Dynamics of Rossby Wave Packets in a Quantitative Potential Vorticity–Potential Temperature Framework

AbstractRossby wave packets (RWPs) have been associated with increased atmospheric predictability but also with the growth and propagation of forecast uncertainty. To address the important question of under which conditions RWPs imply high and low predictability, a potential vorticity–potential temperature (PV–θ) framework is introduced to diagnose RWP dynamics. Finite-amplitude RWPs along the midlatitude waveguide are considered and are represented by the synoptic-scale, wavelike undulations of the tropopause. The evolution of RWPs is examined by the amplitude evolution of the individual troughs and ridges. Troughs and ridges are identified as PV anomalies on θ levels intersecting the midlatitude tropopause. By partitioning the PV-tendency equation, individual contributions to the amplitude evolution are identified. A novel aspect is that the important role of the divergent flow and the diabatic PV modification is quantified explicitly. Arguably, prominent upper-tropospheric divergent flow is associated ...

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