Lightning characteristics and genesis analysis during a bohai sea-effect snow event

In recent years, high-impact thundersnow events have occurred frequently across China. To deepen the understanding of thundersnow mechanisms and enhance forecasting capabilities, this study conducts a detailed investigation of a thundersnow event on December 7, 2024, over the Shandong Peninsula using radar, lightning, atmospheric electric field data, and ERA5 reanalysis. Key findings include the following aspects: (1) This thundersnow event occurred under typical sea-effect (cold-air advection) snowfall conditions over the Bohai Sea, with a temperature difference of 21 °C between the 850 hPa level and the sea surface. The convective instability below 850 hPa, forced by positive vorticity advection and cold advection in the mid-upper levels, generated strong and widespread upward motion below 600 hPa. The lifting of warm-moist air near the sea surface released unstable energy, resulting in thunderstorms. (2) Lightning flashes during this sea-effect snowfall were relatively sparse. Their frequency and polarity distribution resembled those of weak summer thunderstorms. Cloud-to-ground lightning flashes preceded or coincided with heavy snowfall episodes and occurred near or upstream of areas of heavy snowfall. (3) Radar echoes exhibited distinct convective characteristics, with the maximum reflectivity reaching 48.5 dBZ and the echo tops height exceeding 5.2 km. The snow echoes were primarily distributed in a band parallel to the coastline, and the "train effect" was the main cause of heavy snowfall. (4) Polarimetric radar observations indicate abundant pristine ice crystals, graupel, and supercooled water within the convective cells, while ERA5 provides environmental thermodynamic and dynamic conditions consistent with their development. The cloud system possessed the necessary microphysical and dynamic conditions for non—inductive electrification.