@misc{1157826,
  author = {W B Chadwick},
  title = {Variations in frequency of occurrence of sporadic E, 1949-1959:},
  year = {1961},
  month = {1961-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.TN.117},
  language = {en},
}