1. We did not attempt to list all publications of Stoffregen. In addition to the contributions cited here, he published numerous internal reports at the Uppsala Ionospheric Observatory.
2. Appleton, E. V. and Naismith, R.: Scattering of radio waves in polar regions, Nature, 143, 243–244, 1939.
3. Boström, R. and Stoffregen, W: Implementation of Ground-Based Facilities to Study the Ionosphere and Magnetosphere above Scandinavia and their Role in Sounding Rocket Experiments, Fifth ESA Symposium on European Rocket and Balloon Programmes and Related Research, held 14-18 April 1980 in Bournemouth, UK. Edited by T.d. Guyenne and G. Lévy. ESA-SP Vol.152, 421–424, The Netherlands: ESA Scientific & Technical Publications Branch ESTEC, 1980.
4. Boström, R. and Derblom, H.: Obituary Willy Stoffregen, J. Atmos. Terr. Phys. 49, p. 871, 1987.