Solar Cycle 24 Group F
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preflare phase & trigger mechanism | preflare phase & trigger mechanism | ||
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few (12) example event studied. | few (12) example event studied. | ||
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could be some signatures of 'breakout' or tether cutting | could be some signatures of 'breakout' or tether cutting | ||
- | + | Dimmings - local (near neutral line) or remote (associated with breakout?) | |
rise of filament in AR is mins | rise of filament in AR is mins | ||
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also association with flux emergence / cancellation. | also association with flux emergence / cancellation. | ||
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+ | filament is tracer of the overlying loop? | ||
WHAT WILL WE LEARN: | WHAT WILL WE LEARN: | ||
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Clearly Hinode and SECCHI 171 high cadence? | Clearly Hinode and SECCHI 171 high cadence? | ||
so synoptic data modes are fine for this project? | so synoptic data modes are fine for this project? | ||
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=== ATRILL Coronal waves and dimmings === | === ATRILL Coronal waves and dimmings === |
Revision as of 20:12, 11 December 2008
McAteer Notes
INTRODUCTION
STERLING Earliest phases of solar eruptions
preflare phase & trigger mechanism for filaments as tracer of B field, slow rise -> flare + fast rise
few (12) example event studied. 2 may 2007, TRACE & HINODE, good example.
filaments undergo slow rise (few km/s), then fast. the slow rise is linear then flare at start of fast eruption. could be some signatures of 'breakout' or tether cutting
Dimmings - local (near neutral line) or remote (associated with breakout?)
rise of filament in AR is mins rise of quiescent filament is several hours.
also association with flux emergence / cancellation.
filament is tracer of the overlying loop?
WHAT WILL WE LEARN: how common is a slow rise? what triggers slow & fast rise phases?
where to go from here? Clearly Hinode and SECCHI 171 high cadence? so synoptic data modes are fine for this project?
ATRILL Coronal waves and dimmings
EIT waves map the CME footpoints? Angelos -mixing lateral mass expansion & wave? Atrill - the expansion of CME stops when wave stops.
Explains the brightnenings at the CME legs
WD - Tunnelling of waves into coronal hole?
Dimmings: could be evacuation or cooling also agree with deep core and secondary dimmings
Mass measurements from plasma outflows?
Angelos: No brightenings in 304, so not reconnection? McAteer: reflection and refraction problem?
Attril: does not mean there is no wave, the CME footpoints could cause a wave?
why/how do CD disappear while magnetic connectivity of the CME ejecta to Sun is maintained? recovery can be due to Interchange reconnection.
reconnection rate at same speed as the wave? 0.1 X 0.2 alfven speed - too low?
expansion of cme flanks should correspond with eit wave speed.
Occams razor? why add in CME flanks and then introduce wave anyway. Overly complex?
WHAT WILL WE LEARN? New tests from multi viewpoint?
MCATEER CME Kinematics
–Kinematics is the study of the motion
–Energetics is the study of the forces which cause the motion.
•What forces govern the propagation?
•What forces govern the expansion?
from height time profiles -> acceleration profiles
• What are we tracking?
- image to image,
- event to event,
- study to study
• Can we reduce the errors?
• Are we capturing the full profile?
- What about lower down?
combine with mass -> work done, force and power.
WHAT WILL WE LEARN:
Known Knowns
•Well characterized and large sample studies from 3-30RSUN
•Well developed techniques to study energetics and kinematics
Known Unknowns
•Behaviour at 1-3RSUN and greater than 30RSUN
•Even at 3-30RSUN,
–where do the forces act and over what distance?
–when do the forces act and over what timescale?
Unknown Unknowns?
-What is the initiation mechanism?
-What is the CME - flare/filament link?
-The ever-illusive current sheet - any other choice?
from stereo - better H-T low down, and multi direction.
more automated tracking.
STEED locating the solar source
ICME ejecta - components of ICME show a left -handed cloud (-ve helicity)
launch window determined - 80hours before, roughly noon 10-april 2006 no obvious cme signatures (flares, dimmings, etc) survey possible launch regions.
search for source region with -Ve helicity. only one possible no erupting filaments, or possible cmes (because of lack of launch, conclude a back-sided event)
find some evidence of cusp shaped loop - > eruption signature? without vector data- cannot rule out helicity problems.
WHAT WILL WE LEARN?
HOWARD source regions A skeptics view of flare-cme relationship
how do we define a flare and a cme? cme- outward propagation of brightness enhancement in WLC flare - brightening in cr, tr or coronal emmisison
associating lists is dangerous all current theories have a flare as necessary consequence of eruption, but not neccesaary cause and effect.
There are CME without flares -called backside, faint flare (not in GOES) there are cmes which have no chromospheric signatures - 'streamer blowout'
with stereo - we can see these are not backsided.
obvious controversy suggest we are a long way from solving this problem -different people see different conclusions from the same data!
WHAT WILL WE LEARN? Need to nail down an agreed definition? With STEREO we can rule out backsided possibility - can we also rule out the 'too low for GOES? If so, then we have a non-flare CME and we need a new approach.
VERMA A new classification of CMEs?
calculate escape velocity Alphonse- What about LOS projection? - not accounted for.
NEVCME 41%, mostly +ve accleration Ev CMEs 59%, half +ve, half -ve overall 68% show +ve acc
WHAT WILL WE LEARN:
LOS question is vital: problems with just looking at the stats, not looking at the data
EVENTS
WEBB - overall discussion and questions to be addressed
Types of CMES -limb (good for H-T) -earth directed OR spacecraft directed (good for connecting CME / ICME and finding source regions -cradle to grave events
What is source region? dimmings, waves, slow rises extents, locations flares, prominences cavities
How essential are current sheets? 9-Apr-2008 has well observed current sheet?
How do we define an ICME now that we can image ICMEs what do we see in HI and how does this compare to in-situ?
How essential are prominences & eruption - joint with WG J
Campaign Focus events WHI 20 march -16 april 2008 9 apr 2008 event
Events Obs Science
2006 dec 13-15 2 X-ray flare near sun center ICME flux rope, SEP at earth, STEREO space weather event. secchi.nrl.navy.mil/spwx/
2007 Jan 24-25 2 CMEs east limb. SECCHI, SOHO, SMEI papers: Harrison et al, Lugaz et al, Webb et al
2007 May 19-22 2 events near sun center, HINODE & STEREO 3D view of filament lift off
2007 May 23 AR on west, wave, prom eruption, CME HINODE & STEREO
2007 Nov 14-18 3 events, 1 at sun center
2007 Dec 31 east limb
2008 March 25 east limb, during WHI
2008 April 9 west limb, XRT, EIS, SECCHI, UVCS interaction with CH
2008 April 26 near sun center, fast cme & euv wave
2008 May 17 sun - STEREO interaction
2008 Jun 6 magnetic cloud at STEREO B
2008 Feb 4-8 2008 June 2-6 wood et al. 2008 robbrecht et al. 2008
WHAT ARE THE ISSUES?
connection with flares - few large (>M) flares since STEREO launched.
LI - May 19, 2007 CME & B field of AR 10956
B9 flare, 960Km/s sun center AR pre eruption sigmoid structure in XRT B field topology - Li et al, ApJL 2008 classic breakout model configuration?
total B flux in region decreased 17% 48 hours before flare, so weakening of overlying field?
pre flare brigthening - tether cutting?
STERLING - May 20, 2007
B7 flare, well observed with TRACE, STEREO pre flare surges. reduction in B field
Angelos- constant flux cancellation, so what can we say quantitatively?
EIS box also rastered over this region.
-persistent red shifted flow and non thermal broadenings
-strongest shifts are 20Km/s
-typical densities of fewX 10^9 cm^-3
WHAT WILL WE LEARN?
Angelos - anything new?
Sterling - can we predict eruption?
Cartoon picture explanation. again person A see different conclusion from same data than person B.
FILAMENTS , (HOST J)
LIEWER - Stereoscopy
standard model - energy in sheared field marked by filament get confined eruption (surges) and ejective eruption
stereoscopy - -tie point depends on seeing the same feature correctly - constrain it to a 1D problem using the epipolar lines
compare to li et al (2008)
reconstruct the filament and show that H-T shows that ejection follows reconnection consistent with standard model velocity around 100km/s (much slower than CMEs) - kilpua et al. SP 2008)
again different people see different things in the same data- can we get a quantitative test?
compare h-alpha to euv images to discover when filament moves up / moves out of bandpass.
august 31, 2008
promininence eruption on SW and nice CME 3-part structure
good for 3D tracking
SU - Filament Channels
sheared loops with filament channels not all filament eruptions are associated with post-event arcades.
emission on two sides is asymmetric
fc are dark channels. sheared loops in xray, not in euv normally no overlying loops observed both emission and 3d B configuration is asymmetric
Sterling - sigmoids not in EUV, so the sheared loops are hotter.
Comment: What about april 25, 2007 -good cavity above the prominence. dark cavity - flux rope, low cavity, also density at tops is low because they are so high (several scale heights)
YURCHYSHYN - Halo-CME orientation vs. underlying flux rope orientation
cme elongation and flux rope orientation select 100 events many halo cmes can be approx by ellipse (zhao et al 2002, xie et al 2004 events from tripathi et al. 2004
manual fitting of ellipse and fitting parameters. measure orientation fo arcade from TRACe and MDI
plot orientation of CME against orientation of arcade shows nice correlation.
also shows that cme orientation changes with time - gradual rotation. CMES tend to rotate towards equator. agrees with negative helicity in N, filaments rotate CCW
angelos - dependent on the person fitting the eclipse and calibration level of images. need automated fitting processes.
WHAT WILL WE LEARN - need automated processing on well calibrated images.
what is full connection of orientation of flux rope / NL and Magnetic cloud ?
NEW CYCLE APPROACHES
-fully automated approaches
-full appreciate the cailbration
individual events good for getting at the physics, but we end up ignoring the 'boring' events
MODELS
WANG - An Analytical Model Probing the Internal State of CMEs
internal properties of model -polytrpic index -lorentz force how do the forces change as CMEs propagate?
how well do we know the internal state?
analytical model - axisymmetric cyclinder, self similar evolving, axial length proporitonal to distance from Sun
apply model over large radial distance.
results (1) polytropic index decrease 1.35 to 1.0 (decreases quickly at the beginning) (2) Lorentz force to thermal pressure ratio decreases from 1.0 to less than 0.1 at 70R_s (3) loretnx force is inward, thermal pressure is outward.
Future: study axial CMEs and fully developed CMEs Address heating or thermal energy transfer, expansion of flux ropes, in-situ and infer some physical mechanism regarding initiation.
Angelos: thermal component agrees with in-situ
EXTRA DISCUSSION
HUND thermosphere studies
data from 2002-> cooling by NO delays from KP index curve to NO cooling curve normally 2 days to cme
This is the CME hitting the earth.
also CO2 data avaliable.
alphonse: terrestrial consequences? angelos: primary driver is the EUV. russ: we are seeing CIR coming around, and not detected here.
Wills-Davey Notes
Tuesday
Session 1: 14:30 - 16:00 - Intro Talks
Alphonse Sterling: Introduction to Group F Agenda
- Introduction of people involved
- Leader: Sterling
- Assistant: Webb
- Discussion Coordinators/Scribes: Wills-Davey, McAteer
- Structure of discussion
- How do we want to focus discussion?
- Specific events?
- Fundamental aspects of CMEs, eruptions?
- How do we want to focus discussion?
- Discussion of schedule
- Can be modified
- How to conduct joint sessions?
- Who will take lead? (home groups?)
- Introduction of people involved
Alphonse Sterling: The earliest phases of solar eruptions
- Discussion of preflare phase
- Using filaments as tracers of erupting field
- Two phases
- Slow rise
- Flare + fast rise
- Movie: quiet region eruption in EIT
- Microflaring before eruption at filament footpoint
- Movie: Filament eruption in TRACE
- Also seen by Hinode
- Observed characteristics
- Looked at 12 events
- EIT limitations
- Concentrating on larger events
- Prefer slower-rising features
- Slow rise phase is linear (constant velocity?)
- Looked for "breakout" signatures
- Maybe there, Alphonse is not convinced
- Is a definitive mechanism signature possible?
- Dimmings
- "Double dimming" around neutral line
- More remote dimming
- Questions and objectives
- What triggers slow rise phase?
- B cancellation
- Emergence
- Need to examine more good events
- Can we learn about eruption mechanism from slow-rise phase?
- Need good magnetospheric data, particularly for limb events
- What triggers slow rise phase?
- Q: How long is slow rise phase?
- Several hours for quiet regions
- ~10 minutes for active regions
- SXR flare occurs at same time as rise trajectory
- EIT cadence is limiting
- Better observations from TRACE
- Q: Where do we go from here?
- Need better observations
- Already good with STEREO
- AIA will be better
- Need better observations
- Q (Alphonse): How often does EUVI see filament eruptions?
- Every few days
- There are number of good event observations
Gemma Atrill: Coronal ’waves’ and dimmings - what can they tell us about their CME counterparts?
- Technical difficulties (no movies… :( )
- Two types of coronal waves
- "S-wave"
- Diffuse bright front – this will be discussed
- Wave maps footprint of CME in low corona
- Every large CME has a diffuse coronal wave
- Examples of wave mapping onto CME footprint
- Wave will "stop", "disappear" when CME stops expanding
- Closely coupled to CME
- Q: where does the EIT wave match the CME?
- At the flanks, legs
- Comment: if it was a real wave, it would propagate beyond the CME footprint
- Bright fronts can be used to determine CME connectivity
- Polarity related to CME expansion
- Brightening due to interchange reconnection
- Evidence for interchange reconnection: coronal hole boundary retreat at wave interaction
- Q: could it be due to compression?
- Boundary doesn’t change back, couldn’t be compression
- Q: what about tunneling?
- Dimmings: plasma evacuation due to CME
- "Deep core dimmings"
- Flux rope erupting into interplanetary space
- THOUGHTS: Deep dimming just the erupting flux rope footpoints
- "Secondary dimmings"
- Widespread
- Follows bright front
- "Deep core dimmings"
- Gemma’s understanding of a coronal wave
- Base of CME, propagating interchange reconnection
- Secondary dimmings due to interchange reconnection opening low-lying field
- Secondary dimming should create outflow, deposit mass into CME
- See Doppler outflows in deep dimmings, need them for secondary
- Mass outflow has not yet been quantified
- Q: Evidence of a wave in 304?
- Long et al. 2008 does see 304
- Q: results of interchange reconnection should show brightening in 304?
- Very noisy, hard to measure
- Long et al. 2008 does see wave evidence
- Comment: EUV compression wave should also cause interchange reconnection
- Discussion:
- What about the wave "stopping"?
- What about waves "bouncing off" of coronal holes?
- What about "blast wave" light curves?
- Response:
- Wave should likely be generated anyway, wave not excluded
- Other signatures more consistent with CME footprint
- Dimmings as CME source regions
- 28 Oct 2003: Quadrapolar dimming region observed
- Flux doesn’t add up
- Have to include additional dimmings
- Dimming locations, formation can be explained through interchange reconnection on large scale
- 28 Oct 2003: Quadrapolar dimming region observed
- Recovery of dimmings
- 12 May 1997: contraction of dimming region observed
- Interchange reconnection would cause contraction
- Due to topology and adjacent coronal hole, MC should only come from one dimming – consistent with observations (still connected to Sun)
- Detected as transient coronal hole
- Implication: temporary fast solar wind stream
- Recovery due to "dispersal" of open flux
- Diffusion coefficient due to interchange reconnection matches observations
- Q: how are dimmings and transient coronal holes different?
- Transient coronal hole probably only associated with deep dimming, flux rope footpoints
- 12 May 1997: contraction of dimming region observed
- Q: Is wave speed consistent with interchange reconnection speed?
- Yes: should be fraction of Alfven speed
- Q: what drives exchange reconnection rate?
- Internal pressure of flux rope, not local magnetic field
- Conclusions: waves and dimmings can tell us about connectivity, mass supply of ICME
- Q: How to explain global scale of 12 May 1997 event?
- Because halo CME, can’t prove large lateral expansion, but seems likely
- Q: Why not a simple MHD wave?
- Do see dimming "stop"
- Waves can’t account for front "rotation"
- Q: How to account for Linker observations?
- Again, exchange reconnection doesn\’t exclude wave
- COMMENT: possible coupling of EIT wave, base of CME
Session 2: 16:30 - 18:00 - Intro talks (continued)
James McAteer: Kinematics of Coronal Mass Ejections: Theory and Observations
- Definition of kinematics: study of motion
- Definition of energetics: study of forces causing motion
- Forces acting on CMEs
- Derived from Maxwell’s eqns
- Radial force
- Gravity force
- Drag force
- Which force is more important?
- CME Theories
- "Flux-rope type"
- "Breakout type"
- Theories more similar than different
- How to test?
- Both have flux ropes and current sheets
- Kinematics can be used to test theories
- CME acceleration profile
- Forces governing propagation vs. expansion – how to differentiate?
- STEREO (particularly at wide angle) will give halo/plane-of-sky events, allowing for differentiation
- COMMENT: Evidence that faster expansion related to faster propagation
- Below 3 Rsun, acceleration
- After 3 Rsun, no more residual acceleration
- Forces governing propagation vs. expansion – how to differentiate?
- CME acceleration profile
- Does acceleration vary?
- Error bars important, have to bring them down
- To shrink acceleration errors, need to decrease position errors
- Multiple LOS measurements will bring errors down
- Residual acceleration contradicts breakout model
- COMMENT: some don’t think so
- COMMENT: could have KE imparted from outflow from transient coronal hole fast solar wind
- Can’t account for very fast CMEs (>1000 km/s)
- BUT very fast CMEs decelerate, slower CMEs accelerate
- Error bars important, have to bring them down
- Need to do automated studies
- Make sure tracking same features, need reproducible processes ("point & click" not reproducible)
- Need full CME profile
- Higher cadence (example: Long et al. 2008)
- Down to 1 Rsun
- Gallagher work
- Multiple spacecraft to find profile for one event
- Similar study needs to be done for >100’s of events
- Is a CME in EUV the same as in WL coronagraph?
- Flare-CME myth?
- Long-lasting RHESSI source: correlated with residual CME acceleration?
- Another event: as CME moves up, thermal source moves down
- COMMENT: Newton’s third law? (hand-wavy)
- COMMENT: could be used to test initiation model
- CME acceleration can tell you about Work, Force, Power
- Needs to be done with large sample size
- High acceleration, high velocity happens over shorter timescales and vice versa
- Biggest uncertainty: mass
- "Unknown unknowns"
- Initiation mechanisms?
- CME-flare link?
- Are current sheets necessary?
- COMMENT: Tether-cutting doesn’t require current sheet
- COMMENT: classifying pre-CME situation doesn’t fit in here
- Need to:
- Get lower in the atmosphere
- Do large-scale studies
- Take advantage of three directions (STEREO and LASCO)
- Open up possibilities of "serendipitous" discoveries
- SWAP spacecraft (going up Fall 2009):
- Out of Belgium
- EUV 171 instrument going out to 2Rsun
- I-minute cadence
- HI data gives very useful height-time profiles ("whole new ballgame")
- Q: what about NEMO (automated tracking of dimming regions, EIT waves)?
- Good dimming region coverage
- Still don’t see quantitative EIT wave tracking
- Tracking assumptions may be a problem
Kimberley Steed: Solar source of a magnetic cloud; overview of 13 April 2006 event
- Forward fast shock ahead of CME
- MC shows:
- Enhanced B
- Rotation of B
- Cloud is left-handed
- Where is source?
- Expected propagation time: 80 hours
- Need to allow for velocity changes
- No obvious CME source signatures
- Look at 3 AR as possible sources
- Small brightening in launch window, near disk center
- Test source surface magnetic helicity
- Brightening had wrong helicity
- Only one active region had correct helicity
- No filament erupted in launch window
- Coronagraph observations
- One partial halo from back-side
- Expected propagation time: 80 hours
- May come from a BACK-SIDE EVENT
- COMMENT: lack of signature doesn’t necessarily mean back-side - evidence in Yohkoh-SXT
- Another possibility: small, unnamed AR
- Shows evidence of loss of loop structure (eruption?), post-flare loops
- At coronal hole boundary – would make eruption easier
- COMMENT: Flare in right time window (wrong helicity), but w/o vectormagnetograms, can’t tell
- Evidence
- Location, timing, helicity fit
- ACE data consistent
- Enough flux from small AR
- Fast solar wind behind MC – consistent with adjoining coronal hole
- COMMENT: ~40% of MC can’t be associated with solar sources
Russ Howard: A skeptic’s view of CME-Flare relationship
- Analogy: drunk loses his watch…
- Definitions (need to be careful):
- CME: outward-moving coronagraph brightness enhancement
- Flare: brightening in some atmospheric line
- Current CME models require a flare
- Instances of flares w/o CMEs and CMEs w/o flares
- COMMENT: flares probably too weak to be measured
- "Streamer blowouts" have no chromospheric signature
- Occur at a ~constant rate
- Q: Any x-ray image data? –No
- Q: Have streamer blowout with no arcade produced?
- Some don’t produce arcades
- Q: Are blowouts slow?
- Start out slow (~100 km/s), accelerate – can be very big
- Event from 1 June 2008 (STEREO)
- Limb in A, on-disk in B
- No evidence of eruption
- COMMENT: How to know if source region?
- COMMENT: Can see a current sheet off of limb (I see it too.)
- Looks like too dim for GOES to see.
- COMMENT: Would help to look at difference images, EUV movies
- COMMENT: Is there a neutral line? Should be a big one.
- No evidence of neutral line (B. Welsch looked.)
- COMMENT: Even in Skylab, some CMEs with no signatures
- COMMENT: This could be the low energy end of a spectrum
- Could be due to differential rotation, stress build-up
Wednesday
Session 3: 09:00 - 10:30 – Intro talks (continued), Events Talks
Virendra Verma: On the New Classifications of Solar Coronal Mass Ejections Based on LASCO/SOHO Observations (10 min)
- See how CMEs are connected with solar surface phenomena
- Is initial speed of CMEs enough for escape velocity?
- Two kinds – escape v and non-escape v CMEs
- Many CMEs have non-escape v CMEs
- Q: Accounting for LOS?
- No. Using plane-of-sky velocities. (COMMENT: not sure of validity…)
- 59% have escape velocity
- Half show (+) acceleration, half (-) acceleration
- Overall, 2/3 have (+) acceleration (more non-escape have (+) acceleration)
- Correlating flares and CMEs
- 1/4 as many CMEs as flares
- Higher velocities have higher (-) acceleration
- Appears to be a cut-off trend
- COMMENT: most CMEs still have (+) acceleration, though
- 5-10% of non-escape CMEs have zero velocity by 20 Rsun (?!?!)
- Data come from LASCO CDAW catalog
- COMMENT: suggestion that CMEs fade out, become unobservable
- Most CMEs show (+) acceleration to 20 Rsun, a few have zero velocity at 20 Rsun
- Q: How does a decelerating non-escape CME ESCAPE?!?!
- Measuring from edge of LASCO – presumably already escaped!
- COMMENT: does this, plus plane-of-sky problem, negate study results?
- Q: How does a decelerating non-escape CME ESCAPE?!?!
- Conclusion: CMEs velocity affected by solar wind to accelerate or decelerate
- COMMENT: Zhang & Dere (2006) shows (+) acceleration of CMEs , more than solar wind
- Q: How to add acceleration to CMEs?
- Lorentz force?
- Mass deposit for transient coronal holes?
- COMMENT: NEED TO ACCOUNT FOR PLANE-OF-SKY VELOCITIES TO MATCH ESCAPE VELOCITIES
- Track back to sources using dimming regions?
- COMMENT: Large statistical study will help
Dave Webb: Possible Events
- Possible types of CMEs
- Limb events
- Good for accurate tracking, kinematics
- Earth/STEREO-directed CMEs
- Can be connected to ICME
- Can be connected to source region on-disk
- "Cradle to grave"
- Across multiple instruments
- Limb events
- What is a source region?
- Coronal surface phenomena: dimmings, waves
- CME-flare relationship
- Relating "cavities", prominences to 3-part CME
- Necessity of current sheets?
- Sometimes see bright rays in white light
- 9 Apr 2008 shows a good one
- Change of ICME definition now that they can be _imaged_?
- Q: how to explain periodicity domination in HI data at 1 AU? What does in-situ data look like?
- Importance of prominences?
- Campaigns:
- WHI: 20 March-16 April 2008
- 9 Apr 2008: XRT "cartwheel event"
- Anything seen by STEREO, Hinode
- Events (STEREO, Hinode):
- 2006 Dec 13-15
- 2007 Jan 21-25
- 2007 May 19-22
- Set of homologous events
- 2007 May 23
- 2007 Nov 14-18
- Set of homologous events
- 2007 Dec 31
- 2008 March 25
- 2008 April 9
- 2008 April 26
- 2007 May 17
- 2008 June 6
Yan Li: Overview of 19 May 2007 event
- AR had homologous CMEs
- CME is partial halo, pretty faint in LASCO
- First fast CME seen by STEREO
- On-disk origin
- Can see wave, filament eruption, sigmoid
- Complex neutral line structure
- May not be truly "homologous", as different neutral lines erupt
- Can see "Post-CME" loops under filament
- Dimming region near filament location
- Magnetic topology: Breakout is lateral
- Looked at total flux, see cancellation
- Region is decaying
- COMMENT: need to improve vector field analysis, add error bars
Alphonse Sterling: Overview of 20 May 2007 event
- Homologous with previous event, different neutral line
- Small flare: B7
- Filament eruption (surge-like)
- TRACE shows "surge", loop expansion
- Quantitative evidence of cancellation, flux decrease
- COMMENT: Is observed flux cancellation really the CME trigger?
- COMMENT: Large-scale, quantitative study would be useful
- Cancellation could be powering TRACE loops
- Have SOT, EIS data of filament eruption (almost)
- Fe XII shows persistent red-shifted flows (BEFORE eruption )
- Conclusion: cancellation powers eruption
- Q: Why is this event different?
- Events like this might help us figure out how to PREDICT eruptions
- Quantitative understanding of cancellation may help
Session 4: 11:00 - 12:30 – Joint with E (Flares)
NOTE: Group E didn’t know we were coming. Not much CME discussion.
Eduard Kontar: X-ray Measurements of Magnetic Field and Density Structure in the Chromoshere
- Looking at TRACE coronal loops
- Can infer magnetic field from coronal observations
- What is the structure of a flaring loop in the chromosphere?
- Example: funnel
- Limb flare from 6 Jan 2004
- RHESSI data shows footpoints, looptop source
- Energy of high energy electrons determines emission height in chromosphere (Aschwanden 2002)
- Higher energy sources lower in chromosphere
- Source sizes change with energy too
- Increase in source size with height implies strong horizontal B
- What is the actual footpoint shape?
- Changes with energy – higher energy flatter
- At scale height of 900 km, should expect strong horizontal B
- Q: were other effects that would cause small source size considered (higher energy scattering etc.)?
- Q: How get height measurements?
- Use a density measurement
S. Masuda: GEMSIS-Sun: Modeling particle acceleration and transport in solar flares
- Flares related to successive reconnection
- Hard x-ray emission corresponds to particle acceleration
- Plasmoid should an indicator of magnetic reconnection
- Can derive E from footpoint motion
- Particle acceleration/transport related to magnetic field configuration
- Acceleration sources:
- B gradient
- Curvature drift
- Centripetal acceleration
- Numerical model:
- Able to produce a loop-top source
- Produces an upward beam (source of Type III radio burst?)
- Future plans
- Include diffusion in model
- Convert simulation output to emission
- Need to understand multi-wavelength observations
- Q: Does most acceleration come from loop-top? -Yes
- Q: What processes are missing?
Pascal Saint-Hilare: X-ray emission from a current sheet in the wake of a CME & Long data accumulations with RHESSI
- Observations showing temperature goes down in wake of CME
- RHESSI shows plasmoid moving out
- Discontinuities seen at RHESSI flare onset
- Try imaging spectroscopy to eliminate background
- Results in double power law, see no non-thermal x-rays
- No hard x-rays - hidden by soft x-rays?
- Coronal probably not powered by accelerated particles
- Why do higher energies come from higher altitudes?
- Height related to ln(energy), fit not very good
- COMMENT: consistent with high post-flare loops, cusps
- COMMENT: flare driven for 8 hrs, likely a connection during this time between CME and post-flare loops
- Adiabatic heating does not fit
Lindsay Glesener, Sam Krucker: Coronal HXR sources
- HXR emission from:
- Acceleration region and paths away
- Footpoints
- Occulted flares eliminate bright footpoints
- On Masuda flare loop-top source:
- How many electrons necessary to produce HXR source?
- HXR emission related to density
- Assumption: density around 10^9
- COMMENT: Need to account for temperature as well as density. Also, could density be higher?
- Energy of thermal/non-thermal electrons?
- Loop-top source entirely non-thermal (all electrons accelerated)
- Acceleration in loop-top source
- Example: occulted flare from 2007 Dec 31
- Same event as discussed by Webb
- Microwave, HXR sources match
- COMMENT: could be a limb effect