Further evidence of normal mode Rossby waves

It is shown, without using an a priori assumption of meridional structure, that the third antisymmetric modes of zonal wavenumbers 1 and 2, ie (1,4) and (2,4) modes, substantially exist in the real atmosphere. These modes are, however, easily influenced by the nonuniform background field even in the equinoctial season; amplitude submaxima near the equator are apt to be dubious in the upper stratosphere so that the prototype meridional structure becomes obscure. The period of the (1,4) model often falls into that of the (1,3) mode, about 16 days. Hence, these two modes cannot be classified simply by their periods, but the separation is made by their meridional structure. -from Authors