Solar Coronal Loops Resolved by Hinode and SDO
David H. Brooks George Mason University
Harry P. WarrenNaval Research Laboratory
Ignacio Ugarte-UrraGeorge Mason University
Motivation
• We want to solve the coronal heating problem in our lifetimes!
• We need to know the spatial and temporal scales of the heating mechanism.
• Current measurements are averaged properties of loop structures (T, n, r).
• We need to build an instrument that observes fundamental resolved coronal loops.
• We need to know at what spatial scale we resolve fundamental coronal loops? Tens, hundreds, thousands of km?
AIA/SDO
AIA/SDO
Position
Tem
pera
ture
Position
Den
sity
AIA/SDO
Position
Tem
pera
ture
Position
Den
sity
−2000 −1000 0 1000 2000Distance (km)
−2000 −1000 0 1000 2000Distance (km)
−2000 −1000 0 1000 2000Distance (km)
−2000 −1000 0 1000 2000Distance (km)
What size are fundamental loops?Ambiguous.Unknown.
AIA/SDO
Background - Imaging
Aschwanden & Nightingale (2005)
• 18,000 loop segments in TRACE.• Narrow T distributions (only 3 filters).• FWHM = 1420 ± 340 km• TRACE PSF = 900 km ⎬ Resolved!
Background - Imaging
Aschwanden & Nightingale (2005)
• 18,000 loop segments in TRACE.• Narrow T distributions (only 3 filters).• FWHM = 1420 ± 340 km• TRACE PSF = 900 km ⎬ Resolved!
• No density measurements. Volume filled.
Background: 1D hydro models
Warren et al. (2003)
• At least a few threads needed to simulate TRACE light curves.
Multi-strand model - known geometry
Atomic Data ⎨
N strandsRadius rDensity nTemperature T Envelope R
Itot
= ANr2
Itot
= G(T, n)n2V
l2= G(T, n)n2N�r2l
l2
l: pixel length
n: density!
Itot
= ANr2
N=1 N=4 N=4
R
Itot
= ANr2
I
obs
(x) = PSF
inst
⇤ f(r,N,R)
EIS/Hinode AIA/SDO
N=1 N=4 N=4
R
Itot
= ANr2
I
obs
(x) = PSF
inst
⇤ f(r,N,R)
EIS/Hinode AIA/SDO
N=1 N=4 N=4
R
If r =R then N=1 ⇒ resolved!
Resolved loop: 1 strand with 830 km radius
explains EIS and AIA intensities and widths
Data analysis - rare case
Unresolved loop: 5 strands with 280 km radius
needed to explain EIS and AIA intensities and widths
Data analysis - typical case
Results 1 ≤ N ≤ 8 ; Four N = 1 loops ; µ1/2(r) = 470 km
Results 1 ≤ N ≤ 8 ; Four N = 1 loops ; µ1/2(r) = 470 km
Hundreds!
Coronal rain
SOT/Hinode
Coronal rain
SOT/Hinode
Coronal rain2012/04/16 18:53:25 UT
10"
Ca II H line
0 50 100 150 200 250Pixels
0
50
100
150
200
250
Cou
nts/
s
FWHM1=1387km FWHM1=435km
SOT/Hinode
Coronal rain2012/04/16 18:53:25 UT
10"
Ca II H line
0 50 100 150 200 250Pixels
0
50
100
150
200
250
Cou
nts/
s
FWHM1=1387km FWHM1=435km
SOT/Hinode
Antolin et al. (2012)310 km
Conclusions
• Hinode/EIS and SDO/AIA can resolve some coronal loops.
• The majority of loops, however, remain unresolved.
• Our results suggest that a limited number of strands (1-10) is sufficient to explain current observations. Typical sizes are in the hundreds of km (consistent with optical observations).
• Heating mechanism should explain coherence in time of a few threads, on spatial scales of hundreds of km.
• Next generation instrument should be able to resolve loops routinely!
Final Thoughts
• Parker’s nanoflare model appears unable to explain coronal loop observations. -- predicts broad distribution of temperatures (many threads in various stages of heating and cooling).
Ofman & Aschwanden (2002)
Parker (1983)
Final Thoughts
• Parker’s nanoflare model appears unable to explain coronal loop observations. -- predicts broad distribution of temperatures (many threads in various stages of heating and cooling).
Ofman & Aschwanden (2002)
Parker (1983)
• Temperature distributions are narrow.
Final Thoughts
• Parker’s nanoflare model appears unable to explain coronal loop observations. -- predicts broad distribution of temperatures (many threads in various stages of heating and cooling).
Ofman & Aschwanden (2002)
Parker (1983)
• Temperature distributions are narrow.
• Only a few threads.
Final Thoughts
• Parker’s nanoflare model appears unable to explain coronal loop observations. -- predicts broad distribution of temperatures (many threads in various stages of heating and cooling).
Ofman & Aschwanden (2002)
Parker (1983)
• Temperature distributions are narrow.
• Only a few threads.
• No evidence for braiding of hundreds of threads in coronal loops.
Final Thoughts
• Parker’s nanoflare model appears unable to explain coronal loop observations. -- predicts broad distribution of temperatures (many threads in various stages of heating and cooling).
Ofman & Aschwanden (2002)
Parker (1983)
• Temperature distributions are narrow.
• Only a few threads.
• No evidence for braiding of hundreds of threads in coronal loops.
• Consistent with Hi-C?
The End
Results published in Brooks et al. (2012), ApJ, 755, L33
Filling Factors ~ 1/R2
Too Small.