The shape of the Venusian bow shock at solar minimum and maximum: Revisit based on VEX observations

摘要

Several factors control the bow shock position at Venus, including short-term period responses (solar wind dynamic pressure) and long-term period variations (solar activity). Based on Venus Express (VEX) observations, we revisit the influence of solar activity on the Venusian bow shock location, by accurately determining not only the shock terminator distance but also the subsolar point with a three-parameter fit (TPF) method. At the same time, VEX covers a larger range of solar zenith angles (SZA) at the Venusian bow shock (from about 10 to 135 degrees) than the Pioneer Venus Orbiter (PVO) spacecraft. Fitting results display that the Venusian bow shock is farther away from Venus at solar maximum than at solar minimum. The subsolar stand-off distance increases from 1364 planetary radii at solar minimum to 1A59R(V) at solar maximum, while the terminator shock distance changes from 2.087R(V) to 2.146R(V). Inspection of the bow shock and the induced magnetosphere boundary (IMB) locations clearly shows a positive correlation for every orbit, while the average bow shock location is not responsive to changes in the solar wind dynamic pressure. (C) 2015 Elsevier Ltd. All rights reserved.