Abstract

Baroclinic waves are important due to their role in energy, momentum, and moisture transport, and their impacts on surface weather in the mid-latitudes. Life cycles of baroclinic waves have been well studied with numerical spectral or non-spectral models and dynamical diagnostic methods (e.g., energetics and PV diagnostics). However, the relative roles of the radiation of Rossby waves (i.e., downstream development), the momentum exchange between waves and the mean flow (barotropic process), low-level eddy heat flux (baroclinic process), and diabatic heating have not been fully explored, especially in terms of the budget of the nonlinear conservative wave activity, e.g., local finite-amplitude wave activity (LWA).

In this dissertation, we investigated the life cycles of baroclinic waves with the diagnostic method of LWA in reanalysis data and dry and moist two-layer QG models. We found that troughs in the Southern Hemisphere may grow by downstream development, convergence of nonlinear advective LWA flux due to eddies, and diabatic heating and decay by downstream development and divergence of nonlinear advective LWA flux. Anticyclonic advective LWA flux due to the reference flow or eddies transfers LWA into or out of the trough. The differential heating with height is crucial for the non-conservative generation of LWA. In the dry two-layer QG model, convergence (divergence) of radiative LWA flux is the dominant term for the growth (decay) of troughs of all kinds of wave packets (i.e., growing, propagating, and decaying) in the simulation with the weakest vertical shear (i.e., 15 m/s at radiative equilibrium). The barotropic process plays a more and more important role in the life cycle of troughs as the vertical shear increases gradually, though this result depends on the type of wave packet. In the moist two-layer QG model, latent heating can generate negative PV in the upper layer and thus lead to the growth of ridges; however, it is unlikely a source for the growth of troughs due to the absence of vertical structure in the heating. For the mean LWA budget, latent heating is an evident source of LWA for all simulations; however, the total generation of LWA by baroclinic process and latent heating decreases as the latent heating parameter increases, and hence eddies are weaker compared to the dry model forced with the same radiative forcing.

We further applied the formalism of LWA to water vapor (LWA-V), aiming to interpret the moisture displacement in the framework of nonlinear wave activity. The ability of LWA-V to trace down moisture source in a far region is attested by an atmospheric river (AR) event. The LWA-V budget analysis not only reveals that meridional moisture flux is the dominant term for the northward intrusion of moisture but also contains the measure of wave amplitude (i.e., the meridional displacement of moisture contours from the equivalent latitude) by design.

Year

12-2023

Document Type

Dissertation

Keywords

barolinic waves, local finite-amplitude wave activity

Degree Name

Doctor of Philosophy (PhD)

Advisor

Edmund K. M. Chang

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