1. 极圈:极区图 polar chart | 极圈 polar circle | 极距 polar distance
2. 极圆:polar axis 极轴 | polar circle 极圆 | polar conic 极圆锥曲线
3. 极圈纬度平行圈:polar chart 极区海图 | polar circle 极圈纬度平行圈) | polar continentalair 寒带大陆性气团
noun
1. a line of latitude at the north or south poles