Hydromagnetic waves driven by velocity shear instability in the magnetospheric boundary layer |
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| Authors: | Kiyohumi Yumoto Takao Saito |
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| Institution: | Onagawa Magnetic Observatory and Geophysical Institute, Tohoku University, Sendai 980, Japan |
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| Abstract: | The bulk flow of the solar wind plasma in the flank-side of the magnetospheric boundary layer, where the magnetic field lines are closed, has a component transverse to the ambient field. There is quite a strong velocity shear. The theoretical model ignores inhomogeneities in the ambient field and the mass density which occur at the magnetopause on about the same length scale as that of the velocity shear.Consideration is restricted to hydromagnetic waves which have a k-vector nearly normal to the Bo-Vo plane, i.e., approximately the magnetopause surface (kx >kz ～ ky′kxLB > 1 and LB = 0.1 ～ 1.0 RE where LB is a characteristic length of the boundary layer). It is found that a long-period (T ? 40 sec) hydromagnetic wave the Alfvén-like wave ()] driven by velocity shear instability can be excited in the shear plasma. It is also found that the group velocity of the HM-wave is directed almost along the magnetic field line and that the magnetic variance in the shear plasma tends to be parallel to the Bo-Vo plane. The velocity shear instability in the magnetospheric boundary layer is judged to be a likely source of long-period magnetic pulsations. |
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