Spectral broadening of VLF transmitter signals observed on DE 1: A quasi‐electrostatic phenomenon?

Spectrally broadened VLF transmitter signals are observed on the DE 1 satellite using alternatively both electric and magnetic field sensors. It is found that at times when the electric field component undergoes significant bandwidth expansion (up to ∼110 Hz) the magnetic field component has a bandwidth of less than 10 Hz. The results support the theory that the off‐carrier components are quasi‐electrostatic in nature. Measurement of the absolute E and B field magnitudes of the broadened signals are used to determine the wave Poynting vector. It is found that the observed power levels can be understood without invoking any strong amplification process that operates in conjunction with the spectral broadening. The implications of this finding in distinguishing among the various possible mechanisms for spectral broadening are discussed.