Study on the Mesoscale Characteristics and Formation Causes of a Graupel Process at Mianyang Airport in Winter

A rare short‐term winter graupel event occurred at Mianyang Airport in the Sichuan Basin on January 10, 2025, with graupel particles less than 5 mm in diameter and lasting approximately 3 min. Based on surface observations, dual‐polarization radar data, and reanalysis data, this study reveals the triggering mechanism, microphysical characteristics, and early warning applications of the process. The main conclusions are as follows: (1) dynamic triggering mechanism: this process was jointly driven by the southward movement of cold air and the low‐level shear line. The northwest airflow at 500 hPa guided the intrusion of cold advection, and the shear line at 850 hPa formed low‐level convergence. Combined with weak symmetric instability below the inversion layer at 600 hPa, shallow convection was formed, which could support the formation of graupel without significant energy accumulation. This is significantly different from the mechanism of summer severe convection that relies on deep thermal instability. (2) Microphysical and environmental characteristics: the 0°C layer was located at 850 hPa, and the high‐humidity area at 700 hPa provided supercooled water vapor. Dual‐polarization radar showed that the graupel particles had a nearly spherical shape, characterized by low differential reflectivity and a high correlation coefficient. (3) Radar early warning indicators: bow echo, a 50 dBZ strong echo center, an echo top (ET) height of 4 km, relatively fast echo movement speed, and low‐level northeast wind shear can be used as key early warning signals. Combined with parameters such as water vapor flux, an early warning was issued 30 min in advance, providing technical support for low‐altitude meteorological guarantee at the airport.