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Extrapolation vs. MHD Modeling: Insights into 3D Coronal Emission Dynamics

This contribution discusses the differences and synergies between magnetic field extrapolations and magnetohydrodynamic (MHD) modeling of the solar corona, presented by Peter Hardi at the SDO workshop in Monterey, February 2006. The focus is on understanding coronal emission at temperatures around 10^6 K using a 3D MHD model. Key highlights include the dependence of coronal emission on the state of the magnetic field, the effects of plasma dynamics on magnetic lines, and the need for both modeling techniques for accurate representations of solar atmospheric phenomena.

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Extrapolation vs. MHD Modeling: Insights into 3D Coronal Emission Dynamics

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  1. Extrapolation vs. MHD modeling Hardi Peter Kiepenheuer-Institut Freiburg, Germany Contribution to the discussions at the SDO workshop / Monterey Feb 2006

  2. 3D MHD coronal modeling “emission” @ 106 K 20 histogram of currents mean B2 vertical Z [Mm] Bingert et al. (2005) 10 current log10J2 Gudiksen & Nordlund (2002) ApJ 572, L113 MDI magnetogram mean J2 20 0 10 30 40 horizontal X [Mm] horizontal y [ Mm] vertical z [ Mm] horizontal x [ Mm] • 3D MHD model for the corona: • 50 x 50 x 30 Mm Box (1503) • – fully compressible; high order • – non-uniform mesh • full energy equation (heat conduction, rad. losses) • starting with scaled-down MDI magnetogram – no emerging flux • photospheric driver: foot-point shuffled by convection • braiding of magnetic fields (Galsgaard, Nordlund 1995; JGR 101, 13445) â heating: DC current dissipation (Parker 1972; ApJ 174, 499) â heating rate h j2 ~ exp(- z/H ) â loop-structured 106K corona Gudiksen & Nordlund (2002) ApJ 572, L113 (2005) ApJ 618, 1020 & 1031 Bingert, Peter, Gudiksen & Nordlund (2005)

  3. Coronal emission and plasma–b Peter, Gudiksen & Nordlund (2006) ApJ 638 • atmosphere is mostly in low–b state, • numerous b >1 regions even at high T(but mostly at low density) • source region of coronal emission: 90% of emission from log I/áIñ > 0 Êthere ~5% of volume at b >1 • corona is not in a pure low–b state: plasma able to distort magnetic field to some extent

  4. Coronal emission and magnetic field lines I The "usual" paradigm: The coronal emission is aligned with the magnetic field Peter, Gudiksen & Nordlund (2004) ApJ 618 emission synthesized from a 3D coronal model side view / at the limb

  5. Coronal emission and magnetic field lines II synthesized emission top view / at the limb potential field extrapolation Peter, Gudiksen & Nordlund (2004) ApJ 618 Not all emission we see in EUV / X-rays outlines field lines !!! Gudiksen & Nordlund (2002)

  6. Conclusions • field extrapolations (NLFF): – possible to match photospheric B boundary conditions very well – time evolution through sequence of equilibria – do we really "see" field lines in EUV ? • MHD coronal models – proper time evolution – not easy to match observed B at photosphere (all 3 components) – proper interaction of B and plasma – emission properties through forward modeling • One needs both: MHD models and field extrapolations !

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