Occurrence of Warm Freezing Rain: Observation and Modeling Study

Journal Article · 09 February 2022 · Journal of Geophysical Research. Atmospheres

DOI: https://doi.org/10.1029/2021jd036242 · OSTI ID:1846017

Lu, Zhengqi  ^[1]; Han, Yongxiang  ^[1]; Liu, Yangang  ^[2]

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1. Nanjing University of Information Science and Technology (China)
2. Brookhaven National Lab. (BNL), Upton, NY (United States)

Freezing rain has been normally considered to be composed of supercooled raindrops when the 2 m air temperature (hereafter T_as) is below freezing. However, according to a statistical survey of freezing rain observations in China from 2000 to 2019, we find that there were 656 events that occurred at T_as greater than 0°C (hereafter warm freezing rain and denoted by WFR), which account for 7% of the total freezing rain observations. Additionally, nearly 3% (266 observations) of freezing rain events occurred when the near-surface wet-bulb temperature was greater than 0°C. The modeling and sensitivity experiments on the nonequilibrium raindrop temperature (hereafter T_r) how that the temperature difference between raindrops and the atmosphere is the main cause of WFR. The magnitudes of the Δ T_ar (difference between raindrop temperature T _r and air temperature T_a) and Δ T_ur (difference between T_r and wet-bulb temperature T _w) are determined by the raindrop diameter D, temperature lapse rate $$\Gamma$$, and relative humidity RH. Increases of D and $$\Gamma$$, and a decrease of RH enhance Δ T_ar and Δ T_ur and thus the occurrence of WFR. Further simulations of 4 idealized and 370 real sounding profiles reveal that either the T_a or the T_w cannot properly distinguish the WFR events. When considering the temperature difference between raindrops and the atmosphere, the WFR can form by the “melting of solid hydrometeors” or “supercooled warm rain process.” This study can also deepen our understanding of the conditions of WFR and freezing rain formation at different altitudes.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: National Natural Science Foundation of China (NSFC); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC0012704
• OSTI ID: 1846017
• Report Number(s): BNL--222752-2022-JAAM
• Journal Information: Journal of Geophysical Research. Atmospheres, Journal Name: Journal of Geophysical Research. Atmospheres Journal Issue: 5 Vol. 127; ISSN 2169-897X
• Publisher: American Geophysical UnionCopyright Statement
• Country of Publication: United States
• Language: English