West Pacific teleconnection pattern in dynamical seasonal predictions: how is it connected to the Atlantic atmospheric mean bias?

Abstract

This study examines the West Pacific (WP) pattern, one of the primary modes of low-frequency variability during boreal winter, isolated in 11 global climate model seasonal hindcasts. WP mode separation are verified using three metrics: selected mode number, explained variance, and pattern correlation coefficient of the loading vector. When it comes to the pattern reproducibility, it turns out that the WP is tightly linked to the Atlantic jet and stationary wave. To diagnose details of mean biases in terms of WP reproducibility, atmospheric mean fields are composited for two groups: one group replicates well the key feature, a north–south dipole pattern, while the other manifests considerable displacements and magnitude disparities. The group with a lower pattern correspondence to the observation shows noticeable biases with the southeastward-shifted Atlantic dipole of the stationary wave and downstream-expanded Atlantic jet, which is attributed to the increase in meridional gradient of near surface temperature and resultant enhanced local baroclinicity. Magnified jet tail in the eastern North Atlantic (NA) can intensify the barotropic energy conversion thereby the wave energy actively passes toward both east and west. The excessive wave energy over the Arabian Peninsula and the central North Pacific can be favorable for the formation of a ridge, therefore it possibly leads to disorganized WP patterns at both ends of NA basin. A series of analysis suggests the importance of a realistic winter climatology simulation over NA for better WP representation through the interaction between different scales as well as different basins.