“Three-D MHD numerical simulations of coronal loop

oscillations associated with flares”

Miyagoshi et al., PASJ 56, 207, 2004

Issues of coronal seismology

• The dynamic spectrum of the coronal plasma structure has resonances (“normal modes”)

• Several lines of observation show these

• There is controversy with damping

• Their excitation is fundamentally interesting

Literature

• There is quite a bit of observational literature

• Analytic theory has been developed (especially by B. Roberts et al.)

• The problems presented by the oscillations seem ideally suited to ideal MHD theory

• But there are non-ideal effects observed

From Aschwanden et al. 1999(TRACE loop oscillations discovered!)

Case 2. Weird brown surface is density = 0.9.

Foregoing was for an empty loop (uniformhydrostatic potential-field medium.

What about an overdense loop?

Conclusions

• Oscillations found, at P = 2L/VA

• Oscillations damp at damp = -1/2

• Overdense loops oscillate more slowly, as expected

• Trapping effect is weak

Remaining questions

• How do these results compare with the analytic development of Roberts et al.?

• What modes are excited?

• How can this explanation of damping (the mere radiation of Alfven waves) be correct?

Periods

• Oscillations found, at P = 2L/VA

• Theory (Roberts, Edwin, Benz 1984) for “principal kink wave” gives

P = 2L/Ck, where

Ck = sqrt(2/(1+e/o))VA

Possible causes of damping

• Unexpectedly high viscosity

• Phase mixing

• Wave leakage at footpoints

• Resonant absorption

• Direct Alfven-wave losses?

There is good review material in Erdelyi et al., NATO science series vol. 124 (book just receivedas a freeby from Markus, who is a co-editor)