Analysis of Characteristics of a Long-Lived Freezing Rain and Ice Pellet Event in Southern Shandong
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Abstract:
A rare weather event featuring a long-lived period of freezing rain and ice pellets transitioning to snow occurred in the southern Shandong region from February 20-21, 2024. Using conventional observational data, wind profiler radar data, raindrop spectrum data, and ERA5 reanalysis data to analyze this event, the results indicate:?(1)? The event was characterized by return flow precipitation. A southwest warm and humid airflow ahead of the upper-level trough slid upwards along a cold pad caused by a significant temperature drop due to the low-level strong cold air. The interaction between the mid-level warm and humid airflow and the low-level northeastern airflow formed a strong inversion, and the "cold-warm-cold" vertical temperature structure was maintained for a long time, leading to a 12-hour period of freezing rain and ice pellets??(2)? Both freezing rain and ice pellets exhibit typical characteristics of ice-phase melting. The ground temperature during freezing rain is higher, the starting height of the warm layer is lower, and both the thickness and intensity of the warm layer are greater, while the thickness and intensity of the cold layer are smaller. ??(3)? Raindrop spectrum data showed no significant differences in the particle size distribution characteristics between freezing rain and ice pellets. Both had features of small particle size, low number concentration, low precipitation intensity, and high falling speed. The velocity curves of both were similar to those of rainfall but with slight differences. Freezing rain had slightly larger particles and fewer particle numbers than ice pellets. During the snowfall phase, the spectrum widened, characterized by large particle size, high number concentration, high precipitation intensity, and low falling speed.