Cai et al. (2026) Interannual variability of freezing rain over Southern China and its linkage with Eurasian snow cover

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-01-13
• Authors: Zelin Cai, Wen Chen, Xiadong An, Ji Ma
• DOI: 10.1007/s00382-025-08018-7

Research Groups

• Yunnan International Joint Laboratory of Monsoon and Climate Extreme Disasters, Department of Atmospheric Sciences, Yunnan University, Kunming 650500, China
• Yunnan Key Laboratory of Meteorological Disasters and Climate Resources in the Greater Mekong Subregion, Kunming 650500, China
• Southwest United Graduate School, Yunnan University, Kunming 650500, China

Short Summary

This study investigates the interannual variability of freezing rain (FRZR) intensity over southern China and its connection to Eurasian snow cover. It reveals that anomalous November–December snow cover extent over Eastern Europe significantly influences January–February FRZR variability in southern China through troposphere-stratosphere interactions, strengthening the Ural blocking high.

Objective

• To characterize the interannual variations of freezing rain (FRZR) intensity over southern China.
• To determine if there is a connection between preceding snow cover extent (SCE) anomalies over Eurasia and FRZR over southern China.

Study Configuration

• Spatial Scale: Southern China (25°‒35°N, 100°‒120°E), Eastern Europe (45°‒55°N, 30°‒50°E), and broader Eurasia for atmospheric circulation and snow cover.
• Temporal Scale: 1980‒2015 for cold months (November–March), with a specific focus on January–February for FRZR and November–December for snow cover extent. Hourly data for FRZR diagnosis, monthly mean for atmospheric circulation analysis.

Methodology and Data

• Models used:
  • Ramer scheme (Ramer 1993) for diagnosing freezing rain.
  • Stationary Wave Activity Flux (WAF) (Takaya and Nakamura 2001) for horizontal propagation of Rossby waves.
  • Rossby wave source derived from the barotropic vorticity equation (Sardeshmukh and Hoskins 1988; Wang et al. 2019).
  • Vertical component of the Plumb flux (Plumb 1985) for vertical wave propagation.
• Data sources:
  • 5th generation of the European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) dataset (Hersbach et al. 2020): Hourly data (0.5° x 0.5° horizontal resolution, 37 vertical levels) for FRZR diagnosis; monthly mean data (averaged from 6-hourly data) for atmospheric circulation analysis.
  • National Snow and Ice Data Center (Brodzik and Armstrong 2013): Original weekly Northern Hemisphere Snow Cover Extent (SCE) data (25 km spatial resolution), converted to monthly mean on a 1° x 1° grid.

Main Results

• Freezing rain (FRZR) is most severe during January–February (JF) over southern China, accounting for approximately 87.1% of the total temporal variance in cold months (November–March).
• Stronger JF FRZR is significantly linked to an intensified Siberian High (correlation coefficient of 0.47, p < 0.01) and a stronger northern component of the East Asian winter monsoon (correlation coefficient of 0.59, p < 0.01).
• These atmospheric circulation anomalies are driven by a strengthened Ural blocking high (UB).
• The strengthening of the UB is attributed to anomalous snow cover extent (SCE) over Eastern Europe during November–December (ND).
• Positive ND SCE anomalies over Eastern Europe alter vertically propagating Plumb fluxes, which manipulate the phase of stratospheric zonal wavenumber 2 through wave-mean flow interactions.
• The resulting positive geopotential height anomalies over the Ural region propagate downward into the troposphere, thereby strengthening the UB in JF.
• Anomalous ND SCE over Eastern Europe serves as an important indicator for JF FRZR variability over southern China, with a significant correlation coefficient of 0.65, explaining 42.8% of the total temporal variance of JF FRZR.

Contributions

• Provides the first comprehensive analysis of the interannual variability of FRZR intensity (accumulated precipitation) over southern China, distinguishing it from previous studies focusing on frequency.
• Identifies the Ural blocking high as a crucial circulation pattern driving the interannual variability of FRZR intensity over southern China.
• Establishes a novel dynamical connection between preceding November–December snow cover extent anomalies over Eastern Europe and subsequent January–February FRZR intensity over southern China.
• Elucidates the physical mechanism underlying this connection, involving troposphere-stratosphere interaction, modulation of planetary wave activity (specifically zonal wavenumber 2), and the downward propagation of geopotential height anomalies.
• Suggests the potential utility of early-season Eurasian snow cover variability as a predictive indicator for severe FRZR events in southern China.

Funding

• National Natural Science Foundation of China (Grant Nos. W2412059 and 42305061)
• Yunnan Provincial Science and Technology Department (Grant Nos. 202403AP140009 and 202505AB350001)
• Yunnan Southwest United Graduate School Science and Technology Special Project (Grant No. 202302AP370003)

Citation

@article{Cai2026Interannual,
  author = {Cai, Zelin and Chen, Wen and An, Xiadong and Ma, Ji},
  title = {Interannual variability of freezing rain over Southern China and its linkage with Eurasian snow cover},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-025-08018-7},
  url = {https://doi.org/10.1007/s00382-025-08018-7}
}