Comparative analysis of two extreme rain to snowstorm processes in Liaoning

doi:10.11755/j.issn.1006-7639-2025-03-0450

Abstract

Abstract:

It is of great significance to study the formation mechanisms of extreme rain-to-snow weathers under the background of explosive cyclones for improving winter precipitation forecasting and snow disaster prevention. Based on conventional meteorological observation data and ERA5 reanalysis data, this paper compares and analyzes the causes and characteristics of two extreme rain-to-snowstorm processes in Liaoning Province from November 6 to 9, 2021 (Process I), and from November 5 to 7, 2023 (Process II), from the perspectives of influencing systems, water vapor conditions, dynamic mechanisms, and thermal effects. The results show that the combined influence of an upper-level cold vortex and a surface explosive cyclone is the key factor in the formation and development of both events. The coupling of upper and lower level jet streams provides strong dynamic support for extreme precipitation, with heavy rain and snow mainly occurring on the northern side of the surface cyclone. Conditional symmetric instability is identified as the primary dynamic mechanism. Well-developed frontal zones in the lower troposphere, together with the alignment of water vapor convergence zones and fronts, are conducive to the occurrence of heavy precipitation. The phase differences among low-level uplift motion, frontal zones, and water vapor convergence zones are the main reasons for the differences in precipitation center intensity between the two events. The combined effects of dynamic and moisture conditions, along with thermal structures, determine the phase of precipitation. Specifically, the intensity of low-level cold fronts and the timing of cold air intrusion significantly influence the phase transition of precipitation and the spatial distribution of rain and snow.

Key words: snowstorm, explosive cyclone, rain turning into snow, frontogenesis

摘要：

研究爆发性气旋背景下极端雨雪天气的形成机制，对冬季降水预测与雪灾防御具有重要意义。本文基于常规气象观测资料和ERA5再分析资料，从影响系统、水汽条件、动力机制及热力作用等方面，对比分析了2021年11月6—9日（简称“过程Ⅰ”）与2023年11月5—7日（简称“过程Ⅱ”）辽宁地区两次极端雨转暴雪过程的成因与特征。结果表明，高空冷涡与地面爆发性气旋的共同作用是两次过程形成和发展的关键，高低空急流耦合为极端雨雪天气提供了强动力支撑，强降水主要分布在地面气旋北侧；条件性对称不稳定是两次极端雨雪天气的主要动力机制，低层锋区明显，水汽辐合区与锋区配合，有利于强降水形成。低层抬升运动、锋区与水汽辐合区的相位差异，是导致两次过程降水中心强度差异的主要原因。动力与水汽条件的共同作用以及温度条件共同决定降水相态，其中，低层冷锋强度及冷空气入侵时间影响降水相态的转变及雨雪分布。

关键词: 暴雪, 爆发性气旋, 雨转雪, 锋生

CLC Number:

P458.1+21.1

XU Qingzhe, XU Shuang, JIN Wei, TIAN Lu, GAO Qingyuan, TAN Zhenghua, SUN Anni. Comparative analysis of two extreme rain to snowstorm processes in Liaoning[J]. Journal of Arid Meteorology, 2025, 43(3): 450-459.

徐庆喆, 徐爽, 金巍, 田璐, 高清源, 谭政华, 孙安妮. 辽宁两次极端雨转暴雪过程对比分析[J]. 干旱气象, 2025, 43(3): 450-459.

Figures/Tables 6

Fig.1 Cumulative precipitation (a, b; Unit: mm) and snow depth (c, d; Unit: cm) during the process I (a, c) and the process II (b, d)

Fig.2 The 300 hPa positive vorticity advection (the color shaded, Unit: 10-9 s-2), 500 hPa height field (solid lines, Unit: dagpm) and the center position of the surface cyclone (black dots) (a, d), the 300 hPa jet stream (isolines, wind speed greater than or equal to 30 m?s-1), 850 hPa jet stream (wind vector, wind speed greater than or equal to 12 m?s-1), 850 hPa temperature advection (the color shaded, Unit: 10-5 K?s-1) (b, e) at 20:00 on 7 November 2021 (a, b) and 5 November 2023 (d, e) and cyclone center pressure values (black font, Unit: hPa) and movement paths (black dots) during the process I (c) and the process II (f)

Fig.3 Specific humidity at 850 hPa (isolines, Unit: g?kg-1), water vapor flux (arrows, Unit: g?cm-1?hPa-1?s-1), and water vapor flux divergence (the color shaded, Unit: 10-5 g?cm-2?hPa-1?s-1) at 20:00 on November 7, 2021 (a) and November 5, 2023 (b)

Fig.4 The MPV1 (isolines) and MPV2 (the color shaded) (a, b) at 850 hPa and their sections along 41°N (c, d) at 20:00 on November 7, 2021 (a, c) and November 5, 2023 (b, d) (Unit: PVU)

Fig.5 The 925 hPa frontogenesis function (the color shaded, Unit: 10-9 K?m-1?s-1), pseudo equivalent potential temperature (isolines, Unit: K), and wind field (wind vectors, Unit: m·s-1) (a, b) and their sections along 41°N (c, d) at 20:00 on November 7, 2021 (a, c) and 04:00 on November 6, 2023 (b, d)

Fig.6 The time-height sections of specific humidity (the color shaded, Unit: g?kg-1), temperature (isolines, Unit: ℃), synthesis of v and -100 ω (arrows) over Anshan Station during the processⅠ (a) and the process Ⅱ (b)

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