div class=ts-pagebuttonPage 1button div class=ts-image amp-img class=ts-thumb alt=Page 1: Ionisation in the Upper Atmosphere src=https:reader031vdocumentsusreader031viewer2022020223575067c21a28ab0f07ad067fhtml5thumbnails1jpg width=142 height=106 layout=responsive amp-img divp© 1927 Nature Publishing Grouppdiv