Coupled Planetary Wave Dynamics in the Polar Stratosphere Analyzed with Potential Enstrophy and Eddy Energy Budgets

Abstract Anomalies in the stratospheric polar vortex (SPV), such as sudden stratospheric warming (SSW) events, significantly impact surface weather patterns. While the influence of SSWs on the troposphere is robust on average, individual events exhibit large variability, partly due to the substantial difference in dynamics and SPV evolution across events. Understanding the physical processes driving SSWs is therefore important. In this study, we investigate SPV dynamics, focusing on nonlinear coupling between planetary wave modes. We use potential enstrophy and eddy total energy budget analyses to quantify the contributions of different physical processes to SPV evolution. These budget analysis frameworks are unique in being able to study the contribution of nonlinear wave–wave interactions to the dynamical evolution of the SPV. When applying this framework to both an idealized simulation and reanalysis data of the 2003 SSW, we find that nonlinear wave–wave interactions can play a crucial role during SSWs. In the idealized simulation, wave-2 structures emerge in the stratosphere without a prescribed wave-2 source, attributed to the nonlinear transfer of enstrophy and energy from wave 1 to wave 2. In the 2003 case study, interactions between wave 1 and wave 2 contribute to a displacement-to-split transition. We also find indications of quasilinear coupling and upscale enstrophy transfer from wave 2 to wave 1 during this period. The use of the enstrophy budget analyses highlights the significant impact of nonlinear wave–wave interactions in SPV transitions. These complex interactions contribute to the uniqueness of each SSW event and may help explain the variability observed across different SSWs.