Dynamic Synoptic Eddy Feedbacks Contributing to Maintenance and Propagation of Intraseasonal NAO

Abstract

This study examines the dynamic feedbacks generated from synoptic eddies that contribute to maintenance and propagation of the intraseasonal North Atlantic Oscillation (ISNAO) which has significant 20−60-day variability and features clearly westward and slightly northward propagations. The ISNAO-related eddy-vorticity fluxes and induced forcing contribute the positive in-phase feedback and upstream feedback to ISNAO. Due to the accumulated shearing effect of ISNAO zonal wind anomalies, synoptic eddy structures can be statistically changed in a zonally titling way, which forms quadrupole patterns of anomalous eddy structure and further generates meridional eddy-vorticity fluxes by multiplying basic eddy velocity by anomalous eddy vorticity. These meridional fluxes diverge from the ISNAO pattern and the area in its west and mainly induce the eddy-vorticity forcing pattern in phase with and upstream of ISNAO, where the in-phase feedback maintains ISNAO and the upstream feedback with a northward shift contributes to the westward and northward propagations of ISNAO.