The emigratory areas in the northward migrating process in spring-summer are located in the warm sector of warm low on surface and in partial southern air stream on 850 mb isobaric chart, especially in the region controlled by SW air stream.

• 春、夏季的北迁,迁出地一般位于地面热低压系统的暖区和高空850毫巴图上的偏南气流,特别是西南气流的控制区域;