Aeronomic aspects of the polarD-region

The polarD-region has been little studied. A major part of this review concerns observations performed during the 1969, November, 2–5, solar proton event. These extensive measurements and subsequent interpretations constitute a major source of polarD-region knowledge. The aeronomic concepts garnered from the analysis of this event are discussed and compared with results from other events and other polar mesospheric data. Some mid-latitude data are resorted to for supplementary arguments. Ionization rates due to precipitating protons and alpha-particles are reviewed, particularly in view of the fact that some workers have suggested that the more intense events may influence stratospheric ozone chemistry.