A survey of unbalanced flow diagnostics and their application

This paper presents an extensive survey of the most commonly used tools for diagnosing unbalanced flow in the atmosphere, namely the Lagrangian Rossby number, Psi vector, divergence equation, nonlinear balance equation, generalized omega-equation, and departure from fields obtained by potential vorticity (PV) inversion. The basic theory, assumptions as well as implementation and limitations for each of the tools are all discussed. These tools are applied to high-resolution mesoscale model data to assess the role of unbalanced dynamics in the generation of a mesoscale gravity wave event over the East Cost of the United States. Comparison of these tools in this case study shows that these various methods agree to a large extent with each other though they differ in details.