Teleconnection study on PNA pattern based on OpenIFS model simulations

This study examined the formation mechanisms of the Pacific-North American (PNA) pattern based on OpenIFS model simulations and reanalysis data. OpenIFS model simulations were conducted with different SST forcings. The 35-year (1982-2016) observed SST from OISSTv2 was used to driver AMIP experiment, and the 35-year mean climatological SST was used for CLIM experiment. Both experiments successfully reproduce the PNA's spatial structure during winter time. The analysis reveals dual forcing mechanisms: tropical Pacific SST anomalies and Northern Hemisphere zonal winds jointly drive PNA variability in AMIP experiment, while results from CLIM experiment demonstrates that midlatitude zonal winds alone can excite PNA-like patterns through transient eddy activity, independent of SST forcing. The PNA exhibits distinct vertical coupling characteristics—barotropic in AMIP versus baroclinic in CLIM—and stronger teleconnections with AO/NAO in models than in reanalysis. These findings highlight the coexistence of externally forced and intrinsic atmospheric dynamics in PNA formation, advancing mechanistic understanding for improved climate predictability.