Stratospheric wave-mean flow interaction: Simple modeling

We show that the interaction between planetary waves and the stratospheric zonal mean flow results in bi-modal (directreverse flow) or unimodal state depending on wave number of the waves. First we demonstrate this using a simple nonlinear dynamic system of the wave-flow interaction, which has two stable equilibrium states and one unstable state (attractors) in its phase space. Then we compare this model dynamics with the stratosphere dynamics using the same dynamical variables and a similar parameter range in the National Centers for Environmental Prediction (NCEP) Reanalysis data. This comparison supports the tendency for the states of planetary wave-zonal mean flow in the upper stratosphere to be bi-modal for wave number 2 and unimodal for wave number 1.