Science & Mathematics » Geography » On a weather map, what is a purple line with either dashed lines or triangles and circles represent?

On a weather map, what is a purple line with either dashed lines or triangles and circles represent?

I know that blue triangles represent a cold front, red circles represent a warm front, I think I've heard that the mix between a cold and warm front represents an arctic front, but I would like to know what a purple line with either a dashed line or triangles and circles represents.

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