Coronal Structure CSI 769-001/PHYS 590-001 Solar Atmosphere Fall 2004 Lecture 07 Oct. 13, 2004 Coronal Structure

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

Solar Spectrum versus Solar Structure (Cont.) V (visible, 4000 Å – 7000 Å) and IR (Infrared, 7000 Å – 10000 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

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

Absorption versus Emission (cont.)

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

Absorption versus Emission (cont.)

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

Transition Region (cont.) Image: S VI (933 Å) at 200,000 K (SOHO/SUMER) May 12/13 1996 composite Image 9256 raster image, Each with 3 s exposure Collected in eight alternating horizontal scan across the Sun

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

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

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

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. 6.4.1

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

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

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

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

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. 6.4.3

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