Investigating the atmospheric response to a realistic shift in the Oyashio sea surface temperature front

The local atmospheric response to a realistic shift of the Oyashio Extension SST front in the western North Pacific is analyzed using a high-resolution (0.25°, HR) version of the global Community Atmosphere Model version 5 (CAM5). A northward shift in the SST front causes an atmospheric response consisting of a weak surface wind anomaly but a strong vertical circulation extending throughout the troposphere. In the lower troposphere, most of the SST anomaly induced diabatic heating is balanced by poleward transient eddy heat and moisture fluxes. Collectively, this response differs from the circulation suggested by linear dynamics, where extratropical SST forcing produces shallow anomalous heating balanced by strong equatorward cold air advection driven by an anomalous, stationary mean surface low forming to the east. This latter response, however, is obtained, by repeating the same experiment except using a relatively low-resolution (1°, LR) version of CAM5. Comparison to observations suggests that the HR response is closer to nature than the LR response. Strikingly, HR and LR experiments have almost identical vertical profiles of diabatic heating ̇. The results herein suggest that changes in transient eddy heat and moisture fluxes are critical to the overall local atmospheric response to Oyashio front anomalies, which consequently yield a stronger downstream response, with a northward shift in the storm track as it enters North America. These changes may require high resolution to be fully reproduced, warranting further experiments of this type with other high resolution atmosphere-only and fully coupled GCMs.