Macro- and Microphysical Characteristics of Freezing Rain and Their Impacts on Wire Icing Mechanisms in the Southwestern Mountainous Areas of China
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Graphical Abstract
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Abstract
Based on comprehensive observations of 20 wire icing events during winter from 2019 to 2021, we investigated the characteristics of the icing properties, the atmospheric boundary layer structure, the raindrop size distribution, and their associated effects on the ice accretion mechanism in the mountainous region of Southwest China. The maximum ice weight was positively correlated with the duration of ice accretion in the mountainous area. The duration of precipitation accounted for less than 20% of the icing period in the mountainous area, with solid-phase hydrometeors being predominant. Icing events, dominated by freezing rain (FR) and mixed rain–graupel (more than 70%), were characterized by glaze or high-density mixed icing. The relationship between the melting energy and refreezing energy reflected the distribution characteristics of the proportion of FR under mixed-phase precipitation. The intensity of the warm layer and the dominant precipitation phase significantly affected the variations in the microphysical properties of FR. The melting of large dry snowflakes significantly contributed to FR in the mountainous areas, resulting in smaller generalized intercepts and larger mass-weighted mean diameters in the presence of a stronger warm layer. Under a weaker warm layer, the value of mass-weighted mean diameter was significantly smaller because of the inability of large solid particles to melt. Finally, FR in the mountainous area dominated the ice weight during the rapid ice accumulation period. A numerical simulation of FR icing on wires effectively revealed the evolution of disaster-causing icing in mountainous areas.
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