Solar Cycle 24 Group B
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[MV]: Thus, in addtion to B^2/8/pi term, you woulkd have to consider the work done on the field. | [MV]: Thus, in addtion to B^2/8/pi term, you woulkd have to consider the work done on the field. | ||
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| + | WEDNESDAY 10 DECEMBER | ||
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| + | '''Jonathan Cirtain's Presentation''' | ||
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| + | Polar X-ray jets: 7-10 per hour, repeated runs of 'HOP 3' (can search for the data through the Harvard webpage). Wave motions apparent in jets, typical period 180s. The movement/shifting of the jet can give an indirect measurement for what the flux distribution has to be at the lower boundary. | ||
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| + | [Question] Why didn't we see these with TRACE? [Answer] Exposure times were too long. | ||
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| + | [http://adsabs.harvard.edu/abs/2007PASJ...59S.771S Savacheva et al (2007)] presents statistics for jets: average duration ~ 800 seconds, average size ~ 0.8Mm. Upper bound on the size of jet-width-distribution ~ 12Mm. Preference for transverse velocity component: evidence of dynamo process? Perhaps even something like a Hale-like law for jets? | ||
Revision as of 03:07, 11 December 2008
Working Group B: Fast Wind / Plumes
in attendance:
- Jonathan Cirtain
- Craig DeForest
- Yang Liu
- James McLaughlin
- Karin Muglach
- Nour-Eddine Raouafi
- Llan Roth
- Leif Svalgaard
- Luca Teriaca
- Marco Velli
- Yi-Ming Wang
TUESDAY 9 DECEMBER
Marco's Presentations
Discussion of Casalbuoni et al (1999) - an extension of the results of Parker (1964). Paper concludes that adding an ad hoc heating profile is no better than specifying the temperature profile. So how important is expansion profile if you're allowed to make up your own temperature profile?
Discussion of Borovsky (2008) - argument that the inner heliosphere is filled with a network of entangled magnetic flux tubes and that these tubes are fossil structures that originate at the solar surface. Marco doesn't agree with this interpretation of this observation result.
Discussion of Verdini & Velli (2007) - propagation and dissipation of Alfvénic turbulence in a model solar atmosphere.
Leif's New Idea
There are persistent, bright patches in polar regions seen in Nobeyama 17 GHz synoptic limb charts. Furthermore, the Nobeyama 17 GHz Brightness Temperature is a good proxy for WSO solar polar mangeitc field strength (3 aperture).
What is interesting is that these Nobeyama bright points match the polar field strength so well. This suggests that something is going on. Critically, are these the footpoints of plumes? Something is sitting there for a long time - what are these?
So we have Radio emission at 17 GHz (corresponding to brightness temperature of chromosphere) mathcing the magnetic filed, and these bright patches are not behaving like a polar cap should.
Alternatively, are these polar faculae? This proxy for the polar magneitc field may turn out to be better than using magnetograms.
Yang Liu's Presentation
'Magnetic Elements at Higher Latitudes'. Comparing MDI (LOS) magnetograms and Hinode vertical field, not every flux concentration matches up. Hence, some of the strong flux concentrations seen in MDI have horizontal/transverse contributions.
NB: MDI uses Ni line, Hinode uses Fe I 630 nm, but both should have similar formation heights.
Luca's Presentation
Wilhelm claims there is no velocity in plumes. [enter talk/slides here] Luca says there is velocity in plumes.
It seems like there are outflow motions associated with plumes. Are they always there? Luca's results improve on others' work by making a more careful analysis (e.g. using nonlinear distortion removal).
NB: Although plumes are cooler, they do have hot DEM tails.
NB: Yi-Ming Wang: Simulations show that there would be velocity in initial formation of the plume.
Filamentary Structure
Plumes have internal structure / filamentary structure, but this is an open question. Questions for creation mechanism - lots of reconnection events?
How do we get a steady plume when we have implusive heating / filamentary structure?
NB: There are 7-10 jets per hour, all the time, inside a polar coronal hole.
Cyclotron Waves
Proton solar wind distribution function leads to ANISOTROPIC + BEAM (Marsh et al 1982, Helios data). This leads to motivation for cyclotron wave interpretation. But Marco believes a proper model of lower frequency waves with explain this. Also, Cranmer et al (1999) reports on broad line profiles in O VI. Again, this leads to an interpretation that we don't like. Rebuttal put forward by Raoaufi & Solanki (2004a,b;2006a,6;2007), concluding that there is no need for large anisotropies.
General Comments
Luca: When we observe a plume, we are looking through plume and interplume, so we must be careful.
There are 30 - 50 plumes (per polar cap) at any given time, occupying about 5% of a polar cap.
Density measurements are still a problem (depends on how good atomic data is) - unclear if plumes are denser then interplume by 20% or up to a factor of 10.
TRACE observations of plumes in DeForest (2007)
On acceleration mechanisms: You can't make a fast solar wind purely based on the temperature profile; you need to add something extra to push it along.
Maximum energy estimates in a plume
[CDeF]: Clare Parnell and Andrew Haynes conducted experiments of 3D reconnection, taking a footpoint and driving it into another.
[MV]: Surely there is a maximum energy, you are killing a flux fragment, so integral of B^2/8/pi dV is finite.
[CDeF]: No, also energy from compressing the field. Thus, for plumes fudge factor would be how much do you squah/collide the fields.
[MV]: Thus, in addtion to B^2/8/pi term, you woulkd have to consider the work done on the field.
WEDNESDAY 10 DECEMBER
Jonathan Cirtain's Presentation
Polar X-ray jets: 7-10 per hour, repeated runs of 'HOP 3' (can search for the data through the Harvard webpage). Wave motions apparent in jets, typical period 180s. The movement/shifting of the jet can give an indirect measurement for what the flux distribution has to be at the lower boundary.
[Question] Why didn't we see these with TRACE? [Answer] Exposure times were too long.
Savacheva et al (2007) presents statistics for jets: average duration ~ 800 seconds, average size ~ 0.8Mm. Upper bound on the size of jet-width-distribution ~ 12Mm. Preference for transverse velocity component: evidence of dynamo process? Perhaps even something like a Hale-like law for jets?
