@misc{1191171,
  author = {Ernest K Smith},
  title = {Circular of the Bureau of Standards no. 552::worldwide occurrence of sporadic E},
  year = {1957},
  month = {1957-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.CIRC.582},
  language = {en},
}