Abstract:
Based on daily minimum temperature observations data and NCEP/NCAR atmospheric circulation data from 1971 to 2020, this study analyzes the interannual variation and circulation characteristics of winter extreme low temperatures in Hubei Province using the percentile threshold method, linear analysis, and synthetic analysis. The characteristics of extreme low-temperature freezing rain circulation in Hubei in February 2024 were further studied. The findings indicate that within the past 50 years, Hubei Province experienced 460 instances of extreme low temperatures, exhibiting a marked decline in frequency. The frequency of extreme low temperatures at the sub-seasonal scale in winter has also decreased month by month, with the most rapid decrease occurring in December at a rate of −1.37 (10 a)
−1. The intensity of extreme low-temperature events in Hubei exhibited a decrease from southwest to northeast, with a general tendency to weaken; however, these events have increased in frequency over the past decade. The 500-hPa mid-high latitude circulation anomaly is high in the Northern Hemisphere and low in the Southern Hemisphere. Hubei Province is situated within the positive vorticity advection in front of the trough. The northwestern wind at 850 hPa directs cold advection toward the south, thereby fostering the potential for extreme low temperatures in Hubei during December. The increase of meridional circulation in the middle and high latitudes, in conjunction with a robust cold surge, fosters the southward movement of cold air. This results in the entry of low-level cold air into Hubei via an easterly trajectory, a phenomenon that suggests the likelihood of extreme low-temperature events in Hubei during January. The height anomaly field configuration, characterized by “high in the west and low in the east” in Eurasia, is conducive to the strengthening of the blocking situation over the Ural Mountains. The continental high pressure and the Okhotsk Sea high pressure systems are in relative opposition. The state of Hubei Province is susceptible to extreme low temperatures in February, primarily due to the combined influence of northwest and east return cold air. The weakening of the blocking high at 500 hPa results in the southward movement of the cold air. The southern branch trough intersects with the abnormally strong western Pacific subtropical high near 110°E. The ongoing progression of the low-level southwest warm and humid airflow along the frontal zone has been observed. The surface pressure field exhibited high values in the eastern region and low values in the western region. Consequently, the cold air mass propagated eastward, leading to the extreme low temperature rain and snow freezing events that occurred in Hubei in February 2024.