Influence of the solar wind magnetic field on the Earth and Mercury magnetospheres in the paraboloidal model

We study the dependence of Mercury's magnetospheric magnetic field structure on the interplanetary magnetic field (IMF). Special attention is paid to the case of radial IMF. Mercury is the smallest planet in the solar system and it does not have a substantial atmosphere or ionosphere. Mercury is the closest planet to the Sun, and it possesses a week intrinsic magnetic field. Due to these circumstances, IMF plays a major role in the hermean magnetospheric dynamics. Using a paraboloidal model of Mercury's magnetosphere, we study the magnetospheric magnetic field topology for different orientations of IMF including examples representative of the first MESSENGER's flyby. Variations in IMF lead to variations in the Mercury's magnetospheric magnetic field structure, which in turn, lead to changes in the distribution of open and closed magnetic field lines. Comparison with the much better investigated Earth's magnetosphere is fulfilled for clarifying the physical processes (mainly reconnection) existent in the hermean magnetosphere. We also consider the cases when MESENGER, being the Mercury's orbiter, observed flux transfer events (FTEs) in the hermean magnetosphere. When the radial IMF component (BIMFx) is significant, which is character to the Mercury, the quasi-neutral line is placed in one of the cusps (depending on the sign of BIMFx). The FTE generation at Mercury can be connected with this line, similarly to the case of southward IMF at Earth, when FTEs arise at the dayside magnetopause at the quasi-neutral line. We show examples of observations supporting this result for Mercury.