2-DIMENSIONAL SOLITARY KINETIC ALFVEN WAVES AND DIPOLE VORTEX STRUCTURES

A new type of density soliton, which we call ''dipole density soliton, '' is discovered in data from the Freja satellite. Like the dip or hum p density solitons that were recently discovered in the Freja data [D. -J. Wu, G.-L. Huang, and D.-Y, Wang, Phys. Plasmas 3, 2879 (1996)], th e dipole density solitons are also associated with strong electric spi kes (similar to a few 100 mV/m) and have a spatial scale length of a f ew 100 m. This indicates that the three types of density solitons (dip , hump, and dipole) probably have the same physical nature. In this pa per, a two-dimensional solitary kinetic Alfven wave (SKAW) model with a dipole vortex structure is proposed to account for the three kinds o f density solitons (dip, hump, and dipole), in which the differences i n their appearances can naturally be attributed to differences in the positions and directions at which the satellite crosses dipole vortex structures. Some features of this two-dimensional SKAW model are discu ssed, and the results are compared to the one-dimensional cases. (C) 1 997 American Institute of Physics.