Solar Cycle 24 BCHIJ

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Notes of the plenary Overview Session covering Groups B, C, H, I, and J for the Solar Cycle 24 meeting.

DeRosa: Magnetism

• Magnetic fields are pandemic. Review comments emphasize two areas:

1) How does flux at the surface reflect dynamo action? Aimee Norton cartoon showing "tilted toroidal bands". Ephemeral region emergences. Flux "emerges" less frequently at high "unipolarity"?

Judge: what about the scatter vs unipolarity? A: perhaps this is a techincal matter

2) Improving coronal field models. LOS grams may have serious biases. Photospheric vector fields don't deal with the chromosphere properly. Sunsplot flux issues. Chromospheric field interpretation problems. "We don't have any idea" how to map the field, but PFSS is on the way out? The chromosphere is the key to improvements.

Grigis: how about direct coronal field measurements? A: Degeneracy on LOS in optically thick medium. EUV has gone as far as it can go?

Hudson: Div B comment - the problem is 2/3 solved! A: You are very optimistic!

DeWijn: Chromosphere

• Read the manifesto. Four questions

1) general disagreements on what "chromospheric heating" amounts to. Acoustic waves still an open question. Internal gravity waves ditto. Type II spicules a key to the magnetized chromosphere? Corona... The questions have multiplied!

Liewer: what is a type II spicule? A: Time scale of seconds, number density different from classical (type I) spicules.

2) What is the influence of the beta = 1 surface? Inclined fields. "Chromospheric seismology"? Alfven wave propagation?

Strous: Need simulations to handle the Alfven waves properly

3) Numerical models. Now know that we need to deal with neutrals. But which problems require multi-fluid? Synthetic models are much better in the photosphere. 4) Propagation of free energy through the chromosphere. Is the chromosphere a "force-free factory"? Perpendicular resistivity should be very high in the upper chromosphere - so maybe

Vourlidas: where is the top of the chromosphere? A: A difficult question! "We're switching from doing something wrong in the photosphere to doing something wrong, but different, in the chromospehere?"

• Chromosphere and flares. Can we diagnose particle beams?
• Observations: Need B in the chromosphere - time-resolved integral field spectroscopy! Also need compatible resolution.

Panasenco: Need to include filaments in "chromosphere". Good point... also loops. Need another workshop!

Young: Loops

• Spatial structure. Dark regions in ARs show Doppler and line-width signatures in EIS. Sources of wind? Loop resolution? Aided by EIS filling factors of 10-20%. Isothermality? 3-dimensionality? Aschwanden work confirming large inclinations for many loops.
• Temporal evolution: Cooling can be nicely followed in images now. Are all loops heated as transients, ie are there steady loops?

Doschek: see the movie; it's on the Web

Moore: The Markus movie is impressive; does it show any non-potentiality?

DeForest: Recall the overdense and underdense loop types. "Nanoflares" <=> underdense.

Peter: Modeling

• Need synthesis of observables. Need non-equilibrium ionization. Footpoint heating is now heavily preferred.
• Impulsive heating or steady quasi-static heating? Not so clear theoretically.
• Connection to chomospheric modeling has not been dealt with properly. The simulation data cubes ought to be made available to the public.
• Existing instruments: need to deal with straylight and background. Need to make better use of SOT.
• Future with SDO/AIA higher time resolution. Graph of electron mfp vs height in MHD model (Peter 2008) => 100 km.

Welsch: The models requested are uninteresting from the point of view of the chromosphere. Why stop at 5 min scales? Cooling is uninteresting?

Mason: compromises are necessary.

Judge: comment on Markus movie. Why are strands illuminated? Note that tubes are less prominent than ribbon-like structures at the footpoints. Why don't we see sheets instead? We understand almost nothing, it appears.

DeForest: it's worse than you think.

Hudson: Markus is showing us the boring part of the corona. The NLFFF group has noted that the strongly sheared internal structures of an active region are not the ones that Markus can image this way

Muglach: Filaments

• Structure

- 0.1 arcs scales are present, both SOT (over the limb) and also SST ground-based (on disk), but SST shows all horizontal threads while SOT shows mostly vertical downstreaming filaments. How do we reconcile the two views? There are "threads" now resolved as the smallest scales. Threads present even in the barbs and show dynamics, e.g. counterstreaming. Suggested resolution: the "horizontal threads" we see on disk are really highly inclined nearly vertical threads seen in projection. These are the same threads seen in SOT movies at the limb. Major problem with this hypothesis: SST threads are very thin, short, counterstreaming; SOT filaments are long, turbulent, messy, thicker structures that only flow one way: down. The upflows in SOT movies are dark voids, not thin threads.

- There are dome structures, on Mm scales, now observed to show remarkable dynamical behavior. What is the source of these "inflating bubbles" below prominences?

• Fields

- Now have have actual He D3 field observations (Casini). Also 10830 (Lopez Ariste). Fields can be up to 80--100G, much larger than the 10 G assumed in most models.

Moore: what direction of B? A: horizontal.

• Wish list: stereographic observations in H-alpha to resolve structure ambiguities. Space-based magnetic field measurements to get spatial and temporal resolution missing from the preliminary ground-based results. UV and IR wavelength coverage to cover much broader temperature/density ranges.

• Formation/maintenance: there are only 5 papers on observations of filament origin! Many more modeling papers exist!

- Time sequence shown in Wang-Muglach (2007).

• Models. "emerging flux rope" (e.g. Magara) approach vs. surface flux models (e.g. Mackay). All models are good at achieving the observed "end state" - how do we test models against the initial and developing states? Many more observations are needed.

Moore: There should be good observations if even MDI can see formation. Berger: A question for the community - why is neutral gas in quiescent prominences assumed to follow the field lines? A: collisions. Berger: this seems to be a good answer for the much denser lower chromosphere or active region prominences - not so good for the much lower density quiescent prominences. My point is this: the role of neutrals in partially ionized prominences is not well understood and it may be that the gas we see raining down in Hinode/SOT movies is driven by neutrals that are not bound to follow magnetic field lines at all. This would remove the observed contradiction of horizontal magnetic fields and vertical flows.

McLaughlin: Plumes

• A new plume cartoon! The Wang 1994 cartoon is to be supplanted. A two-stage formation of which (1) is a formation via a jet (Raouafi et a. 2008). Then decrease of height of X-point. DeForest 2007 shows how to develop a steady plume structure (hours, rather than the minutes of the "reconnection" event).

- There is high FIP in the plumes. - Parnell papers on many-separator reconnection.

• Transition to wind. Why are plumes not observed in situ? How much of the wind originates in the plumes (not all, but at least some?). Why are the scale heights so large?
• Seven main questions

(1) what distinguishes plumes/interplumes?

(2) what sustains plumes?

(3) what is the true 3D structure?

(4) what causes the acceleration? ("curtain vs tube" debate; need both energy and momentum)

(5) How far out do plumes extend?

(6) What are the Svalgaard Nobeyama observations?

(7) Spatial distribution/plume suppression. No plumes >85 degrees?

Obligatory Moore question: Step 2 not good, since plumes have mixed polarity.

De Pontieu: what does "explicit detection" require of the observations? A: would like to see propagating waves.

De Pontieu: It's in the Science paper, supporting material.

Judge: Solar cycle of plume statistics and flux concentrations? A: none at solar max, but low-latitude holes may show them (Wang).