Impact of the SST-front on subseasonal predictions of North Atlantic winter circulation using the JMA operational seasonal prediction system

This study evaluates the impact of the mid-latitude oceanic front (MOF) on forecasts using the latest Japan Meteorological Agency seasonal prediction system. We focus on subseasonal predictions of the North Atlantic winter circulation by comparing hindcast experiments with different ocean model resolutions from 1991 to 2020. We find that the higher resolution of sea surface temperatures (SSTs) in the higher resolution model reveals SST warming south of the MOF and strengthening of local lower tropospheric circulation consistent with previous studies. Anomaly correlation coefficients of the atmospheric field are improved by about 0.1-0.2 in the lower-to-upper troposphere near the MOF for the higher ocean resolution. The influence of the MOF on ambient atmospheric fields is independent of El Niño Southern Oscillation conditions in both reanalysis and model. The greater accuracy of some predictions during La Niña years is probably due to the smaller errors of our model during La Niña compared with El Niño.