1. 2 nd Solaire Network Meeting Catania, 12 - 15 January 2009 Investigating the characteristics of coronal loop heating by 1D hydrodynamic simulations R. Susino 1, A. F. Lanza 2, A. C. Lanzafame 1, D. Spadaro 2 1 Dipartimento di Fisica e Astronomia – Università di Catania 2 INAF – Osservatorio Astrofisico di Catania

2. Introduction Open question: is the coronal heating an impulsive or steady process? Uniform or localized in space? Steady uniform heating is consistent with a number of observed EUV and X-ray loops ( e.g. Porter and Klimchuck 1995; Schijver et al. 2004, Warren & Winebarger 2006 ) Steady heating cannot explain over/under density of warm/hot loops observed with TRACE, SOHO and Yohkoh ( e.g. Aschwanden et al. 1999, 2001; Winebarger et al. 2003; Patsourakos et al. 2004, Klimchuk 2006 ) Impulsive (in case localized) heating: nanoflare theory Problems: multi-thermal structure of loops along the LOS, cospatiality of X-ray and EUV loops… Importance of forward modeling to provide observational signatures of heating mechanisms Roberto Susino2 2 nd Solaire Network Meeting

3. Numerical model and simulations Simulations of an AR coronal loop… ARGOS 1-D hydrodynamic code with PARAMESH package: Adaptive grid essential to resolve the thin chromospheric-coronal transition region sections of the loop Different kinds of energy deposition: Impulsive vs. steady Localized at loop footpoints vs. uniform Roberto Susino3 2 nd Solaire Network Meeting

4. Loop length: 80 Mm Loop height: 14 Mm Loop model: geometry Loop radius ≈ 200 km Sub-resolution magnetic strand s1s1 CHROMOSPHERE CORONA s →s → 60 Mm chromospheric section T ≈ 30000K Roberto Susino4 2 nd Solaire Network Meeting

5. Loop model: initial conditions T max = 0.75 MK (TR loop) N min = 1.4 x 10 8 cm -3 v ≈ 0.1 ÷ 0.2 km s -1 τ cool ≈ 1000 s Spatially uniform, steady background heating: 2.0 x 10 -5 erg s -1 cm -3 Roberto Susino5 2 nd Solaire Network Meeting

6. Heating rate functions Localized heating - Uniform: F(s)=1 Impulsive heating - Steady: G(t)=const. f = asimmetry parameter (0.75) λ = heating scale-length (10 Mm) E I = total heating per unit volume τ = heating time-scale (25 s) Roberto Susino6 2 nd Solaire Network Meeting

7. Loop dynamic evolution Localized vs. uniform heating Localized heating Uniform heating Energy per pulse: 10 24 erg Cadence time: 250 s Roberto Susino 2 nd Solaire Network Meeting 7

8. Loop dynamic evolution Impulsive localized heating: cadence variation Cadence time: 250 s 1000 s (≈ τ cool ) Energy per pulse: 10 24 erg Roberto Susino 2nd Solaire Network Meeting 8

9. Loop dynamic evolution Impulsive localized heating: energy variation Energy per pulse: 10 24 erg 0.5 × 10 24 erg Cadence time: 250 s Roberto Susino 2nd Solaire Network Meeting 9

10. Loop dynamic evolution Impulsive localized heating: energy variation Energy per pulse: 10 24 erg 2.0 × 10 24 erg Cadence time: 250 s Roberto Susino 2 nd Solaire Network Meeting 10

11. Loop dynamic evolution Impulsive vs. steady heating Localized heating Impulsive heating Energy per pulse: 10 24 erg Cadence time: 250 s Steady heating Equivalent energy: 10 24 erg Roberto Susino 2 nd Solaire Network Meeting 11

12. Loop dynamic evolution Impulsive vs. steady heating Uniform heating Impulsive heating Energy per pulse: 10 24 erg Cadence time: 250 s Steady heating Equivalent energy: 10 24 erg Roberto Susino 2 nd Solaire Network Meeting 12

13. Differential Emission Measure Mean DEM computed averaging the DEMs at 300 different times, randomly selected all over the simulation: Representation of 300 independent strands observed at the same time Equivalent to a simulated snapshot observation in a single multistranded loop Roberto Susino13 2 nd Solaire Network Meeting

14. DEM results Localized vs. uniform heating Localized heating Impulsive Steady Uniform heating Impulsive Steady Energy per pulse: 10 24 erg Cadence time: 250 s Initial state SERTS89 AR data Roberto Susino 2 nd Solaire Network Meeting 14

15. DEM results Impulsive localized heating: cadence variation Cadence time: 250 s 500 s 1000 s (≈ τ cool ) Energy per pulse: 10 24 erg Initial state SERTS89 AR data Roberto Susino 2 nd Solaire Network Meeting 15

16. DEM results Impulsive localized heating: energy variation Energy per pulse: 0.5 × 10 24 erg 10 24 erg 2.0 × 10 24 erg 4.0 × 10 24 erg Cadence time: 250 s Initial state SERTS89 AR data Roberto Susino 2 nd Solaire Network Meeting 16

17. Summary The localization of the heating near the loop footpoints is essential to reproduce the observed DEM: Condensation formation → Contribution to the TR temperature part of the DEMs Uniform heating is inconsistent at low temperatures Critical dependence on energy deposition details: Pulse energy, inter-pulse cadence… Heating temporal variation (steady vs. impulsive heating ) appears to be non influential… Roberto Susino17 2 nd Solaire Network Meeting