Solar Wind Interaction With Induced Magnetosphere Of Venus

Although there is no intrinsic magnetic field at Venus,the convected interplanetary magnetic field piles up to form an induced magnetosphere around the Venusian ionosphere,and also form a draped magnetotail,magnetosheath,and bow shock,similar to the Earth.By using the observation data from Venus Express,we investigate solar wind interactions with the induced magnetosphere of Venus,and also their solar cycle variations.Our results are shown as follows:1.Solar cycle variation of the Venus magnetic barrierWe perform a comprehensive statistical study of the magnetic barrier near the terminator during almost a complete solar cycle by using Venus Express magnetic data.The magnetic barrier configuration is located at the dayside even near the terminator and a hemispheric asymmetry exists during the whole solar cycle.We also demonstrate that the general magnetic barrier configuration is controlled by the interplanetary magnetic field(IMF)orientation and solar cycle dependent.The magnetic barrier under IMF quasi-perpendicular to the solar wind flow is stronger than quasi-parallel to the solar wind flow during the solar cycle,and this difference becomes larger with the increase in solar activity.2.Hemispheric asymmetry in the near-Venusian magnetotail during solar maximumDuring solar minimum the near-Venusian magnetotail exhibits a hemispheric asymmetry in the cross-tail field distribution.It implies that the magnetic field lines in the-E hemisphere are wrapped more tightly around Venus than in the +E hemisphere.Therefore,a strong field reversal region occurs in the magnetotail,which is prone to the magnetic reconnection.Since the Venus magnetotail is formed due to the solar wind interaction with the ionosphere and the ionosphere is modulated by the solar activity,it is interesting to study the solar cycle dependence of the induced magnetosphere.Here we statistically examine the Venus Express magnetotail data during solar maximum.We find that the magnetic field configuration asymmetry in Venus magnetotail is very much similar to that during solar minimum.The hemispheric asymmetry in the magnetotail persists through the whole solar cycle and magnetic reconnection in the near-Venusian magnetotail might occur during solar minimum as well as solar maximum conditions.3.Low-frequency magnetic field fluctuations near Venus during the solar cycleWe 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.4.Magnetic fluctuations and turbulence in the Venusian magnetosheath downstream of different types of bow shockWe statistically examine the characteristic scaling features of fluctuations in the dayside Venusian magnetosheath downstream of different types,quasi-parallel(Q//)and quasi-perpendicular(Q?),of bow shock based on Venus Express data.Although the properties of magnetic fluctuations show differences in the downstream of Q//and Q? bow shock,we found that they have similar characteristic scaling features.Independent on the type of a bow shock,1/f noisy fluctuations dominate in the dayside magnetosheath.Surprisingly,the type of bow shock does not play a role in the characteristic scaling features of magnetic fluctuations.That means that the IMF orientation near bow shock has no effect on the development of turbulence or noisy fluctuations in Venusian magnetosheath.