Polar mesospheric clouds: The year-to-year changes shown in 17 years of images from both hemispheres Original Research Article

Meteosat images recorded from December 1983 to December 2000 have been examined systematically to determine the year-to-year change in frequency of occurrence. The statistics from the southern hemisphere are poor because of what appears to be a systematic difference between the two hemispheres with the southern hemisphere showing many fewer days with polar mesospheric clouds present. There is some indication of a local time dependence in the occurrence of the clouds in the northern hemisphere which may arise from the passage of a planetary wave through the regions available for observation from geostationary orbit. There are eleven years in the data when night-to-night observations (NLC) from Europe of noctilucent clouds are available. Comparison of 341 nights using the NLC and the northern satellite data show no significant level of simultaneous occurrence.