1. Coronal Structure CSI 769-001/PHYS 590-001 Solar Atmosphere Fall 2004
Lecture Oct. 13, 2004
Coronal Structure

2. Solar Spectrum versus Solar Structure
The complex spectral shape is due to the contribution of multiple layers of solar atmosphere with different temperature

3. Solar Spectrum versus Solar Structure (Cont.)
V (visible, 4000 Å – 7000 Å) and IR (Infrared, 7000 Å – Å
From Photosphere, the largest component of solar irradiance
UV (Ultraviolet, 1200 Å – 4000 Å)
Mainly from chromosphere
EUV (300 Å – 1200 Å)
Mainly from transition region
XUV (100 Å – 300 Å) and Soft X-ray (< 100 Å)
Mainly from Corona

4. Absorption versus Emission
(4000 Å – 7000 Å)
Absorption lines in photosphere and chromosphere
Emission lines in Transition region and corona
(300 Å – 600 Å)

5. Absorption versus Emission (cont.)

6. Absorption versus Emission (cont.)
Hα line at 6563Å

7. Absorption versus Emission (cont.)

8. Transition Region Image: C IV (1548 Å) at 100,000 K (SOHO/SUMER)
Outline the top of chromosphere
Limb brightening instead
of limb darkening

9. Transition Region (cont.)
Image: S VI (933 Å) at 200,000 K
(SOHO/SUMER)
May 12/ composite Image
9256 raster image,
Each with 3 s exposure
Collected in eight alternating horizontal scan across the Sun

10. Coronal plasma properties and ideal MHD The issue of coronal heating
Large scale coronal structures
Coronal plasma properties and ideal MHD
The issue of coronal heating
Coronal activities

11. Large Scale Coronal Structure
1. Coronal holes 2. Active region loops 3. Quiet sun regions
X-ray
Corona
> 2 MK
Continuum
05/08/92
YOHKOH
SXT

12. Large Scale Coronal Structure (cont.)
Coronal holes
Regions where the corona is dark
A coronal hole is dark because plasma density is low there

13. Large Scale Coronal Structure (cont.)
Coronal holes
Coronal holes are associated with “open” magnetic field lines that are often found at the pole
Particles easily flow away along the “open” field lines
From text book
Figure 6.5, P. 183
Read Chap

14. Large Scale Coronal Structure (cont.)
Coronal active region loops
Bright loops with enhanced plasma density and temperature
They are associated with photospheric sunspot
They are tracing coronal magnetic field lines that have been “selectively” heated

15. Large Scale Coronal Structure (cont.)
Coronal loops
Sunspots
3-D coronal magnetic model
side-view of the model

16. Large Scale Coronal Structure (cont.)
Coronal loop Evolution: from TRACE 171 Å, Fe IX/Fe X, 1.0 MK

17. Large Scale Coronal Structure (cont.)
Quiet Sun regions
Generally, regions outside coronal holes and active regions
Properties, such as density and temperature, in-between the coronal holes and active regions
Many transient bright points associated with small magnetic dipoles.
From SOHO/EIT
195 Å band
Fe XII, 1.5 MK
Nov. 10, 1997

18. Large Scale Coronal Structure (cont.)
Quiet Sun regions
Bright points associated with small magnetic dipoles or so called ephemeral regions.
From text book
Figure 6.10, P. 191
Read Chap

19. β Ξ gas pressure / magnetic pressure
Low β Coronal Plasma
For a magnetized plasma, plasma β is defined as
β Ξ gas pressure / magnetic pressure
In CGS unit, Pth=nKT, and PB=B2/8π
β = 8πnKT/ B2
If β >> 1, gas pressure dominates, flows control B
If β << 1, magnetic pressure dominates, B control plasma flow
HW04: calculate β for photosphere and corona, and discuss the implication