Coronal Micro-Events and Doppler Oscillations in Hot Active Region Loops Werner Curdt Max-Planck-Institut für Aeronomie Collaborative effort of: Tong Jiang Wang Ingolf Dammasch Bernhard Kliem Davina Innes et al.

Loop Oscillations, Orsay 2003 Prolog Non-scientific need for off-limb observations May 1999: first limb flare (size M8) –spectroscopy (Feldman et al.) / flare (Innes et al.) –Nov 1999: oscillation event in hot/cold plasma (Kliem et al. 2002) > 100 events in tailor-made observing sequence SUMER events have 2 aspects: –the oscillations and coronal seismology –the trigger, and insights into the physics of flares

Loop Oscillations, Orsay 2003 Contents Introduction Observational approach Observational facts Interpretation and modeling –oscillations & coronal seismology –comparison of SUMER and TRACE oscillations –the trigger of hot loop transient events –heating and cooling of active region loops Conclusion

EIT 171 Å SUMER: 7 slit position Å 9 Mar 2001

Ca XIII 1133 Å 2.4 MK Fe XVII 1153 Å 3.0 MK Fe XIX 1118 Å 7.7 MK

 Two recurring events in Fe XIX, showing Doppler shift oscillations Si III 1113 Å 3-6  10 4 K Ca X /2 557 Å 7  10 5 K Ne VI 1117 Å 3  10 5 K Fe XIX 1118 Å 6.3  10 6 K 200 arcsec

Fe XIX 28 Sep 2000

time distance Ca X radiance Ca X Doppler flow 28 Sep 2000

Loop Oscillations, Orsay 2003 Basic observational facts Doppler oscillations occur frequently Only seen in T e >7 MK lines Some events correlated to cold emission Periods in the order of minutes Strongly damped, decay in ~ 10 minutes events are often re-occuring

Loop Oscillations, Orsay 2003 Coronal Seismology Theoretical work: –Aschwanden (1987) –Roberts (1984) little observational evidence new observational facts available now: –TRACEtransverse loop oscillations – SUMERtoday’s topic

 Interpretation by MHD waves (Edwin & Roberts 1983; Roberts, Edwin & Benz 1984) Fast modes: Impulsively generated propagating MHD waves (e.g. Roberts et al. 1984; Murawski et al. 1998)   (1) symmetric (sausage) (2) asymmetric (kink) phase speed longitudinal wavenumber Slow modes:  B > 0,  < 0 V V B > 0,  > 0  = 0 (acoustic) (Alfvenic)  Expected periods 1) Slow modes: P = 7  70 min 2) Kink modes: P = 1.4  14 min 3) Sausage modes: P = 0.1  5 s 4) Fast mode MHD waves: P  1 s (Aschwanden 2003)

Doppler shift in FeXIX Line intensity, backgroud trend removed Fe XIX light curve (20 px smooth) Doppler shift in Fe XIX Line intensity, background trend removed Continuum intensity P = 17.6 min T d = 37 min (T d /P ~ 2.1) Fe XIX intensity P = 17.1 min T d = 21 min (T d /P ~ 1.2)

Loop Oscillations, Orsay 2003 Loop models Standing magnetoacoustic wave in slow mode: c =  / P(1) 1/c 2 = 1/c A 2 + 1/c s 2 (2) where c s 2 =  p 0 /  0 (Laplace) c A = f (B) c A Alfvén speed, c s sound speed,  adiabatic compressibility (Roberts 2002)

time distance Fe XIX Doppler flow 1 Oct 2000 a

time distance Fe XIX Doppler flow 1 Oct 2000 b

time distance Fe XIX Doppler flow 29 Sep 2000

Overview of measured parameters for 54 SUMER oscillation cases (Wang et al 2003)

Distinct difference in periods Similar range in decay times Similar range in velocity amplitudes Distinct difference in displacement amplitudes  Comparison between SUMER and TRACE results Wang SUMER TRACE

 Excitation of oscillations SUMER TRACE Oscillations observed by Occurrence rate Relation with flares Response of emission Possible trigger styles 1) 6/15 flares (1X, 3M, 11C) 2) Many small events 3) 15/27 belong recurring events 1) 17 (6%) of 255 flares (4C, 10M, 2X, 3 filament erpt.) 2) a trend of larger possibility by larger flares 6 of 27 events associated with flares (4C, 2M) All 17 events associated with strong flares (70% are M or X class) 1) visible in Fe XIX or Fe XXI of T > 6 MK 2) flare-like light curves without periodicities for the most cases 1) visible in 171 Å (Fe IX, Fe X) or 195 Å (Fe XII) of T < 2 MK 2) initial increase in loop brightness (Aschwanden et al. 1999) 1) disturbances or injected flows from one of loop footpoints due to small or micro- flares 2) osci. loops likely involved in energy release (loop-loop) 1) excitations by flare shocks, erupting filaments, or CMEs. 2) osci. loops are passively effected by disturbances from the activities

Loop Oscillations, Orsay 2003 SUMER / TRACE comparison SUMER events look similar to TRACE events, but: –TRACE has no filters for hot emission –TRACE sees only M- and X-flares (Doppler-shifts much more sensitive) –SUMER and TRACE are complementary: TRACE can see only transverse bulk flow SUMER sees axial standing acoustic wave

Loop Oscillations, Orsay 2003 The trigger comes from below is impulsive, often seen as photospheric flash starts with a flow, brightning comes often later is a minor event, often below detection limit of GOES, EIT, etc. often repeated –loop system still intact –always comes from the same footpoint 2 examples show more details:

Fe XIX Dopplershift Fe XIX radiance Fe XVII Ca XIII Ca X Light curves x-t and v-t diagrams Case 1: Event on 8 May 2002

Loop Oscillations, Orsay 2003 Case 2:

Loop Oscillations, Orsay 2003 Immedeate implications: (a) heating is impulsive (b) loops are isothermal

Loop Oscillations, Orsay 2003 Heating and cooling Heating is impulsive After the trigger the oscillation is undisturbed –SUMER HLTE seem to be ‚atomic‘ heating events Plasma is at one temperature at a given time Cooling curves seem to support runaway cooling models during the heating phase we often observe Bremsstrahlung HESSI sees “sea of microbursts“ in 5 keV

Loop Oscillations, Orsay 2003 Conclusion Doppler oscillations in 10 MK loops never been observed before Relevance for solar physics: –(a) contribution to spectroscopy / atomic physics –(b) Fe XIX emission is a proxy for soft x-rays –(c) coronal seismology: new method for coronal magnetic field measurements –(d) new insights into the physics of flares –bibliography: demonstration of the importance of spectroscopy

Loop Oscillations, Orsay 2003 Feldman et al. 2003

Loop Oscillations, Orsay 2003