Three Cold Surges in China during the Winter of 2020/2021 and Their Low-Frequency Features

During the 2020/2021 winter, strong cold air processes frequently emerged in East Asia, resulting in persistently low temperature, strong wind, heavy snow and rainfall, and serious impacts on the people’s production and life in China. Using the daily atmospheric circulation grid data and station temperature data, this paper revealed the low-frequency characteristics of the Siberian high (SH) and its significant impact on the three strong cold surges in China (Dec 13–15, 2020; Dec 29, 2020–Jan 1, 2021; and Jan 6–8, 2021). Both the SH and temperature in eastern China showed significant quasi-biweekly (10–30 d) and 30–60 d low-frequency oscillation (LFO) features, stronger in the earlier than the later winter of 2020/2021. However, the specific LFO features were totally different among the three cold surges. In the first one, the quasi-biweekly oscillation exhibited a significant positive contribution, while the 30–60 d LFO showed a negative contribution. However, the second and third cold surges experienced a combined effect of quasi-biweekly and 30–60 d LFO. The third one was in the strongest period of the above two LFO waves, also leading to the largest cooling range and the widest low-temperature range in China and the strongest SH development. The enhanced quasi-biweekly SH displayed a significant impact on the cold air outbreak and the strong cooling in eastern China by about one pentad (5 days) ahead, with its most significant impact on the cold air outbreak 1–2 days earlier and on the low temperature in eastern China 2–3 days earlier.