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

Abstract. Quasi-stationary waves (QSWs), atmospheric Rossby waves with near constant phase that persist on subseasonal timescales, are not distributed homogeneously across the globe, even at a given latitude. The climatological 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, eight simulations were conducted using CAM6 with prescribed SSTs. These simulations range from realistic, semi-realistic (with some stationary forcings matching reality) to fully idealized (with idealized forcings added in aquaplanet simulations). The control simulation was validated against ERA5 reanalysis data. Stationary forcings tend to extend the duration of QSWs and move the zonal-mean amplitude of QSW northward in the midlatitudes. The stationary forcings also strongly impact the zonal asymmetric distribution of QSWs. 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. In some cases, QSW strength is also associated with the strength of the stationary waves. When the timescale of the QSWs is changed (e.g. from 15–30 days to >30 days), 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.