This work focuses on investigating the internal dynamics of different types of sudden stratospheric warmings (SSWs) through an explicit assessment of nonlinear interactions among planetary waves and between the waves and the zonal mean flow, as well as through the analysis of wave activity. The wave dynamics were examined using an approach based on the variability of perturbed potential enstrophy. This method enables a detailed examination of wave–mean flow interactions and allows quantification of the relative contributions of potential enstrophy flux divergence and advection to wave activity changes. Based on existing climatological classifications of SSWs observed in recent decades and on hydrometeorological fields from the MERRA-2 reanalysis dataset, events associated with either displacement or splitting of the stratospheric polar vortex were identified and categorized accordingly. Ultimately, five SSW cases were selected for each category. For every selected event, the individual terms of the perturbed potential enstrophy balance equation were calculated for stationary planetary waves with zonal wave numbers 1 and 2 (SPW1 and SPW2). The analysis of multiple SSW cases of different types revealed that nonlinear wave–wave interactions—represented by third-order terms that are commonly neglected—provide a substantial contribution to wave activity changes prior to and during vortex-displacement SSWs. The strongest interaction between SPW1 and the mean flow occurs approximately 1–3 weeks before vortex-splitting SSWs, whereas SPW2–mean flow interaction peaks during the week preceding the event. During the SSW and in the five days leading up to it, SPW2 wave activity becomes comparable to or exceeds that of SPW1. For vortex-displacement SSWs, the exchange terms describing interactions of SPW1 and SPW2 with the mean flow intensify 1–3 weeks prior to the onset. Further statistical analysis of these results may contribute to identifying potential precursors of SSW formation.
This study is supported by Russian Science Foundation: grant #25-47-00122.
 

nonlinear wave,SSW,Planetary waves