AUSTRALIAN SOUTHERLY BUSTERS .2. THE DYNAMICAL STRUCTURE OF THE OROGRAPHICALLY MODIFIED FRONT

A methodology is presented for comparing nonlinear 3D model output to the physical principles embodied in idealized and analytical models, t hrough the use of the transformation of wind components (v, v(g), v(a) ) to accelerations k/f x (-fk x v, del p/rho, dv/dt). This methodology is applied to numerical simulations of the interaction of a cold fron t with coastal topography, leading to the formation of a ''southerly b uster'' current along Australia's east coast. It is found that while t he front is moving along the south coast mountain chain, the dynamics of the perturbation are similar in character to an orographically trap ped density-current-type perturbation on the background front. Along t he east coast, however, the southerly buster current bears no dynamica l relationship to either an orographically trapped density current or a Kelvin wave, the balance of forces here being dominated by inertial terms.