New waves at multiples of the plasma frequency upstream of the Earth's bow shock

The first observations of waves at harmonics higher than the second of the electron plasma frequency are reported. The observations were made by the ISEE 1 spacecraft upstream of the earth's bow shock. The waves are interpreted as electromagnetic radiation at the fundamental and up to the fifth harmonic of the plasma frequency, with effective temperatures decreasing from 5×10 17 K to 10 10 K over this range. Two models for the emission of the waves are sketched.