B. P. Pandey, Mark Wardle
Macroscopic motion of the gas is widespread throughout the solar atmosphere and shearing motions couple to the non-ideal MHD effects, altogether destabilising low frequency fluctuations in the medium. The origin of such non-ideal magnetohydrodynamic instability lies in the collisional coupling of the neutral particles to the magnetized plasma in the presence of sheared background flows. Expectedly the maximum growth rate and most unstable wavenumber depend on the flow gradient and ambient diffusivities. The orientation of the magnetic field, velocity shear and perturbation wavevector play crucial role in assisting the instability. In the presence of only vertical field and vertical wavevector, ambipolar and Ohm diffusion can be combined together as Pedersen diffusion and causes only damping; in this case only Hall drift in tandem with shear flow drives the instability. However, for non-vertical field and oblique wavevector, both ambipolar diffusion and Hall drift assist the instability. We investigate the stability of a magnetic element in the network and internetwork. The shear scale is not yet observationally determined and thus, assuming typical shear flow gradient $\sim 0.1 s^{-1}$ we show that the magnetic diffusion shear instability grows over a minute. Thus, it is plausible that network-internetwork magnetic elements are subject to this fast growing, diffusive shear instability. This fast-growing instability could play important role in driving low frequency turbulence in the photosphere-chromosphere plasma.
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http://arxiv.org/abs/1207.7182
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