Magnetosheath fluctuations at Venus for two extreme orientations of the interplanetary magnetic field

Abstract

Using the magnetosheath crossings of Venus Express on two consecutive days, we investigate magnetic fluctuations in the same locations for two extreme interplanetary magnetic field orientations, i.e., nearly along and nearly perpendicular to the solar wind flow. It is shown that the properties of the fluctuations are drastically different at basically the same location of the spacecraft in the magnetosheath. The strength and properties of the fluctuations are strongly controlled by the types of the upstream bow shock. The magnetic fluctuations behind a quasi-parallel bow shock are quite strong and turbulent, having a strongly variable angle αeB between maximum variance direction of the fluctuations and the direction of the magnetic field, which may be convected from the upstream waves in the foreshock. The magnetic fluctuations behind a quasi-perpendicular bow shock are less intensive and wave-like, showing a less perturbed angle αeB, which are probably generated locally. Copyright 2009 by the American Geophysical Union.