@misc{indiciaefc7049ea11af,
  title = {The geomagnetic jerk of 1969 and the DGRFs},
  author = {D. Thompson and J.C. Cain},
  year = {1987},
  doi = {10.1016/0031-9201(87)90163-4},
  url = {https://pubs.usgs.gov/publication/70014204},
  note = {Source identifier: 70014204}
}