Variable coefficient nonlinear systems derived from an atmospheric dynamical system

Variable coefficient nonlinear systems,the Korteweg de Vries (KdV),the modified KdV (mKdV) and the nonlinear Schro¨dinger (NLS) type equations,are derived from the nonlinear inviscid barotropic nondivergent vorticity equation in a beta-plane by means of the multi-scale expansion method in two different ways,with and without the so-called yaverage trick.The non-auto-B¨acklund transformations are found to transform the derived variable coefficient equations to the corresponding standard KdV,mKdV and NLS equations.Thus,many possible exact solutions can be obtained by taking advantage of the known solutions of these standard equations.Further,many approximate solutions of the original model are ready to be yielded which might be applied to explain some real atmospheric phenomena,such as atmospheric blocking episodes.