Physics – Plasma Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh11a0247c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SH11A-0247
Physics
Plasma Physics
2101 Coronal Mass Ejections (7513), 2114 Energetic Particles (7514), 2134 Interplanetary Magnetic Fields, 7800 Space Plasma Physics, 7863 Turbulence (4490)
Scientific paper
The two-component model of magnetic turbulence, a reasonable model for turbulent magnetic field in interplanetary space, consists of slab and two-dimensional (2D) fluctuations. Field lines can be trapped within magnetic islands due to the topology of 2D turbulence while the slab turbulence contributes to escape and field line random walk. Therefore, the field lines in the two-component model can be both trapped and diffusive. Here we perform numerical simulations to examine trapping within 2D islands when field lines initially are located near 2D O-points or X-points until they escape and become diffusive. The results show that diffusion of field lines starting near O-points systematically changes, with a delay at the beginning and then approaching the 2D+slab turbulent diffusion rate at long distance. In contrast, field lines starting near X-points spread rapidly at the 2D+slab rate from the beginning. To have a better understanding of the mechanism of trapping and escape, we also model a single 2D island. We find that a strong 2D field can suppress the random walk of field lines due to the slab component. The simulations show that field lines starting deeply inside the island initially diffuse in radius but at a rate lower than when they are outside the 2D island; this is theoretically explained by applying a quasi-linear approach. In 2D+slab turbulence, sharp boundaries of trapping occur at intermediate distance. These boundaries can be empirically defined as trajectories of 2D turbulence where the appropriately averaged 2D field is a local maximum. Furthermore, we numerically measure the trapping length and show how it changes with various parameters. This study explains the underlying causes of inhomogeneity and sharp gradients in solar energetic particles from impulsive solar flares. This work was supported by US National Science Foundation grant ATM 0105254 and Thailand Research Fund.
Chuychai Piyanate
Matthaeus William H.
Meechai J.
Ruffolo David
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