Survey of 1-Hz waves in the near-Venusian space: Venus Express observations

摘要

With 32 Hz magnetic field data of Venus Express from May 2006 to August 2012, the global spatial distributions of 1-Hz waves in the near-Venusian space are presented in this paper. The occurrence rate of 1-Hz waves is maximized near the Venusian bow shock and decreases in the upstream with the distance away from the shock. Downstream of Venusian bow shock, some 1-Hz waves are swept in the magnetosheath. However, these waves cannot enter the induced magnetosphere. The distribution of 1-Hz waves shows a solar cycle variation which could be the influence of the newborn pickup ions. The wave occurrence rate is higher near the bow shock in the -E hemisphere, and the waves can propagate upstream farther in the +E hemisphere, while the occurrence rate of the downstream 1-Hz waves shows no clear hemispheric asymmetry. In addition, the 1-Hz waves in the near-Venusian space have a higher occurrence rate and a more widespread distribution in the quasiparallel foreshock region than in the quasi-perpendicular region. It can be inferred that the 1-Hz waves in the quasi-parallel region are less affected by Landau damping and they can propagate farther in the foreshock.