Transcript Acceleration of Coronal Mass Ejection In Long Rising Solar

Introduction to Space Weather
The Sun: The
Structure
Sep. 10, 2009
Jie Zhang
Copyright ©
CSI 662 / PHYS 660
Fall, 2009
Roadmap
•Part 1: The Sun
•Part 1: The Sun
1.
•Part 2: The Heliosphere
2.
•Part 3: The Magnetosphere 3.
•Part 4: The Ionsophere
•Part 4: Space Weather
Effects
4.
The Structure of the Sun: Interior
and Atmosphere
Solar Magnetism: Sunspots, Active
Regions, Solar Cycle, and Solar
Dynamo
Solar Corona: Coronal Heating,
Magnetic Effects, and Activities
Major Solar Activities: Flares and
Coronal Mass Ejections
CSI 662 / PHYS 660
September 10
2009
The Structure of the Sun:
Interior and Atmosphere
References:
•Kallenrode: Chap. 6
•NASA/MSFC Solar Physics at
http://solarscience.msfc.nasa.gov/
The Sun: Basic Facts
Distance 1 AU = 1.5 × 108 km
Radius: Rs = 696, 000 km
Mass: Ms = 1.99 × 1033 kg
Density: ρs = 1.91 g/cm3
Luminosity: Ls = 3.86 × 1023 kW
Solar Constant: LE = 1380 W/m2
Effective Temperature: Ts = 5780 K
Sun from Unaided Eyes
Given solar constant, calculate the Sun’s surface
effective temperature using Stefan-Boltzmann’s Law
(Eq. 6.2) ?
F = σ T4
and σ = 5.67 J m-2 s-1 K-1
Stratified Structure of the Sun
•Gravitational stratification: caused by the spherically
symmetric gravitational force, which always points toward the
center of the gas ball
•Density varies by 10 order of magnitude
•Temperature varies by 3 order of magnitude
Stratified Structure of the Sun
Atmosphere
(4) Corona
(3) Transition Region
(2) Chromosphere
(1) Photosphere
Surface
(3) Convection Zone
Interior
(2) Radiative Zone
(1) Core
Core
Core
• Depth: 0 – 0.3 Rs
• Temperature: 15 MK  7 MK
• Density: 150 g/cm3
Core
Core
• 90% of H, and 10% of He in particle numbers
• Energy generation: through nuclear fusion process
called PP chain (Proton-Proton chain)
41H  4He + 2e+ + 2ν + 26.73 Mev
or, the chain reaction formula:
1H(p,e+υ )2D(p,γ)3He(3He,2pγ)4He + 26.2 Mev
e
• Mean free path of particles
• Photons: a few cm
• Neutrinos: 7000 AU
• Thermal Equilibrium maintains the stability of the core
Radiative Zone
Radiative Zone
•depth: 0.30 – 0.70 Rs
•Temperature: 7 MK to 2 MK
•Density: 20 g/cm3 to 0.2 g/cm3
•Energy transport region
•through radiation transfer, or photon diffusion; conduction
is negligible; no convection
Inside the Sun: Convection Zone
(3) Convection Zone
• Depth: 0.70 – 1.00 Rs
• Temperature: ~ 2 MK to 0.06 MK
• Density: 0.2 g/cm3 – 10-7 g/cm3
• Opacity increase:
• at 2 MK, opacity increases as
heavy ions (e.g., C, N, O, Ca, Fe) starts to hold electrons
from fully ionized states. As a result, energy transfer
through radiation or photon leaking is less efficient, and
temperature gradient increases
• Convection occurs: when the temperature gradient becomes
so large, larger than the adiabatic gradient, the buoyancy
force starts to drive the convection
Convection Zone
•Numerical calculation shows that temperature decreases
rapidly in the convection zone
Convection Zone
•Evidence of convection seen as granules in the photosphere
Atmosphere
•Layered, but complex and dynamic
Atmosphere
•Temperature and Density Profiles
Photosphere
•
•
•
•
Surface of the Sun seen in visible wavelength (4000 – 7000 Å)
Thickness: a few hundred kilometers
(Effective) Temperature: ~5700 K
Density: 1019 to 1016 particle/cm3
• Surface mass density: ~ 10-8 g/cm3
• As a comparison, Earth atmosphere density ~ 10-3 g/cm3
Chromosphere
• A layer above the photosphere, transparent to broadband visible
light, but can be seen in spectral lines
• Hα line at 6563 Å (Hydrogen spectral line between level 3 to
level 2, first line in Balmer Series)
• Thickness: 2000 km in hydrostatic model
•
~5000 km in reality due to irregularity
• Temperature: 6000 K plateau, up to 20000 K at the top
• Density: 1016 to 1010 particle/cm3
Transition Region
• A very thin and irregular interface layer separating the
chromosphere and the much hotter corona
• Thickness: about 50 km, assuming homogeneous
• Temperature: 20,000 K to 1000,000 K (or 1 MK)
• Density: 1010 to 109 particle/cm3
• Can’t be seen in visible light or Hα line, but in UV light
from ions, e.g, C IV (at 0.1 MK), O IV, Si IV
Corona
•
•
•
•
•
Extended atmosphere of the Sun
Thickness: ~ Rs and extended further into the heliosphere
Temperature: 1 MK to 2 MK
Density: 109 to 107 particle/cm3
Difficult to be seen in visible light, nor in UV from light ions,
(C,O)
• Seen in EUV from heavy ions, e.g., Fe X (171 Å)
• Seen in X-rays (1 – 8 Å)
Corona was revealed by
eclipse observations
Interior versus Atmosphere
• Standard solar model explains well the structure of the
interior, up to the photosphere
• Based on the assumption of hydrostatic equilibrium
• Based on knowledge of radiation transfer, thermal
statistics, atomic physics and nuclear physics
• However, the standard solar model can not explain the
existence of chromosphere and corona
• Due to the existence of magnetic field
• Magnetohydrostatics and/or magnetohydrodynamics
(MHD) should be used as the model, instead of the
hydrostatic assumption
Solar Spectrum
•Continuum black-body radiation in visible light and Infrarad
•The effective temperature is 5780 K (Wien’s Law Eq. 6.3)
•Excessive continuum and line emission in EUV and X-ray from
corona and transition region
Spectral Lines
•Bohr’s atomic model
•Emission: electron deexcitation from high to low
orbit
•Absorption: electron
excitation from low to high
orbit
•Lyman series, Lα = 912 Å
•Balmer series, Hα = 6563 Å
Absorption and Emission Lines
(4000 Å – 7000 Å)
•Absorption lines in
photosphere and
chromosphere
•Emission lines in
Transition region and
corona
(300 Å – 600 Å)
Features in Photosphere
•Sunspot: umbra/penumbra
•Granules, Supergranule
Photosphere: sunspot
•Observed in visible light as
Galileo did
1. Umbra: a central dark region,
2. Penumbra: surrounding region
of a less darker zone
Photosphere: sunspot
•Sunspot is darker because it is cooler
•Big Sunspot is about half of the normal brightness.
•F = σT4 ,or T ~ B ¼ (Stefan-Boltzman Law Eq. 6.2)
•Tspot/Tsun=(Bspot/Bsun)1/4=(0.5)1/4 = 0.84
•Tsun = 5700 K
•Tspot = 5700 * 0.84 = 4788 K
•Sunspot is about 1000 K cooler than surrounding photosphere
Photosphere: sunspot
•In 1930s, it was realized that sunspot is a magnetic feature
•Magnetic field has pressure, describe by
PB = B2/8π (in CGS unit)
(see Eq 3.63 in MKS unit)
where B: magnetic field strength (Gauss)
•Gas pressure: Pg = N K T
•N: particle number density
•K: Boltzmann’s constant
•T: gas temperature
Photosphere: sunspot
•Sunspot’ internal pressure is the gas pressure combined
with the magnetic pressure, in balance with the external gas
pressure
Pg_in + PB_in = Pg_ext
Given a sunspot with a magnetic field of 3000 Gauss,
(1) calculate its magnetic pressure ?
(2) Calculate the typical gas pressure ?
(3) If the plasma density is the same inside and
outside the sunspot, what is the temperature of the
sunspot?
(4) How much darker is the sunspot?
Photosphere: Granules
Granules
• Small (about 1000 km across) cellular features
• Cover the entire Sun except for areas of sunspots
• They are the tops of convection cells where hot fluid
(bubble) rises up from the interior
•They cools and then sinks inward along the dark lane
•Individual granules last for only about 20 minutes
•Flow speed can reach 7 km/s
Photosphere: Supergranules
Supergranules
• much larger version of granules
(about 35,000 km across)
• Cover the entire Sun
• They lasts for a day to two
• They have flow speed of about 0.5
km/s
• Best seen in the
measurement of
the “Doppler shift”
•Small magnetic elements outside the
sunspot tend to concentrate along the
supergranule boundaries
Chromosphere
•Mainly seen in Hα line
•Plage
•Filament/Prominence
Chromosphere: Plage
Plage (beach in French)
•Bright patches surrounding sunspots that are best seen in Hα
•Associated with concentration of magnetic fields
Chromosphere: Filament/Prominence
Filament/Prominence
•Dense clouds of chromospheric material suspended in the
corona by the tension force of magnetic field
•Filaments and prominences are the same thing
•Prominences, as bright emission feature, are seen
projecting out above the limb of the Sun,
•Filaments as dark absorption feature, are seen projecting
on the disk of the Sun,
Chromosphere: Filament/Prominence
Filament/Prominence
•They can be as small as several thousand km
•They can be as large as one Rs long, or 700,000 km
•They can remain in a quiet or quiescent state for days or
weeks
•They can also erupt and rise off of the Sun over the course of
a few minutes or hours
Chromosphere: Filament/Prominence
Prominence Eruption
•e.g., so called granddady prominence in 1945
Transition Region
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
Corona
1. Coronal holes 2. Active regions 3. Quiet sun regions
Best seen in X-rays and EUV
X-ray
Corona
> 2 MK
Continuum
05/08/92
YOHKOH
SXT
Corona: Coronal Holes
Coronal holes
•Regions where the corona is dark
•A coronal hole is dark
•plasma density is low
•open magnetic field line
Corona: Active Region
Coronal active region:
•Consists of bright loops with enhanced plasma density and
temperature
•They are above the photospheric sunspots
•They are formed of closed magnetic loops
Corona: Active Region
Active region
loops trace
magnetic field
lines that are
selectively
heated
(a)Active Region
(b) Sunspots
(c)3-D coronal
magnetic
model
(d) side-view of
the model
Corona: Quiet Sun Region
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
The End