Kein Folientitel

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

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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 Ha, 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?

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Flare wave event Moreton wave of 2 May 1998
Above Ha difference movie (1338 -
1347 UT) Left Moreton fronts
(black) and EIT fronts (white)
Kanzelhöhe Solar Observatory
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The physical nature of flare waves

• all signatures follow closely associated
  kinematical curves
• one common physical disturbance

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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

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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 (Mms 2-4)

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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 (Mms 2-4)
• deceleration, perturbation broadening and
  weakening
• shock formed from large-amplitude simple wave
  
• eventually shock decays to ordinary
  fast-mode wave

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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 (Mms 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

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

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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) 5 - 22 min
  (mean 8.8 min) ? less than average
• GOES SXR max. temperature 13-28 MK (mean 20
  MK)
• comparatively hard power-law photon spectra
  (mean g 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
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Extrapolated wave onset times Comparison with HXR
burst

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Extrapolated wave source points Off-set of
starting location

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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

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Small-scale ejecta Ha and SXR
Upper row Bright Ha 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)
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Small-scale ejecta Characteristics

• Morphology/types of ejecta
• Ha 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 40-1500 km/s (mean 600 km/s)

inhomogeneous group, wide range of characteristics
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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 lt 50 of events ejecta which may be
  accounted for wave generation
• no precise timing/kinematics for ejecta due to
  observational constraints

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CMEs Characteristics

• Spatial characteristics
• angular widths 45 - 360 (mean 177), 25
  halo CMEs ? wider than average
• Kinematics
• linear CME speeds 227 - 1200 km/s (mean 683
  km/s) ? faster than average

CMEs are more energetic than the average, but
wide range in parameters
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CMEs Relation with waves

• Association
• high ( gt 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 Rs
• ? 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

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Current status
Association favors flares CMEs Timing favors
flares Spatial aspects favors small-scale
ejecta No conclusive results on wave initiation
mechanism

• 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

search for events with TRACE RHESSI coverage
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The X4.8 flare of 23 July 2002 First wave event
with TRACE RHESSI coverage
W
W
NR
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23 July 2002 - Ha 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

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23 July 2002 - TRACE 195 Å Overview
EL erupting loop/bubble 0022 - 0027 UT v 170
km/s W small wavefront 0027 - 0030 UT v 150
km/s BL moving/brightening loop 0028 - 0030 -
0034 UT vmax 120 km/s NR depression of
coronal structures 0024 - 0030
(max) red contours RHESSI 6-12 keV blue
contours RHESSI 50-100 KeV
W
BL
NR
EL
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23 July 2002 - 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
• 002330 - 003413 UT

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23 July 2002 - CME Timing Kinematics

• by courtesy of the Catholic University of America
  
• energetic CME halo, speed 1726 km/s, IP type II
  burst
• starting time 0011UT ? rough agreement with
  flare
• but only 2 measurements (both at R gt 20 Rs)
• ? uncertainty in timing kinematics of early
  phase

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23 July 2002 - Summary

• 002212 EUV loop/bubble starts to erupt
• 002422 coronal structures in NR start being
  pushed down
• 002615 abrupt increase in HXR emission
• 002645 BR begins to brighten in Ha
• 002718 small wave in EUV starts
• 002800 type II burst starts
• 002845 BR has transformed into (patchy)
  Moreton front
• perturbation probably initiated in the range
  0024 - 0027 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?