The Role of Topography, Land and Sea Surface Temperatures on Quasi-Stationary Waves in Northern Hemisphere Winter: Insights from CAM6 Simulations

The climatological quasi-stationary waves (QSW) amplitude has a distinct spatial pattern, with clear zonal asymmetries, particularly in the Northern Hemisphere; those asymmetries must be impacted by stationary forcings such as land, topography, and sea surface temperatures (SSTs). To investigate the effects of stationary forcings on QSW characteristics, including their duration and spatial distribution, we conducted eight CAM6 simulations with prescribed SSTs, spanning realistic, semi-realistic, and fully idealized configurations. Stationary forcings tend to extend the duration of QSWs and strongly impact their zonal asymmetric distribution. QSWs are primarily influenced by both the local stationary wavenumber Ks, which depends on jet speed and its second-order meridional gradient, and by the strength of transient eddies. However, the covariation between transient eddies and QSWs varies across different types of stationary forcings. For example, in experiment pairs showing the impact of zonal SST patterns, the correlation between changes in QSW strength and transient eddies is stronger, while the correlation with stationary wavenumber is of similar magnitude across all experiments. In some cases, QSW strength is also associated with the strength of the stationary waves. When the timescale of the QSWs is changed, the relative contributions from different mechanisms changes, but stationary wavenumber Ks and transient eddies strength are important in all time scales for experiments with realistic land. This work suggests that transient Rossby waves with given wavenumbers can become stationary under background conditions with the corresponding stationary wavenumbers.