Identification of types of kink modes in coronal loops: principles and application to TRACE results

Details Identification of types of kink modes in coronal loops: principles and application to TRACE results Identification of types of kink modes in coronal loops: principles and application to TRACE results

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsp31c..08w&link_type=abstract

American Geophysical Union, Spring Meeting 2008, abstract #SP31C-08

Astronomy and Astrophysics

Astrophysics

7500 Solar Physics, Astrophysics, And Astronomy, 7509 Corona, 7519 Flares, 7549 Ultraviolet Emissions

Scientific paper

We explore the possible signatures of different types of kink modes (horizontal and vertical oscillations in their fundamental mode and second harmonic) which may arise in coronal loops. Based on the 3D geometrical parameters of 14 TRACE loops of transverse oscillations, we simulate qualitatively the loop displacements due to these types of kink mode oscillations. We find that for many combinations of viewing and loop geometry it is not straightforward to distinguish between the two types of kink modes. We have also considered Doppler signatures and found that these can in principle help to obtain unique identifications of the oscillation modes. We then compared the simulated spatial signatures with the observations for 14 TRACE loops. We find that two cases of loop oscillations previously identified as a fundamental horizontal mode appear to be a fundamental vertical mode, while in two other cases it is not possible to clearly distinguish between a horizontal oscillation of the fundamental mode and the second-harmonic, and in six cases it is not possible to clearly distinguish between a fundamental horizontal mode and a second-harmonic vertical mode. In addition, for the particular case that the oscillating loop has a S-shape, we find that the fundamental vertical oscillation can take on the appearance of the horizontal second harmonic due to projection effects. We also present numerical results of three dimensional MHD model of an idealized active region field with S-shaped field-lines. The active region is initialized as a force-free dipole magnetic configuration with uniform density and contains a loop with a higher density than its surroundings. We introduce a velocity pulse which models the impact of a flare on surrounding fields. Both the qualitative study and the MHD simulation support the conclusion of the presence of fundamental mode of vertical kink oscillations in an S-shaped loop. Our interpretation can naturally solve the puzzle of the absence of the fundamental mode and the apparent presence of second harmonic oscillations observed in a TRACE loop by De Moortel and Brady (2007).

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