MESOSCALE INSTABILITY OF A BAROCLINIC BASIC FLOW—PART II:TRANSVERSAL INSTABILITY

This is the second part of “Mesoscale Instability of a Baroclinic Basic Flow” which discusses theinstability of a basic flow against mesoscale perturbations of transversal type.A bi-mode instability spectrum is obtained by generalizing the Eady model to ageostrophic regime inan f-plane:Eady modes present at the synoptic and subsynoptic scales,while the ageostrophic baroclinicmesoscale modes present at the inertial scales of a few tens to hundreds kilometers.The mesoscale modeis featured by an asymmetric "eat eyes" pattern in the vertical cross section and by an alternative distri-bution of divergence and vorticity in the horizontal direction.The growth rates of the mesoscale modesare about four times larger than those of Eady modes in magnitudes for the same wind profile.The majorenergy source for development both Eady mode and mesoscale mode is the baroclinic available energy storedin the rotational basic flow.