or both ends in active regions is consistent with this rule-of-thumb. Are these loops then simply a reflection of the particular field connections of active regions at a given time in the solar magnetic cycle? We test this interpretation by examining a model coronal magnetic field during the period of Yohkoh SXT observations to visualize the subsets of large scale field lines connected to the strongest photospheric fields. The general characteristics of these strongest footpoint field flux tubes are then compared with the solar cycle trends in Yohkoh SXT images.


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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.