气旋是三维空间上的大尺度涡旋，其中心气压低、四周气压高，是一种近地面气流向内辐合，中心气流上升的天气系统。由于地球自转与科氏力(Coriolis effect)作用，使得气旋在北半球作逆时针旋转，在南半球做顺时针旋转。气旋与低压是对同一天气系统的不同描述，气旋针对气流状况，而低压指气压分布状况.。

春 · 夏 · 秋 · 冬

卷云 · 积云 · 层云

风暴 · 雷暴 · 龙卷风
飓风 · 气旋 · 雪暴

液态：毛毛雨 · 雨 · 暴雨
固态：雪 · 冰珠 · 钻石尘 · 霰 · 雹
其他：雨夹雪 · 冻雨

液态：霭 · 雾 · 露
固态：霜 · 雾凇 · 冰

In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low pressure. They are usually characterized by inward spiraling winds that rotate counterclockwise in the Northern Hemisphere and clockwise in the southern. All large-scale cyclones are centered on areas of low atmospheric pressure. The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones of the largest scale (synoptic scale). According to the National Hurricane Center glossary, warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within the smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the Tropical Upper Tropospheric Trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. Cyclogenesis describes the process of cyclone formation and intensification. Extratropical cyclones form as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract to form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, cyclones occlude as cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.