The results are presented from a careful, systematic search for reports of stratospheric clouds over the period 1870–1972. For the high-latitude Northern Hemisphere, a total of 156 dates are listed on which mother-of-pearl clouds (MPC) were reported. A small number of other Norwegian sightings exist for which specific dates were not obtained. Several references to general aircraft sightings of clouds above the tropopause are also given.

Five mid- or low-latitude sightings are listed, some of which are perhaps related to rocket firings.

In the Southern Hemisphere, the reported sightings occurred in Antarctica, being either of the MPC type or of more extensive and longer-lasting stratospheric cloud veils. The latter apparently are due to the extremely cold stratospheric temperatures experienced over the Antarctic in winter. Reports of veil-type stratospheric clouds are listed from two Antarctic expeditions, in 1912 and 1950–51. In addition to these, 139 cases of Antarctic MPC sightings were reported, although specific dates were not obtained for all of these cases. Considering the sparsity of Antarctic observers, it appears that stratospheric clouds occur much more frequently in the high-latitude Southern Hemisphere than in the corresponding region of the Northern Hemisphere.

The results of the present investigation are believed to represent the most extensive listing presently available for stratospheric cloud observations.

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1 Advanced Study Program. On Faculty Improvement Leave (September 1972–August 1973) from the Physics Department of Iowa State University, Ames, Iowa 50010.

2 The National Center for Atmospheric Research is sponsored by the National Science Foundation.