Coronal Loop Oscillations and Flare Shock Waves H. S. Hudson (UCB/SSL) & A. Warmuth (Astrophysical Institute Potsdam) Coronal loop oscillations: introduction (Fig. 1) The coronal magnetic field is highly elastic and can oscillate Various time-series observations exist Theoretical eigenmode structures have been calculated TRACE has now observed oscillating loops at few-minute periods SUMER has also observed oscillations, with different morphology Survey: Schrijver et al., Solar Phys. 206, 69, 2002; Aschwanden et al., Solar Phys. 206, 99, 2002 ABSTRACT A preliminary statistical analysis of coronal loop oscillations observed by TRACE shows that 12/30 cases were associated with metric type~II bursts. The timing is consistent with the idea that the loop oscillations represent the passage of a disturbance launched by an eruption in an active region; the GOES classifications for these flares range from C4.2 to X20. Typically the oscillating structures are not disrupted, implying that the disturbance has passed through the medium. This is consistent with the Uchida interpretation of the disturbance as a weak fast-mode blast wave propagating in the ambient corona. We note that all twelve of the events were also associated with CMEs. Fig. 1. TRACE “global kink mode” oscillations, from Aschwanden, De Pontieu, Schrijver & Title (Solar Phys. 206, 99, 2002) for July 14, This shows (top left) TRACE difference image, with analysis box; (bottom left) fitted loop; (top right) raw coordinates (with parameter values for fit); (bottom right) absolute coordinates. This (and all events) shows rapid damping, suprising considering basic theoretical ideas about dissipation in the solar corona. Note the geometrical relationship between flare core (diffraction pattern) and loop top. 19:35 19:40 19:45 19:50 19:55 20:00 20:05 20:10 20:15 20:20 20:25 20:30 20:35 20:40 Type II radio bursts: introduction (Fig.2) Meter-wave “Slow drift” radio bursts were detected in the 1950’s Plasma-frequency emission => outwardly propagating disturbance Uchida suggests a weak fast-mode MHD shock as the origin Uchida’s theory also explains H  Moreton waves These blast waves are created by solar flares (hence “flare waves”) We now have new channels for observing them: X-rays, EUV, He I 10830, microwaves, meter waves Lines of evidence for blast-wave excitation 12/30 oscillation events have reported type II bursts The flare/oscillation timing is consistent Blast waves are known to excite “winking filaments” Blast waves also excite remote H  and metric brightenings Flare/loop locations are consistent; the CME is further out The loops generally stay nearly in place and are not involved with the dimming flow Flare GOES distributions are similar (Fig. 3) A fast disturbance may couple better to loop structure Fig. 3. Distribution of GOES classes of flares for the TRACE loop oscillations (triangles) with flares having type II bursts (diamonds; NOAA listings for ). Fig. 2. Representative (and completely atypical) meter-wave radio event, showing nice type III bursts at around 07 min, together with type II starting at about 11 min. Event of June, 1992, recorded by the Culgoora radio spectrograph. Distinguishing blast (flare) waves, and CME-driven shocks The chromospheric and other data show that a wave can run away from its radiant point near a flare site; this is a blast wave (simple wave) propagating in an essentially undisturbed corona CMEs can support shocks in the interplanetary medium, observable directly and as SSCs, as they disturb the solar wind The driven CME shocks are hard to observe by remote- sensing techniques, e.g. coronagraphs; see Fig. 4. Fig. 4. SOHO coronagraphic observations of a shock structure on April 2, 1999 (Vourlidas et al., ApJ 598, 1392). Note the surprising invisibility of any bow wave. The “shock candidate” at the flank of the CME is interpreted as a fast-mode MHD shock with Mach number of order 2. We do not believe that this type of wave usually excites the observed loop oscillations, but the event of March 22, 2001, is a possible case. Conclusions There is strong evidence that the exciter of the oscillations goes on to become the shock-wave source of a type II burst. We hope that detailed study, involving realistic numerical simulations in the MHD approximation, can relate the loop motions to the nature of the restructuring and help us to understand how the eruption starts. Not all oscillation events can readily be explained this way.