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The Yohkoh observations of solar flares

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Title: The Yohkoh observations of solar flares


1
The Yohkoh observations of solar flares
  • Hugh Hudson
  • UCB

2
The Yohkoh observations
  • Structure in soft X-rays
  • Dynamics in soft X-rays
  • Footpoint behavior
  • Coronal hard X-ray sources
  • Microflares/nanoflares
  • Waves

3
Yohkoh 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

4
More discoveries
  • TILs
  • Hard X-ray ribbons
  • Jets
  • Coronal-hole channels
  • Loop-top features
  • Cusps

5
All of the preceding images came from the Yohkoh
science nuggets, to be found at http//solar.phy
sics.montana.edu/nuggets
6
What 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)?

7
Topics
  1. Coronal structure and conjugacy
  2. Fine structure in the corona
  3. Particle acceleration
  4. Global waves
  5. Extraordinary events

8
1. Coronal structure and conjugacy
Fletcher et al., 2001
Cargill Priest, 1995?
http//isass1.solar.isas.ac.jp/hudson/cartoons
9
Coronal 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

10
B. Somov, 2002
11
Warren Warshall ApJ 560, L87, 2001
Asai et al., Y10 proceedings, 2002
12
2. 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)
13
Observations of spatial fine structure for
coronal non-thermal source (White et al.,
preprint 2002)
14
Another example of fine structure at high
energies (White et al., ApJ 384, 656, 1992).
15
Hard X-ray footpoints systematically trace out
fine-scale features (T. Metcalf, fall AGU meeting
2001)
16
Metcalf 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.
17
3. Particle acceleration and energy release
  • Neupert effect
  • Soft-hard-soft vs soft-hard-harder

18
Neupert effect
RHESSI 20-25 keV (purple) GOES 1-8 A (green)
19
Lessons 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)
21
F. Farnik, 2001
22
Lessons 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

23
Comments
  • 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

24
4. Global waves
Hudson et al., submitted 2002
Thompson et al., Solar Phys. 193, 161, 2000
25
Lessons 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

26
5. Extraordinary events
  • April 18, 2001 a major X-class flare two days
    behind the west limb

27
Lessons 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!)

28
Conclusions 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

29
Conclusions 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
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