Parker solar wind model

http://www-solar.mcs.st-andrews.ac.uk/~alan/sun_course/Chapter6/node3.html

In this website, the 'log' in the formula is 'ln'.

https://www.tcd.ie/Physics/people/Peter.Gallagher/lectures/PY4020/lecture03_solar_wind.pdf

http://lasp.colorado.edu/~cranmer/ASTR_3760_2017/LecNotes/astron3760_cranmer_lec11.pdf