Ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves

With the use of a simple primitive equation model, it is demonstrated that the convergence/divergence of ageostrophic geopotential fluxes can be a major source/sink of kinetic energy for both downstream and upstream development of baroclinic waves, and can play a dominant role during the early stages of wave development. It is also shown that both surface friction and β effects lead to an asymmetry in the upstream versus downstream development, with downstream development much stronger. A total group velocity is defined based on ageostrophic fluxes, and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed. -Authors