Turbulence Near the Venusian Bow Shock: Venus Express Observations

Abstract

AbstractIn terms of composition and size, Venus is an Earth‐like planet without a global intrinsic magnetic field. The Venusian bow shock and magnetosheath, reaching only 10% of the size of the Earth, are formed from the interaction of the solar wind with the Venusian ionosphere. Energy injection from the solar wind to the Venusian space environment can be studied at the bow shock. In this respect, we hypothesize that the spectral scaling features of magnetic fluctuations near the bow shock represent important information. Nine years (2006–2014) of Venus Express magnetic observations are used to study the spectral features of fluctuations near the bow shock over the frequency range from 0.05 to 0.3 Hz. Our results show that in terms of the spectral scaling features of magnetic fluctuations, the dayside‐nightside shock crossings exhibit a clear asymmetry. Magnetic fluctuations at the dayside shock crossings are associated with spectral indices of ~1, resembling the scaling of 1/f noise. At the nightside shock crossings, the spectral indices are closer to 3/2, resembling the magnetohydrodynamic turbulence scaling. We speculate that the noise at the dayside is the consequence of the newborn strong fluctuations near the dayside bow shock, which can mask or destroy the turbulence convected from the solar wind. The spectral scaling features of magnetic fluctuations at bow shock crossings do not exhibit solar cycle dependence. Although the fluctuations differ downstream of quasi‐parallel or quasi‐perpendicular shocks in the magnetosheath, the shock geometry has no influence on the scaling properties of fluctuations at the dayside‐nightside shocks.