Solar polar plumes are bright radial rays rooted at the sun's polar areas. They are widely believed to have the structure of expanding tube. A four degree polynomial function was assumed to represent the change of cross section diameter as a function of height and four unknown parameters were calculated with measured average widths of total 31 plumes at 4 heights (1.04Rs,1.10Rs,1.16Rs,1.20Rs).
@article{arxiv.1205.0267,
title = {A geometrical model for polar plumes observed by STEREO SECCH},
author = {Beidi Peng},
journal= {arXiv preprint arXiv:1205.0267},
year = {2012}
}