Influence of Preconditioned Stratospheric State on the Surface Response to Displacement and Split Sudden Stratospheric Warmings

Sudden stratospheric warmings (SSWs) can affect tropospheric weather and climate, while the factors affecting surface response to SSWs are not fully understood. This study shows important effects of preconditioned state on displacement split using ERA5 reanalysis historical simulations from 12 Coupled Model Intercomparison Project 6 (CMIP6) models. Both CMIP6 models show that signals (e.g., positive meridional potential vorticity gradient anomaly in upper stratosphere) promote upward propagation planetary waves by decreasing negative refractive index frequency before SSWs. The modulation strong preconditions causes larger upper-stratospheric anomalies for subsequent prominent barotropic downward impacts Meanwhile, preexisting variability, masking is thus weaker than with weak preconditions.