@misc{indiciae1699d77a827b,
  title = {Approximations in the theory of solar-cycle modulation},
  author = {Axford, W. I. and Fisk, L. A. and Gleeson, L. J.},
  year = {1970},
  url = {https://ntrs.nasa.gov/citations/19710037413},
  note = {Source identifier: 19710037413}
}