Clusters of small eruptive flares produced by magnetic reconnection in the Sun.

Clusters of small eruptive flares produced by magnetic reconnection in the Sun.

Clusters of small eruptive flares produced by magnetic reconnection in the Sun.Vasilis Archontis1 & Viggo H. Hansteen2,3

1Mathematical Institute, St Andrews University 2Institute of theoretical astrophysics, University of Oslo3Lockheed Martin Solar and Astrophysics Laboratory14th European Solar Physics Meeting, Dublin IrelandOverviewNumerical experiments: initial conditions.

Flux emergence at/above the photosphere.

Plasmoid-induced-reconnection.

Fragmentation of current layers / intermittent heating.

Onset of small flares (nano/micro-flares).

Heating of the active corona.

Bifrost simulations

Hansteen 2004, Hansteen, Carlsson, Gudiksen 2007, Martnez Sykora, Hansteen, Carlsson 2008, Gudiksen et al 2011To model granular motions and magnetic fields caught up in these.Numerical set-upInitial ambient field of B~0.1 G with inclination of 45o with respect to z axis.Flux sheet (Bx=3300 G at bottom boundary) within [x,y]=[0-24,3-16 Mm] for 105 min.

CZ (z=-2.5 Mm). PHOT./CHR. (z=0-2.5 Mm). T~ 5 103 O(105) K.TR (z~2.5-4 Mm). COR. (z~4 Mm). T ~ O(106) K.24x24x17 Mm, 504x504x496 grid.

Convection zonePhotosphere/ChromosphereTransition regionCoronaXYZEmerging field (flux sheet).Ambient magnetic field (oblique, space filling).Convection is driven by optically thick radiative transfer from the photosphere. Radiative losses in the chrom. include scattering, optically thin in the corona. Field-aligned thermal conduction is included.Hyper-diffusion is included.Stratification & magnetic fieldArchontis & Hansteen, 2014To model granular motions and magnetic fields caught up in these.1st phase: emergence to the photosphereB-flux elements pile up (surface) for ~15 min.Bphot = 500-600 G (max=1-1.5 kG).B-field emerges above the surface after ~2hrs.

Chromospheric temperature structure set by acoustic shocks, oscillations etc. until magnetic field emerges into outer atmosphere.

Photospheric and chromospheric intensity little changed by flux emergence during 1st phase.

Larger granules appear at the beginning of 2nd phase.

Vertical slices at y~10 Mm.Horizontal slices at z~700 km above phot.Intensity: continuum, 630 nm & CaII 854.2 nm.The emerging field enters the corona.

Emerging loops: dense and cool (adiabatic expansion).

Photosphere: granule size change, bright points.

Chrom/corona: local temperature increase.

(Low) chromosphere intensity and contrast increase.

Acoustic shock structure severely modified by magnetic field as waves are expelled from cool emerging bubbles.

Magnetic loops interact (e.g. reconnect).2nd phase: emergence above the photosphereSee Ortiz et al. 2014, ApJ 781, 126. for this phase.

Multi-scale emergence of magnetic flux

Evolution across the current sheetLong, thin current layer.

Tearing instability plasmoids.

Ejection of plasmoids reconnection X-ray temperatures.

Jets (V~200-400 km/s, T~2.5 mK).

Small flare loops (T~ 2 mK).

Heat conduction Chrom. heating.

Lifetime of flaring: