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Roadmap Part 1: The Sun Part 1: The Sun Part 2: The Heliosphere 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 Part 1: The Sun Part 2: The Heliosphere Part 3: The Magnetosphere Part 4: The Ionsophere Part 4: Space Weather Effects
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Introduction to Space Weather
The Sun: The Structure Sep. 10, 2009 CSI 662 / PHYS 660 Fall, 2009
Jie Zhang Copyright Roadmap Part 1: The Sun Part 1: The Sun Part 2:
The Heliosphere
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 Part 1: The Sun
Part 2: The Heliosphere Part 3: The Magnetosphere Part 4: The
Ionsophere Part 4: Space Weather Effects The Structure of the Sun:
Interior and Atmosphere
CSI 662 / PHYS September The Structure of the Sun: Interior and
Atmosphere References: Kallenrode: Chap. 6 NASA/MSFC Solar Physics
at The Sun: Basic Facts Distance 1 AU = 1.5 108 km
Radius:Rs = 696, 000 km Mass: Ms = 1.99 1033 kg Density: s= 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 Suns surface effective temperature
using Stefan-Boltzmanns Law (Eq. 6.2) ? F = T4 and = 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
(4) Corona (3) Transition Region (2) Chromosphere (1) Photosphere
Atmosphere Surface (3) Convection Zone (2) Radiative Zone (1) Core
Interior 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+ + 2 Mev or, the chain reaction
formula: 1H(p,e+e)2D(p,)3He(3He,2p)4He Mev 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/cm3to 0.2 g/cm3 Energy
transport region through radiation transfer, or photon diffusion;
conduction is negligible; no convection Inside the Sun: 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 )
Thickness: a few hundred kilometers (Effective) Temperature: ~5700
K Density: 1019 to 1016 particle/cm3 Surface mass density: ~ g/cm3
As a comparison, Earth atmosphere density ~ g/cm3 Chromosphere A
layer above the photosphere, transparent to broadband visible
light, but can be seen in spectral lines H line at 6563 (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 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 Cant be seen in visible light or H line, but in UV
light from ions, e.g, C IV (at 0.1 MK), O IV, Si IV Corona Corona
was revealed by eclipse observations
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 )
Seen in X-rays (1 8 ) 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
SolarSpectrum Continuum black-body radiation in visible light and
Infrarad The effective temperature is 5780 K (Wiens Law Eq. 6.3)
Excessive continuum and line emission in EUV and X-ray from corona
and transition region Spectral Lines Bohrs atomic model
Emission: electron de-excitation from high to low orbit Absorption:
electron excitation from low to high orbit Lyman series, L = 912
Balmer series, H = 6563 Absorption and Emission Lines
(4000 7000 ) Absorption lines in photosphere and chromosphere
Emission lines in Transition region and corona (300 600 ) Features
in Photosphere
Sunspot: umbra/penumbra Granules, Supergranule Photosphere: sunspot
Observed in visible light as Galileo did
Umbra:a central dark region, Penumbra:surrounding region ofa less
darker zone Photosphere: sunspot Sunspot is darker because it is
cooler
Big Sunspot is about half of the normal brightness. F = T4,or T ~ B
(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 = B2/8 (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: Boltzmanns
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
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
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 H
line Plage Filament/Prominence Chromosphere: Plage Plage (beach in
French)
Bright patches surrounding sunspots that are best seen in H
Associated with concentration of magnetic fields Chromosphere:
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
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 ) 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
Corona 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 Active
Region Sunspots 3-D coronal magnetic model 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 band Fe XII, 1.5 MK Nov. 10, 1997 The End