SHEAR-FLOW VORTICES IN MAGNETOSPHERIC PLASMAS

Theory and numerical simulations are used to investigate the nonlinear evolution of vortices generated by the Kelvin-Helmholtz (KH) instabil ity of sheared plasma hows in the Earth's magnetosphere. The extent of broadening of the shear flow, and the energy and enstrophy exchange b etween the shear how and KH vortices, is characterized. A new stationa ry vortex street solution is found, and two distinct phases of the non linear dynamics are identified. The first involves a transient phase i n which burst-like pulsations of the flow lead to a rapid dissipation of enstrophy. After the transient phase, an asymptotic state is reache d that corresponds to a periodic chain of pairs of monopolar vortices. The consequences of the model results for the dynamics of field line resonances (FLRs) in the Earth's magnetosphere are discussed, and it i s shown, in particular, that broadening of the Row correlates well wit h observations of periodic reforming of FLR structures. (C) 1997 Ameri can Institute of Physics.