Modeling of the solar chromosphere

Transcription

1 Modeling of the solar chromosphere Viggo H. Hansteen, Mats Carlsson, Boris Gudiksen, Wolfgang Hayek, Jorrit Leenaarts, Juan Martinez Sykora & Bart De Pontieu Workshop on Partially Ionized Plasmas in Astrophysics Tenerife, June 19-22, 2012

2 The chromosphere Chromosphere chrooma = [Greek] color; sphairos = [Greek] ball. The chromosphere is a layer in the Sun that is roughly between about 400 km and 2100 km above the solar surface. The temperature in the chromosphere varies between about 4000 K at the bottom (the so-called temperature minimum) and 8000 K at the top. The chromosphere shows up in images taken in the center of the H-alpha spectral line and also (briefly) near the beginning and end of a total solar eclipse. (SacPeak web-page)

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4 Chromosphere is dynamic - Ca II K2V bright grains explained by acoustic waves Carlsson & Stein 1992, 1995, 1997

5 No temperature rise predicted......and dangers of averaging made clear...an isothermal slab through which waves propagate? Carlsson & Stein 1992, 1995, 1997

6 No temperature rise predicted......and dangers of averaging made clear Temperature as derived from model intensities Time average gas temperature in model...an isothermal slab through which waves propagate? Carlsson & Stein 1992, 1995, 1997

7 SOHO/SUMER show acoustic waves in upper chromosphere, but something important is missing from the calculations Carlsson, Judge & Wilhelm 1997, ApJ 486 L63

8 Groundwork done early, with competing theory of acoustic heating coming at about the same time...

9 Schematic Coronal Heating Parker, E.N., 1991, Reviews in Modern Astronomy, p 1-17

10 Schematic Coronal Heating Parker, E.N., 1991, Reviews in Modern Astronomy, p 1-17 Galsgaard, K. & Nordlund, Å., 1996, JGR101 p Gudiksen, B. & Nordlund, Å., 2005, ApJ 618 p 1031

11 Schematic Not only schematic Coronal Coronal Heating Heating! Parker, E.N., 1991, Reviews in Modern Astronomy, p 1-17 Galsgaard, K. & Nordlund, Å., 1996, JGR101 p Gudiksen, B. & Nordlund, Å., 2005, ApJ 618 p 1031

12 Schematic Not only schematic Coronal Coronal Heating Heating!...but remember flux emergence!! Parker, E.N., 1991, Reviews in Modern Astronomy, p 1-17 Galsgaard, K. & Nordlund, Å., 1996, JGR101 p Gudiksen, B. & Nordlund, Å., 2005, ApJ 618 p 1031

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14 Luc Rouppe van der Voort, Michiel van Noort, SST/ITA October Luc Rouppe van der Voort, Michiel van Noort, SST/ITA October

15 Luc Rouppe van der Voort, Michiel van Noort, SST/ITA October

16 Luc Rouppe van der Voort, Michiel van Noort, SST/ITA October

17 What physics need to be included when modeling the solar chromosphere and corona?

18 The MHD equations ρ (ρu ) t + = 0 e t + (eu) + p u = F r + F c + ηj 2 + = r (u B)+ r2 B +... ρu t + (ρuu + τ) = p + j B gρ with some equation of state... T g,p g = eos(r, e)

19 In Norse mythology, Bifröst or Bilröst is a burning rainbow bridge between Midgard, the world, and Asgard, the realm of the gods. The bridge is made from fire, water and air, the traditional hydrodynamic variables.... The bridge's destruction at Ragnarök by the forces of Muspell is foretold.... A significant investment in code development and analysis of which physics Scholars have proposed that the bridge may have originally represented the Milky Way and have noted parallels between the bridge and another bridge in Norse mythology, Gjallarbrú. need to be included - of order 10 years... from Wikipedia

20 BIFROST: Basic assumptions Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martínez Sykora, Hansteen, Carlsson 2008, Gudiksen et al th order scheme, with artificial viscosity/diffusion Open vertical boundaries, horizontally periodic Possible to introduce field through bottom boundary Realistic EOS Detailed radiative transfer along 48 rays Multi group opacities (4 bins) with scattering NLTE radiative losses in the chromosphere, optically thin in corona Conduction along field lines Operator split and solved by using multi grid method Time dependent Hydrogen ionization Generalized Ohm s Law

21 BIFROST: Basic assumptions Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martínez Sykora, Hansteen, Carlsson 2008, Gudiksen et al th order scheme, with artificial viscosity/diffusion Open vertical boundaries, horizontally periodic Possible to introduce field through bottom boundary Realistic EOS Detailed radiative transfer along 48 rays Multi group opacities (4 bins) with scattering NLTE radiative losses in the chromosphere, optically thin in corona Conduction along field lines Operator split and solved by using multi grid method Time dependent Hydrogen ionization Generalized Ohm s Law

22 BIFROST: Basic assumptions Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martínez Sykora, Hansteen, Carlsson 2008, Gudiksen et al th order scheme, with artificial viscosity/diffusion Open vertical boundaries, horizontally periodic Possible to introduce field through bottom boundary Realistic EOS Detailed radiative transfer along 48 rays Multi group opacities (4 bins) with scattering NLTE radiative losses in the chromosphere, optically thin in corona Conduction along field lines Operator split and solved by using multi grid method Time dependent Hydrogen ionization Generalized Ohm s Law

23 BIFROST: Basic assumptions Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martínez Sykora, Hansteen, Carlsson 2008, Gudiksen et al th order scheme, with artificial viscosity/diffusion Open vertical boundaries, horizontally periodic Possible to introduce field through bottom boundary Realistic EOS Detailed radiative transfer along 48 rays Multi group opacities (4 bins) with scattering NLTE radiative losses in the chromosphere, optically thin in corona Conduction along field lines Operator split and solved by using multi grid method Time dependent Hydrogen ionization Generalized Ohm s Law

24 BIFROST: Basic assumptions Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martínez Sykora, Hansteen, Carlsson 2008, Gudiksen et al th order scheme, with artificial viscosity/diffusion Open vertical boundaries, horizontally periodic Possible to introduce field through bottom boundary Realistic EOS Detailed radiative transfer along 48 rays Multi group opacities (4 bins) with scattering NLTE radiative losses in the chromosphere, optically thin in corona Conduction along field lines Operator split and solved by using multi grid method Time dependent Hydrogen ionization Generalized Ohm s Law

25 Change from HD to MHD - from no free parameters, to many Corona Transition region Chromosphere Photosphere

26 Change from HD to MHD - from no free parameters, to many Corona Transition region Chromosphere Photosphere

27 Solar magnetic fields structure of photospheric field still unknown Summarize flux as are, of course, emergence the problems: chromospheric i.e. what does field look like on small scales and short time scales? and coronal fields Fodder for simulations! i.e. the magnetic field is not well constrained high quality observations, and inversions(?), required

28 Transition Region & Coronal Lines What does Bifrost have to say? see also Hansteen et al. 2010, ApJ 718.

29 Coronal Heating from braiding (& flux emergence)

30 Coronal Heating from braiding (& flux emergence) H chrom 200 km < H j2 / <H cor 50 Mm

31 Average ηj 2 /ρ vs. -Lr/ρ

32 ηj 2 /ρ concentrated near TR and upper chromosphere Hansteen et al. 2010, ApJ 718 p. 1070

33 Chromospheric structure Upper photosphere/ lower chromosphere is (usually) high β, dominated by shocks. Upper chromosphere is low β, shocks compete with other heating mechanisms? Large range in height range, Lorentz force likely important.

34 Chromospheric structure Upper photosphere/ lower chromosphere is (usually) high β, dominated by shocks. Upper chromosphere is low β, shocks compete with other heating mechanisms? Large range in height range, Lorentz force likely important.

35 3D NLTE: Ca II 8542 Observed (top panels) vs simulation Leenaarts et al 2009: ApJ 694,L128

36 Ca II 8542; seems we are doing well, or...? Spatial mean spectrum

37 Ca II 8542; better resolution gives wider line

38 Ca II 8542; better resolution gives wider line

39 Back to Hα...

40 Back to Hα...

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43 Type I Spicules similar to Dynamic Fibrils (AR plage), Mottles (QS) Well reproduced by 2/3D radiative MHD Simulations (OSC) H-alpha linecenter log T Velocity Swedish Solar Telescope by Rouppe van der Voort & van Noort (University of Oslo) Type I spicules (fibrils/mottles on disk) are driven by magneto-acoustic shocks caused by leakage into the chromosphere of photospheric flows and oscillations channeled along mag-netic flux concentrations [De Pontieu et al 2004] For details, see Hansteen et al., 2006, De Pontieu et al., 2007, Rouppe van der Voort et al., 2007, Heggland et al., 2007, Martinez Sykora et al. 2009, Heggland et al. 2011

44 Hα blue wing -51mÅ Hα red wing +51mÅ movie courtesy of Luc Rouppe van der Voort Spicules type II at the limb, RBEs, (and RREs)

45 Hα blue wing -51mÅ Hα red wing +51mÅ only upward motion accelerate sometimes lifetimes s velocities km/s widths km sideways (and swaying) motion period of order minutes de Pontieu et al PASJ 59, Langangen et al ApJL 679, Rouppe van der Voort et al ApJ 705, McIntosh et al Nature 475 movie courtesy of Luc Rouppe van der Voort Spicules type II at the limb, RBEs, (and RREs)

46 An example of a simulated feature with similarities to a spicule of type II Corona 256x128x160 points 64 km dx,dy 32 km dz except in corona TR Photosphere TR: Temperature High speed upflow >45km/s Joule heating Hot loop (1.3MK) Photospheric vertical speed: redblue. Magnetic field: red & blue lines. Martínez-Sykora et. al 2011

47 An example of a simulated feature with similarities to a spicule of type II Corona 256x128x160 points 64 km dx,dy 32 km dz except in corona TR Photosphere TR: Temperature High speed upflow >45km/s Joule heating Hot loop (1.3MK) Photospheric vertical speed: redblue. Magnetic field: red & blue lines. Martínez-Sykora et. al 2011

48 Hα workhorse for chromospheric observers Hα formation poorly understood consequently Hα data can be over-interpreted:..chromospheric fibrils seen in the Hα line center are threads of mass... (2011) Mottles can be considered as straight, cylindrical, high density magnetic flux tubes... (2012) Care should be taken not to project one s favorite atmospheric structure on Hα data without good reason to do so.

49 1D line center intensity

50 3D line center intensity

51 3D line center intensity Hα and Lyα are scattering lines: 3D effects essential Leenaarts et al. 2012

52 Numerical models bridge the gap between IRIS observations and the physical mechanisms driving solar events and dynamics Simulated Mg II k images with IRIS spectral resolution Simulated Mg II k spectra along slit

53 Numerical models bridge the gap between IRIS observations and the physical mechanisms driving solar events and dynamics Simulated Mg II k images with IRIS spectral resolution Simulated Mg II k spectra along slit

54 Disk-centre intensity [W m 2 Hz 1 sr 1 ] Observations Staath & Lemaire (1995) Mg II K OSCB1 typeb0double unipolar big33 cb24bih cb24ii dynamo Åke Wavelength [nm]

55 Conclusions Chromosphere/corona highly dynamic and finely structured and globally coupled......need to treat the complete system convection zone - corona Can synthesize chromspheric, transition region and coronal lines well enough to compare with observations - see also de la Cruz this meeting for polarimetry... Need realistic physics Radiation non-equilibrium ionization ion-neutral effects Computing intensive but doable