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Geomagnetism and Aeronomy

, Volume 56, Issue 8, pp 972–977 | Cite as

The vorticity of Solar photospheric flows on the scale of granulation

  • A. A. PevtsovEmail author
Article

Abstract

We employ time sequences of images observed with a G-band filter (λ4305Å) by the Solar Optical Telescope (SOT) on board of Hinode spacecraft at different latitude along solar central meridian to study vorticity of granular flows in quiet Sun areas during deep minimum of solar activity. Using a feature correlation tracking (FCT) technique, we calculate the vorticity of granular-scale flows. Assuming the known pattern of vertical flows (upward in granules and downward in intergranular lanes), we infer the sign of kinetic helicity of these flows. We show that the kinetic helicity of granular flows and intergranular vortices exhibits a weak hemispheric preference, which is in agreement with the action of the Coriolis force. This slight hemispheric sign asymmetry, however, is not statistically significant given large scatter in the average vorticity. The sign of the current helicity density of network magnetic fields computed using full disk vector magnetograms from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) does not show any hemispheric preference. The combination of these two findings suggests that the photospheric dynamo operating on the scale of granular flows is non-helical in nature.

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References

  1. Abramenko, V.I., Wang, T., and Yurchishin, V.B., Analysis of electric current helicity in active regions on the basis of vector magnetograms, Sol. Phys., 1996, vol. 168, pp. 75–89.CrossRefGoogle Scholar
  2. Blackman, E.G. and Ji, H., Laboratory plasma dynamos, astrophysical dynamos and magnetic helicity evolution, Mon. Not. R. Astron. Soc., 2006, vol. 369, pp. 1837–1848.CrossRefGoogle Scholar
  3. Cattaneo, F., On the origin of magnetic fields in the quiet photosphere, Astrophys. J. Lett., 1999, vol. 515, pp. L39–L42.CrossRefGoogle Scholar
  4. Fisher, G.H. and Welsch, B.T., FLCT: A fast, efficient method for performing local correlation tracking, in ASP Conf. Ser. 383, Subsurface and Atmospheric Influences on Solar Activity, Howe, R., Komm, R.W., Balasubramaniam, K.S., and Petrie, G.J.D., Eds., San Francisco: ASP, 2009, pp. 373–380.Google Scholar
  5. Keller, C.U. NSO staff, SOLIS, A modern facility for synoptic solar observations, in ASP Conf. Ser. 154, Cool Stars, Stellar Systems, and the Sun, Donahue, R.A. and Bookbinder, J.A., Eds., San Francisco: ASP, 1998, pp. 636–649.Google Scholar
  6. Pevtsov, A.A., Canfield, R.C., and Metcalf, T.R., Patterns of helicity in solar active regions, Astrophys. J. Lett., 1994, vol. 425, pp. L117–L199.CrossRefGoogle Scholar
  7. Pevtsov, A.A., Canfield, R.C., and Metcalf, T.R., Latitudinal variation of helicity of photospheric magnetic fields, Astrophys. J. Lett., 1995, vol. 440, pp. L109–L112.CrossRefGoogle Scholar
  8. Pevtsov, A.A. and Acton, L.W., Soft X-ray luminosity and photospheric magnetic field in quiet Sun, Astrophys. J., 2001, vol. 554, pp. 416–423.CrossRefGoogle Scholar
  9. Pevtsov, A.A. and Longcope, D.W., Origin of helicity in the quiet Sun, in ASP Conf. Ser. 236, Advanced Solar Polarimetry— Theory, Observation, and Instrumentation, Sigwarth, M., Ed., San Francisco: ASP, 2001, pp. 423–430.Google Scholar
  10. Pevtsov, A.A. and Longcope, D.W., Helicity as the ultimate test to the surface dynamo problem, in ASP Conf. Ser. 369, New Solar Physics with Solar-B Mission, Shibata, K., Nagata, S., and Sakurai, T., Eds., San Francisco: ASP, 2007, pp. 99–102.Google Scholar
  11. Rieutord, M., Roudier, T., Ludwig, H.-G., Nordlund, A., and Stein, R., Are granules good tracers of solar surface velocity fields?, Astron. Astrophys., 2001, vol. 377, pp. L14–L17.CrossRefGoogle Scholar
  12. Schekochihin, A.A., Cowley, S.C., Taylor, S., Maron, J.L., and McWilliams, J.C., Simulations of the small-scale turbulent dynamo, Astrophys. J., 2004, vol. 612, pp. 276–307.CrossRefGoogle Scholar

Copyright information

© Pleiades Publishing, Ltd. 2016

Authors and Affiliations

  1. 1.National Solar ObservatorySunspotUS

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