Seasonal variation characteristics of the subarctic front in North Pacific and its relationship with the mid-latitude atmosphere

Statistical analysis and dynamical diagnosis of high-resolution oceanic and atmospheric reanalysis data are conducted to reveal the characteristics and causes of seasonal intensity variation of the Subarctic Oceanic Frontal Zone (SAFZ) in the North Pacific, and elucidate the characteristics of mid-latitude atmospheric circulation anomalies associated with the SAFZ seasonal variation and corresponding dynamic processes. The results indicate that the SAFZ is strong in autumn, winter and spring, and relatively weak in summer. The meridional advection process of Sea Surface Temperature (SST) is the dominant factor that maintains SAFZ's intensity in autumn, winter and spring, while the net heat flux exchange process at the sea-air interface plays a decisive role in the weakening of SAFZ's intensity in summer. Accompanied with the SAFZ's intensity variability in different seasons, the boundary layer turbulent heat flux anomalies develop, and the diabatic heating anomalies lead to anomalies of low-level atmospheric meridional temperature gradient and atmospheric baroclinicity above the SAFZ, and then lead to the anomalies of atmospheric transient eddy activities. Due to the dominant influence of anomalous atmospheric transient eddy vorticity forcing, equivalent barotropic structure anomalies of atmospheric geopotential height field and wind field occur over the regions of mid-latitude North Pacific and eastern and northeastern China, and the corresponding anomalous field of atmospheric circulation exhibiting seasonal differences.