a severe storm that develops very fast, in which the air pressure at its centre falls quickly by a large amount

Bomb cyclones form when air near Earth's surface rises quickly in the atmosphere, triggering a sudden drop in barometric pressure — at least 24 millibars within 24 hours. 炸弹气旋的形成是因为靠近地球表面的空气在大气中迅速上升，引发气压突然下降——在24小时内至少下降24毫巴。