Vertical Propagation of Stationary Planetary Waves in the Winter Northern Hemisphere

Abstract

Planetary-scale, stationary disturbances in the winter stratosphere are considered to be upward propagating internal Rossby waves forced from below. Numerical solutions to the linearized equation for wave propagation are obtained by assuming a realistic profile of zonal winds as the basic state and imposing observed monthly mean heights of the 500-mb surface as the lower boundary condition. The computed wave structures in the meridional section show good agreement with the observed state for the component of zonal wavenumber 1. For wavenumber 2, the computed amplitude is too small to compare with the observed. Wave energy density attains a maximum in the lower and middle stratosphere at high altitudes, where strong upward transfer of wave energy appears. A region of small latitudinal gradient of potential vorticity of the basic state is found above the tropospheric jet, which acts as a barrier for wave propagation and confines wave energy to the polar region. Above 40 km the wave tends to spread to lower latitudes. A line of zero zonal winds in the tropics is a major sink of up-flowing planetary wave energy.