Statistical investigation on the power-law behavior of magnetic fluctuations in the Venusian magnetosheath

The present work aims to develop a better understanding of wave and turbulence processes in the planetary magnetosheath region. We study the plasma conditions (temperature, flow velocity, and magnetic field), the low-frequency wave properties, and the energy spectra for magnetic field fluctuations in the Venus magnetosheath. We use the magnetic field data of 101 magnetosheath flank crossings from the Venus Express magnetometer experiment in the years 2006 and 2008. The statistical investigation of the plasma conditions shows that the mean magnetic field amplitude is about 10 nT, the average proton temperature of the order of MK, and the super-Alfvenic, subsonic bulk plasma flow. Below 0.07 Hz, the angle of propagation is about 80. for the most of the cases, and it varies from 10. to 90. above the frequency 0.07 Hz. The compressibility shows similar distribution at low (below 0.07 Hz) and high frequencies (above 0.07 Hz). The energy spectra in the spacecraft frequency frame reveal the power-law behaviors which give physical insight on the energy transfer from larger to smaller scales due to wave-wave interaction. A spectral break (sudden change in slope) is observed at 0.25 Hz, above which the spectral curve becomes steeper with spectral indices between -4 and -1.5 (close to the Kolmogorov slope, -5/3). The low-frequency part (below 0.07 Hz) having a spectral index close to -1 indicates the energy cascades due to mirror mode waves, and the steepen spectra at high frequencies (above 0.07 Hz) with spectral indices between -4 and -0.5 are interpreted as the energy accumulation due to mirror mode and proton cyclotron waves.