HR: 09:00h
AN: SH51C-05    [Abstracts]
TI: Understanding Warm Coronal Loops
AU: * Klimchuk, J A
EM: klimchuk@nrl.navy.mil
AF: Naval Research Lab, 4555 Overlook Ave., Washington, DC 20375, United States
AU: Karpen, J T
EM: karpen@nrl.navy.mil
AF: Naval Research Lab, 4555 Overlook Ave., Washington, DC 20375, United States
AU: Patsourakos, S
EM: patsourakos@nrl.navy.mil
AF: Naval Research Lab, 4555 Overlook Ave., Washington, DC 20375, United States
AB: One of the great mysteries of coronal physics that has come to light in the last few years is the discovery that warm (~ 1 MK) coronal loops are much denser than expected for quasi-static equilibrium. It has been shown that the excess density can be explained if loops are bundles of unresolved strands that are heated impulsively and quasi-randomly to very high temperatures. This picture of nanoflare heating predicts that neighboring strands of different temperature should coexist and therefore that loops should have multi-thermal cross sections. In particular, emission should be produced at temperatures hotter than 2 MK. Such emission is sometimes but not always seen, however. We offer two possible explanations for the existence of over-dense warm loops without corresponding hot emission: (1) loops are bundles of nanoflare heated strands, but a significant fraction of the nanoflare energy takes the form of a nonthermal electron beam rather then direct heating; (2) loops are bundles of strands that undergo thermal nonequilibrium that results when steady heating is sufficiently concentrated near the footpoints. We verify these possibilities with numerical hydro simulations. Time permitting, we will show FeXVII line profile observations from EIS/Hinode that support the existence of nanoflare heating. Work supported by NASA and ONR.
DE: 7509 Corona
DE: 7514 Energetic particles (2114)
DE: 7549 Ultraviolet emissions
DE: 7846 Plasma energization
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting