The relative role of wavenumbers one and two during SSWs

In this study, we investigate the dynamical differences between two types of sudden stratospheric warmings (SSWs) and how they affect surface climate. Charlton and Polvani (2007) found statistically significant differences in the zonal wind fields and momentum fluxes between splits (wavenumber 2) and displacements (wavenumber 1) without identifying a clear dynamic reason for the differences. We calculate energy and enstrophy budgets of the stratosphere during SSWs for each wavenumber using MERRA reanalysis data to gain further insight into dynamical differences between the events. Preliminary results suggest that, against common belief, the dominant wavenumber of the energy flux into the stratosphere might not determine the type of the SSW as the wavenumber 1 component is largest at almost all times. Instead, differences in the wave-wave interactions within the stratosphere are responsible for the split of the polar vortex. We further investigate the vertical structure as well as the orientation of the polar vortex during split events to study the importance of barotropic mode excitation as a possible mechanism to explain wavenumber two events. While splits are, on average, more barotropic than displacements we are unable to identify the near constant vortex orientations presented in Matthewman et al. (2008).