ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Analysis on the Formation Mechanism of a Serious Disaster Process Caused by Wire Icing in Yuanqu, Shanxi Province
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Abstract:
In mid-December 2023, Shanxi Province experienced a weather event of low temperatures, rain, snow, and icing. On 13 December, wire icing occurred in Yuanqu County, located in southern Shanxi, and significantly disrupted people"s lives and production activities. Conventional meteorological observations, Doppler weather radar data and the ERA5 reanalysis datasets are used to investigate the formation mechanism of this severe disaster-causing wire icing event on 13 December in 2023. The results show that: this wire icing event in Yuanqu belonging to the form of mixed rime and glaze is caused by the combined effects of short-duration freezing rain in the early stage and prolonged freezing fog in the subsequent period. Freezing fog plays a more significant role than freezing rain. In the north frontal zone at 500 hPa, the horizontal trough in front of the high pressure ridge near the Ural Mountains and a deep cold vortex near the Sea of Okhotsk both remain stable and move slowly. The short-wave trough ahead of the bottom of the horizontal trough moves rapidly eastward and affects Shanxi. In the south frontal zone, the southwest jet stream at 700 hPa is strong. The cold temperature trough in the northeast-southwest direction at 850 hPa is located over North China. The surface inverted trough in Hetao area develops strongly and interacts with the return-flow weather pattern. The southwest warm and humid airflow ascends along the low-level cold air cushion, providing a favorable large-scale circulation background for the formation of freezing rain and freezing fog in Yuanqu. In the vertical direction, warm temperature advection above and cold temperature advection at bottom lead to a cold-warm-cold temperature structure in Yuanqu from low to high altitudes, with the middle-layer temperature above 0℃ and the lower-layer temperature below 0℃. The short-term freezing rain in Yuanqu, triggered by the short-wave trough, is attributed to the melting mechanism. The vertical humidity advection configuration of "wet above and dry at bottom", coupled with sinking motion together make the lower atmosphere highly saturated. Additionally, temperature inversion continues in the lower atmosphere. These conditions collectively facilitate the long-term persistence of freezing fog in Yuanqu. Abundant supercooled water droplets, undergoing two phases of rapid growth, continuously impinge on the wire surfaces, causing ice accretion to thicken progressively. Southeasterly airflow ascends along the windward slopes of the horn-shaped topography, which plays a certain role in promoting the thickening of accretion on wires.
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