@article{oai:nipr.repo.nii.ac.jp:00004240,
 author = {Sugiyama, Takuya},
 journal = {Proceedings of the NIPR Symposium on Upper Atmosphere Physics},
 month = {Jan},
 note = {P(論文), Amateur reports of noctilucent cloud (NLC) displays during 1964 to 1992 in north-west Europe are analyzed. A 5-day variation in occurrence of bright NLC has already been noted in the same reports during 1964 to 1982 by M. GADSDEN (Ann. Geophys., 3,119,1985). In this paper the 5 to 6-day periodicity is confirmed to be even more pronounced if negative reports (clear night with no NLC) are taken intoaccount in statistical analysis. This result stresses that the periodicity is not due to weather conditions but it reflects the intrinsic nature of NLC formation. The cause of 5 to 6-day periodicity is discussed, whether it is due to planetary waves in the mesosphere or due to the in situ origin of NLCs, ionic nucleation of ice particles. To see long-term trends of NLC occurrences a requirement for objective recording of NLCs by equipment such as CCD cameras in both polar regions is suggested.},
 pages = {81--87},
 title = {Statistical study of noctilucent cloud occurrence in Western Europe},
 volume = {11},
 year = {1998}
}