Blocking as a wave-wave interaction

The paper investigates the possibility that blocking may be one of the multiple steady states that are possible in a low-order nonlinear system based on wave—wave interaction rather than zonal—wave interaction. The model is based on an equivalent barotropic system forced by a Newtonian forcing and dissipated by boundary layer friction. Three waves are permitted to interact in a nonlinear way giving a system of six nonlinear equations since each wave has a sine and a cosine component. The multiple steady states are determined by a mixture of analytical and numerical methods. The kinetic energy of each of these states is calculated, and the structure of the stable steady states is shown. It may be concluded that wave—wave interaction, just as interaction between the zonal flow and the waves, is a possible mechanism for the formation of blocking patterns. However, both mechanisms, expressed as interaction in low order systems, have difficulties in providing at the same time a fair comparison between theory and observations with respect to horizontal scale and levels of kinetic energy.