Small-scale Dynamo Action in the Quiet Sun : Observational Aspects

1. Small-scale Dynamo Action in the Quiet Sun : Observational Aspects Valentina Abramenko Big Bear Solar Observatory, CA Email: avi@bbso.njit.edu Big Bear Solar Observatory 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

2. Turbulence is ubiquitous in the photosphere. A question is: are velocities capable to ensure the increasing, or, al least, non-decreasing magnetic flux?

3. Kinetic and Magnetic Energy Spectra Kinetic Spectrum Power Spectrum Magnetic Spectrum wavenumber Spatial scale Magnetic dissipation scales, λ η Batchelor 1959 Nakagawa & Priest 1973 Schekochinin+ 2003 Kinetic dissipation scales , λ ν Case of High Prandtl number, Pr= λ ν/ λ η >> 1 Small-scale dynamo action is ensured 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

4. Kinetic and Magnetic Energy Spectra Kinetic Spectrum Power Spectrum Magnetic Spectrum Magnetic dissipation scales, λ η wavenumber Spatial scale Boldyrev and Cattaneo 2003 Iskavov +2007 Pietarila Graham + 2010 Kinetic dissipation scales , λ ν Case of Low Prandtl number, Pr= λ ν/ λ η <<1 Small-scale dynamo action is questionable 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

5. Kinetic and Magnetic Energy Spectra Observed Velocity Spectra 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

6. Kinetic and Magnetic Energy Spectra Observed Magnetic Spectra -1/3 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

7. Kinetic and Magnetic Energy Spectra Comparison 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

8. λη? Kinetic and Magnetic Energy Spectra Comparison λη~ η3/4 = K3/4 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

9. Diffusivity Regime on small Scales 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

10. Bright points detection Detection criteria: lifetime longer than 20 s; area larger than 2 pixels; brightness above the mean image brightness. Total: 13597 tracked BBs for th=85 DN 7148 tracked BPs for th=120 DN 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

11. Trajectory coordinates measurements (black) vs residual jittering of the telescope (red) Max jittering: 0.2 pixel = 0.2 x 0.0375” = 5.4 km on the solar surface 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

12. This is placeholder copy This is also placeholder copy Trajectories of BPs Typical examples of BPs trajectories. Time intervals between adjacent circles is 10 s. The blue large circles mark the start points of the trajectories. For each tracked BP, the average diameter was calculated. Big Bear Solar Observatory 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

13. Size Distribution of BPs 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

14. Then for each we average displacements from all tracked BPs. Diffusivity in the Photosphere (x0,y0) For each BP, we compute a set of displacements from the start point: (Δ l)2i = (xi-xo)2+(yi-y0)2 (x10,y10) and a set of corresponding time delays: (xN,yN) We thus obtain Displacement Spectrum: Big Bear Solar Observatory 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

15. Diffusivity: Displacement Spectrum 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

16. Slide Title Here Manso Sainz+2011 Hinode SOT/SP Big Bear Solar Observatory 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

17. Diffusivity : Some Definitions 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

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19. λη λη Kinetic and Magnetic Energy Spectra 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

20. Conclusions The tendency observed in the magnetic energy spectra and the regime of super-diffusivity on small scales indicated very favorable conditions for the small-scale turbulent dynamo action in the photosphere. Big Bear Solar Observatory 7/05/2011 XXV IUGG/IAGA, Melbourne, Australia

21. λη