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.