Coronal Loop Oscillations Observed with the T Ransit Ion Region and Coronal Expl Orer

We report here, for the Ðrst time, on spatial oscillations of coronal loops, which were detected in extreme-ultraviolet wavelengths (171 with the T ransition Region and Coronal Explorer, in the temAŽ ) perature range of MK. The observed loop oscillations occurred during a Ñare that began at T e B 1.0È1.5 1998 July 14, 12 :55 UT and are most prominent during the Ðrst 20 minutes. The oscillating loops connect the penumbra of the leading sunspot to the Ñare site in the trailing portion. We identiÐed Ðve oscillating loops with an average length of L \ 130,000^ 30,000 km. The transverse amplitude of the oscillations is A\ 4100 ^ 1300 km, and the mean period is T \ 280 ^ 30 s. The oscillation mode appears to be a standing wave mode (with Ðxed nodes at the footpoints). We investigate di†erent MHD wave modes and Ðnd that the fast kink mode with a period q\ 205(L /1010 cm~3)1@2 cm)(n e /109 (B/10 G)~1 s provides the best agreement with the observed period. We propose that the onset of loop oscillations in distant locations is triggered by a signal or disturbance that propagates from the central Ñare site with a radial speed of B700 km s~1. Because the observed loop oscillation periods are comparable to photospheric 5 minute oscillations, a resonant coupling between the two systems is possible. We further Ðnd evidence for global extreme-UV dimming in the entire active region possibly associated with a coronal mass ejection. Subject headings : Sun: corona È Sun: Ñares È Sun: oscillations È Sun: UV radiation