Global transport calculations with an equivalent barotropic system

Transport properties of the two-dimensional equations governing equivalent barotropic motion are investigated on the sphere. Horizontal transport properties of this system are investigated under adiabatic and diabatic conditions, for different forms of dissipation, and over a range of resolutions. Integrated numerically on the sphere with a Hough spectral algorithm, the equivalent barotropic system conserves potential vorticity Q very accurately, even at low resolution. Forcing representative of time-mean and amplified conditions at 10 mb leads to behaviour typical of observations at this level. With forcing representative of time-mean conditions, irreversible mixing is confined to a narrow zone adjacent to the tropical zero wind line. However, amplified forcing leads to stirring across much of the winter hemisphere, at least under adiabatic conditions. -from Authors