Solar Cycle 24 Group F
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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'
dimmings - local (near neutral line) or remote (associated with breakout?)
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 2 min 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
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