Spatially high-resolved solar-wind-induced magnetic field on Venus

Abstract: The current work investigates the Venusian solar-wind-induced magnetosphere at a high spatial resolution using all Venus Express (VEX) magnetic observations through an unbiased statistical method. We first evaluate the predictability of the interplanetary magnetic field (IMF) during VEX's magnetospheric transits, and then map the induced field in a cylindrical coordinate system under different IMF conditions. Our high-resolution mapping enables resolving structures on various scales, ranging from the thin ionopause and the associated electric currents to the classical global-scale draped IMF. Our mapping also resolves two recently-reported structures, a low ionospheric magnetization over the terminator and a global "looping" structure in the near magnetotail, both of which are not depicted in the classical draping configuration. In contrast to the reported IMF-independent cylindrical magnetic field of both structures, our results illustrate their IMF dependence. In both structures, the cylindrical magnetic component is stronger in the hemisphere with an upward solar wind electric field ($E^{SW}$) than in the opposite hemisphere. Under downward $E^{SW}$, the "looping" structure even breaks, which is attributable to an additional draped magnetic field structure wrapping toward $-E^{SW}$. In addition, our results suggest that these two structures are spatially not overlapping with each other. The low ionospheric structure occurs in a very narrow region, at about 87--95$^\circ$ solar zenith angle and 190--210~km altitude, implying that future simulation to reproduce the structure entails at least a spatial resolution of about 10 km. We discuss this narrow structure in terms of a Cowling channel.