Simultaneous observation of upstream waves with ISEE and AMPTE

Measurements obtained by ISEE-2 and the UKS spacecraft upstream of the earth's bow shock are examined. Simultaneous observations show that upstream waves are excited over a broad frequency range. Even when peaked spectra occur the peaks can occur at different frequencies in different regions of space. Generally the spectra seen at the two locations are most similar at high frequencies and least similar at low frequencies. The position dependent nature of the upstream waves indicates that comparisons between ground-based measurements and in situ observations must be undertaken with some caution.