Turbulence Near the Venusian Bow Shock: Venus Express Observations

Abstract

In 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.

The spectral scalings of magnetic fluctuations upstream and downstream of the Venusian bow shock

“…In the kinetic frequency range, the turbulence has a larger value of α ~ 2.8, in which regime the magnetic energy dissipates into plasma or accumulates by exciting some dispersive waves, like the whistler. The spectral scaling indices have been extensively used to analyze the magnetic field fluctuations and turbulence in the solar wind (e.g., Alexandrova et al 2008Alexandrova et al , 2009Kiyani et al 2009;Bruno and Carbone 2013), in the planetary space environments near Earth (e.g., Vörös et al 2004Vörös et al , 2007Vörös 2011), Mars (e.g., Ruhunusiri et al 2017), and Venus (e.g., Vörös et al 2008a, b;Dwivedi et al 2015;Xiao et al , 2020a.…”

“…It suggests that the shock geometry has an effect on the spectral scalings of downstream magnetic fluctuations, and the bow shock plays a role on the turbulence distribution in the near-Venusian space. Xiao et al (2020a) presented a description of the spectral scalings of magnetic fluctuations at the Venusian bow shock crossings. In terms of the spectral scalings, the dayside-nightside shock crossings exhibit a clear asymmetry.…”

The spectral scalings of magnetic fluctuations upstream and downstream of the Venusian bow shock

“…In the kinetic frequency range, the turbulence has a larger value of ~ 2.8, in which regime the magnetic energy dissipates into plasma or accumulates by exciting some dispersive waves like the whistler. The spectral scaling indices have been extensively used to analyze the magnetic field fluctuations and turbulence in the solar wind (e.g., Alexandrova et al, 2008Alexandrova et al, , 2009Kiyani et al, 2009;Bruno and Carbone, 2013), in the planetary space environments near Earth (e.g., Vörös et al, 2004;2007;2011), Mars (e.g., Ruhunusiri et al, 2017), and Venus (e.g., Vörös et al, 2008aVörös et al, , 2008bDwivedi et al, 2015;Xiao et al, 2018Xiao et al, , 2020aXiao et al, , 2020b.…”

The spectral scalings of magnetic fluctuations upstream and downstream of the Venusian bow shock

“…In the kinetic frequency range, the turbulence has a larger value of ~ 2.8, in which regime the magnetic energy dissipates into plasma. The spectral scaling indices have been extensively used to analyze the magnetic field fluctuations and turbulence in the planetary space environments near Mars (e.g., Ruhunusiri et al, 2017), Earth (e.g., Vörös et al, 2004), and Venus (e.g., Vörös et al, 2008aVörös et al, , 2008bDwivedi et al, 2015;Xiao et al, 2018Xiao et al, , 2020aXiao et al, , 2020b.…”

“…magnetic fluctuations, and the bow shock plays a role on the turbulence distribution in the near-Venusian space Xiao et al (2020a). presented a description of the spectral scalings of magnetic fluctuations at the Venusian bow shock crossings.…”