MHD and Hall MHD simulations of 3-D turbulence lead by the Kelvin-Helmholtz instability

Details MHD and Hall MHD simulations of 3-D turbulence lead by the Kelvin-Helmholtz instability MHD and Hall MHD simulations of 3-D turbulence lead by the Kelvin-Helmholtz instability

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm51b0530m&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM51B-0530

Other

2724 Magnetopause And Boundary Layers, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2784 Solar Wind/Magnetosphere Interactions, 4490 Turbulence (3379, 4568, 7863), 7859 Transport Processes

Scientific paper

The entry process of the solar wind plasma into the magnetosphere during the northward IMF condition has been controversial in contrast to the Dungey's reconnection model for the southward IMF case. The major candidate processes are the double lobe reconnection model [Song et al., 1999], in which newly closed magnetic field lines on the dayside magnetopause capture the solar wind plasma, and the turbulent transport by the Kelvin- Helmholtz instability (KHI) driven by the fast solar wind flow. We have shown by simulation studies that the strong flow turbulence is a natural consequence of the nonlinear development of the KHI through the secondary instability [Matsumoto and Hoshino, 2004, 2006], which significantly contribute to the formation of a large scale mixing area (e.g., LLBL).
Recently, we have studied the 3-D nonlinear evolution of the KHI by performing MHD simulations [Matsumoto and Seki, 2007]. The KH vortex is also susceptible to "the 3-D secondary instability" which converts the rotating energy into the magnetic energy by generating large amplitude magnetic fluctuations which finally lead the system to turbulent state. The fundamental mechanism is similar to the magneto-rotational instability (MRI) which has usually been applied to the accretion disk. Sano and Stone [2002] showed that the Hall term (ion kinetic) effect is important in the nonlinear saturation of the MRI as well as in the linear growth [Balbus and Terquem, 2001]; the direction of the initial magnetic field with respect to the angular velocity separates the fate of the instability. By analogy with their studies on the MRI, we have also examined an ion kinetic effect on the 3-D nonlinear evolution of the KHI. 3-D Hall MHD simulation showed a faster and more turbulent evolution of the secondary instability when the magnetic field directed opposite to the angular velocity of the vortex. On the other hand, it was inhibited when the magnetic field was set in the same direction. The results indicate importance of the ion dynamics in rapidly rotating plasma in which a vortex finally collapses into turbulence. The detailed mechanism which separates the natures of the secondary instability is also addressed in this presentation.

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