Transcript Onset Conditions for Impulsive Magnetic Energy Release James A. Klimchuk NASA Goddard Space Flight Center.

Onset Conditions for Impulsive
Magnetic Energy Release
James A. Klimchuk
NASA Goddard Space Flight Center
Important properties:
• Energy release in the corona is impulsive, not steady
(nanoflares)
Important properties:
• Energy release in the corona is impulsive, not steady
(nanoflares)
• The time delay between successive events can be long or short
Important properties:
• Energy release in the corona is impulsive, not steady
(nanoflares)
• The time delay between successive events can be long or short
• There is often a collective behavior where multiple events occur together
(coronal loops & nanoflare “storms”)
Important properties:
• Energy release in the corona is impulsive, not steady
(nanoflares)
• The time delay between successive events can be long or short
• There is often a collective behavior where multiple events occur together
(coronal loops & nanoflare “storms”)
• Onset conditions are important for determining the magnitude of energy rel.
(instant. and time-avg. coronal heating rates)
Turbulent convection in the high-b photosphere (solar surface)….
Swedish Solar Telescope
….“stirs” the low-b coronal magnetic field….
Quiet Sun
Loop cross-section
SUNRISE / IMaX
….causing it to become twisted and tangled (stressed).
Electric
current
sheet
TRACE
Strong
guide field
When it breaks, small bursts of energy called nanoflares heat the gas.
Millions of nanoflares occur every second across the Sun.
Parker (1983)
How do we confirm the existence of nanoflares?
Must overcome confusion from unresolved spatial scales & LOS averaging
Compare actual observations with predictions based on simulations
1D hydro (passive magnetic field, assumed heating)
3D MHD (heating part of solution)
To make meaningful predictions, must account for the coupling between
the corona and lower atmosphere (chromospheric evaporation)
Models of single isolated coronal current sheets cannot be observationally
tested
Simulated Loop Observations
Monolithic loop
3 MK
Simulated Loop Observations
SDO / AIA light curves
Single Nanoflare
Monolithic loop
3 MK
1 MK
AIA Channels
Viall & Klimchuk (2011)
131
94
335
211
193
171
Hot
Cool
Each coronal loop (observational feature) is a bundle of many
unresolved strands that is heated by a “storm” of nanoflares.
What about the diffuse emission between loops?
Also heated by nanoflares.
Intensity
Time Lag
Viall & Klimchuk (2012, 2013)
Why is there collective behavior in some places (loops) and not others?
Nanoflare Delay (Frequency)
Low frequency
Dt >> tcool
High frequency
Dt << tcool
Emission Measure Distribution
(thermal distribution of the plasma)
Slope indicates
nanoflare frequency
Tripathi, Klimchuk, & Mason (2011)
Bradshaw, Klimchuk, & Reep (2012)
Possible Unifying Picture
Diffuse component
(low energy, intermed. freq. nanoflares)
Loop
(high energy, low freq. nanoflares)
Nanoflare
Storm
Needs time to
“recharge”
Onset Conditions
Poynting flux of energy into the corona from footpoint driving:
Early onset
(weak heating)
Delayed onset
(strong heating)

vh
vh
Equate with observed energy loss rate, using observed Bv and Vh implies
  20o
“Parker angle”
Coronal Mass Ejections and Flares
Karpen, Antiochos, & DeVore (2012)
Karpen, Antiochos, & DeVore (2012)
Karpen, Antiochos, & DeVore (2012)
What physical parameter determines onset?
• Current sheet thickness
‒ Slow “complex” quasi-static driving
‒ Tearing instability
‒ Ideal instability (e.g., kink)
Kink Instability of Twisted Flux Tubes
field lines,
current sheet (red)
Hood, Browning, & Van der Linden (2009)
current
density
Hood, Browning, & Van der Linden (2009)
What physical parameter determines onset?
• Current sheet thickness
‒ Slow “complex” quasi-static driving
‒ Tearing instability
‒ Ideal instability (e.g., kink)
• Magnetic field misalignment angle (rotation across sheet)
‒ Secondary instability
Secondary Instability
Vertical dimension “squashed” by factor 10
Misalignment
“Heating rate”
Nanoflare occurs when magnetic
misalignment reaches ~35o
Consistent with “Parker angle”!
Dahlburg, Klimchuk, … (2005, 09)
Klimchuk, Lopez Fuentes, DeVore (2006)
Conclusions
• Energy release in the corona is impulsive, not steady
• The time delay between successive events can be long or short
• There is often a collective behavior where multiple events occur together
• Onset conditions are important for determining the magnitude of energy rel.
Conclusions
• Energy release in the corona is impulsive, not steady
• The time delay between successive events can be long or short
• There is often a collective behavior where multiple events occur together
• Onset conditions are important for determining the magnitude of energy rel.
Are there similarities with the magnetosphere?
Can we make progress by comparing the two
systems?
Conclusions
• Energy release in the corona is impulsive, not steady
• The time delay between successive events can be long or short
• There is often a collective behavior where multiple events occur together
• Onset conditions are important for determining the magnitude of energy rel.
Are there similarities with the magnetosphere?
Can we make progress by comparing the two
systems?
Triennial Heliophysics Summit
April 27 – May 1, 2015 Indianapolis