INSTABILITY OF THE LEMBEGE-PELLAT EQUILIBRIUM UNDER IDEAL MAGNETOHYDRODYNAMICS

The magnetotail-like equilibrium model of Lembege and Pellat [Phys. Fl uids, 25, 1995 (1982)] has been used in a number of stability calculat ions over the past 13 years. Most of these computations examine collis ionless tearing-a mode of tail instability first suggested by Coppi et al. [Phys. Rev. Lett. 16, 1207 (1966)]-or other kinetic modes and inv olve both analytical and computer analysis. In this Communication it i s shown, analytically, that the equilibrium model of Lembege and Pella t is unstable according to ideal magnetohydrodynamics (MHD). More prec isely, for the ideal MHD stability theory of Bernstein et al. [Proc. R . Soc. London Ser. A 244, 17 (1958)] it is proven that Lambda = p' + G amma p (upsilon ''/upsilon') < 0. (C) 1996 American Institute of Physi cs.