Ulf waves upstream of the Venus bow shock: Properties of one‐hertz waves

Abstract

Pioneer Venus orbiter data are used to examine the properties of a class of ULF upstream waves with relatively high observed frequencies (1.1–1.3 Hz). In the spacecraft frame these waves are most often left‐hand elliptically polarized. They have amplitudes up to 3 nT (near the bow shock) and propagate obliquely to the magnetic field at angles from 10° to 50°. These waves show significant similarity in their properties to “one‐Hertz” waves identified at the Earth in the ISEE 1 and 2 observations and the whistler waves identified earlier with IMP 6 observations. The waves appear almost immediately after the spacecraft crosses the magnetic field tangent line to the bow shock surface into the region of connected field lines. The amplitude of these waves decreases with distance from the shock measured along the magnetic field line. We have used the cold plasma dispersion relation in order to study the propagation of these waves and to explain their observed polarization. Calculated group velocities indicate that those waves have sufficient upstream velocities to propagate from the shock into the solar wind. The totality of observations, including the observed wave damping and the observation of right‐handed waves, seems best explained by a source of right‐handed whistler mode waves at the bow shock.

Upstream whistler-mode waves at planetary bow shocks: A brief review

“…They have been observed at Mercury (Fairfield and Behannon, 1976;Orlowski et al, 1990); Venus (Orlowski and Russell, 1991;Orlowski et al, 1993); Saturn (Orlowski et al, 1992); as well as by many authors at Earth, including Russell et al (1971), Fairfield (1974, and Orlowski et al (1995). Fig.…”

“…However, this mechanism could not predict all the properties of the upstream whistlers. In a series of papers, D. Orlowski and co-workers (Orlowski et al, 1990(Orlowski et al, , 1993Orlowski and Russell, 1991) reopened the study of these waves and concluded that the Fairfield hypothesis was indeed correct.…”

Dispersion of low frequency plasma waves upstream of the quasi-perpendicular terrestrial bow shock

“…Fairfield, 1974;Balikhin et al, 1997). Nevertheless, these waves have been reported at many other other locations such as Venus (Orlowski and Russell, 1991) and Saturn (Orlowski et al, 1992) concluding that they are a fundamental phenomena associated with collisionless shocks. Whistler waves are believed to play a fundamental role in shock structure and therefore have attracted considerable interest in both theoretical and experimental studies.…”

Statistical analysis of monochromatic whistler waves near the Moon detected by Kaguya

“…These results provide important clues for understanding the wave properties and their generation process. Based on previous studies of the upstream whistler waves from planetary bow shocks for which the wave intensity decreases with distance from the source region (Orlowski and Russell, 1991), the distribution of the high average intensity (Fig. 2a and c) indicates the intense wave source region.…”