34th Solar Physics Division Meeting, June 2003
Session 1 Corona I
Oral, Monday, June 16, 2003, 9:00am-12:00noon, Auditorium

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[1.05] Linear force free field models of observed coronal loops

M.C. Lopez-Fuentes (Naval Research Laboratory and George Mason University), J.A. Klimchuk (Naval Research Laboratory)

Although active region magnetic fields have an overall expansion with height, soft X-ray and EUV loops are observed to have nearly constant cross sections. To investigate this apparent discrepancy, we have compared coronal loops observed by TRACE in the 171 A band with corresponding magnetic flux tubes obtained from linear force-free extrapolations (Demoulin et al. 1997) of nearly concurrent MDI magnetograms. The flux tubes were determined using a procedure that varies the force-free parameter alpha and searches for the field line that most closely coincides with the observed loop axis. Once the axis field line is identified, we construct flux tubes from the model field using a variety of assumed footpoint shapes and orientations.

Our detailed comparison confirms the mystery of constant loop cross sections. Although the expansion of the extrapolated flux tube as seen projected onto the plane-of-the-sky varies depending on the footpoint shape and orientation, it is always considerably greater than the expansion of the corresponding TRACE loop. This result implies that the magnetic structure and possibly also the heating of coronal loops are more complex than we currently understand.

This work was funded by NASA and the Office of Naval Research.

The author(s) of this abstract have provided an email address for comments about the abstract: lopezf@nrl.navy.mil

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