The atmospheric responses to the intensity variability of subtropical front in the wintertime North Pacific

The atmospheric responses to the intensity variability of subtropical front zone (STFZ) in the wintertime North Pacific are investigated in both observation and sensitivity experiments using weather research and forecasting model (version 3.4.1). The STFZ is artificially intensified by applying a sea surface temperature (SST) anomaly within STFZ in sensitivity experiments. Results from observation and experiments indicate that the enhanced STFZ strengthens the meridional temperature gradient and thus the atmospheric baroclinicity, inducing more active transient eddies. The stronger transient eddy vorticity forcing accelerates the polar front jet with equivalent barotropic structure. The results of sensitivity experiments suggest the atmospheric responses are linear and symmetrical to the variation of STFZ intensity within its natural variability. However, the anomalies of atmospheric upstream condition and large-scale SST also have great impacts on the midlatitude atmosphere over North Pacific, in comparison with the effect of STFZ intensity variability. Therefore, It suggests carefully verification of the atmospheric responses found in the observations and numerical experiments.