Narrow band VLF signals with a structure similar to that of chorus were observed on a rocket payload launched from ESRANGE (European Space Range) near Kiruna, Sweden. The payload penetrated a proton glow aurora and flew over an auroral arc. It is shown that the signals which occurred in the frequency range 3.0--3.4 kHz probably are generated in the lower ionosphere, and the high-frequency two-stream instability developed by K. Lee et al. (1971) is suggested as the generation mechanism.