The Yohkoh observations of solar flares

Hugh Hudson

UCB

The Yohkoh observations

Structure in soft X-rays

Dynamics in soft X-rays

Footpoint behavior

Coronal hard X-ray sources

Microflares/nanoflares

Waves

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

More discoveries

TILs

Hard X-ray ribbons

Jets

Coronal-hole channels

Loop-top features

Cusps

Slide 5

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)?

Topics

Coronal structure and conjugacy

Fine structure in the corona

Particle acceleration

Global waves

Extraordinary events

1. Coronal structure and conjugacy

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

Slide 10

Slide 11

2. Fine structure in the corona

Slide 13

Slide 14

Slide 15

Slide 16

3. Particle acceleration and energy release

Neupert effect

Soft-hard-soft vs soft-hard-harder

Slide 18

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

Slide 20

Slide 21

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

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

4. Global waves

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

5. Extraordinary events

April 18, 2001: a major X-class flare two days behind the west limb

Lessons from this extraordinary event

Tail of electron distribution function

(>20 keV) contained >0.2% of the total population

Non-thermal particles may be the dominant source of gas pressure in a CME interior (speculation!)

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

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


	Structure in soft X-rays
	Dynamics in soft X-rays
	Footpoint behavior
	Coronal hard X-ray sources
	Microflares/nanoflares
	Waves


	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


	TILs
	Hard X-ray ribbons
	Jets
	Coronal-hole channels
	Loop-top features
	Cusps


	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)?


	Coronal structure and conjugacy
	Fine structure in the corona
	Particle acceleration
	Global waves
	Extraordinary events


	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


	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


	Non-thermal time scales are usually not determined by trapping
	The spectral evolution at high energies is an intrinsic property of the acceleration mechanism


	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


	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


	April 18, 2001: a major X-class flare two days behind the west limb


	Tail of electron distribution function
	(>20 keV) contained >0.2% of the total population
	Non-thermal particles may be the dominant source of gas pressure in a CME interior (speculation!)


	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


	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