1. PIC code simulations of solar flare processes Astronomical Institute
Marian Karlický
Miroslav Bárta
Dieter Nickeler
Astronomical Institute
Ondřejov
Czech Republic

2. Contents: 2. Tearing and coalescence processes in
1. Introduction to solar flare theory
2. Tearing and coalescence processes in
the current sheet (2.5-D PIC model)
Drifting pulsation structures
3. Fragmentation of the current sheet
(3-D PIC model)
4. Spatial separation of accelerated particles
in magnetic reconnection
5. Return current simulations (3-D PIC model)
6. Conclusions

3. CME-flare phenomenon Forbes and Acton 1996, ApJ 459, 330
Lin and Forbes
2000, JGR 105, 2375

4. Particle-in-cell simulations:

5. Particle-in-cell simulations:
Drake et al. 2005, Phys. Rev. Lett. 94,
Pritchett 2006, J. Geophys. Res. 111, A10212
Karlický and Bárta 2007, AA 464, 735
2.5 D electromagnetic relativistic PIC code
(Saito, Sakai: 2004, ApJ 616, L179)
Numerical box 2000x600 grids
Current sheet, half-width 10 grids
Parallel code, Ondřejov Cluster for
Astrophysical Simulations

11. July 11, 2002

12. Current sheet fragmentation
3D PIC model (Karlický and Bárta, 2007)
25x105x805 grids, 2 current sheets, periodic boundary
conditions, guiding field Bz=5xB0, mi/me=1836, wce/wpe=0.2
Times: wpet = 0, 250, 500, 750
See also Jaroschek et al. 2004, Phys. Plasmas 11, 1151

13. Times: wpet = 0, 250, 500, 750
Resulting ratio of resistivities ha/hC ~ 105

15. Separation of accelerated electrons and positrons
in the relativistic reconnection
electrons
positrons
Separation of electrons and protons in RHESSI
observations of the July 23, 2002 flare (Hurford et al. 2003)

16. Return current simulations
Motivation:
Bombardment of the chromosphere by electron beams.
Effects in intensities and polarization of the optical
chromospheric lines during solar flares
(Karlický et al. 2004, AA 416, L13).
Model:
3-D PIC (Buneman 1993)
5x5x800 mi/me=1836, Te= 105 and 104 K, vb/c = 0.36,
nb/ne = 1.66x10-2 and 1.66x10-3 (transition region
and chromoshere) (20/1200 and 20/12000 particles per cube)

17. Electron distribution functions
Times: wpet = 0, 100, 250, 2500 (TR)

18. The time evolution of electric field energy (TR)

19. The time evolution of total electric current (TR)

21. Electron distribution functions
Times: wpet = 0, 1250, 2500, 5000 (CHR)

22. The energy electron distribution function
In the chromoshere without (left) and with (right)
electron beam and return current

23. Conclusions:
The PIC models show that the current sheets are unstable due to tearing mode instability and they become very fragmented due to Buneman and kinetic kink instability. These processes support fast dissipation of the magnetic field energy.
Magnetic reconnection with the guiding magnetic field
spatially separates particles.
3. Observational evidence of these processes is:
moving plasmoids, radio drifting pulsation structures,
evolving X-ray and radio loop-top sources.
A formation of the return current is presented. This current is formed by electrons from the bulk as well as from the tail of the distribution function. Resuls are
very important for computations of intensities and
polarization of optical chromospheric lines.