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
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.”
>From Louis Strous >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 US- Japan 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 (1995- 1999) 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:http://www.astro.uu.nl/~rutten/node18.html 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). 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) 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)
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, B 2 /8B=Dv 2 => 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
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