Investigating the characteristics of coronal loop heating by 1D hydrodynamic simulations

1. Investigating the characteristics of coronal loop heating by 1D hydrodynamic simulations R. Susino1, A. F. Lanza2, A. C. Lanzafame1, D. Spadaro2 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 2ndSolaire 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 2nd Solaire Network Meeting

4. Loop model: geometry Loop length: 80 Mm Loop height: 14 Mm CORONA s1 CHROMOSPHERE Loop radius ≈ 200 km Sub-resolution magnetic strand T ≈ 30000K s→ 60 Mm chromospheric section 2ndSolaire Network Meeting

5. Loop model: initial conditions Tmax= 0.75 MK (TR loop) Nmin= 1.4 x 108 cm-3 v ≈ 0.1 ÷ 0.2 km s-1 τcool ≈ 1000 s Spatially uniform, steady background heating: 2.0 x 10-5 erg s-1 cm-3 2ndSolaire 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) EI = total heating per unit volume τ = heating time-scale (25 s) 2ndSolaire Network Meeting

7. Loop dynamic evolutionLocalized vs. uniform heating Localized heating Uniform heating Energy per pulse: 1024 erg Cadence time: 250 s 2nd Solaire Network Meeting

8. Loop dynamic evolution Impulsive localized heating: cadence variation Cadence time: 250 s 1000 s (≈ τcool) Energy per pulse: 1024 erg 2nd Solaire Network Meeting

9. Loop dynamic evolution Impulsive localized heating: energy variation Energy per pulse: 1024 erg 0.5 × 1024 erg Cadence time: 250 s 2nd Solaire Network Meeting

10. Loop dynamic evolution Impulsive localized heating: energy variation Energy per pulse: 1024 erg 2.0 × 1024 erg Cadence time: 250 s 2ndSolaire Network Meeting

11. Loop dynamic evolution Impulsive vs. steady heating Localized heating Impulsive heating Energy per pulse: 1024 erg Cadence time: 250 s Steady heating Equivalent energy: 1024 erg 2ndSolaire Network Meeting

12. Loop dynamic evolution Impulsive vs. steady heating Uniform heating Impulsive heating Energy per pulse: 1024 erg Cadence time: 250 s Steady heating Equivalent energy: 1024 erg 2ndSolaire Network Meeting

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 2ndSolaire Network Meeting

14. DEM resultsLocalized vs. uniform heating Localized heating Impulsive Steady Uniform heating Impulsive Steady Energy per pulse: 1024 erg Cadence time: 250 s Initial state SERTS89 AR data 2nd Solaire Network Meeting

15. DEM results Impulsive localized heating: cadence variation Cadence time: 250 s 500 s 1000 s (≈ τcool) Energy per pulse: 1024 erg Initial state SERTS89 AR data 2ndSolaire Network Meeting

16. DEM results Impulsive localized heating: energy variation Energy per pulse: 0.5 × 1024 erg 1024 erg 2.0 × 1024 erg 4.0 × 1024 erg Cadence time: 250 s Initial state SERTS89 AR data 2ndSolaire Network Meeting

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… 2ndSolaire Network Meeting