Balanced dynamics and inertia-gravity wave generation in upper-tropospheric jets

The generation of inertia-gravity waves (IGWs) in association with jets and fronts in the upper troposphere remains a complex and elusive problem. There is ample evidence from observational and numerical studies that upper-tropospheric jets and fronts are significant source regions of IGWs, but many questions remain concerning the fundamental dynamical mechanisms involved in this generation, and the dependence of these mechanisms on the structure and evolution of the jet-front systems. The difficulty associated with this problem is closely related to the difficulty of accurately defining the concept of balance, particularly for situations in which the Rossby number is large, and of describing the nature of the breakdown of balance that leads to IGW generation.

In an effort to obtain basic insight into this problem, idealized numerical simulations of baroclinic-wave life cycles using two-layer and multi-level primitive equation (PE) models are examined for evidence of the generation of IGWs by baroclinic jets. In simulations of the multi-level PE model, IGWs are observed throughout the stratosphere; several simulations with different basic-state baroclinic jets will be presented to assess the dependence of IGW generation on the parameters of the jet and on the nature of the evolution of the baroclinic-wave life cycles. Simulations using the two-layer model exhibit many of the same characteristics as those of the multi-level model, and are employed in an effort to identify the relevant parameter regimes and flow signatures for which balance may be expected to break down.