Robuta

https://www.aanda.org/articles/aa/abs/2007/22/aa4495-05/aa4495-05.html Force-free magnetic field extrapolation for MHD boundary conditions in simulations of the solar... force free magnetic field https://www.aanda.org/articles/aa/ref/2007/22/aa4495-05/aa4495-05.html Force-free magnetic field extrapolation for MHD boundary conditions in simulations of the solar... force free magnetic field