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

Abstract

We statistically investigate the spectral scalings of magnetic fluctuations at the upstream and downstream regions near the Venusian bow shock and perform a differentiation by shock geometry. Based on the Venus Express data, 115 quasi-parallel ($Q_{\Vert }$) bow shock crossings and 303 quasi-perpendicular ($Q_{\perp }$) bow shock crossings are selected. The statistical results suggest that the bow shock tends to modify the upstream spectra flatter to 1/f noise in the magnetohydrodynamics (MHD) regime and steeper to turbulence in the kinetic regime after the magnetic fluctuations crossing the bow shock, and this modification for the $Q_{\Vert }$ and $Q_{\perp }$ bow shocks is basically consistent. However, the upstream spectral scalings are associated with the shock geometry. The changes of the spectral scalings of magnetic fluctuations near the $Q_{\Vert }$ bow shocks are not as significant as near the $Q_{\perp }$ bow shock crossings. That might result from the fluctuations generated by the backstreaming ions which can escape across the $Q_{\Vert }$ bow shock into the foreshock. Our results suggest that the energy cascade and dissipation near Venus can be modified by the Venusian bow shock, and the $Q_{\Vert }$ bow shock plays an important role on the energy injection and dissipation in the solar wind interaction with Venus. The large dispersion of spectral scalings indicates that this fluctuation environment is complicated, and the shock geometry is not the only key factor in the fluctuations across the Venusian bow shock. Other possible factors in the shock modification to the upstream fluctuations will be explored in future.