Statistical study of low‐frequency magnetic field fluctuations near Venus during the solar cycle

Abstract

We statistically investigate the solar cycle dependence of the magnetic field fluctuations in the frequency range 30–300 MHz based on Venus Express data. We present the spatial distributions of fluctuation properties during three typical periods of the solar cycle, and a comparative study is also performed. With the increase of solar activity, the magnetic field is still quiet in the magnetotail region and the wave intensity becomes weaker in the magnetosheath. The transverse component of fluctuations becomes stronger in the magnetosheath region and weaker in the tail region. The proportion of circularly polarized components to incoherent noise of the fluctuations decreases in the magnetosheath region. The proportion of dominant parallel propagation fluctuations tends to be larger in the nightside magnetosheath, and more perpendicular propagation component is shown in the tail region.

Turbulence Near the Venusian Bow Shock: Venus Express Observations

“…A clear increase in the magnetic field strength can be observed at the bow shock in Figures a and b, and the induced magnetosphere and magnetosheath are also indicated in these two panels. Solar cycle variations of the magnetic structures and fluctuation properties near Venus have been reported by previous studies (e.g., Shan et al, ; Xiao et al, ; Xiao & Zhang, ). As shown in Figures e and f, the noisy fluctuations appear more in the dayside bow shock and nightside magnetosheath, while turbulence can be observed upstream of the bow shock and the magnetosheath boundary layers containing the nightside bow shock.…”

“…Turbulence and the multiscale energy cascade seem to occur preferentially at the nightside bow shock. Although there are some solar cycle variations in the magnetic field and fluctuations near Venus (e.g., Xiao et al, ; Xiao & Zhang, ), this study shows no clear solar cycle dependence of the spectral scaling features near the Venusian bow shock. This result is clearly indicated in Figure , in which the variations of spectral scaling indices with the SZA exhibit the same trend between solar maximum and minimum.…”

“…The solar wind interacts directly with the Venusian ionosphere, forming an induced magnetosphere above the ionosphere (e.g., Phillips & McComas, ; Zhang et al, , ), and the bow shock and the magnetosheath are also formed in this interaction (e.g., Luhmann, ). Prior studies suggested that the Venusian magnetosheath is filled with strong magnetic field fluctuations, which can be convected from the upstream foreshock or can be locally generated (e.g., Du et al, ; Luhmann et al, ; Xiao et al, ). The magnetic field fluctuations play an important role in the transfer of momentum and energy in the space plasma environment of the planet (e.g., Guicking et al, ; Luhmann, ).…”

“…The Venusian bow shock is weaker when solar activity is strong (Lu et al, ). However, the spectral scaling features of fluctuations in the Venusian magnetosheath exhibit no clear solar cycle variation (Xiao et al, ), even though the solar activity does have effects on the fluctuation properties near Venus (Xiao et al, ). Therefore, the role of solar activity in the spectral scaling features of fluctuations near the Venusian bow shock has to be investigated more carefully.…”

Magnetic Fluctuations and Turbulence in the Venusian Magnetosheath Downstream of Different Types of Bow Shock

“…The fluctuations convected from the upstream region have been observed by Hoppe and Russell (). Some other studies also suggested that the dayside magnetosheath is filled with strong fluctuations convected from the foreshock and the bow shock (e.g., Du et al, ; Xiao et al, ).…”