The Demagnetization of the Venusian Ionosphere under Nearly Flow-aligned Interplanetary Magnetic Fields

Abstract

Previous studies suggested that the interplanetary magnetic field (IMF) has a significant influence on the Venusian-induced magnetosphere. We present observations by Venus Express under a nearly flow-aligned IMF condition to investigate the demagnetization of the Venusian ionosphere. Our results show that the magnetic barrier becomes weak and narrow, and the ionosphere can be demagnetized under the IMF with the dominating flow-aligned component while the solar wind dynamic pressure remains almost unchanged. The demagnetization of the Venusian ionosphere implies that the total pressure of the magnetic barrier above the ionopause decreases. The magnetic field lines upstream from Venus drape differently under the nearly flow-aligned IMF condition. And thus the upstream solar wind flow is affected by the outward magnetic tension, which leads to the decrease of the dynamic pressure that directly acts on the magnetic barrier.