The Venus Express Observation Of Venus' Induced Magnetosphere Boundary At Solar Maximum

The Venusian plasma environment is divided into two distinct regions by the induced magnetosphere boundary (IMB): the domain of solar wind protons and the domain of local planetary ions. Previous studies on the identification of the IMB gave various IMB definitions. Here we study the well-structured Venusian IMB with a sudden magnetic field rotation and a sharp magnetosheath plasma decrease using Venus Express observations. We statistically investigate the location of such well-structured IMB and give an average location of the IMB at solar maximum. The solar activity and solar wind controls of the Venusian IMB location is also studied in this work. Our results show that the dayside Venusian IMB distance increases with solar activity, but it decreases with increasing solar wind dynamic pressure and interplanetary magnetic field cone angle. The behaviors of the IMB under these conditions are similar to those of the ionopause, indicating that the distance of the Venusian IMB is much correlated with the scale of the ionosphere. We suggest that the variation of the IMB is partially contributed to by the variation of the ionopause, whose altitude is determined by the pressure balance between ionospheric thermal pressure and external magnetic pressure.