Thursday, 9-Jun-05, WG4 Notes by S. Christe

Hudson :  White Light Flares: Trace and RHESSI Observations

Original (white) light flare, Carrington 1859, first flare
terrestrial response, three axis compas readings is noted to this flare, evidence of a shock wave
a few days later possibly from CME from that flare, top 5% of CMEs speed, 2000 km/s
white light usually formed deep in the photosphere, associates very well with x-rays
10 MeV protons can get down to 10^24 cm^2 so down to photosphere
contribution functions needs to be used to calculate where th emission is coming from
fluctuations of white light are too fast to be caused by the protons
11 well covered events X:0 M7 C3
all had white light so no tresholding effect...?
excess of ultraviolet associated with solar activity, this emission may be detected by TRACE
24 jul 04 C1.6 world record small white light flare
good coincidence between ultraviolet and white light contours for that event
M4.9 july 26 02, white light time curve is impulsive, neupert like
white light kernel emission from a loop top, 12 nov 02, gradual emission with impusilve emission
from white light footpoints
conclusions, trace show rapid small scale features resembling UV
sources are small patches
every flare is a white light flare, emission correlated to total energy
contrasts can exceed 100% compared to background photosphere
seeing bright low-temperature emission like 10000 C just like stellar flares
not just UV extension
(white light is created by recombination)
uv/wl footpoints are tiny, a few arcseconds

Henoux : Information on particle acceleration and transport derived from solar
solar flare spectropolarimetry

anysotropy leads to polarization in halpha
polarization fraction is related to electron energy as measured in the laboratory
polarization switches above a certain energy, E0 = 200 keV.
polarization is dependent on direction and therefore along the B field, need to assume whether they are circling
the B field or not
15-jun-01 event
deriving the stokes parameters is tricky
images are create by scanning a slit across the sun
polarization island is found to be on the border of the flare, ~4%
polarization is always a little higher in hbeta
one minute of time to scan over 100 arcseconds
peaks in radial polarization could be from low enery protons moving along B
or electrons circling around B or return current electrons moving along B
norma and smith used to estimate return current spectrum
return current energy can be either above or below E0 depending on 
ambient density.
interpretation : tangential polarization is associated with upflow
related to reconnection.

Fletcher : 17 Jul 2002

tracking individual flare kernels in TRACE UV, 4 ribbon flare
complex ribbons
developped an algorithm to track each little kernel
interactions between two different active regions
calculated the rate of change of magnetic flux, reconnection rate
good correlation in time between reconnection rate and intensity variations
25% of peaks are correlated which is significant compared to monte carlo simulation
RHESSI contours lie along ribbons and seem to be where reconnection rate is highest
finding correlations in peaks in time is difficult, used wavelet a trous
can seperate out bursts from overall evolution
find good correlation between some kernels
some are found with delays, 5 sec delays

Fletcher (Hudson notes resume)

Re-analysis of 17-jul-02 UV footpoints
Wavelet a trous as a method to isolate elementary flare burst correlations
Gallagher comment on Greenfield et al. paper dealing with analogous problem
Some correlations found; some quick-and-dirty correlations go awa y
Time delays of 5 sec in some cases
Repeated peaks at given footpoints would represent successive reconnections
  with different partners?
Conclusions - HXR sources occur where "reconnection rate" is highest; highly
  correlated UV footpoints hard to find, still looking; 

Pick

Three topics...
June 05 ApJ paper, Pick et al.
Moving, stationary, type II sources; RHESSI; interpretation via Demoulin
  in terms of plasmoid reconnection (discussion)
He3 analysis with Mason (eg 05-oct-02) - is this one of Linghua's events? =
  narrow CME in direction of 164 MHz source
Good correlation with RHESSI, ask Sa"m
17-mar-02 RHESSI/radio event with CME; successive type III burst locations
  move out from RHESSI source along leg of CME
WL shock may exist away from CME leg (argument from Hudson that LASCO
  never unambiguously sees shocks)
Note high starting frequencies far from RHESSI source in type III sequence;
  how can this be?
Yan potential-field extrapolation shows open fields in path of CME

Fletcher: discussion of inputs to theorists

1. soft-hard-soft

SHS well discussed by theory group, who find general consistency with
  better views of diffusive acceleration. But they don't rule out 
  other mechanisms
Different physics may be involved in SHH?

2. preflare nonthermal components - NEW WITH RHESSI

Heavy discussion of what "nonthermal" means in this context
Canonical example of 23-Jul-02
Schmahl's example of 03-nov-03 
Schmahl cites Sui's early-phase plasmoid observations
Pick & Vilmer do not find this to be rare, but just a new way to see
  pre-flare activity. Schmahl suggests high AR densities prior to event
  lead to this set of observation
Bone suggests 14-Apr (Veronig) as possibly another example

3. Dense coronal sources - NEW WITH RHESSI?

Kane, Bone event (20-jul-02)... require 10^11 cm^-3 and still probably
  cannot support 100 keV emission
Rapid variability as reported by Balciunate & Krucker equally a problem
  in terms of coronal density
Vlahos comment about evaporation and formation of dense loops with HE
  particles. This seems to be a different source of density
Grigis asks about X-ray emission lines - yes, it would be useful for sure

4. Descending loop-top sources - NEW WITH RHESSI

Veronig event 3-Nov-03 shows clear dip before rise
Ji observation of decreasing footpoint separation in such a phase (9-sep-02)

5. Footpoint size

TRACE white light and UV suggest few 10^3 cm, area < 10^17 cm^2; also in IR
Not only compact, but also fragmented (Grigis comment) 
Extensive debate - Schmahl points out that visibility techniques allow
  direct HXR size estimates, and they are not consistent with tiny footpoints
Vilmer and Grigis ask about protons, Hudson goes out on a limb and denies
  this possibility on the basis of timing
Dennis also does not like small footpoint areas...