This study analyzes the daily temperature observation data from 6 national meteorological stations in Dalian, including the southern area (Dalian, Lvshun, Jinzhou) and northern area (Wafangdian, Pulandian, Zhuanghe) in winter from 1971 to 2021, as well as NCEP/NCAR monthly reanalysis data. Using methods such as linear tendency rate, Mann-Kendall abrupt test, extreme temperature thresholds defined by using percentiles and synthetic analysis, the cold and warm variation trends and unusual characteristics of winter over the past 51 years are analyzed. The atmospheric circulation causes of cold and warm winter in Dalian are further investigated. The results indicate that the winter temperature and monthly temperature have shown an increasing trend over the past 51 years, with a higher warming rate observed in the southern region compared to the north. The most significant rise in minimum temperatures occurs in south of Jinzhou and in Wafangdian, with notably impacting winter warming; Lvshun shows the highest increase in minimum temperatures, while Pulandian and Zhuanghe exhibit the most substantial rises in maximum temperatures; the increase in maximum temperatures has the most significant impact on winter warming, with Pulandian experiencing the highest rise in maximum temperatures. The temperature rise in February contributes the most to winter warming in Dalian. The period from the 1970s to 1980s was predominantly cold, while the 1990s were the warmest, but the warming slowed down in 2006. A significant transition from cold to warm around 1986 in winter mean temperature in Dalian. Over the past 51 years, there has been a significant decrease in the number of low-temperature days, although cold years still fluctuate within relatively warm periods, particularly in January when the highest number of low-temperature days occurs. Extreme cold days have significantly decreased, while extreme warm days have notably increased over the past 51 years, leading to greater interannual fluctuation and instability in climate anomalies. The winter temperature anomalies in Dalian are primarily attributed to anomalies of the Siberian high in surface, the East Asian trough at 500 hPa, Ural mountain high and Okhotsk sea high. When the Siberian high in surface is stronger (weaker) during winter, and the middle-high latitude of Eurasian continent experiences predominantly meridional (zonal) circulation, the Ural mountain high, Okhotsk Sea high and East Asian trough are stronger (weaker) than normal at 500 hPa. This results in a stronger (weaker) winter monsoon in East Asia, it is favorable (unfavorable) for polar cold air moving southward to affect Dalian area, and thereby contributing to cold (warm) winters in Dalian.
