Interdependence of solar plasma flows and magnetic fields

1. Interdependence of solar plasma flows and magnetic fields E.J. Zita & C. Smith, The Evergreen State College, Olympia, WA 98505; N.E. Hurlburt, LMSAL, Palo Alto, CA 94304 D. Discussion I. Abstract A-B: Testing for Proctor Effect (PE) in Hinode Data Interactions between flows and magnetic fields in the Sun’s plasma can affect surface phenomena such as sunspots, can reveal deeper magnetic connections via changes in solar flows and oscillations, and drive dynamics in the long-term solar magnetic cycle, e.g. the recent “weird solar minimum.” We have observed changes in solar surface flow patterns (Smith et al. 2010) consistent with the Proctor effect, which depends on magnetic field strength and orientation in active regions. Other investigators have observed relationships between solar torsional oscillations and mean field strengths. Zonal flow velocities correlate roughly with field strengths, and may serve as diagnostics or predictors of solar cycles. We explore a possible relationship between the Proctor effect and the magnetic interdependence of zonal flows. Our study potentially deepens understanding of fundamental solar magnetic dynamics underlying convection and dynamo processes. Simulations predict that magnetic field tilt can affect flow speeds. The Proctor Effect: As the mean inclination of the magnetic field through a layer of compressible fluid increases, (1) the pattern of cells formed by magnetoconvection travel at an increasing horizontal rate, vp, and (2) increasing mean shear flows produce surface flows that can be comparable to the convective flow speeds, u. from Hurlburt, Matthews, and Proctor, 1996 Flow and B field data in AR10944 Figs.2 Fig.1.b. The phase speed vp and mean surface speed u as functions of obliquity angle fof magnetic field lines, for solutions with R = 66,000 and Chandrasekhar number Q = 10,000. The waves travel to the right and in the same direction as the mean surface flow. Both speeds increase roughly linearly with angle for f < 0.45p. Fig.1a. A simulation mimicking flows in the outer penumbra, with Rayleigh number R = 80,000, Q = 1000 (proportional to B2), b =120, magnetic Prandtl number z = 0.2, and obliquity f = p/4, with potential boundary conditions imposed on the magnetic field. The tall thin cells give way to a single large cell that also travels rightward. B: The corresponding Hinode vector magnetograms were aligned and binned to comparable resolution (field strength and inclination angle – not disambiguated). v: C. Smith applied the LMSAL correlation tracking tool (Hurlburt, Shine & Simon 1995) to G-band datasets using a 32x32 grid on the 1024x1024 images. The resulting flow vectors were then averaged over a one-hour time interval. The 2D vector fields obtained are shown below (black & white). Observations of Proctor Effect in active regions References D.H. Hathaway & L. Rightmire, 2010, “Variations in the Sun’s Meridional Flow over a Solar Cycle,” Science 327, 135 R. Howe, J. Christensen-Dalsgaard, F. Hill, R. Komm, J. Schou, M.J. Thomson, “A Note on the Torsional Oscillation at Solar Minimum,” 2009 ApJ 701, L87 R.Howe, R.Komm, F.Hill, T.Larson, J.Schou, M.J.Thompson, R.K.Ulrich, “The Torsional Oscillation and the Solar Cycle,” 2009 ASP Conference Series, Vol.416 N.E. Hurlburt, P.C. Matthews, M.R.E. Proctor, “Nonlinear Compressible Convection in Oblique Magnetic Fields,” 1996, ApJ 457, 933 M.R.E. Proctor,1992, in Sunspots: Theory and Observations, ed. J.H. Thomas and N.O. Weiss (Dordrecht: Kluwer), 175 C. Smith, E.J. Zita, N.E. Hurlburt, “Solar Plasma Flows and Convection in Oblique Magnetic Fields,” 2010 APS-NW #D 1.005 E.J. Zita et al., “Physics of the weird solar minimum,” 2010 APS-NW #H1.005 II. Outline C. Connections between Proctor Effect and theories for recent extended solar minimum? A. Proctor effect: Simulations predict changes in flows (v), depending on orientation and strength of local field (B) B. Hinode data: test for Proctor effect (PE) C. Observe changes in flows and fields associated with recent extended solar minimum: 1. meridional circulation 2. torsional oscillations D. Compare flow/field interactions in 1 & 2 with Proctor Effect. Acknowledgements Christina Smith, graduate of The Evergreen State College, performed the Hinode data analysis at LMSAL. Thanks to Dick Shine for assistance and guidance. This work was supported by NSF grant 0807651, NASA grants NAS5-38099, NNM07AA01C, NNG04EA00C, and Lockheed Martin Internal Research Funds.