The Role of Moisture on Barotropic and Baroclinic Annular Mode in a Moist Two-Layer Quasi-Geostrophic Model

Jet stream and large-amplitude Rossby waves are important for regulating weather systems, yet it remains elusive how moisture may affect the shape and variability of jetstream and storm track. A long-standing puzzle is that the timescale of a dry atmosphere's jetstream variability (i.e. Barotropic Annular Mode) is substantially longer than that in the observed atmosphere by a factor of five or more. More recently, it has been reported that the leading mode of Rossby waves variability - a 20-30 day periodic variability (i.e., Baroclinic Annular Mode) can significantly increase with more moisture in a warming climate. This suggests interesting feedback processes may exist in a moist atmosphere.

Using the diabatic heating - wave activity framework and a moist two-layer quasi-geostrophic model that include diabatic heating contributions, we explicitly incorporate and quantify the role of diabatic heating on the development of wave activity, such as that of Rossby wave packets, and the impacts on the barotropic and baroclinic annular mode. With a large ensemble approach and a parameter sweep and overriding approach, we present a local finite-amplitude wave activity budget analysis, including diabatic heating, eddy PV fluxes, and wave activity in a quasi-geostrophic framework. We will demonstrate a conceptual understanding of the role of moisture on Annular Modes and the 20-30 Day Periodic Variability.