First VIKING results: low frequency wave measurements

Abstract

The low frequency wave experiment on Viking comprises waveform as well as power spectrum analysis of high temporal and spectral resolution and with a large dynamic range. As sensors any two of a set of triaxial electric field probes and two Langmuir probes can be used simultaneously, the latter providing measurements of plasma density fluctuations at two spatially separated points, which is a unique and very useful feature of the Viking low frequency wave experiment. Three interesting low frequency wave phenomena with characteristics different from those reported from other spacecraft experiments are reported here. Solitary structures of a vertical thickness of less than 80 m have been found to propagate at about 10 kms−1 along the fieldlines away from the Earth. Ion cyclotron harmonic waves have been observed at frequencies slightly above high harmonics of the proton gyrofrequency. Low frequency harmonic waves have also been observed where the frequency of the harmonics are multiples of the fundamental rather than being separated by the proton gyrofrequency as usually reported, and where the direction of propagation is closely perpendicular to the Earth's magnetic field.