Quasi‐Stationary Atmospheric Rivers as the Primary Driver of Rossby Wave Activity in the Global Subtropics

Abstract Hovmöller plots of upper‐tropospheric local (Rossby) wave activity (LWA) show that the subtropics of the North Pacific/Atlantic basins are relatively wave‐free in the upstream and wavier in the downstream of quasi‐stationary atmospheric rivers (QSARs). This study investigates the physical mechanism behind the pronounced enhancement of LWA downstream of QSARs using the LWA budget analysis. The analysis reveals that diabatic effects of latent heating within QSARs play a greater role as a wave source than the dynamical forcing (Eliassen‐Palm flux convergence) in the subtropics. The LWA generated by QSARs is transported downstream by the jet and the flux converges downstream of QSARs, leading to the observed enhancement. Removing the QSAR‐induced diabatic sources from the budget leads to a substantial reduction in LWA downstream of QSARs and a ∼70 percent reduction globally. This highlights the importance of QSARs as a leading wave maker in the subtropical upper troposphere.