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 temperature (SST). 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 reproduces the relevant fields well compared to ERA5 reanalysis data. 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. 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 to >30 d), the relative contributions from different mechanisms changes, but stationary wavenumber Ks and transient eddy strength are important in all time scales for experiments with realistic land.