Title: The Yohkoh observations of solar flares
1The Yohkoh observations of solar flares
2The Yohkoh observations
- Structure in soft X-rays
- Dynamics in soft X-rays
- Footpoint behavior
- Coronal hard X-ray sources
- Microflares/nanoflares
- Waves
3Yohkoh discoveries
- Large-scale arcades
- The Masuda phenomenon
- Dimming (3 kinds?)
- Sigmoids and CMEs
- Foot-point motions
- Coronal hard X-ray sources
- X-ray detection of waves
4More discoveries
- TILs
- Hard X-ray ribbons
- Jets
- Coronal-hole channels
- Loop-top features
- Cusps
5All of the preceding images came from the Yohkoh
science nuggets, to be found at http//solar.phy
sics.montana.edu/nuggets
6What are some meaty problems?
- How do flares launch global waves?
- How do we understand the symbiosis of energy
release and particle acceleration? - What is the nature of the geometrical evolution
of the corona in the impulsive phase of a flare
(or the acceleration phase of CME)?
7Topics
- Coronal structure and conjugacy
- Fine structure in the corona
- Particle acceleration
- Global waves
- Extraordinary events
81. Coronal structure and conjugacy
Fletcher et al., 2001
Cargill Priest, 1995?
http//isass1.solar.isas.ac.jp/hudson/cartoons
9Coronal separatrix structure
- The separatrix surfaces deform during an
energy-release event - The flare ribbons in the chromosphere should map
into these separatrices - Ribbon brightening not only reveals the energy,
but also describes the coronal restructuring
10B. Somov, 2002
11Warren Warshall ApJ 560, L87, 2001
Asai et al., Y10 proceedings, 2002
122. Fine structure in the corona
Higher-temperature things in the corona look
fuzzier than lower-temperature things (eg,
yellow line vs red line)
TRACE/Yohkoh comparison from Warren et al, ApJ
572, 121 (1999)
13Observations of spatial fine structure for
coronal non-thermal source (White et al.,
preprint 2002)
14Another example of fine structure at high
energies (White et al., ApJ 384, 656, 1992).
15Hard X-ray footpoints systematically trace out
fine-scale features (T. Metcalf, fall AGU meeting
2001)
16Metcalf made a potential- field extrapolation and
found that the separatrix structure correlated in
interesting ways with the in-plane motions, but
not with the out-of-plane (perpendicular to B)
motions.
173. Particle acceleration and energy release
- Neupert effect
- Soft-hard-soft vs soft-hard-harder
18Neupert effect
RHESSI 20-25 keV (purple) GOES 1-8 A (green)
19Lessons from the Neupert effect
- The energy release that fills coronal loops with
hot plasma has a direct relationship with
particle acceleration - To a first approximation, this relationship is
independent of the scale or intensity of the
energy release
20(No Transcript)
21F. Farnik, 2001
22Lessons from soft-hard-soft
- Non-thermal time scales are usually not
determined by trapping - The spectral evolution at high energies is an
intrinsic property of the acceleration mechanism
23Comments
- The flares that exhibit departures from the
Neupert effect or from soft-hard-soft spectral
morphology are the most interesting - There is more non-thermal physics in the corona
than is evident from the impulsive (CME
acceleration) phase alone
244. Global waves
Hudson et al., submitted 2002
Thompson et al., Solar Phys. 193, 161, 2000
25Lessons from global waves
- The Uchida model (weak fast-mode shock, as a
blast wave) works well - The X-rays show the initiation of the disturbance
close to the flare core, and we may learn
something fundamental about the restructuring
from this
265. Extraordinary events
- April 18, 2001 a major X-class flare two days
behind the west limb
27Lessons from this extraordinary event
- Tail of electron distribution function
- (gt20 keV) contained gt0.2 of the total
population - Non-thermal particles may be the dominant source
of gas pressure in a CME interior (speculation!)
28Conclusions for FASR - I
- The FASR spectral domain offers the best chance
to track the coronal restructuring responsible
for flare/CME energy - Clues to the restructuring may come from global
waves - The FASR frequency agility may be essential for
studying the invisible hand at work in the
restructuring
29Conclusions for FASR - II
- The Yohkoh data confirm and extend our view that
particle acceleration must be considered as an
integral part of the energy release - Interpretation of FASR will require modeling the
evolution of distribution function and geometry
self-consistently - The frequency agility will be a key to success