Solar Surface Anisotropy effect on the Magnetic Field

Transcription

1 view out of the THEMIS telescope dome (Tenerife) Solar Surface Anisotropy effect on the Magnetic Field Véronique Bommier LESIA, Observatoire de Paris IAU Symposium 305 Punta Leona (Costa Rica), 30 November-5 December 2014

2 NOAA Hinode 1 May 2007 VECTOR MAGNETIC FIELD MAPS 2 lines: Fe I and Å vector current density independent ME inversion (UNNOFIT code, Bommier et al. 2007) lines of the same multiplet: constant ΔH (simulation quiet Sun & AR by Khomenko & Collados 2007) formation depth difference: 98 km vector Lorentz force ambiguity removed by divb + J z minimization (DIVB2, modified ME0 code of Leka et al., simulated annealing) 119 maps available 96 THEMIS campaigns & 23 HINODE Véronique Bommier's homepage

3 Fe I Å and Å are 2 lines of the same multiplet 816 parallelism from Khomenko, E., & Collados, M., 2007, ApJ 659, 1726 Direct measurement of h by phase shift method (cross-spectral analysis): quiet Sun, HINODE data: h = 63.2 ± 0.9 km (Faurobert et al., 2009, A&A 507, L29) confirmed by 3D simulations of solar magneto-convection: h = 69 km Stein & Nordlund's + Uitenbroek's codes (Grec et al., 2009, A&A 514, A91)

4 plot of B X X B Y Y B Z Z divb THEMIS observation of a double sunspot (δ-spot) on 13 September 2005 MULTILINE plot of 10 B X X 10 B Y Y B Z Z divb scaled by the aspect ratio color scale: scaled to the measurement inaccuracy level (including inversion)

5 vertical gradient dbz/dz: 3 G/km Westendorp Plaza et al., 2001, ApJ 547, lines Fe I & Å observed with ASP (Sac Peak) SIR inversion, provides also d/dz result: G/km (4 G/km in a previous analysis) Balthasar & Schmidt, 1993, A&A 279, lines Fe I & Å & Fe II Å spectropolarimetry with the VTT (Izaña, Tenerife) inversion by comparison with theoretical profiles by Grossmann-Doerth et al. (1988), G-D (1994) Unno-Rachkovsky sol. in a model atmosphere d/dz is derived result: 2.5 to 3 G/km Pahlke & Wiehr, 1990, A&A 228, lines Si I , Zr I , Fe II , Ti I , Fe I , Na I Å circular polarization observed with the Gregory-Coudé telescope (Tenerife) direct field measurement in umbra by Zeeman splitting best agreement between the 6 lines if a gradient of 2 G/km is assumed. Bruls, Solanki, Rutten & Carlsson, 1995, A&A 293, 225 reanalyze FTS (Kitt Peak) observations by Hewagama et al. (1993) 2 infrared lines Mg I & m (formed in the upper photosphere) MULTI code (non-lte multilevel, Carlsson 1986) + DELO Stokes profile synthesis (Rees et al., 1989, Murphy, 1990, Murphy & Rees, 1990) result: 2-3 G/km horizontal gradient dbx/dx+dby/dy: 0.3 G/km Balthasar, 2006, A&A 449, lines Fe I 15648, & Å observed with the TIP mounted on the VTT (Tenerife) 8 sunspots SIR inversion result: 0.5 G/km Hagyard et al., 1983, Sol. Phys. 84, 13 1 highly sensitive line Fe I Å MSFC magnetograph (Hunstville, Alabama) 1 sunspot result: G/km suppose a regular sunspot diameter 10,000 km suppose that Bx varies from 1500 G to G from one penumbra side to the other penumbra side the mean horizontal gradient results into 0.3 G/km models Eibe, Aulanier, Faurobert, Mein, Malherbe, 2002, A&A 381, 290, report a factor of 10 between observations: longitudinal field Na I D1 observed with THEMIS/MSDP depth probing along the highly resolved line profile via response functions computed with the MULTI code (Carlsson 1986) theory: force-free extrapolation (Démoulin, Bagala, Mandrini, Hénoux, Rovira, 1997, A&A 325, 305) Pizzo, 1986, ApJ 302, 785 magnetostatic equilibrium modelling (not force-free) result: G/km (Fig. 15, for large tube radii that model sunspots)

6 This cannot be ascribed to the lack of resolution Demonstration in the spatial Fourier space real space Fourier transform spatial Fourier space f (x) ˆf (kx ) e ikxx f (x)dx derivation: x f (x) multiplication: k ˆf x (k x ) filtering: convolution product normal product F(x) (x x ˆF(kx ) ˆ (k x ) ˆf (k x )

7 What is measured: H or B? I

8 What is measured: H or B? II

9 Anisotropic Debye shielding (local dynamo) Open Access paper by Bommier in Physics Research International + Bommier, 2014, Comptes Rendus Physique, 15, 430 (available from the ADS)

10 The photosphere: a strongly stratified medium viscosity-affected From Brethouwer, Billant, Lindborg, Chomaz, J. of Fluid Mechanics, 585, 343: The horizontal Froude number in the photosphere is found F h the photosphere is a strongly stratified medium (not the solar Corona, having F h 3) The Reynolds number is R e 500 1, but the buoyancy Reynolds number is R b R e F 2 h the photosphere lies in the "viscosity-affected flow regime": no inertial cascade can develop the typical horizontal/vertical length ratio ("aspect ratio") is R e 20 the horizontal/vertical velocities and then Debye lengths are different: anisotropy Temporary conclusion

11 An experimental proof? Physical conditions of the experiment taken from Van Compernolle, Bortnik, Pribyl, Gekelman, et al., 2014,Phys. Rev. Letters 112, Description of the experiment in Gekelman et al., 1991, Rev. Sci. Instrum. 62, 2875

12 NOAA observed on 13 September 2005 with THEMIS THEMIS

13 NOAA observed on 13 September 2005 with THEMIS magnetic field vector THEMIS