Download The Sun - challenge for scientists

The Sun - challenge for scientists
M.L. Khodachenko
Institut für Weltraumforschung,
Österreichische Akademie der Wissenschaften
Graz, Austria
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
The Sun – our star
● Why do we study the Sun?
♦ The Sun is the nearest star: Many physical processes important for our understanding of the Universe can be observed and studied on the Sun.
♦ The Sun sustains the life on Earth, it
A year (1992) of the Sun in
soft X-rays (Yohkoh)
2 weeks during Jan. 2005.
SOHO / MDI (~6,768 Å)
controls terrestrial environment and
impacts our technological civilization.
♦ The Sun is unique plasma physics laboratory of an astrophysical scale, close
enough for precise measurements.
SOHO/MDI magnetogram
Sun in white light (HAO, Mauna
Loa coronameter)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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The Sun – our star
Unsolved problems of the solar physics stimulate progress
in the fundamental science, as well as in the technological
and engineering branches.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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The Sun – our star
● Two main focus areas of the modern solar science
♦ Understanding of the physical mechanisms of the solar dynamics and
magnetism. Determination of ways by which the energy generated in
the Sun’s core is released into space
Detailed study of interaction of the solar plasmas and magnetic field. Theoretical analysis and modelling of the fundamental physical processes underlying the dynamic phenomena on the Sun should be combined with observations which are able to resolve scales and time intervals characteristic to
these processes.
♦ Understanding and prediction of the geo-spheric and bio-spheric
effects of the Sun
Study of the solar activity phenomena and their manifestation in the heliosphere and the near Earth space, performed in close collaboration with
life-sciences (biology, climatology, meteorology, ecology, etc.)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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The Sun – our star
The Sun – challenge for scientists
Challenge to see
Challenge to understand
The main structure of the lection:
♦ What do we know (see and understand) about the Sun ?
♦ What is still the unclear (open questions) ?
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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The Sun – our star
Hα
15,000 K
He II, EUV
60,000 K
Fe IX/X, EUV
1 MK
UV 1600 Å
8000 K
Magnetic field
5000 K
Visible
5000 K
Fe XII,
EUV
1.5 MK
Fe XIV,
EUV
2 MK
Broad window
to the Sun
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
X-rays
4-6 MK
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The Sun : basic parameters
Spectral type: G2 V (dwarf)
Age:
4.5 billion years
Diameter:
1,39 million km
(108 Earth diameters)
Mass:
1.99 x 1030 kg
(333,000 Earth masses, or 99.9% of all matter in Solar System )
Luminosity:
~ 3.9 x 1026 W
Temperature
at Core:
at surface:
in Sunspots:
Solar Cycle:
15 million K
5,700 K
4,000 K
8 - 11 years
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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The Sun : basic parameters
Composition
percentage of total number of atoms:
92.1% hydrogen (H)
7.8% helium (He)
0.1% other elements
percentage of total mass:
74% hydrogen (H)
25% helium (He)
1% other elements
Rotation Period (relative stars / relative Earth)
at Equator:
at Poles:
~ 25 / 27 Earth days
~ 30 / 32 Earth days
Distance to Nearest Star: 4.3 light years
Average Distance to Earth: 149,600,000 km (1AU)
(147,100,000 km in January / 152,100,000 km in July)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Structure of the Sun : Inner regions
● Three main sections inside the Sun:
♦ Core – the innermost part of the Sun.
- T= 15 million K
- Occupies 1/50 of the solar volume,
- Contains 1/2 of the whole solar mass
- Generates 99% of the solar energy
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Structure of the Sun : Inner regions
● Three main sections inside the Sun:
♦ Radiative zone (RZ) – the largest layer
of the Sun (overlaps partially with the Core)
-T ä
from 15 million K to 2 million K
- Outward transfer of energy by radiative
diffusion
- High opacity fi
Multiple absorptions
and re-emissions of photons (radiation
diffusion time to the surface â up to 107 years)
- Multiple collisions fi
wavelength â from high-energy gamma-rays (in the core)
to visible light (at the solar surface)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Structure of the Sun : Inner regions
● Three main sections inside the Sun:
♦ Convection zone – the outermost part
of the Sun.
- occurs at
-T ä
~ (0.7 - 0.8) R from center
from 2 million K to 6000 K
- Material convection is dominating
mechanism of energy transport
- Energy reaches the surface mainly in
the form of visible light.
♦ Altogether, across inner regions of the Sun
- Temperature ä 3 ½ orders of magnitude (down to 6000 K)
- Density ä 8 ½ orders of magnitude (down to 4 x 10-4 kg/m3)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar power supply : Nuclear fusion in the Core
● Extremely hot and dense plasma conditions in the solar Core :
♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core
from reaching the solid state.
♦ High density and temperature
fi nuclear fusion reactions fi energy release
in the form of electromagnetic energy (gamma-rays) and energetic particles.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar power supply : Nuclear fusion in the Core
● Extremely hot and dense plasma conditions in the solar Core :
♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core
from reaching the solid state.
♦ High density and temperature
fi nuclear fusion reactions fi energy release
in the form of electromagnetic energy (gamma-rays) and energetic particles.
● Hydrogen fusion cycle inside the Sun (proton-proton reaction) :
involves: 4 Hydrogen nuclei (protons) and 2 electrons
yields:
Helium nucleus, 2 neutrinos and 6 photons
0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar power supply : Nuclear fusion in the Core
● Extremely hot and dense plasma conditions in the solar Core :
♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core
from reaching the solid state.
♦ High density and temperature
fi nuclear fusion reactions fi energy release
in the form of electromagnetic energy (gamma-rays) and energetic particles.
● Hydrogen fusion cycle inside the Sun (proton-proton reaction) :
involves: 4 Hydrogen nuclei (protons) and 2 electrons
1 + 2 e → 4He + 2 neutrinos + 6 photons
Helium nucleus, 2 neutrinos and 6 photons
yields: 4 H
0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar power supply : Nuclear fusion in the Core
● Extremely hot and dense plasma conditions in the solar Core :
♦ The temperature of 15 million K prevents the dense (160,000 kg/m3) core
from reaching the solid state.
♦ High density and temperature
fi nuclear fusion reactions fi energy release
in the form of electromagnetic energy (gamma-rays) and energetic particles.
● Hydrogen fusion cycle inside the Sun (proton-proton reaction) :
involves:
4 Hydrogen
and
electrons tons of He
Every second
700,000,000
tonsnuclei
of H is(protons)
converted
to 2695,000,000
and 4,900,000 tons of energy (E = mc2)
Helium nucleus, 2 neutrinos and 6 photons
yields:
⇓
0.7 % of the Hydrogen supply mass turns into energy (typical for a main sequence star)
Sun loses 4,900,000 tons of mass each second.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar power supply : Nuclear fusion in the Core
● Fusion reaction
4 1H + 2 e → 4He + 2 neutrinos + 6 photons
goes in 3 steps
1. Fusion of Hydrogen into Deuterium :
1H
+ 1H → 2H + antielectron + neutrino
2 protons collide
⇓
proton 1
proton 2
antielectron
→
bounds to
annihilates with
neutron + antielectron + neutrino
neutron → heavy Hydrogen (Deuterium)
electron → 2 high-energy photons.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar power supply : Nuclear fusion in the Core
● Fusion reaction
4 1H + 2 e → 4He + 2 neutrinos + 6 photons
goes in 3 steps
1. Fusion of Hydrogen into Deuterium :
1H
+ 1H → 2H + antielectron + neutrino
2 protons collide
⇓
proton 1
proton 2
antielectron
→
bounds to
annihilates with
neutron + antielectron + neutrino
neutron → heavy Hydrogen (Deuterium)
electron → 2 high-energy photons.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar power supply : Nuclear fusion in the Core
● Fusion reaction
4 1H + 2 e → 4He + 2 neutrinos + 6 photons
2. Formation of Helium-3 :
2H
+ 1H → 3He + photon
Deuterium captures a proton
⇓
emittion of
formination of
photon
3He nucleus.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
goes in 3 steps
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Solar power supply : Nuclear fusion in the Core
● Fusion reaction
4 1H + 2 e → 4He + 2 neutrinos + 6 photons
3. Recombination of Helium-3 into Helium :
3He
+ 3He → 4He + 1H+ 1H
2 Helium-3 recombine
⇓
emission of
formination of
2 protons
He nucleus.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
goes in 3 steps
¾
Solar power supply : Nuclear fusion in the Core
● Fusion reaction
4 1H + 2 e → 4He + 2 neutrinos + 6 photons
goes in 3 steps
Reaction summary
+ 1H → 2H + antielectron + neutrino
1H + 1H → 2H + antielectron + neutrino
electron + antielectron → photon + photon
electron + antielectron → photon + photon
1H
Step 1
Step 2
Step 3
+ 1H → 3He + photon
2H + 1H → 3He + photon
2H
3He
+ 3He → 4He + 1H+ 1H
⇓
6 1H + 2 e → 4He + 2 1H + 2 neutrinos + 6 photons
net energy release is 26 MeV
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Helioseismology:
- Primary physics: wave motions excited and propagating in the solar interior
- Sources of solar waves: processes in convection region (continuum source)
- 3 kinds of waves in helioseismology:
acoustic (p-modes),
gravity (g-modes),
surface gravity waves (f-modes)
♦ Sun acts as a resonant cavity:
about 107 p- and f- modes
- On the Sun's surface: waves appear
Red / blue – opposite displacements
f = 2935.88 +/- 0.2 microHz (SOHO/MDI)
as up and down motions observed
as Doppler shifts of spectrum lines
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Helioseismology:
♦ Each oscillation mode is sampling different parts of the solar interior
Periods of analyzed oscillations: ~ 1.5 min … ~ 20 min
Wavelengths: 1000 km … 2 R
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Helioseismology:
♦ L-nu Diagram – shows amount of acoustic
energy per frequency for each spatial
mode
ℓ – angular degree = the number of node
lines in a wave pattern at solar surface
n – mode‘s order = number of radial nodes
(different n → different curved lines)
♦ Most of the power (yellow) is concentrated
in a band near 3 mHz (~ 5 min)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
Measure travel time
for sound waves
fi
Sonogram image
(subsurface structure
of the sound speed)
fi
Temperature
distribution &
Subsurface Inhomogeneities
= Acoustic tomography
♦ Temperature variation
inside the Sun
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Subsurface flows of gas measured by SOHO/MDI
convection flows
motion from the equator towards the poles
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Change of the time averaged
rotation rate on/in the Sun
red
– faster then average
blue – slower then average
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Rotation rate of the solar sphere:
Orange – rotation of the bulk of the
Sun (~30 degrees latitude)
Red – faster than average rotation
Yellow / blue – slower than average
rotation
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Depth and latitude variation
of the solar rotation rate:
- The inner 70% of the Sun rotates at
nearly the same rate
- Differential rotation in the outer 30%
of the Sun (in convection zone)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Depth and latitude variation
of the solar rotation rate:
- Change in rotation rate with depth,
in a very thin layer just under the
surface - yellow line
- Jet-stream at about 75 degrees
latitude and about 45,000 km
below the surface
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Spatial and temporal variation
of the solar rotational flows
speed
red
– faster then average
blue – slower then average
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
Speed change measurements give
more details on the structure and
dynamics of the solar surface
and sub-surface flows
- Jet-stream at about 75 degrees
latitude and about 45,000 km
below the surface
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar interior :
Look under the surface
● Time-distance helioseismology (with SOHO/MDI):
♦ Difference in speed between various areas on the Sun (SOHO/MDI)
- Jet-stream at about 75 degrees
latitude and about 45,000 km
below the surface
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Photosphere – the most dense part of the solar atmosphere (0.02 g/m3)
-
550 km thick layer in which the solar material changes from
being completely opaque (to radiation) to being transparent.
Visible surface of the Sun.
-
the layer which emits most of the solar energy (in white light)
-
one of the coolest regions of the Sun (6000 K)
fraction (0.1% ) of the gas is ionized
-
Photospheric minimum: T ~ 4200 K (at 550 km above the surface)
fi only a small
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● View in white-light: a disk with dark spots.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Photospheric Convection / granulation
Maretial convection inside the Sun fi granulation pattern on the solar surface
♦ Granulation parameters:
- Size of granula:
700-1500 km
- Average granula life time: ~10 min
- Convection velosity: 0.2 - 0.5 km/s
♦ Super-ganulation: organized granula
clusters (20,000 – 30,000 km)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Photospheric Convection / granulation
♦ Numeric simulation of solar convection on super-computers
There is still a lot of work to include all the appropriate physics
into the numerical models
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Sunspots – the sites of strong magnetic fields (2000-5000 G)
- Low temperature of sunspots (~ 4000 K)
is due to strong magnetic field
which promotes material cooling fi dark appearance on the photospheric
background (~ 6000 K)
- Size: ~1500 km – 50000 km in diameter
- Structure: umbra, penumbra
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Sunspots – the sites of strong magnetic fields (2000-5000 G)
- Low temperature of sunspots (~ 4000 K)
is due to strong magnetic field
which promotes material cooling fi dark appearance on the photospheric
background (~ 6000 K)
- Size: ~1500 km – 50000 km in diameter
- Structure: umbra, penumbra
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Complex dynamics and evolution of sun spots
- Appearance / disappearance by successive fragmentation into smaller
elements (formation: days – weeks; life time: weeks – months)
- Rotation
- Mutual interactions
SOHO/MDI Mar. – May 2001
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Complex dynamics and evolution of sun spots
- Appearance / disappearance by successive fragmentation into smaller
elements (formation: days – weeks; life time: weeks – months)
- Rotation
- Mutual interactions
Sun spot birth
TRACE (white light)
Jul. 27- Aug. 06, 2001
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Magnetograph measurements of solar magnetic fields at the photosphere
♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields
- Sunspots are usually grouped in pairs
of opposite magnetic polarities
- Sunspots are confined to low latitudes
(< 40 degrees)
- Sunspots pairs tend to line
up in the
East-West direction and drift towards
higher latitudes
- Magnetic polarities of sunspot pairs in
the northern and southern solar hemispheres are reversed (Hale’s law)
SOHO MDI magnetogram
Light – south polarity; Dark – north polarity
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Magnetograph measurements of solar magnetic fields at the photosphere
♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields
- Sunspots are usually grouped in pairs
of opposite magnetic polarities
- Sunspots pairs tend to line
up in the
East-West direction and drift towards
higher latitudes
- Magnetic polarities of sunspot pairs in
the northern and southern solar hemispheres are reversed (Hale’s law)
Light – south polarity; Dark – north polarity
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Magnetograph measurements of solar magnetic fields at the photosphere
♦ Full disk magnetograms – monitoring of sunspots and large-scale m. fields
- Each next sunspot cycle, magnetic polarities of the sunspot pairs undergo
a reversal fi full solar cycle is ~ 22 years
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Magnetograph measurements of solar magnetic fields at the photosphere
♦ High resolution magnetograms – study of dynamics of small-scale m. fields
Magnetic carpet
Light – south polarity
Dark – north polarity
SOHO/MDI
Numeric simulations
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Origin and development of sunspots
♦ Solar dynamo: stretch of the magnetic
field lines by differential rotation
♦ Magnetic buoyancy
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Origin / development of sunspots
Artist concept of magnetic flux emergence
Numeric simulation of magnetic flux emergence
(Naval Research Laboratory, USA)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● 3-D structure of sun spots – subsurface temperature profile (with SOHO/MDI):
Blue
Red
– cooler then average;
– warmer then average
Magnetic field blocks the
Higher temperatures below the
surprisingly
shallow (just
~6000temperatures
km)
flowsSunspots
that carryare
heat
up fi blockage
and cooler
from the solar interior
above.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Subsurface structure and material circulation in sunspots (with SOHO/MDI):
Blue – cooler then average;
Red – warmer then average
Strong m. fields
promote cooling
fi
Cool material sinks down
(speed up to 6000 km/h)
fi
Inward flow, holding the
sunspot together (while
m.field is strong enough)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Photosphere
● Monitoring of sun spots behind visible solar disk spots
♦ sonogram imaging of the solar far side
Important for the tasks of
forecasting of sunspots
appearance on the Earth
directed side of the Sun
⇓
Space Weather
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Chromosphere – the layer of the solar atmosphere located above the
photosphere and beneath the corona
- ~ 2500 kilometers thick layer
- appears as a thin reddish ring prior and just after the
peak of a total solar eclipse
- slow â of T from 4300 K to 104 K at heights 550-1700 km
and sharp â from 104 K to 3x105 K at ~ 50 km interval
near 2000 km fi
Transition region
- Strongly inhomogeneous: cold
(~104 K) structures co-exist with
hot (~106 K) plasmas
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II)
♦ Chromosphere in H-alpha (λ = 6563 Å) : - bright regions – plages, actve regions
- dark features - filaments (prominences)
H-alpha image (NSO at Sacramento Peak)
Sun in H-alpha (1/1/95-4/9/95)
(HAO, Mauna Loa Solar Obs.)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II)
♦ Chromosphere in Ca K (λ = 3933 Å) :
- magn. sensitivity of Ca K line
⇓
contrast between magn. active
regions and the rest of the solar
surface
- features of the solar disk seen
in white light remain visible
⇓
sunspots can be seen
- plages (faculae) appear as bright
Ca K image (NSO)
areas surrounding the sunspot
groups (associated with regions
of ~100G m.field)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II)
♦ Chromosphere in Ca K (λ = 3933 Å) :
High solar activity - Mar. 28, 2001
(NASA/GSFC)
Moderate solar activity - Apr. 27, 2002
(NASA/GSFC)
Low solar activity - Oct.28, 1998
(NASA/GSFC )
♦ hotter than sunspots faculae contribute to increasing the solar flux
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II)
♦ Chromosphere in UV: He I (λ = 584,3 Å), He II line (λ = 304 Å)
Sun in He I line
(upper chromosphere: 2 x 104K)
SOHO/SUMMER
Sun in He II line (upper chromosphere: 6 x 104K)
SOHO/EIT
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● Most easily chromosphere is viewed in emission lines: H-alpha, Ca K, UV (He II)
♦ The sources of EUV radiation in the Transition region (T ~ 2.5 x 105 K) are
connected to the chromospheric parts of magnetic loops
Correlation of location of the EUV
emission sources in transition region
and the photospheric magnetic fields
SOHO/MDI/CDS
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Chromosphere
● On the limb: jets of plasma shooting up from supergranule boundaries – Spicules
Spicules (Big Bear Observatory)
- Diameter: 500-1200 km
- Height: 10000-15000 km
- Temperature: (1..2) x 104 K
- Material upward speed: 20-30 km/s
- Life-time: 5 - 10 min
♦ Macro-spicules in polar regions of open m.field
- Diameter: 4000-11000 km
- Height: 4000-40000 km
- Material upward speed: 10-150 km/s
- Life-time: 8 - 45 min
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Corona
● Corona – the outermost layer of the solar atmosphere
visibility only during solar
Small density (108 cm-3); fi higher transparency fi eclipses (natural/artificial)
i.e. when light from the
decrease with distance
than the inner layers
photosphere is blocked
- Temperature > 1 x 106 K (200 times hotter
Nov.3, 1993, Bolivia (Fred Espenak)
than the Sun‘s surface)
- Coronal heating mechanism is still in question (should
be connected with complex m.fields and related phenomena: flares; electr.currents; waves)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Corona
magnetogram based reconstruction
● Coronal structure elements:
- coronal loops
- streamers (up to 10 R) with 3-10 times
higher density
SOHO/LASCO: Solar corona in 05-07/1996
3-D reconstruction of solar corona
- coronal holes (open m.field line regions) → fast
solar wind
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
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Solar atmosphere :
Corona
● The heat and energy release in the corona cause its soft X-rays, UV radiation
♦ Solar corona in soft X-rays:
- Dark areas – coronal holes (above poles)
- Bright X-ray regions – T > 2 x 106 K
(typical in active regions, near sunspots)
- Flares – short increases in brightness
Yohkoh X-ray image
- Streamers are connected to large
active regions (sunspot groups)
- coronal holes are dark in white light
because of lower gas densities
White-light (Mauna Loa Solar Obs.) and soft X-ray (Yohkoh)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● The heat and energy release in the corona cause its soft X-rays, UV radiation
♦ Solar corona in EUV :
- Fe XII line (195 Å):
Corresp. temperature: ~ 1.5 x 106 K
SOHO/EIT movie
- active regions are seen as bright;
- flares followed by proton shower
- coronal holes
SOHO/EIT movie
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● The heat and energy release in the corona cause its soft X-rays, UV radiation
♦ Solar corona in EUV :
- Composite view in 3 wavelengths:
Fe IX/X (171 Å) blue: ~ 1.0 x 106 K
Fe XII (195 Å) green: ~ 1.5 x 106 K
Fe XIV (284 Å) orange: ~ 2.0 x 106 K
- active regions
- hot coronal loops
- coronal holes
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● The heat and energy release in the corona cause its soft X-rays, UV radiation
♦ Extended solar corona (above 1.25 R) in UV :
- Outer corona in 3-D
- Helmet streamer (~ 3 x 106 km) in
- Lyman-alpha (atomic Hydrogen)
- Oxygen VI
combined UV/EUV observations
(SOHO: UVCS / EIT)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● The heat and energy release in the corona cause its soft X-rays, UV radiation
♦ Solar corona in EUV / UV :
- Composite UV image the Sun's
extended corona:
SOHO/UVCS (outside black circle)
SOHO/EIT (inside circle).
♦ Recent finding:
Protons and the more massive
ions (oxygen, magnesium etc.)
are hotter than the electrons in
the outflowing coronal gas.
Preferential heating and acceleration of heavy particles may be due to
absorption of high frequency MHD waves.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal holes (CH) in white light and X-rays and EUV/UV
lower gas densities
in CH
less heating
in CH
dark appearance of CH in white light
(as compared to bright helmet streamers)
dark appearance of CH
in X-rays and EUV/UV
› › › › › › › › › › › ›
CH are regions of open magnetic field lines fi easy and fast outflow of
coronal gas (as solar wind) along the field lines.
In helmet streamers the coronal material is trapped by the closed magnetic
field lines fi enhanced densities fi detectable levels of X-ray emission
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
♦ 5 Types of CLs (observed in X-rays & EUV):
- Active region (AR) loop – part of an AR structure
L ~ (10-100)x103 km; T ~ 104-2.5x106 K;
n ~ (0.5-5.0)x109 cm-3
- Quite region loop – not related to an AR
L ~ (20-700)x103 km; T ~ 1.8x106 K;
n ~ (0.2-1.0)x109 cm-3
- Connecting loop – link different ARs
SOHO/EIT: EUV
L ~ (20-700)x103 km; T ~ (2-3)x106 K;
n ~ 7x108 cm-3
- Flare loop L ~ (5-50)x103 km;
T ≤ 4x107 K; n ≤ 1012 cm-3
- Post-flare loop L ~ (10-100)x103 km;
T ~ 104-4x106 K; n ~ 1011 cm-3
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
Yohkoh: X-ray
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
1. Active region (AR) loop – part of an AR structure
L ~ (10 - 100) x 103 km
T ~ 104 - 2.5 x 106 K
n ~ (0.5 - 5.0) x 109 cm-3
♦ AR loops with different T:
He I: 2 x 104 K
O V: 2.5 x 105 K
Mg IX: 106 K
Si XII: 2 x 106 K
SOHO/CDS
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
2. Quite region loop – not related to an AR
TRACE (171Å), May 5, 1998
L ~ (20 - 700) x 103 km
T ~ 1.8 x 106 K
n ~ (0.2 - 1.0) x 109 cm-3
♦ Quiet corona and limb loops
observed by TRACE (171Å)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
3. Connecting loop – link different ARs
L ~ (20 - 700) x 103 km
T ~ (2 - 3) x 106 K
n ~ 7 x 108 cm-3
♦ 2 days of development of
connecting loops seen by
SOHO/EIT:
Fe XII (195Å): 1.5x106 K
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
4. Flare loop
L ~ (5 - 50) x 103 km
T ≤ 4 x 107 K
n ≤ 1012 cm-3
X-ray M1 flare, May 16, 1999,TRACE (171Å)
X-ray M2 flare, May 10, 1999, TRACE (171Å)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
5. Post-flare loop
L ~ (10 - 100) x 103 km
T ~ 104 – 4 x 106 K
n ~ 1011 cm-3
♦ Post-flare loops observed by TRACE
on the disk: flare on 14.07.2000 (195Å)
(„Bastille Day flare“)
on the limb: flare on 15.04.2001 (171Å)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
♦ Hot plasma tends to flow along the magnetic field lines, making the CLs
to be visible in X-rays & EUV corresponding to high temperatures
CLs observed in EUV (by TRACE)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
♦ Hot plasma tends to flow along the magnetic field lines, creating the CLs
which are visible in X-rays & EUV corresponding to high temperatures
CLs observed in EUV (by TRACE)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Coronal loops (CL) – one of the main structural elements of the solar atmosphere
♦ 3-D reconstruction of the solar CLs structure based on magnetogram and
EUV (SOHO/MDI/EIT) data:
Magnetogram data were processed through the Potential Field Source Surface
(PFSS) model which constructs the magnetic field above the solar surface.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Solar prominences or filaments (when observed on the disk)
♦ Cold and dense (as compared to surrounding plasma) condensations of
coronal material supported by the magnetic field
Typical values:
T ~ 5000 – 10000 K
n ~ 1010 – 1011 cm-3
⇓
Visible in H-alpha
on the limb: bright
on the disk: dark
H-alpha image (NOAA, Aug. 1980)
♦ Two different types of the solar prominences:
- Quiescent prominence
- Active prominence
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Quiescent prominence (quiet filament) – very stable and long living object
(usually located along the magnetic neutral line)
Life-time:
up to several months
Temperature: 5000 – 8000 K
Density:
1010 – 1011 cm-3
Length:
6 x 104 – 106 km
TRACE (171Å), May 21, 1998
Height:
1.5 x 104 – 105 km
Thickness:
4000 – 1.5 x 104 km
Magnetic field: ≤ 40 G
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Quiescent prominence (quiet filament) – very stable and long living object
(usually located along the magnetic neutral line)
Dancing prominences (TRACE 171 Å, Jul. 27, 1998)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Quiescent prominences tend to form along the boundaries between regions of
opposite magnetic polarity, i.e. along the magnetic neutral line
The fact that filaments are usually aligned with magnetic neutral lines strongly
suggests that magnetic fields are responsible for supporting filaments
against the gravity.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Support of a quiescent prominence against gravity:
Prominence fibrils are confined in the dipped top part of a magnetic arcade
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Active prominence – dynamical object with intensive motion of material
(located in active regions and usually connected with solar flares)
Life-time:
minutes – hours
Temperature: 10000 – 80000 K
Density:
≥ 1011 cm-3
Filament eruption (SOHO/EIT: 195Å)
Height:
TRACE, 171Å, Jul.19, 2000
1.5 x 104 – 2 x 105 km
Magnetic field: ≤ 100 – 200 G
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Activation of prominences → Eruptive prominences
- Increase of the size and brightness
- Increase of material flow speed fi
- Oscillations (T ~ 6 – 40 min)
Prominence oscillations after flare
material eruption (up to 100 km/s)
Eruptive prominences observed by SOHO/EIT,
He II line (304Å): 60000 – 80000 K
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Activation of prominences → Eruptive prominences
Eruptive prominences observed by SOHO/EIT,
He II line (304Å): 60000 – 80000 K
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Activation of prominences → Eruptive prominences
Eruption of a prominence observed by SOHO/EIT in He II line (304Å)
The whole process took 3 hours
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Activation of quiescent prominences – development of an instability in a
filament, “disparition brusque”
- Filament lifts up as an eruptive prominence and completely disappears.
- The whole process takes from several min to several hours.
- Brightness increase in X-rays and H-alpha → flare
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
♦ Activation of quiescent prominences – development of an instability in a
filament, “disparition brusque”
Filament eruption with formation of a
set of hot, bright, activated coronal
loops (500,000 – 2,000,000 K)
Oct. 20, 1999 TRACE (195Å)
SOHO/EIT, He II line (304Å): 60000 – 80000 K
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar atmosphere :
Corona
● Solar corona is a non-stationary, dynamic object:
- Magnetic loops
- Filaments & Prominences
- Flares, Eruptions
- Coronal Mass Ejections (CMEs)
Long-time evolution of active regions
dynamics of coronal structures
The corona extends outward as solar wind
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Solar Flare – rapid release of energy from a localized region on the Sun in
the form of electromagnetic radiation, energetic particles, and mass motions.
- sudden, localized, transient increases in brightness occurred in active
regions near sunspots
- most easily seen in H-alpha and X-rays, but have also effects in all the
elecromagnetic spectrum
Flare in H-alpha
Flare in EUV (171 Å)TRACE
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● Energy release of solar flare:
Solar flares
1029 – 3 x 1032 erg
♦ Distribution of energy in solar flare:
- Electromagnetic radiation (up to X-ray): 35 %
- Interplanetary shock wave: 35 %
- Energetic electrons (hard X-ray): 15 %
- Sub-relativistic protons: 6 %
- Relativistic protons: 9 %
♦ Energy source – the solar magnetic field
Annihilation of 500 G magnetic field
in a 30000 x 30000 x 30000 km cube
„Bastille Day flare“ in EUV
(TRACE, Jul. 14, 1998)
3 x 1032 erg
Details of the flaring energy release mechanism are still a puzzle
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● 3 different phases of a typical
Solar flares
solar flare:
observed in electromagnetic and particle
radiation (from Kane 1974)
Precursor
~5-10 min (before)
Impulsive phase
~2 - 5 min
Extended phase
- Flash phase
- Main phase
(~10 min + ~1 h)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Indication of physical processes in flaring phenomena:
● Presence of energetic particle fluxes
● Indication of running
shock waves
● Presence of hot
plasma clouds
¾
Solar phenomena :
Solar flares
● Development and structure of solar flares
♦ Trigger of flare – emergence of a new magnetic flux
♦ Two types of flares:
1. Simple loop flare (compact
flare)
- increase of brightness of a separate loop
- one pulse of X-rays (~ 1 min)
- main energy release in an impulsive
phase
- high temperature (~ 3 x 107 K) kernel
1500 – 4000 km in the top of the loop
- whole duration
~ 1-2 hours
Loop flare in EUV (TRACE)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Development and structure of solar flares
♦ Trigger of flare – emergence of a new magnetic flux
♦ Two types of flares:
2. Two-ribbon flare – large flare
- eruption of filament (begins 10-60 min
before the flash phase)
- Flash phase: formation of two bright
ribbons – footpoints of flaring magnetic
arcade
- bright post-flare loops
- whole duration several hours
flare in EUV (TRACE)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Development and structure of solar flares
Combined observations (AR10720) – simultaneous TRACE & RHESSI imagery
RHESSI: gamma-rays (blue) – energetic
protons. High-energy emission
marks the footpoints of coronal
loops
X-rays (red) – the hottest part
of flare. Emission from the loop
structure
TRACE: UV images
Flare ribbons - multiple hot-spots at the loop footpoints
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Development and structure of solar flares
Theoretical model:
Primary energy release in the corona
Particle acceleration
Collisional interaction of fast
electrons with a background plasma
• thick-target bremsstrahlung
• heating of the low chromosphere to
soft X-ray emitting temperatures
• creation of steep pressure gradients
resulting in material upflows
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Development and structure of solar flares
Simultaneous obstervations of “Bastille Day flare” (Jul. 14, 2000):
by
SOHO (EUV + Coronographs)
TRACE (close up EUV)
and
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Solar flares
● Long-distance (heliospheric) effects of solar flares:
Multi instrument & multi spacecraft observations of solar flares in Oct-Nov. 2003:
SOHO: EUV + Coronographs (C2,C3) SORCE: (X-ray photometry )
Record-breaking solar flares
in the Fall of 2003:
● X17 flare on Oct. 28, 2003
● X11 flare on Oct. 29, 2003
● X28 flare on Nov. 4, 2003
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Coronal Mass Ejection (CME) – a huge cloud of plasma that erupts from the
Sun's corona and travels through space (in the solar wind) at high speed
- High speed (~ 200-2000 km s-1);
- Intrinsic magnetic field;
- Billions of tons of material
⇒
Significant disturbances
in Interplanetary medium
♦ CMEs are considered as critical element of solar dynamo
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Origin of CMEs, Relation to flares
- CMEs are associated with flares and prominence eruptions
- CME source location:
active regions (groups of sunspots), prominence
sites (not only in active regions)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Origin of CMEs, Relation to flares
CME originate from closed magnetic field regions on the Sun
⇓
Presence of a closed magnetic field structure – basic characteristic
of CME Producing regions
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Origin of CMEs, Relation to flares
Probability of CME–flare association increases with a duration of a flare:
~ 26% for duration < 1 h
100% for duration > 6 h
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Origin of CMEs, Relation to flares
There is a physical link between flares and CMEs (yet poorly known...)
Common-cause scenario: falres and CMEs are manifestations of the
same large-scale magnetic process
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Multi-thermal structure of CMEs
- coronal material in the front region (~ 2 MK)
- prominence material (~8000 K), or hot flare plasma (~10 MK)
♦ CME with an ordered magnetic field → Magnetic Cloud (MC)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● Parameters of CMEs:
Coronal Mass Ejections
speed
- Tracking a CME feature ⇒
vCME from tens km/s to > 2500 km/s
(average vCME 489 km/s )
- Annaual average vCME has a tendency to increase towards solar maximum
(Yashiro, et al., Adv. Space Res., 32, 2631, 2003)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● Parameters of CMEs:
Coronal Mass Ejections
size
- angular width ΔCME increases in the beginning
(< 5 RSun ) of propagation
- Annual average widths of CMEs range from
45° (solar minimum) to 61° (close before
activity maximum)
● Parameters of CMEs:
density
- No direct measurements of nCME close to the Sun (< 30 Rsun = 0.14 AU)
- Analysis of CMEs brightness in the white-light (Thomson scattering) ⇒
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
nCME
¾
Solar phenomena :
● Parameters of CMEs:
Coronal Mass Ejections
size
- angular width ΔCME increases in the beginning
(< 5 RSun ) of propagation
- Annual average widths of CMEs range from
45° (solar minimum) to 61° (close before
activity maximum)
● Parameters of CMEs:
density
white light (Vourlidas, A., et al., ESA SP-506, 1, 91, 2002),
radio (Gopalswamy & Kundu, Solar Phys., 143, 327, 1993),
UV (Ciaravella, A., et al., ApJ., 597, 1118, 2003)
⇒
similar values at (3 - 5) RSun:
nCME ~10 6 cm –3
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● Parameters of CMEs:
Coronal Mass Ejections
latitude distribution ± Θ
- Θ depends on distribution of closed magnetic field regions (active regions)
on the solar surface. Average Θ = 60° (near the equatorial plane)
- In the maximum of solar activity cycle, Θ spread up to all latitudes (± 90°)
● Parameters of CMEs:
occurrence rate fCME
correlates with Sunspot number ( SSN ), but differences in details: fCME peaks
with a delay (~ 2 years) after the peak in the SSN
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
● Parameters of CMEs:
Coronal Mass Ejections
latitude distribution ± Θ
- Θ depends on distribution of closed magnetic field regions (active regions)
on the solar surface. Average Θ = 60° (near the equatorial plane)
- In the maximum of solar activity cycle, Θ spread up to all latitudes (± 90°)
● Parameters of CMEs:
occurrence rate fCME
correlates with Sunspot number ( SSN ), but differences in details: fCME peaks
with a delay (~ 2 years) after the peak in the SSN
Sunspot activity is confined to the active regions belt, but the CME
activity occurs during the maxima at all latitudes
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar phenomena :
Coronal Mass Ejections
● Numeric simulation of CME eruptions (2.5D AMR-MHD numerical code)
(S. Antiochos, J. Klimchuk, MacNeice, Naval Research Laboratory, USA)
♦ Key features of the model:
- multipolar topology of mag. filed
( >2 flux systems with a null point
above the erupting arcade);
- strong photospheric
shear near
the central arcade neutral line
- magnetic reconnection above the
central arcade decreases the stabilizing effect of unsheared flux
and allows the low-lying sheared
flux to erupt.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar activity :
Solar cycle
● Varying level of solar activity is closely related to the number of sunspots
- 1843:
Discovery of cyclic, ~ 11 year, variation
in sunspot counts, i.e. in topology & strength
of the global solar magnetic field (S. H. Schwabe, Germany) – the “Sunspot Cycle”
- The 11 year sunspot cycle is related to 22 year
cycle for reversal of the Sun's magnetic field
Sunspot number variation (11-year cycle)
Change of sunspot number and of solar UV
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar activity :
Solar cycle
● Monitoring of solar cycle
♦ Wolf number – method of sunspots counting (1848, J. R. Wolf, Switzerland):
R = K ( 10 g +f )
K – observer’s personal features (~ 0.6)
f – number of sunspots
g – number of sunspot groups
♦ Variations of solar cycle in the past: Maunder Minimum (1645 – 1715)
- corresponds to a “Little Ice Age” in Europe
- Almost no sunspots on the Sun
♦ 11 years – the approximate value
- 1750–1958: average period
between max 10.9 yrs (7.3 - 17.1yrs)
between min 11.1 yrs (9.0 - 13.6 yrs)
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Solar activity :
Solar cycle
● Butterfly diagram – first constructed in 1904 by E.W. Maunder
♦ Location of sunspots (latitudes) varies throughout the sunspot cycle:
- solar min: around of 30° to 45° North & South
- solar max: around of 15° North & South
- end of a cycle (approaching the solar min): around 7° North & South
Latitude migration of sunspot sites during the solar cycle forms butterfly pattern
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
The Sun : Open questions
● The
most critical questions of the solar physics deal with the problems
of the solar interior as well as with its outer atmosphere and heliosphere:
♦ How are the magnetic fields, observed at the solar surface, generated by
dynamo processes and how are they destroyed ? The nature of Solar Cycle?
♦ What role do magnetic fields play in the organization of plasma structures
and impulsive release of energy during the solar flares ?
♦ What are the mechanisms for heating of the solar corona and acceleration
of the solar wind ?
♦ What magnetic configurations and evolutionary paths lead to formation of
solar prominences and CMEs?
♦ What are the influences of the Sun on the Earth’s climate and on the
near-Earth space weather ?
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
The Sun : Open questions
Theoretical analysis and numeric modelling of the fundamental
physical processes underlying the dynamic phenomena on the
Sun should be combined with observations providing a resolution sufficient to observe scales characteristic to these processes.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
A: The Sun starts nuclear fusion in
its core.
`Birth' of the Sun.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
B: About half of the hydrogen supply
in the core has been used up.
The present time situation.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
C: There is no more hydrogen in
the core. Fusion of hydrogen in
the shell around the core starts.
Radius:
R → 1.4 x R
Luminosity: L → 2 x L
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
D: About 5 billion years from now:
R → 3.3 x R and T ~ 4300 K.
The temperature on Earth will â by
~ 100 degrees. The seas will be
evaporated and present life will be
destroyed.
Within another 250 million years:
R → 100 x R and L → 500 x L
→ Red Giant
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
E: The core temperature of the Sun
will rise so high that in one bang,
all the rest of the He will fuse into
carbon. By this explosion 1/3 of
the solar envelope will be thrown
out into space.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
The Sun will become brighter and the
outer layers will be blown out into
space in the form of a very dense solar
wind → planetary nebula.
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
Then, only a white dwarf remains, with
a mass of about half of the mass of the
current sun, but with a density of 2 tons
per cm^3.
This white dwarf will slowly cool down.
The end of the solar system:
Black dwarf
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Final Remark
● Herzsprung-Russell (H-R) diagram:
the life cycle of the Sun (Change of the
temperature and the luminosity)
So is the final…
But we still have some time
to learn more about our star
the Sun
☺
Welcome on board !!!
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz
¾
Credits
● SOHO – Solar and Heliospheric Observatory:
MDI - Michelson Doppler Imager;
EIT - Extreme ultraviolet Imaging Telescope;
SUMER - Solar Ultraviolet Measurements of Emitted Radiation;
UVCS - Ultraviolet Coronagraph Spectrometer;
CDS - Coronal Diagnostic Spectrometer
LASCO - Large Angle Spectroscopic Coronagraph
● TRACE – Transition Region and Coronal Explorer
● NASA/Goddard Space Flight Center, Scientific Visualization Studio
● High Altitude Observatory which is a division of the National Center for
Atmospheric Research, sponsored by the National Science Foundation
● Solar Theory section of Naval Research Laboratory, USA
● Windows to the Universe (http://www.windows.ucar.edu/) at the University
Corporation for Atmospheric Research (UCAR)
● Jörg Weingrill – technical support and help in material preparation
Summer University, Graz in space 2006 – Sep. 7-8, 2006, Graz