Download Solar Interior 2 (Petrie)

The Solar Interior
Free stuff from NASA Goddard
Space Flight Center
• Courtesy Jack Ireland, L3
Communications, Lab of Astrophysics and
Solar Physics, NASA GSFC, Greenbelt,
MD
Why study the solar interior
• Sheer curiosity
• Solar-stellar connection
• Interior’s influence on exterior including
Earth
Convective Regimes
• Granulation/mesogranulation/supergranulation in
>0.97 R, radiative transfer, ionization
• Global convection in >0.7 R
• Granulation 1 Mm 1 km/s velocity doppler
measurements
• Mesogranulation 5Mm 60 m/s correlation tracking
• Supergranulation 30 Mm 400 m/s correlation
tracking, doppler, local helioseismology
• Giant cells 100 Mm 50 m/s global and local
helioseismology
GONG observations of
differential rotation
The Flows
The Magnetic Sun
“If the Sun did not have a magnetic field, it
would be as uninteresting a star as most
astronomers believe it to be.”
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>From Louis Strous <[email protected]>
>23 Aug 1999 RE: Boring sun quote
As of 23 August 1999, twelve respondents agreed that the famous "solar magnetic field" quote should be
attributed to R.B. Leighton, four suggested E. Parker, and one offered H. Zirin as responsible.
R. Noyes writes that R.B. Leighton, his thesis supervisor, made the comment in a colloquium he gave at
Harvard around 1965. P. Sturrock reports that Leighton started his presentation with the quote at the USJapan Solar Conference in Hawaii in February 1965. B. LaBonte adds that during conversations at CalTech in
the early 70s Leighton denied having said it. B. Howard says that Leighton used the quote in the early 1960s
and that Leighton did not attribute it to someone else. V. Gaizauskas reports that E. Parker said it as early as
1977 in a workshop at the University of Michigan.
It seems, then, that Leighton is the original source (despite his protestations to the contrary), that he made the
comment at various occasions during the 60s, perhaps in slightly different forms, and that it has since been
repeated by many. There does not appear to be a "master copy" we can refer to.
Versions of the quote have appeared in print, in at least the following places:
R. Moore & D. Rabin: Annual Reviews of Astronomy and Astrophysics 23, 239 (1985)
J. Linsky: Solar Physics 121, 187 (1989)
R. Rutten: "Radiative Transfer in Stellar Atmospheres", http://www.astro.uu.nl/~rutten/node18.html (19951999)
The respondents give slightly different versions of the quote, using either "boring," "uninteresting," or "dull,"
and claiming this impression of the Sun for "most astronomers," "many astronomers," or "nighttime
astronomers." Here's a sample of the versions:
1. "If the Sun did not have a magnetic field, it would be as uninteresting a star as most astronomers believe it
to be." (quoted by J.L. Linsky).
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2. "If the sun didn't have a magnetic field, then it would be as boring a star as most astronomers think it is."
(reported by R. Noyes)
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3. "If it were not for its magnetic field, the Sun would be as dull a star as most astronomers think it is."
(reported by P. Sturrock)
Linsky lists another quote, which (R. Rutten reports) Linsky personally heard its author
say:
"Magnetic fields are to astrophysics what sex is to psychoanalysis." (H.C. van de Hulst)
Joy’s law
A Solar Dynamo
• is a process by which the magnetic field in
an electrically conducting solar plasma is
maintained against Ohmic dissipation.
• Parker's picture became relevant when
Babcock~(1959) discovered that solar poloidal
field reverses with sunspot
cycle.Babcock~(1961) and Leighton~(1964,
1969) developed phenomenological models
incorporating and illustrating Parker's ideas.
• Non-uniform rotation of convection zone acting
on weak dipolar poloidal field generates strong
subphotospheric toroidal field.
• Toroidal field becomes unstable and pops up
through surface and to produce bipolar active
regions, including sunspots.
• Toroidal field twisted by coriolis force to give
poloidal field opposite to that already there.
• Opposites cancel, starting new half-cycle.
• In this picture, alpha-effect manifest in axial tilt of
bipolar active regions.
(Parenthesis: why
phenomenological?)
Hydrodynamical simulation including more
or less detailed physics
• is extremely time-consuming,
• is restricted to small region of Sun,
• requires approximate treatment of
unresolved scales.
• Babcock-Leighton model revived by Wang
\& Sheeley~(1991), Wang et al.~(1991),
Dikpati & Charbonneau (1999), Dikpati et
al.(2002) among many others.
• Most important change: introduction of
large-scale circulation, superposed on
granulation, mesogranulation and
supergranulation components of
turbulence.
• A poleward motion at surface of about
10m/s to explain observations of polar
fields at sunspot minimum.
• By mass conservation there must be
return flow, equatorward, below surface.
Coherence of Active-Region Flux
Tubes
• For coherence of flux tubes at base of
convection zone,
B2/8B=Dv2 => B ~ 10 to 100 kG.
• Fields of this strength fight back against
cyclonic fluid convection – no alpha effect
• Conventional models have omega and
alpha effects coinciding
• Problem for dynamo models until Parker’s
(1993) interface dynamo
References
• Paul Charbonneau, Dynamo Models of the Solar Cycle,
Living Reviews in Solar Physics, 2005
• Yuhong Fan, Magnetic Fields in the Solar Convection
Zone, Living Reviews in Solar Physics, 2004
• Johan Goedbloed & Stefaan Poedts, Principles of
Magnetohydrodynamics, Cambridge UP, 2004
• Russell Kulsrud, Plasma Physics for Astrophysics,
Princeton UP, 2004
• Leon Mestel, Stellar Magnetism, Oxford UP, 1999
• Eric Priest, Solar Magnetohydrodynamics, Reidel, 1982
• http://ircamera.as.arizona.edu/NatSci102
• http://solarscience.msfc.nasa.gov