Astronomy & Astrophysics

Free access article

A&A 482, L9-L12 (2008)
DOI: 10.1051/0004-6361:20079340

Letter

Hinode observations of transverse waves with flows in coronal loops

L. Ofman and T. J. Wang

Dept. of Physics, The Catholic University of America and NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771, USA
e-mail: ofman@waves.gsfc.nasa.gov

(Received 28 December 2007 / Accepted 12 March 2008)

Abstract
Aims. We report the first evidence for transverse waves in coronal multithreaded loops with cool plasma ejected from the chromosphere flowing along the threads. These observations are good candidates for coronal seismology.
Methods. We analyzed observations made with Solar Optical Telescope (SOT) on board the Hinode satellite in the Ca II H line filter.
Results. The oscillations are visible for about 3 periods, with a period lasting about 2 min, with weak damping. We see the oscillations in thin threads (~ $0.5\arcsec$ ) of cool plasma flowing in the coronal loops with speeds in the range 74-123 km s^-1.
Conclusions. Observations indicate that the waves exhibit different properties in the various threads. In some threads, the waves are nearly standing fundamental kink modes with a phase speed of about 1250 km s^-1, whereas the dynamics of other threads is consistent with propagating fast magnetosonic waves. Based on the observed wave and loop properties and the assumed active region loop density in the range (1-5) $\times$ 10⁹ cm^-3, the estimated energy flux is sufficient to heat the loops to coronal temperatures, and the average magnetic field in the threads is estimated as 20 $\pm$ 7 G.

Key words: Sun: flares -- Sun: corona -- Sun: magnetic fields -- Sun: oscillations -- waves