Investigating the local atmospheric response to a 5 realistic shift in the Oyashio sea surface 6 temperature front 7 8 9

22 23 The local atmospheric response to a realistic shift of the Oyashio Extension SST front in 24 the western North Pacific is analyzed using a high-resolution (0.25°, HR) version of the 25 global Community Atmosphere Model version 5 (CAM5). A northward shift in the SST 26 front causes an atmospheric response consisting of a weak surface wind anomaly but a 27 strong vertical circulation extending throughout the troposphere. In the lower 28 troposphere, most of the SST anomaly induced diabatic heating ( ) Q is balanced by 29 poleward transient eddy heat and moisture fluxes. Collectively, this response differs from 30 the circulation suggested by linear dynamics, where extratropical SST forcing produces 31 shallow anomalous heating balanced by strong equatorward cold air advection driven by 32 an anomalous, stationary surface low to the east. This latter response, however, is 33 obtained by repeating the same experiment except using a relatively low-resolution (1°, 34 LR) version of CAM5. Comparison to observations suggests that the HR response is 35 closer to nature than the LR response. Strikingly, HR and LR experiments have almost 36 identical vertical profiles of Q . However, diagnosis of the diabatic quasi-geostrophic ω 37 budget reveals that HR has a substantially stronger Q response, which together with 38 upper level mean differential thermal advection balances stronger vertical motion. The 39 results herein suggest that changes in transient eddy heat and moisture fluxes are critical 40 to the overall local atmospheric response to Oyashio front anomalies, which may 41 consequently yield a stronger downstream response. These changes may require high 42 resolution to be fully reproduced, warranting further experiments of this type with other 43 high resolution atmosphere-only and fully coupled GCMs. 44