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Upstream conditions at Mercury during the first MESSENGER flyby: Results from two independent solar wind models

The primary goal of this paper is to provide estimates of upstream solar wind plasma conditions at Mercury during the January 2008 MESSENGER flyby, based on two completely independent solar wind models. The first is a steady‐state three‐dimensional (3‐D) magnetohydrodynamic (MHD) model of the solar corona and inner heliosphere, which simulates the solar wind propagation from the source surface outward to Mercury, using synoptic charts of the photospheric magnetic field as input. The second model is a time‐dependent 1‐D MHD model of solar wind propagation that employs actual solar wind data at 1 AU as boundary conditions and propagates the solar wind backward in time to Mercury. We compare and validate the two models with each other as well as with actual magnetic field data from the MESSENGER Magnetometer instrument. Our combined method can produce the most accurate results for the solar wind speed and the sector structure of the interplanetary magnetic field.