The orange and blue lines depict the opposite north and south polarity of Earth's field lines.
橙色和蓝色的线条分别表示地球磁场中南极、北极两种相反磁性的磁力线。
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But it could be that, well, imagine that my vector field accidentally goes in the opposite direction then this part of the curve, while things are flowing to the left, contributes negatively to flux.