The main mode of winter atmospheric circulation affected by sea surface temperature anomalies in the North Pacific during autumn and its thermal and dynamic characteristics

To explore the impact of sea surface temperature in North Pacific on extreme weather in China, based on daily and monthly NCEP/NCAR reanalysis data from 1977 to 2023, through Maximum Covariance Analysis (MCA), regression, and correlation analysis after removing the influence of ENSO,the thermal and dynamic diagnostic method combining ocean-atmosphere coupling and weather transient eddies were adopted to study the role and possible mechanism of surface sea temperature anomaly (SSTA) in North Pacific affecting atmospheric circulation anomalies. The results indicate that the early autumn (ASO) North Pacific SSTA significantly affects the early winter (OND) atmospheric circulation (with the corresponding spatial distribution pattern as the main mode), the main mode of early autumn (ASO) North Pacific SSTA has a clear "west negative east positive dipole" distribution characteristic, and the corresponding early winter (OND) atmospheric circulation anomaly shows a "PNA like" distribution;the positive and negative abnormal circulation centers are northward and eastward compared to the SST anomaly center, and their vertical distribution is a fairly positive pressure structure. The interaction between the ocean-atmosphere in the North Pacific during autumn and winter is coupled through diabatic heating and transient forcing; in late summer, the anomalous wave train of the "East West Dipole" type atmospheric circulation deepens the low-level Aleutian low pressure circulation, strengthens the cold (warm) advection, and releases (obtains) turbulent heat flux and diabatic heating (cooling);correspondingly,the "East West Dipole" SSTA in early autumn strengthened, the southern sea front of negative SSTA area strengthened, the atmospheric low-level oblique pressure activity increased, and the upper transient activity increased; diabatic heating anomalies are transmitted upwards with the seasons and generate oblique pressure reactions,transient activity forces the formation of negative (positive) changes of high and (anti) cyclonic circulation to the north (south) of the upper level jet stream, with stronger upper levels. The upper transient activity forcing increase with the seasons and move southward,and under its combined effect with diabatic heating anomalies, the anomalous wave train of atmospheric circulation changes from an "east-west dipole" to a "PNA like" mode distribution, the upper and lower structures and intensities undergo a transition process of "equivalent positive pressure-weak oblique pressure-equivalent positive pressure" and "strong-slightly weakened-significantly strengthened", respectively; on the contrary, anomalous atmospheric circulation forces SSTA to transform from an "east-west dipole" to a "horseshoe shaped" distribution, undergoing a "strong-weak-weak" transition in intensity from early autumn (ASO) to early winter (OND). The North Pacific SSTA in early autumn (ASO) causes a significant increase in atmospheric circulation anomalies in early winter (OND) through sustained effects and transient activity forcing, achieving statistical significance. The atmospheric circulation anomaly corresponding to the "PNA like mode" in early winter (OND) is a significant wave train propagating downstream to North America, which contributes to the formation of the intrinsic variability PNA mode in the winter atmosphere. When the atmospheric circulation anomaly in early winter (OND) is in the same (opposite) phase as the winter PNA mode, the PNA mode strengthens (weakens), and the changes in the strength of the PNA mode have certain indicative significance for predicting extreme weather in China.