Solar Convection - ABSTRACT

One look at a high-resolution optical image of the solar photosphere easily reveals the prominent network of convection cells known as granulation. These convection patterns evolve rapidly, vigorously advecting and shearing magnetic fields and transporting heat outward into the solar atmosphere. However, granulation is only part of the story. Most of the solar convection zone is occupied by larger-scale motions which redistribute angular momentum on a global scale and which ultimately drive the solar activity cycle. I'll review solar convection in all it's glorious complexity, including how we probe it with surface measurements and helioseismic inversions and how we model it with high-resolution numerical simulations. Dramatic advances in both of these areas in the past few decades have provided unprecedented insight into the highly turbulent dynamics of the solar interior and promise much more excitement to come.

The following is a list of background materials for my "Tutorial on Solar Convection" to be given at the SPD Summer School.

To get a good feel for what I'll be talking about, the best place to start is with this online review article straight from the horse's mouth:

Miesch, M. S., 2005, "Large-Scale Dynamics of the Convection Zone and Tachocline", Living Reviews in Solar Physics, 2, 1--137 URL: http://www.livingreviews.org/lrsp-2005-1

This presents the subject from my point of view and it has plenty of references to keep you busy for some time. However, this article focuses on the deep convection zone. Little is said about the more vigorous convection near the photosphere (granulation, mesogranulation, supergranulation) which is more easily observed. For an introduction to this (which I'll also talk about), take a look at this nice review paper:

Stein, R. F. & Nordlund, A., 2000, "Realistic Solar Convection Simulations", Solar Physics, 192, 91-108 URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2000SoPh..192...91S

Numerical simulations of granulation are getting more exciting, fueled by advances in supercomputing and more sophisticated modeling techniques. For recent results see:

Vogler, A., Shelyag, S., Schussler, M., Cattaneo, F. & Emonet, T., 2005, "Simulations of Magneto-Convection in the Solar Photosphere. Equations, Methods, and Results of the MURaM code", Astron. Astrophys., 429, 335-351, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2005A&A...429..335V

Rincon, F., Lignieres, F. & Rieutord, M., 2005, "Mesoscale Flows in Large Aspect Ratio Simulations of Turbulent Compressible Convection", Astron. Astrophys., 430, L57-L60, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2005A&A...430L..57R

Carlsson, M., Stein, R. F., Nordlund, A. & Scharmer, G. (2004). Observational Manifestations of Solar Magnetoconvection: Center-To-Limb Variation", Astrophysical Journal, 610, L137-L140, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2004ApJ...610L.137C

The papers above consider solar convection in the near-surface layers from a numerical modeling perspective. Recently, improved solar telescopes have returned stunningly detailed images of convective patterns in the solar photosphere. For a sample, see

Berger, T. E. et al. 2004, "Solar magnetic elements at 0.1 arcsec resolution. General appearance and magnetic structure", Astronomy & Astrophysics, 428, 613-628 URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2004A&A...428..613B

The convective patterns in these observations are due to granulation. Supergranulation and mesogranulation are a bit more subtle but they can be detected in surface velocity fields through correlation tracking and other means. For an observational perspective on these see:

DeRosa, M.L. & Toomre, J., 2004, "Evolution of Solar Supergranulation", Astrophysical Journal, 616, 1242-1260, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2004ApJ...616.1242D

Muller, R. et al. 1992, "Evolution and Advection of Solar Mesogranulation", Nature, 356, 322-325, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?1992Natur.356..322M

Deep convection is even more difficult to get a handle on observationally. However, it does redistribute angular momentum on a global scale, giving rise to a differential rotation of the solar envelope which can be probed with helioseismology. See this recent review on the subject which discusses both helioseismic inversions and modeling efforts:

Thompson, M.J., Christensen-Dalsgaard, J., Miesch, M.S. & Toomre, J., 2003, "The Internal Rotation of the Sun", Annual Reviews of Astronomy & Astrophysics, 41, 599-643, URL:http://adsabs.harvard.edu/cgi-bin/bib_query?2003ARA&A..41..599T

Solar convection, both large-scale and small-scale, is intimately tied to dynamo action; convective motions generate magnetic fields which then feed back on the motions themselves via the Lorentz force. For an excellent review on all aspects of solar dynamo theory which is both very readable and very comprehensive, see:

Ossendrijver, M., 2003, "The Solar Dynamo", Astronomy & Astrophysics Reviews, 11, 287-367, URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2003A&ARv..11..287O

The most familiar manifestation of solar magnetic fields is undoubtedly the ubiquitous but still enigmatic sunspot. For an insightful and entertaining look at our current understanding see:

Tobais, S. M. & Weiss, N. O. 2004, "The Puzzling Structure of a Sunspot", Astronomy & Geophysics, 45, 4.28-4.33 URL: http://adsabs.harvard.edu/cgi-bin/bib_query?2004A&G....45d..28T