This sub-subseries consists of 12 files containing material relating to Edward Appleton’s research into ionospheric storms. Most of it relates to his collaborative papers on the subject with W.R. Piggott ('World morphology of ionospheric storms', Nature, 165, 1950, and 'The morphology of storms in the F2 layer of the ionosphere: I. Some statistical relationships', Journal of Atmospheric Terrestrial Physics, 1952-referred to in the correspondence as 'the big paper'). It seems that follow-up papers were planned, but these are not listed in the bibliography. Appleton continued research on storms at Edinburgh with the assistance of Mrs. Pritchard.