The Sun Part 3 Dynamics of the Sun - raleightutor.com file• The Sun is a hot ball of Plasma with...
Transcript of The Sun Part 3 Dynamics of the Sun - raleightutor.com file• The Sun is a hot ball of Plasma with...
2/7/2012
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The Sun Part 3
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Dynamics of the Sun
• The Sun is a hot ball of Plasma with imbedded
magnetic fields frozen into it.
• The magnetic fields carry charged particles and
the charged particles move magnetic fields.
• The Convection layer carries large currents of
plasma, magnetic fields, and energy from lower
to higher regions of the Sun.
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• These are the underlying dynamics of the Sun.
• But we have an additional complication:
• The Sun rotates differentially with the central
portion rotating in ~ 26 days and the pole regions
rotating in ~ 35 days.
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During the time of minimum solar activity, the Sun
has relatively weak internal magnetic field lines that
are lined up with the geographic poles (a poloidal
field).
And the Sun is rotating differentially…..
The result is that the poloidal magnetic field starts
to wind up into a toroidal field in the direction of
rotation.
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The Sun rotates differentially, winding up
the magnetic field of the Sun.
poloidalfield
toroidalfield
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As the magnetic field lines are pulled along the
equator, the line density increases and
magnetic flux tubes are formed.
Kinks develop in the flux tubes and the kinks
may protrude through the photosphere as the
flux tubes rise.
The flux lines become tangled and instabilities
develop in the outer regions of the Sun.
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During the time of maximum disruption of the
magnetic field, the Sun is most active.
Sunspots develop where flux tubes rise up through
the photosphere.
Flares, prominences, and coronal mass ejections
occur frequently during the Sun’s most active time.
The Sun continues its differential rotation.
The magnetic field begins to smooth out and the
intense solar activity subsides.
After 11 years, the magnetic field weakens, the
field becomes more uniform and poloidal,
But after 11 years the field is reversed!
This period of 11 years is called the Sunspot cycle.
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Sunspots
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Sunspots are cooler regions in the
photosphere where the rising flux tubes
interfere with the heat flow in the convection region.
They are still very hot
and bright, but look dark against the much brighter photosphere
surface.
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Typical
sunspots
Penumbra
Umbra(dark center)
magnetic
North pole
magnetic
South pole
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A recent
Solar flare
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Solar Flare Characteristics• A solar flare is a sudden, intense increase in brightness on
the Sun’s surface, usually near a sunspot.
• It occurs when magnetic energy in the Sun’s lower
atmosphere is suddenly released.
• Charged particles are accelerated to high speeds, and radiation at all wavelengths is emitted.
• The energy released in a typical flare is ~ 1020 J/s, but some
flares have energies as high as 1026 J/s.
This is equivalent to 10 million volcanic explosions, about a tenth of the total energy the Sun generates every second.
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1. Precursor stage: Built up magnetic energy is
triggered (flux lines break and reconnect).
2. Impulsive stage: charged particles are
accelerated to high speeds, with typical
temperatures in the flare of 20 million degrees.
3. Decay: build up and decay of soft x-rays
These stages last from seconds up to an hour.
During this stage, radio waves, x-rays and gamma
rays are emitted.
Stages of a Solar Flare
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Solar prominence, observed in uv
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Solar prominence, observed in uv
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• A prominence is a bright loop (a magnetic flux tube)
filled with hot plasma that grows up through the
chromosphere and extends into the corona.
• A prominence appears dark against the bright Sun
because it does not glow in visible light.
• The loop typically contain around 1014 kg of material,
develops in a day and can last for months.
• The loop extends over 10,000 km, and sometimes
as much as 400,000 km.
Characteristics of Prominences
20Massive coronal ejection, observed in x-rays
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Coronal Mass Ejection (CME)
• A typical CME consists of three parts:
- a cavity of low (plasma) particle density
- a dense core of plasma (a prominence)
- a bright leading edge
• CME’s are initiated in the Corona which is
dominated by magnetic fields.
• They are thought to result from large scale
restructuring of the Sun’s magnetic field.22
• A CME will rise up with speeds that can be as high as
2700 km/sec, but typically around 500 km/sec as they
accelerate upward.
• A CME usually starts to rise slowly, then it rapidly
accelerates to a near-constant speed.
• The average mass ejected in a CME is about 1012 kg
• CME’s occur about three times per week during the
solar minimum and up to 5-6 times per day during the
solar maximum.
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The Sun’s conona during a Sun cycle peak.24
Sunspot cycles last eleven years
Butterfly diagram
During that time the magnetic field of the Sun reverses
A few sunspots occur far from the equator at the beginning of the
sunspot cycle. Sunspots occur
more frequently and closer to the equator later in the sunspot cycle.
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The full cycle of two magnetic field reversals is called the Solar Cycle
Two sunspot cycles = 1 solar cycle
(22 years).
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