New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth...
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![Page 1: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/1.jpg)
New inferences on the physical nature and the causes
of coronal shocks
Alexander Warmuth
Astrophysikalisches Institut Potsdam
![Page 2: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/2.jpg)
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?
![Page 3: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/3.jpg)
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?
![Page 4: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/4.jpg)
Flare wave eventMoreton wave of 2 May 1998
Above: Hdifference movie (13:38 - 13:47 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
![Page 6: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/6.jpg)
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
![Page 7: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/7.jpg)
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)
![Page 8: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/8.jpg)
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
![Page 9: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/9.jpg)
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
flare waves and metric type II bursts are signatures of the same underlying disturbance
![Page 10: New inferences on the physical nature and the causes of coronal shocks Alexander Warmuth Astrophysikalisches Institut Potsdam.](https://reader035.fdocuments.in/reader035/viewer/2022062422/56649f115503460f94c24623/html5/thumbnails/10.jpg)
Passage of thefast-mode MHD shock through the corona (C) and its signatures in the transition region (TR) and chromosphere (Ch).
The fast-mode MHD shockGeometry of the disturbance
type II source
HeI patch
magnetic field lines
agent causing HeI forerunner
HeI intensity profileT enhancement
H line center intensity profile
filament
H blue wing intensity profileDoppler velocity profile
H 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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FlaresCharacteristics
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 ~ 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 timesComparison with HXR burst
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Extrapolated wave source pointsOff-set of starting location
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FlaresRelation 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 ejectaHand 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)
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Small-scale ejectaCharacteristics
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 40-1500 km/s (mean 600 km/s)
inhomogeneous group, wide range of characteristics
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Small-scale ejectaRelation 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
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CMEsCharacteristics
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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CMEsRelation 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 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• CMEs associated with class 2 events even more energetic
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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 & CMEsTiming: favors flares
Spatial aspects: favors small-scale ejecta
No conclusive results on wave initiation mechanism
search for events with TRACE & RHESSI coverage
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The X4.8 flare of 23 July 2002First wave event with TRACE & RHESSI coverage
W
W
NR
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23 July 2002 - HMoreton 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
BL
W
EL: erupting loop/bubble00:22 - 00:27 UTv ~ 170 km/s
W: small wavefront00:27 - 00:30 UTv ~ 150 km/s
BL: moving/brightening loop00:28 - 00:30 - 00:34 UTvmax ~ 120 km/s
NR: depression of coronal structures00:24 - 00:30 (max)
red contours: RHESSI 6-12 keV
blue contours: RHESSI 50-100 KeV
NR
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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
00:23:30 - 00:34:13 UT
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23 July 2002 - CMETiming & 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 Rs) uncertainty in timing & kinematics of early phase
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23 July 2002 - 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 00:24 - 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?