Does the jet stream generate gravity waves?

Numerical simulations of the baroclinic lifecycle of the jet stream show gravity wave-like structures in the upper troposphere. Here, we employ a novel method to decompose any flow into slow (geostrophically) balanced part and fast wave part to these structures. The method originates from the optimal potential vorticity balance method by Viudez and Dritschel (2004) but is modified to be applied to general flow. It was compared earlier to the asymptotic decomposition method by Warn et al (1995) and was shown to perform equally well. Here, we apply the novel method to an idealised  numerical model of the baroclinic lifecycle of the jet stream and show how much of the gravity wave-like structures in the upper troposphere are part of the balanced part of the flow, and how much of it are really gravity waves.