Transcript Advanced Solar Theory (MT5810)

Advanced Solar Theory (MT5810)
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OUTLINE
Observational properties of the Sun
MHD equations (revision)
Induction equation - solutions when Rm <<1, >>1
Magnetic equilibria
Waves
Solar wind
Reconnection
Instabilities
Books:
Solar MHD -- ER Priest
Camb. Encyc. of the Sun -- K Lang
Nearest Star -- L Golub & J Pasachoff
1.1 History
1. Observations
Ancient observations - sunspots (chinese, greeks) - forgotten
Galileo (1610) rediscovered sunspots
1851 -- first photograph of corona (eclipse)
1859 -- first solar flare observed
1908 -- sunspots have strong B
1956 -- foundations of MHD (Cowling)
1957 -- satellite observations of interplanetary medium
1980’s & 90’s
-- development of MHD
-- space observations (Skylab 73-74, Yohkoh 91-05,
SOHO 95 - …, TRACE 98 - …, RHESSI 02 - …
Future Space Missions
STEREO (NASA) April 2006
* Two satellites
* _ _ _ _ _ _ _ _ _ _ _ _ _*
Solar B (Japan-US-UK) Sept 2006
* Connections surface/corona
Solar Dynamics Observatory 2008
* _ _ _ _ _ _ _ _ _ _ _ _*
Solar Orbiter (ESA) 2012
*____________
*
1.2 Properties of the SUN
Ball of gas held
together by
gravity
? Tsurface_ _ _ _ _
? Mass/ s.
system _ _ _ _ _
? Chemical composition _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
? Radius _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
? Age _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Some other properties
? Mean distance from Earth
93 million miles = 150 million km _ _ _ _ _ _ _ _ _
__________
? Rotation period = 25 days (equator), 37 days (poles)
? Mean density =
1.4 x 103 kg m-3 _ _ _ _ _ _ _ _ _ _
? Surface gravity =
274 m s-2 _ _ _ _ _ _ _ _ _ _
? Escape velocity at surface = 618 km s-1 _ _ _ _ _
Overall Structure
Interior -->
Core,
Convection zone
__________
__________
Atmosphere -->
Photosphere,
Chromosphere,
Corona
Photosphere
Temperature 6000 K
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Covered with
turbulent
convection cells:
*_ _ _ _ _ _ _ _ _ _ *
(1 Mm)
*_ _ _ _ _ _ _ _ _ _ *
(15 Mm)
?? why
Amazing
images
[70 km]
from
La Palma
(Canaries)
In closeup:
points,
flowers,
ribbons
(created by
magnetic
fields)
1.3 SUNSPOTS
Photosphere -->
Sunspots
Galileo discovered
(1610) w. telescope
Dark because cool
But why cool ?
*_ _ _ _ _ _ _
_ _ _ _ _ _ _*
??? why
Stunning
Image
from La Palma
Penumbral
structure
created by B
Map of Photospheric Magnetic Field
White -- towards
you;
Black -- away from
you
Regions around
sunspots -bipolar
*_
______*
SURPRISES: -1. Intense
magnetic fields
over whole Sun
•_ _ _ _ _ _
_ _ _ _ _ _*
?? why
2. Patterns of
sunspots/active
regions
?? why
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
1.4 CORONA (Turkey, 1999)
Fine structure
Magnetic tubes
“prominences”
SURPRISE (1940)
*_ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _ _ _*
??why
Next: Egypt,
March 2006
Picture with X-ray telescope:
*
*
Yohkoh
A
magnetic
world
Amazingly rich variety of MHD phenomena
TRACE (Active region) - from above
From side:
*_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ *
Magnetic
field
dominates
plasma
creates
intricate
structure/
heats
?? how
1.5 Solar Activity
On top of the “Quiet Sun”
(ie the background photosphere, chromosphere &
corona),
there are several types of transient phenomena:
(i) _ _ _ _ _ _ _ _ _
(ii) _ _ _ _ _ _ _ _ _
(iii) _ _ _ _ _ _ _ _ _
(iv) _ _ _ _ _ _ _ _ _
(ii) Prominences
On disc in
chromosphere,
see as long,
thin structures
Dark - cutting out
light from below
*
_______
_______
_ _ _ _ _ _ _ _*
???
Sometimes
erupt [look like
twisted
tube]
why ??
(iii) Solar Flare
Sudden brightening in
chromosphere & corona
near sunspots
*_ _ _ _ _ _ _ _ _ _ _
___________*
How ??
(iv) Coronal Mass Ejections
SOHO Coronagraph -- Artificial eclipse
Discovered huge ejections of plasma
??
*_ _ _
_ _ _ _*
Can reach Earth - communications / satellites
1.6 SOHO(Solar & Heliospheric Observatory)
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Launched 1995.
Orbiting Sun at
point in phase
with Earth
Observing Sun continuously for 1st time (ESA/NASA)
--> 1st comprehensive view of Sun
MANY NEW SURPRISES