PhD defence of Valentino Neduhal: Vertical Momentum Fluxes associated with the Rossby, mixed Rossby-gravity, inertia-gravity, and Kelvin waves on the sphere

Abstract:

Generated in the troposphere, vertically propagating Rossby, inertia-gravity (IG), and equatorial Kelvin and mixed Rossby-gravity (MRG) waves transport horizontal momentum into the stratosphere, where they interact with the mean flow. This wave-mean flow coupling is diagnosed through vertical momentum fluxes (VMFs) and is responsible, among other phenomena, for the leading mode of variability in the tropical stratosphere, the Quasi-Biennial Oscillation (QBO). Quantifying VMFs and attributing them to individual wave types is therefore essential for understanding the stratospheric dynamics, particularly processes behind the QBO.

In my thesis I propose a new normal-mode function (NMF) based decomposition method for quantifying VMFs by wave type. Decomposition is based on spatial structure of waves rather than wavenumber-frequency properties, making the separation of VMFs by wave type less ambiguous since different modes can be distinguished even though they coexist at the same wavenumber and frequency.