We show that the main characteristics of ion acoustic solitary waves and weak double layers observed by the Swedish satellite Viking can be well reproduced assuming the presence of two electron components in the auroral plasma. The characteristics of the ion acoustic solitons excited in such a plasma are derived with the help of the Sagdeev potential. The results show that the interactions between the hot and the cold electron component in the presence of a finite ion temperature produce rarefactions of the localized density. Such nonlinear structures exist in a more extended range of plasma parameters than the one previously studied in the small amplitude limit case using the Korteweg-de-Vries equation. We find that the density of the cold population must be always smaller than the hot one, while the hot to cold temperature ratio must be greater than ~10. The characteristics of these structures are quite different from those obtained in the small amplitude limit case and better reproduce the Viking observations in terms of their velocity, width, and amplitude scales. ¿ 1998 American Geophysical Union