New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam

Motivation coronal shocks: have important consequences: role in acceleration of particles, SEP events,... can be used to probe corona: Alfven speed, magnetic field strength,... give information on flare/CME processes consider here: signatures of propagating shocks in low corona metric type II bursts: long discussion on cause (flare-launched blast wave vs. CME-associated piston-driven shock) flare waves (a.k.a. Moreton waves): not much discussion until discovery of EIT waves relation type II bursts - flare waves?

A multiwavelength study of flare waves use advantages of flare waves to study nature & origin of shocks imaging observations  good kinematics & spatial information no dependence on coronal density model back-extrapolation of shock initiation time & location  comparison with possible causes study of 12 flare wave events imaging observations in H , He I, EIT, SXT, Nobeyama 17 GHz radiospectral data study association, morphology, kinematics & evolution of waves study associated phenomena (flares, CMEs, ejecta,...) 12 additional “class 2” events some signatures of flare waves, but no nice coherent wavefronts low-amplitude limit of phenomenon?

Flare wave event Moreton wave of 2 May 1998 Above: H  difference movie (13: :47 UT) Left: Moreton fronts (black) and EIT fronts (white) Kanzelhöhe Solar Observatory

The physical nature of flare waves all signatures follow closely associated kinematical curves one common physical disturbance

The physical nature of flare waves all signatures follow closely associated kinematical curves one common physical disturbance morphology of the signatures, down-up swing of chromosphere wave-like disturbance

The physical nature of flare waves all signatures follow closely associated kinematical curves one common physical disturbance morphology of the signatures, down-up swing of chromosphere wave-like disturbance waves travel perpendicular to field lines, are compressive, initial speeds of nearly 1000 km/s fast-mode MHD wave, waves are (at least initially) shocked (M ms ~ 2-4)

The physical nature of flare waves all signatures follow closely associated kinematical curves one common physical disturbance morphology of the signatures, down-up swing of chromosphere wave-like disturbance waves travel perpendicular to field lines, are compressive, initial speeds of nearly 1000 km/s fast-mode MHD wave, waves are (at least initially) shocked (M ms ~ 2-4) deceleration, perturbation broadening and weakening shock formed from large-amplitude simple wave; eventually shock decays to ordinary fast-mode wave

The physical nature of flare waves all signatures follow closely associated kinematical curves one common physical disturbance morphology of the signatures, down-up swing of chromosphere wave-like disturbance waves travel perpendicular to field lines, are compressive, initial speeds of nearly 1000 km/s fast-mode MHD wave, waves are (at least initially) shocked (M ms ~ 2-4) deceleration, perturbation broadening and weakening shock formed from large-amplitude simple wave; eventually shock decays to ordinary fast-mode wave 100% association with metric type II bursts, correlations in timing & kinematics flare waves and metric type II bursts are signatures of the same underlying disturbance

Passage of the fast-mode MHD shock through the corona (C) and its signatures in the transition region (TR) and chromosphere (Ch). The fast-mode MHD shock Geometry of the disturbance type II source HeI patch magnetic field lines agent causing HeI forerunner HeI intensity profile  T enhancement H  line center intensity profile filament H  blue wing intensity profile Doppler velocity profile H  red wing intensity profile

What launches the waves? Possible triggers of the fast-mode shock Flares: may launch disturbance via pressure-pulse mechanism (classical blast wave scenario) Small-scale ejecta (sprays, erupting loops or plasmoids,...): may act as temporary piston which creates initially driven shock which later continues propagation as free blast wave CMEs: may either create a piston-driven shock or launch a blast wave

Flares Characteristics Spatial characteristics: flares often near the dominating spot, invariably at periphery of the sunspot group Energetics: flare importances: C8.6 - X4.9 (mean: X1.4; median: M8.3)  no importance threshold GOES SXR rise times (begin-max): min (mean: 8.8 min)  less than average GOES SXR max. temperature: MK (mean: 20 MK) comparatively hard power-law photon spectra (mean  ~ 3) wave-associated flares have higher SXR impulsiveness class 2-associated flares are less impulsive, only slightly cooler Flares seem to form distinct class, but rather wide range in characteristics

Extrapolated wave onset times Comparison with HXR burst

Extrapolated wave source points Off-set of starting location

Flares Relation with waves Temporal relation: extrapolated wave onset times near begin/initial rise of HXR bursts Spatial relation: wave source points clearly dislocated from flare center Energetics: no significant correlations between flare energetics and wave parameters

Small-scale ejecta H  and SXR Upper row: Bright H  flare ejecta in the event of 2 May 1998 (Kanzelhöhe Solar Observatory) Lower row: Ejected SXR blob/loop in the event of 18 Aug 1998 (Yohkoh/SXT)

Small-scale ejecta Characteristics Morphology/types of ejecta: H  : bright ejecta (sprays) in impulsive phase, dark ejecta in later phase SXR: erupting loops and blobs (plasmoids), jets Spatial characteristics: originate in or near flare, propagate away from AR/main spot Kinematics: maximum speeds km/s (mean 600 km/s) inhomogeneous group, wide range of characteristics

Small-scale ejecta Relation with waves Association: in ~85% of events some kind of ejecta present Temporal relation: in ~75% of events starting times of ejecta agree roughly with wave initiation times Spatial relation: rough agreement between ejecta and wave starting points direction of ejecta agree with wave direction in all events Kinematics: in majority of events (66%) ejecta significantly slower than wave in only < 50% of events ejecta which may be accounted for wave generation no precise timing/kinematics for ejecta due to observational constraints

CMEs Characteristics Spatial characteristics: angular widths: 45° - 360° (mean: 177°), 25% halo CMEs  wider than average Kinematics: linear CME speeds: km/s (mean: 683 km/s)  faster than average CMEs are more energetic than the average, but wide range in parameters

CMEs Relation with waves Association: high ( > 90%, possibly 100%) Temporal relation: most CMEs start well before flare/wave, but onset times are inaccurate Spatial relation: at time when wave becomes observable: - mean distance wave-starting point: 100 Mm - mean CME height above photosphere: 1,9 R s  can such a large-scale structure drive/launch small & sharp disturbances? Kinematics: in most events CMEs slower than waves (78%) or type II bursts (88%) no significant correlations between CME kinematics and wave parameters CMEs associated with class 2 events even more energetic

Current status What is needed: direct observation of initial disturbance and of the transformation to the more familiar flare wave signatures better data on kinematics of ejecta better data on flare energetics  need for high-cadence and high-resolution data Association: favors flares & CMEs Timing: favors flares Spatial aspects: favors small-scale ejecta No conclusive results on wave initiation mechanism search for events with TRACE & RHESSI coverage

The X4.8 flare of 23 July 2002 First wave event with TRACE & RHESSI coverage W W NR

23 July H  Moreton wave atypical Moreton wave: protracted activity near flare (in region NR) before wave initiation diffuse & irregular morphology („class 1.5 event“) difficulty in determining kinematics & starting time/location

23 July TRACE 195 Å Overview EL BL W EL: erupting loop/bubble 00: :27 UT v ~ 170 km/s W: small wavefront 00: :30 UT v ~ 150 km/s BL: moving/brightening loop 00: : :34 UT v max ~ 120 km/s NR: depression of coronal structures 00: :30 (max) red contours: RHESSI 6-12 keV blue contours: RHESSI KeV NR

23 July TRACE 195 Å Evolution in region NR erupting loop EL further erupting/opening loops depression of coronal structures in NR small wave at N edge of FOV 00:23: :34:13 UT

23 July CME Timing & Kinematics by courtesy of the Catholic University of America energetic CME: halo, speed 1726 km/s, IP type II burst starting time 00:11UT  rough agreement with flare but: only 2 measurements (both at R > 20 R s )  uncertainty in timing & kinematics of early phase

23 July Summary 00:22:12: EUV loop/bubble starts to erupt 00:24:22: coronal structures in NR start being pushed down 00:26:15: abrupt increase in HXR emission 00:26:45: BR begins to brighten in H  00:27:18: small wave in EUV starts 00:28:00: type II burst starts 00:28:45: BR has transformed into (patchy) Moreton front perturbation probably initiated in the range 00: :27 UT perturbation originates from/above region BR/DM wave initiation more gradual than in typical Moreton event  different generation mechanisms? motions & restructuring of coronal magentic fields is prevalent  cause or effect of wave/shock?